RESUMEN
Third trimester-equivalent alcohol exposure causes significant deficits in hippocampal and cortical neuroplasticity, resulting in alterations to dendritic arborization, hippocampal adult neurogenesis, and performance on learning tasks. The current study investigated the impact of neonatal alcohol exposure (postnatal days 4-9, 5.25 g/kg/day) on expression of brain-derived neurotrophic factor (BDNF) and the tropomyosin-related kinase B (TrkB) receptor in the hippocampal and frontal cortex of infant Long-Evans rats. Levels of BDNF protein were increased in the hippocampus, but not frontal cortex, of alcohol-exposed rats 24h after the last dose, when compared with undisturbed (but not sham-intubated) control animals. BDNF protein levels showed a trend toward increase in hippocampus of sham-intubated animals as well, suggesting an effect of the intubation procedure. TrkB protein was increased in the hippocampus of alcohol-exposed animals compared to sham-intubated pups, indicating an alcohol-specific effect on receptor expression. In addition, expression of bdnf total mRNA in alcohol-exposed and sham-intubated pups was enhanced in the hippocampus; however, there was a differential effect of alcohol and intubation stress on exon I- and IV-specific mRNA transcripts. Further, plasma corticosterone was found to be increased in both alcohol-exposed and sham-intubated pups compared to undisturbed animals. Upregulation of BDNF could potentially represent a neuroprotective mechanism activated following alcohol exposure or stress. The results suggest that alcohol exposure and stress have both overlapping and unique effects on BDNF, and highlight the need for the stress of intubation to be taken into consideration in studies that implement this route of drug delivery.
Asunto(s)
Factor Neurotrófico Derivado del Encéfalo/metabolismo , Depresores del Sistema Nervioso Central/efectos adversos , Etanol/efectos adversos , Lóbulo Frontal/efectos de los fármacos , Regulación del Desarrollo de la Expresión Génica/efectos de los fármacos , Hipocampo/efectos de los fármacos , Efectos Tardíos de la Exposición Prenatal/patología , Receptor trkB/metabolismo , Factores de Edad , Animales , Animales Recién Nacidos , Peso Corporal/efectos de los fármacos , Factor Neurotrófico Derivado del Encéfalo/genética , Corticosterona/sangre , Ensayo de Inmunoadsorción Enzimática , Femenino , Lóbulo Frontal/crecimiento & desarrollo , Hipocampo/crecimiento & desarrollo , Masculino , Embarazo , ARN Mensajero/metabolismo , Ratas , Ratas Long-Evans , Receptor trkB/deficiencia , Estrés Psicológico/complicaciones , Estrés Psicológico/patologíaRESUMEN
Corticotropin-releasing factor (CRF)- and norepinephrine (NE)-containing neurons in the brain are activated during stress, and both have been implicated in the behavioral responses. NE neurons in the brain stem can stimulate CRF neurons in the hypothalamic paraventricular nucleus (PVN) to activate the hypothalamic-pituitary-adrenocortical axis and may affect other CRF neurons. CRF-containing neurons in the PVN, the amygdala, and other brain areas project to the area of the locus coeruleus (LC), and CRF injected into the LC alters the electrophysiologic activity of LC-NE neurons. Neurochemical studies have indicated that CRF applied intracerebroventricularly or locally activates the LC-NE system, and microdialysis and chronoamperometric measurements indicate increased NE release in LC-NE terminal fields. However, chronoamperometric studies indicated a significant delay in the increase in NE release, suggesting that the CRF input to LC-NE neurons is indirect. The reciprocal interactions between cerebral NE and CRF systems have been proposed to create a "feed-forward" loop. It has been postulated that a sensitization of such a feed-forward loop may underlie clinical depression. However, in the majority of studies, repeated or chronic stress has been shown to decrease the behavioral and the neurochemical responsivity to acute stressors. Repeated stress also seems to decrease the responsivity of LC neurons to CRF. These results do not provide support for a feed-forward hypothesis. However, a few studies using certain tasks have indicated sensitization, and some other studies have suggested that the effect of CRF may be dose dependent. Further investigations are necessary to establish the validity or otherwise of the feed-forward hypothesis.
Asunto(s)
Encéfalo/fisiopatología , Hormona Liberadora de Corticotropina/fisiología , Norepinefrina/fisiología , Estrés Fisiológico/fisiopatología , Animales , Encéfalo/citología , Electroquímica , Microdiálisis , Neuronas/fisiologíaRESUMEN
Intracerebroventricular (i.c.v.) administration of corticotropin-releasing factor (CRF) increases the activity of noradrenergic neurons in the locus coeruleus (LC) assessed by electrophysiological and neurochemical studies. It has been suggested that this effect of i.c.v. CRF is exerted directly on LC noradrenergic (LC-NE) neurons. Infusion of CRF directly into the LC increases cortical and hippocampal release of norepinephrine (NE) as indicated by in vivo microdialysis studies, but the electrophysiological studies have shown both increases and decreases. The present study used in vivo voltammetry to study changes in the extracellular concentrations of NE in the rat hippocampus in response to infusion of CRF (100 ng) into the LC. When the infusion cannula was located in or very close to the LC, the immediate response to CRF was a small decrease in the NE-like oxidation current, followed by a robust increase after about 6-7 min. The oxidation current reached a peak around 13 min and returned to baseline by about 30 min after CRF infusion. By contrast with CRF, infusion of glutamate into the LC increased the oxidation current with a delay of around 30 s and a peak within 90 s. The responses to LC infusion of CRF in rats treated with DSP-4 to deplete hippocampal NE were substantially smaller than those in untreated rats, suggesting that the oxidation signals in untreated rats reflected changes in concentrations of NE. The response to glutamate was markedly augmented by pretreatment with the NE reuptake inhibitor, desmethylimipramine, suggesting that the observed responses reflected changes in NE. Infusion of the same dose of CRF into brain structures outside the LC did not elicit consistent changes in oxidation current in the hippocampus. The time course of the responses to CRF is compatible with previously reported electrophysiological responses of LC-NE neurons to CