RESUMEN
The noradrenergic nucleus locus coeruleus (LC) has been reported to regulate luteinising hormone (LH) secretion in female rats. Both oestrogen and progestin receptors have been demonstrated in LC neurones, suggesting that these cells are possibly responsive to variations in circulating levels of ovarian steroids. We therefore evaluated changes in the activity of LC neurones during the oestrous cycle and after ovarian-steroid treatment in ovariectomised (OVX) rats, as determined by immunoreactivity to Fos-related antigens (FRA), which comprises all of the known members of the Fos family. Effects of ovarian steroids on the firing rate of LC neurones were also determined in a slice preparation. The number of FRA/tyrosine hydroxylase (TH)-immunoreactive (ir) neurones in the LC increased from 14.00-16.00 h on pro-oestrus, coinciding with the onset of the LH surge and rise in plasma progesterone. FRA immunoreactivity was unaltered during dioestrus. Oestradiol-treated OVX rats (OVX+E) displayed marked reduction in FRA/TH-ir neurones in LC compared to oil-treated OVX rats. Accordingly, oestradiol superfusion significantly reduced the spontaneous firing rate of LC neurones in slices from OVX rats. Compared to OVX+E, oestradiol-treated rats injected with progesterone at 08.00 h (OVX+EP) exhibited higher number of FRA/TH-ir neurones in the LC at 10.00 h and 16.00 h, and great amplification of the LH surge. Bath application of progesterone significantly increased the spontaneous firing rate of OVX+E LC neurones. Our data suggest that ovarian steroids may physiologically modulate the activity of LC neurones in females, with possible implications for LH secretion. Moreover, oestradiol and progesterone appear to exert opposite and complementary effects (i.e. whereas oestradiol inhibits, progesterone, after oestradiol priming, stimulates LC activity).
Asunto(s)
Estrógenos/metabolismo , Ciclo Estral/fisiología , Locus Coeruleus/fisiología , Hormona Luteinizante/metabolismo , Neuronas/fisiología , Progesterona/metabolismo , Potenciales de Acción , Animales , Estradiol/farmacología , Estrógenos/farmacología , Femenino , Técnicas In Vitro , Locus Coeruleus/efectos de los fármacos , Neuronas/efectos de los fármacos , Ovariectomía , Progesterona/sangre , Progesterona/farmacología , Progestinas/farmacología , Proteínas Proto-Oncogénicas c-fos/metabolismo , Ratas , Ratas Wistar , Factores de Tiempo , Tirosina 3-Monooxigenasa/metabolismoRESUMEN
Previous work from our laboratory has shown that in cultures of hypothalamic neurons obtained from male fetuses at embryonic day 16 the axogenic response to estradiol (E2) is contingent upon culture with medium conditioned by astroglia from a target region for hypothalamic axons. E2 also induced increased levels of TrkB that were necessary for the axonal growth to occur. This convergence between estrogenic and neurotrophic signals prompted investigation of the mitogen activated protein kinase (MAPK) cascade. Analysis of the temporal course of MAPK activation showed increased levels of phosphorylated ERK up to 60 min after E2 exposure, with a maximal response at 5-15 min. UO126 (specific inhibitor of MEK 1/2) blocked E2 induced axonal elongation and ERK phosphorylation, confirming the involvement of ERK in the neuritogenic effect of E2. The membrane impermeable construct E2-BSA proved as effective as free E2 to induce axon elongation, suggesting that E2 exerted its effect through a membrane-associated receptor. This possibility received additional support from experiments showing that E2-BSA also increased ERK phosphorylation with the same time course than E2. These results indicate that ERK signaling is necessary for E2 to induce axon growth and this activation is mediated by a membrane bound estrogen receptor.
Asunto(s)
Estradiol/farmacología , Neuronas/citología , Neuronas/efectos de los fármacos , Animales , Axones/efectos de los fármacos , Diferenciación Celular/efectos de los fármacos , División Celular/efectos de los fármacos , Células Cultivadas , Medios de Cultivo Condicionados , Femenino , Feto/citología , Sistema de Señalización de MAP Quinasas/efectos de los fármacos , Masculino , Neuronas/metabolismo , Oligodesoxirribonucleótidos Antisentido/genética , Oligodesoxirribonucleótidos Antisentido/farmacología , Embarazo , Ratas , Receptor trkB/antagonistas & inhibidores , Receptor trkB/genética , Diferenciación Sexual/efectos de los fármacosRESUMEN
17-beta-estradiol (E2) increases axonal growth and tyrosine kinase receptor (Trk)B levels of male-derived hypothalamic neurones in vitro. To investigate whether the axogenic response depends on the upregulation of TrkB, we analysed neuritic growth and neuronal polarization in cultures treated with an antisense oligonucleotide against TrkB mRNA. In cultures without E2, treatment with 7.5 or 10 micro m antisense reduced TrkB levels and the percentage of neurones showing an identifiable axon; the number and length of minor processes were increased. In cultures treated with 5 micro m antisense, morphometric parameters were normal although total TrkB levels were reduced. The same dose prevented the E2-dependent increase of TrkB levels and suppressed the axogenic effect of E2. These results indicate that TrkB is necessary for normal neuronal growth and maturation and further suggest that an increase in TrkB is necessary for E2 to exert its axogenic effect in male-derived neurones.
Asunto(s)
Estradiol/farmacología , Hipotálamo/citología , Neuronas/efectos de los fármacos , Receptor trkB/metabolismo , Animales , Western Blotting/métodos , Recuento de Células/métodos , Diferenciación Celular/efectos de los fármacos , Células Cultivadas , Relación Dosis-Respuesta a Droga , Embrión de Mamíferos , Inmunohistoquímica/métodos , Técnicas In Vitro , Masculino , Neuritas/efectos de los fármacos , Neuroglía/efectos de los fármacos , Neuronas/fisiología , Oligonucleótidos Antisentido/farmacología , Ratas , Ratas Wistar , Receptor trkB/antagonistas & inhibidores , Receptor trkB/genética , Factores de TiempoRESUMEN
Previous work from our laboratory has shown that in cultures of hypothalamic neurons obtained from male fetuses at embryonic day 16, the axogenic response to estrogen (E2) is contingent on coculture with target glia or target glia-conditioned media (CM). Neither the estrogen receptor blockers tamoxifen nor ICI 182,780 prevented the axogenic effects of the hormone. Estradiol made membrane-impermeable by conjugation to a protein of high molecular weight (E2-BSA) preserved its axogenic capacity, suggesting the possibility of a membrane effect responsible for the action of E2. Western blot analysis of extracts from homogenates of cultured neurons grown with E2 and CM from target glia had more TrkB than cultures with CM alone or E2 alone. To further investigate the interaction between E2 and the neurotrophin receptors, we used a specific antisense oligonucleotide (AS) to prevent the estradiol-induced increase of TrkB. The effect of E2 was suppressed in cultures in which TrkB was down-regulated by the AS, showing decreased axonal elongation when compared with neurons treated with E2 without AS or with sense TrkB. In cultures grown with AS, the axonal length of E2-treated cultures was not different from cultures without E2. Evidence suggesting cross-talk between E2 and neurotrophic factor(s) prompted investigation of signaling along the MAPK cascade. Immuno blotting of E2-treated cultures showed increased levels of phosphorylated ERK1 and ERK2. UO126 but not LY294002 blocked E2-induced axonal elongation, suggesting that the MAPKs are involved in this response.
Asunto(s)
Axones/metabolismo , Estradiol/metabolismo , Hipotálamo/metabolismo , Factores de Crecimiento Nervioso/metabolismo , Animales , Axones/efectos de los fármacos , Relación Dosis-Respuesta a Droga , Estradiol/farmacología , Antagonistas de Hormonas/farmacología , Humanos , Hipotálamo/efectos de los fármacos , Neuronas/efectos de los fármacos , Neuronas/metabolismo , Receptores de Estrógenos/antagonistas & inhibidores , Receptores de Estrógenos/metabolismoRESUMEN
The purpose of the present work was to investigate the participation of estradiol receptors (ER) in estrogen-induced axon growth in vitro. Hypothalamic neurons from 16 day (E16) male rat fetuses were cultured with or without 17-beta-estradiol at 1 x 10(-7) M in basal medium or medium conditioned by astroglia derived from ventral mesencephalon (CM). After 48 hr in vitro, neurite outgrowth was quantified by morphometric analysis. An axogenic effect could be demonstrated for estradiol added to CM. With RT-PCR, the mRNA transcript for ERalpha was found in the donor tissues as well as in the neuron cultures. In this model two specific nuclear ER blockers (tamoxifen and ICI 182,780) were ineffective in blocking the neuritogenic effect, and a membrane-impermeable estrogen-albumin construct (E2-BSA) was as effective as estradiol. These results indicate that the axogenic effect of estradiol at E16 is not exerted through the classical intracellular receptor signal transduction system and suggest the possibility of a membrane-mediated mechanism. The data are discussed in light of our previous findings pointing to the interdependent activation of the estrogenic and the trophic factor signaling pathways that mediate stimulated axon growth.
Asunto(s)
Diferenciación Celular/fisiología , Estradiol/metabolismo , Conos de Crecimiento/metabolismo , Hipotálamo/embriología , Factores de Crecimiento Nervioso/metabolismo , Receptores de Estrógenos/genética , Transducción de Señal/genética , Animales , Diferenciación Celular/efectos de los fármacos , Membrana Celular/efectos de los fármacos , Membrana Celular/metabolismo , Células Cultivadas , Medios de Cultivo Condicionados/farmacología , Estradiol/farmacología , Antagonistas de Estrógenos/farmacología , Moduladores de los Receptores de Estrógeno/farmacología , Feto , Genoma , Conos de Crecimiento/efectos de los fármacos , Conos de Crecimiento/ultraestructura , Hipotálamo/citología , Hipotálamo/efectos de los fármacos , Masculino , Factores de Crecimiento Nervioso/farmacología , ARN Mensajero/efectos de los fármacos , ARN Mensajero/metabolismo , Ratas , Receptores de Estrógenos/antagonistas & inhibidores , Reproducción/efectos de los fármacos , Reproducción/fisiología , Albúmina Sérica Bovina/farmacología , Factores Sexuales , Transducción de Señal/efectos de los fármacosRESUMEN
To determine whether soluble products from different CNS regions differ in their ability to support oestrogen-stimulated neurite growth, hypothalamic neurons from sexually segregated embryos were cultured with astroglia-conditioned medium (CM) derived from cortex, striatum and mesencephalon, with or without 17-beta-oestradiol 100 nM added to the medium. After 48 h in vitro, neurite outgrowth was quantified by morphometric analysis. Astroglia-CM from mesencephalon (a target for the axons of hypothalamic neurons) induced the greatest axogenic response in males and in this case only a neuritogenic effect could be demonstrated for oestradiol. On the other hand, astroglia-CM from regions that do not receive projections from ventromedial hypothalamus inhibited axon growth. A sexual difference in the response of hypothalamic neurons to astroglia-CM and oestradiol was found; growth of neurons from female foetuses was increased by astroglia-CM from mesencephalon, but no neuritogenic effect could be demonstrated for oestradiol in these cultures. Blot immunobinding demonstrated the presence of receptors for neurotrophic factors in cultures of hypothalamic neurons; Western blot analysis of these cultures demonstrated that oestradiol increased the concentration of trkB and IGF-I Rbeta, whereas trkA was not detected and the concentration of trkC was not modified. These results support the hypothesis that target regions produce some factor(s) that stimulate the growth of axons from projecting neurons and further indicate that in the case of males this effect is modulated by oestradiol, perhaps mediated through the upregulation of trkB and IGF-I receptors.
Asunto(s)
Medios de Cultivo Condicionados/farmacología , Estradiol/farmacología , Neuronas/efectos de los fármacos , Caracteres Sexuales , Núcleo Hipotalámico Ventromedial/citología , Animales , Astrocitos/fisiología , Diferenciación Celular/efectos de los fármacos , Diferenciación Celular/fisiología , Células Cultivadas , Femenino , Immunoblotting , Masculino , Factor de Crecimiento Nervioso/farmacología , Neuritas/efectos de los fármacos , Neuritas/fisiología , Neuronas/química , Neuronas/ultraestructura , Embarazo , Ratas , Ratas Wistar , Receptor trkA/análisis , Receptor trkB/análisis , Receptor trkC/análisisRESUMEN
In order to investigate the role of the peripeduncular nucleus (PP) in the control of lordosis in female rats, activation of neurons after mounts without intromission was investigated by means of FOS immunoreactivity (FOS-IR). Ovariectomized rats were injected with estradiol and progesterone and submitted to approximately 50 mounts by the male. The vaginal area was covered with masking tape to prevent intromission and vaginocervical stimulation. This limited stimulation produced FOS-IR in the ventrolateral division of the ventromedial hypothalamic nucleus (VMHVL), in the lateral periaqueductal grey (LPAG), in the peripeduncular nucleus (PP), and in the posterior intralaminar thalamic nucleus (PIL). No significant differences were found in the anterodorsal or posterodorsal parts of the medial amygdaloid nucleus, in the medial part of the medial preoptic nucleus, in the dorsomedial periaqueductal grey and in the medial division of the posterointermediate part of the bed nucleus of the stria terminalis. The same experiment was performed in rats with unilateral lesion of the PP. Both VMHVL and LPAG activation were significantly reduced in the ipsilateral PP lesion side, leading to the conclusion that those structures are primary targets for the somatic stimuli that trigger lordotic reflexes and which are relayed in the PP. Taking into account what is known about the function of the target structures, it is proposed that afferences relayed in the PP reaching the VMHVL would contribute to control the long range level of sexual receptivity, whereas stimuli reaching the LPAG would serve to control lordotic responses in a moment to moment fashion.
Asunto(s)
Mesencéfalo/metabolismo , Proteínas Proto-Oncogénicas c-fos/metabolismo , Conducta Sexual Animal , Núcleo Hipotalámico Ventromedial/metabolismo , Animales , Femenino , Masculino , Mesencéfalo/fisiología , Ratas , Ratas WistarRESUMEN
In order to test the hypothesis that circulating levels of estrogen modulate synaptic plasticity in the hippocampus, we have studied the induction of long term potentiation (LTP) in awake rats. Ovariectomized animals, chronically implanted with a recording electrode in the cell body layer of CA1 and a stimulating electrode in stratum radiatum, were used to record evoked field potentials (population spike (PS) and summed EPSP) daily for at least 4 days before injection of sesame oil or 100 microg of estradiol benzoate per kg b.w. (E2). Basal levels of response to single square pulses (0.01 ms pulse width) delivered at 0.05 Hz through the stimulating electrode were recorded daily for 2 days after injection. To induce LTP a high-frequency 'theta pattern' stimulation was administered. Basal recordings at low-frequency stimulation did not change after injection. After high-frequency stimulation all (7/7) E2 injected animals showed LTP whereas only 1/6 oil injected controls did so; the mean increase in amplitude of the PS and slope of the EPSP after high-frequency stimulation were significantly greater in E2 treated rats. Input/output curves did not change significantly after E2 administration. These results show that at low-frequency stimulation, transynaptic responses of pyramidal neurones in CA1 are not affected by changes in levels of circulating estrogen, while synaptic plasticity -- which is at the basis of proposed hebbian associative memory -- is facilitated by estrogen treatment.
Asunto(s)
Estradiol/farmacología , Hipocampo/fisiología , Potenciación a Largo Plazo/efectos de los fármacos , Animales , Estado de Conciencia , Potenciales Postsinápticos Excitadores/fisiología , Femenino , Hipocampo/efectos de los fármacos , Memoria/efectos de los fármacos , Plasticidad Neuronal/efectos de los fármacos , Ovariectomía , Ratas , Ratas WistarRESUMEN
In sexually segregated cultures of dissociated neurons taken from ventromedial hypothalamus of rat fetuses at embryonic day 16 (E16), it is demonstrated that only neurons from males respond with increased axonal growth to the addition of 17-beta-estradiol 100 nM (E2) to the culture medium. Moreover, this response is contingent upon co-culture with heterotopic glia from a target region (amygdala), whereas in the presence of homotopic glia or in cultures without glia, E2 has no effect. It is concluded that before neurons are exposed to gonadal steroids in utero there is a sexual difference in the response to E2, probably explained by earlier maturation of neurons from males as compared to females. The possibility that the observed axogenic effect may be the consequence of an interaction among E2, cells equipped with specific receptors, and glia-producing trophic factors is discussed.
Asunto(s)
Estradiol/farmacología , Neuritas/efectos de los fármacos , Neuroglía/efectos de los fármacos , Neuronas/efectos de los fármacos , Núcleo Hipotalámico Ventromedial/citología , Animales , Supervivencia Celular/efectos de los fármacos , Células Cultivadas , Técnicas de Cocultivo , Femenino , Procesamiento de Imagen Asistido por Computador , Inmunohistoquímica , Masculino , Neuritas/fisiología , Neuritas/ultraestructura , Neuroglía/fisiología , Neuroglía/ultraestructura , Neuronas/fisiología , Neuronas/ultraestructura , Ratas , Ratas Wistar , Caracteres Sexuales , Núcleo Hipotalámico Ventromedial/efectos de los fármacosRESUMEN
Cultures of dissociated hypothalamic cells taken from rat fetuses of 19 days of gestation were studied using time-lapse recording and sequential microphotography from 1 to 5 days in vitro (DIV) and at 7 and 21 DIV. Cultures were seeded with cells taken from fetuses grouped by sex or sexually mixed; experimental cultures were raised in medium containing 17-beta-estradiol 100 nM (E2). Cells were plated on poly-D-lysine-coated coverslips at a culture density of approximately 4,000 cells/cm2. Immunocytochemistry of cell cultures was performed using a Tau monoclonal antibody (clone Tau-1 PC1C6) and a monoclonal antibody against MAP-2 (clone AP-20). Cells started to produce lamellipodia and neuritic processes approximately 4 hr after plating. Forty-eight hours later a few neurons had defined their morphological polarity by the differentiation of an axon-like process that grows faster than the others; at 5 DIV almost all neurons had defined their axons. At this time, monoclonal antibody against MAP-2 clearly stained soma and dendrites, but not axons. Tau immunoreactivity (lots CCA101 and CCA101N from Boeringher Mannheim) was differentially distributed, with a clear predominance in axon and soma. Results on the morphometric analysis of control and E2 treated neurons provide direct evidence for the existence of sex related differences in the neurite outgrowth response of hypothalamic neurons, since cultured neurons taken from female fetuses differentiated axons later and had fewer primary neurites and shorter dendrites than neurons taken from male fetuses or sexually mixed cultures. Also, it was demonstrated in living neurons that E2 effectively enhances outgrowth and elongation in axons. The frequency distribution curves of axonal length for control and E2 treated cultures was unimodal, suggesting that the effect of E2 was a uniform increase in the axonal length of all neurons. The structural differences between neurons from both sexes and the changes induced by E2 may contribute to explain the differences in brain function found between the sexes.
Asunto(s)
Estradiol/farmacología , Hipotálamo/fisiología , Neuritas/fisiología , Neuronas/fisiología , Animales , Anticuerpos Monoclonales , Axones/fisiología , Axones/ultraestructura , Células Cultivadas , Dendritas/fisiología , Dendritas/ultraestructura , Embrión de Mamíferos , Femenino , Edad Gestacional , Hipotálamo/citología , Inmunohistoquímica , Masculino , Proteínas Asociadas a Microtúbulos/análisis , Neuritas/efectos de los fármacos , Neuritas/ultraestructura , Neuronas/citología , Neuronas/efectos de los fármacos , Ratas , Análisis de Regresión , Caracteres Sexuales , Factores de Tiempo , Grabación en Video , Proteínas tau/análisisRESUMEN
The hippocampal synaptic plasticity of rats with an inborn high (HP) or low (LP) learning capacity to perform in a shuttle box is closely related to their percentage of conditioned responses (Crs). HP rats show less sensitivity to the blocking effect of 2-aminophosphonopentanoic acid (AP5) on the generation of long-term potentiation (LTP) than do LP rats. Results described in the present report are indicative of an increased density of N-methyl-D-aspartate (NMDA) receptors in HP rats compared to control and LP rats. We postulate that the differential pharmacological sensitivity of LTP in these rats is a reflection of this biochemical difference. Also, from these results we suggest that the learning capacity may be related to the density of glutamate NMDA receptors of HP, LP and control rats.
Asunto(s)
Hipocampo/fisiología , Aprendizaje/fisiología , Receptores de N-Metil-D-Aspartato/fisiología , 2-Amino-5-fosfonovalerato/farmacología , Animales , Condicionamiento Operante , Hipocampo/efectos de los fármacos , Cinética , Masculino , Piperazinas/metabolismo , Ratas , Ratas Endogámicas , Receptores de N-Metil-D-Aspartato/antagonistas & inhibidores , Valores de ReferenciaRESUMEN
Rats with an inborn high (HP) or low (LP) learning capacity were used to study the sensitivity to the blocking effect of 2-amino-phosphonopentanoic acid (AP5; 10 and 20 microM) on long-term potentiation (LTP) produced in hippocampal slices by a 1-s tetanus at 200 Hz. The potential evoked by stimulation of the perforant path was recorded from the granule cell layer of the dentate gyrus in 400 microns slices perfused with standard Krebs' solution or the AP5. Under perfusion with 10 microM of AP5, in 100% of slices from HP rats, LTP generation was not blocked; when AP5 20 microM was used, in 85% of the cases LTP was not blocked. In 60% of slices from LP rats, AP5 10 microM and in 100% of the cases at 20 microM AP5 blocked LTP generation. These results are coherent with the hypothesis that the different inborn learning ability of HP and LP rats is related to the different population or sensitivity of N-methyl-D-aspartate (NMDA) receptors.
Asunto(s)
Hipocampo/fisiología , Aprendizaje , Plasticidad Neuronal , Receptores de Aminoácidos , Receptores de Superficie Celular/fisiología , Sinapsis/fisiología , 2-Amino-5-fosfonovalerato/farmacología , Animales , Estimulación Eléctrica , Electrofisiología , Granulocitos/fisiología , Hipocampo/citología , Técnicas In Vitro , Masculino , Ratas , Análisis de RegresiónRESUMEN
To gain insight into the mechanisms responsible for differentiation of hippocampal neurons growing in vitro, the effects of estrogen on neuritic development and on activity and distribution of isoforms of the Na, K-ATPase, were evaluated. Dissociated cells from hippocampi of 19-day-old rat fetuses were raised for 5 days in the presence or absence of 100 nM estradiol-17 beta (E2) in minimum essential medium supplemented either with 10% untreated fetal calf serum (MEM-10) or with 10% fetal calf serum previously adsorbed with dextran-activated charcoal (MEM-10-Cha). Cultures in MEM-10 showed larger neuritic length and increased levels of Na, K-ATPase activity than cultures in MEM-10-Cha. In cells cultured in MEM-10 medium, the addition of E2 resulted in selective enhancement of axonal length with a concomitant increase in the alpha-2 isoform of the Na, K-ATPase, whereas a decrease was found in the form most sensitive to ouabain; the total enzymatic activity remained unchanged. Conversely, in cultures raised in MEM-10-Cha, E2 did not affect Na, K-ATPase activity or neuritogenesis. These results show that two presumably independent probes of cellular differentiation of hippocampal neurons (i.e., neuritogenesis and patterns of Na, K-ATPase activity) were concurrently regulated by E2 and that such regulation depended on interaction with factor(s) present in calf serum. The well-known neuritogenic effect of E2 is hereby extended to hippocampal neurons, although for these cells it seems to be restricted to axons.
Asunto(s)
Estradiol/farmacología , Hipocampo/efectos de los fármacos , Isoenzimas/metabolismo , Neuronas/efectos de los fármacos , ATPasa Intercambiadora de Sodio-Potasio/metabolismo , Animales , Axones/efectos de los fármacos , Axones/ultraestructura , Compartimento Celular/efectos de los fármacos , Diferenciación Celular/efectos de los fármacos , Células Cultivadas , Carbón Orgánico , Medios de Cultivo/farmacología , Inducción Enzimática/efectos de los fármacos , Hipocampo/citología , Hipocampo/embriología , Neuronas/enzimología , Neuronas/ultraestructura , RatasRESUMEN
Extracellular action potentials were recorded from the organum vasculosum laminae terminalis (OVLT) in rat brain slice preparations; the effect of different concentrations of NaCl on spontaneous firing frequency was studied. From 72 neurons, 67 (93%) were responsive to various perfusion media, while 5 neurons (7%) were not responsive. The change from the standard medium (SM; 124 mM NaCl) to 99 mM, decreased the firing frequency in 24 (65%) and increased it in 13 (35%) out of 37 responsive cells. The change from the SM to 149 mM evoked an increase in the firing rate in 33 (73%) and a decrease in 12 (27%) of 45 responsive neurons; the change to 174 mM, increased the firing rate in 5 (100%) neurons tested. The excitatory effect of increasing [NaCl] in the perfusion medium persisted even in low Ca2+ and high Mg2+ medium. Mannitol (55 mM) added to the SM increased the firing rate of cells; no significant decrease in the firing rate was seen with sodium mannitol 99/55 mM. Ouabain (OUA) (0.1 x 10(-3) mM) added to the SM increased the firing rate in 16 (84%) and decreased it in 3 (16%) out of 19 cells. Diphenylhydantoin (DPH) (1 mM) added to the SM decreased the firing rate in 12 (67%) and increased it in 6 (33%) of 18 cells tested. Hypo- or hypertonic NaCl solutions had no consistent effect on the spontaneous activity of 14 pyramidal cells recorded from the hippocampus (area CA3). The results emphasize the importance of intracellular Na content as a physiological trigger regulating the activity in neurons of the OVLT.
Asunto(s)
Encéfalo/fisiología , Neuronas/fisiología , Cloruro de Sodio/farmacología , Potenciales de Acción/efectos de los fármacos , Animales , Encéfalo/efectos de los fármacos , Relación Dosis-Respuesta a Droga , Técnicas In Vitro , Masculino , Neuronas/efectos de los fármacos , Ouabaína/farmacología , Fenitoína/farmacología , Ratas , Ratas EndogámicasRESUMEN
The amounts of time spent by females in the sector of an open field close to the cage housing a normal male or a castrated male were measured in order to quantitate the tendency of the female to reach physical proximity to a sexually active male (androtropism). Intact proestrous or ovariectomized females primed with 100 micrograms of estradiol benzoate/kg b. wt. (EB) or EB plus 2 mg progesterone/kg b. wt. (P) spent significantly more time close to the sexually active (intact) male than in the proximity of the orchidectomized male. In order to determine whether olfactory clues were sufficient for female rats to distinguish between intact and castrated males, the males were removed from the stimulus cages, leaving the soiled bedding in place. Ovariectomized rats primed with EB or EB plus P clearly preferred proximity to the cage where the intact male had been living. No preference was evident after transection of olfactory nerves in proestrous rats or in ovariectomized rats primed with EB plus P. Resection of the vomeronasal organ also suppressed preference. These results indicate that olfactory input is necessary and sufficient for androtropism to occur, and suggest that the accessory olfactory system is involved in the analysis of olfactory signals used by female rats to identify the endocrine status of prospective sexual partners. In a different group of animals, it was demonstrated that destruction of the posteromedial cortical amygdaloid nucleus also suppressed preference for the intact male. It is proposed that this structure serves as a relay station for the analysis and integration of olfactory input significant for the motivational control of sexual behavior in the female rat.(ABSTRACT TRUNCATED AT 250 WORDS)
Asunto(s)
Nivel de Alerta/fisiología , Sistema Nervioso Central/fisiología , Estro/fisiología , Vías Olfatorias/fisiología , Conducta Sexual Animal/fisiología , Olfato/fisiología , Amígdala del Cerebelo/fisiología , Animales , Mapeo Encefálico , Femenino , Masculino , Mucosa Nasal/fisiología , Bulbo Olfatorio/fisiología , Nervio Olfatorio/fisiología , Ratas , Medio SocialRESUMEN
The effect of perfusion with gangliosides (1 x 10(-6) M) on the response evoked in the granule cell layer of dentate gyrus by stimulation of perforant path in hippocampal rat slices was studied. Gangliosides induced both a decrease in the frequency threshold of stimulation necessary to generate long-term potentiation (LTP) and greater potentiation than under control conditions. It is proposed that gangliosides improve the mechanisms responsible for synaptic plasticity which generate LTP.
Asunto(s)
Gangliósidos/farmacología , Hipocampo/fisiología , Plasticidad Neuronal/efectos de los fármacos , Potenciales de Acción/efectos de los fármacos , Animales , Gangliósidos/fisiología , Hipocampo/efectos de los fármacos , Técnicas In Vitro , Masculino , RatasRESUMEN
The relationship between the learning ability of normal rats and the facility to induce long-term potentiation (LTP) in the same animals was investigated. Behavioral performance was measured in a shuttle box avoidance paradigm, using a buzzer as conditioned stimulus. Three days later animals were sacrificed; frequency threshold necessary to induce LTP was determined in transverse hippocampal slices taken from these animals and maintained in vitro. A linear regression analysis on the behavioral and electrophysiological data showed a negative correlation (Spearman rank correlation coefficient rs = -0.705; P less than 0.001) between percent of conditioned responses in the shuttle box and threshold frequency necessary to induce LTP in gyrus dentatus in response to tetanic stimulation of the perforant path. It is concluded that learning ability of normal rats in a shuttle box avoidance paradigm is correlated with hippocampal synaptic plasticity.
Asunto(s)
Reacción de Prevención/fisiología , Hipocampo/fisiología , Sinapsis/fisiología , Animales , Condicionamiento Psicológico/fisiología , Electrofisiología , Potenciales Evocados , Masculino , Ratas , Análisis de RegresiónRESUMEN
In order to localize the sites in the brain where serotonergic (5-HT) input may affect the performance of lordotic responses, the serotonin neurotoxin 5-7-dihydroxytryptamine was injected in the ventromedial hypothalamic nucleus (VMN) or in the medial amygdala (AM) in ovariectomized rats. Estrogen induced receptivity as measured by the lordotic quotient was significantly greater in animals injected in AM, but it was smaller in animals injected in the VMN, as compared to controls or animals injected with the vehicle. No differences were found when the same animals were injected with progesterone. It is proposed that serotonergic afferents exert facilitatory influences in the hypothalamus and inhibitory influences in the amygdala, as concerns estrogen-induced sexual receptivity. The integrity of 5-HT terminals in VMN and AM is not necessary for progesterone to exert its potentiating effects.
Asunto(s)
Dihidroxitriptaminas/farmacología , Postura , Serotonina/farmacología , Conducta Sexual Animal/efectos de los fármacos , Amígdala del Cerebelo/efectos de los fármacos , Animales , Encéfalo/patología , Femenino , Hipotálamo/efectos de los fármacos , RatasRESUMEN
In order to localize the sites in the brain where serotonergic (5-HT) input may affect the performance of lordotic responses, the serotonin neurotoxin 5-7-dihydroxytryptamine was injected in the ventromedial hypothalamic nucleus (VMN) or in the medial amygdala (AM) in ovariectomized rats. Estrogen induced receptivity as measured by the lordotic quotient was significantly greater in animals injected in AM, but it was smaller in animals injected in the VMN, as compared to controls or animals injected with the vehicle. No differences were found when the same animals were injected with progesterone. It is proposed that serotonergic afferents exert facilitatory influences in the hypothalamus and inhibitory influences in the amygdala, as concerns estrogen-induced sexual receptivity. The integrity of 5-HT terminals in VMN and AM is not necessary for progesterone to exert its potentiating effects.
RESUMEN
Threshold of stimulation frequency in the perforant path to induce long-term potentiation (LTP) in dentate gyrus was determined in hippocampal slices obtained from two different lines of rats inbred for 30 generations according to their performance in an avoidance escape test in a shuttle box. High-performance (HP) rats were defined as those giving at least 70% conditioned responses (CRs) and low-performance (LP) rats as those giving less than 15% CRs. LTP was defined as a 30% or more increase in the amplitude of the evoked population spike (PS), lasting at least 20 min. Stimulation frequency threshold was determined by stimulating with a train of pulses of 0.5 ms duration during 1 s. The same slice was stimulated with trains of increasing frequency from 5 to 400 Hz, each train separated by an interval of at least 20 min. HP rats showed a lower threshold (13 +/- 4 Hz) than LP rats (92 +/- 42 Hz) for the induction of LTP; there were no differences in the magnitude of LTP. The greater learning ability of HP rats may be related to the plasticity of hippocampal synaptic transmission.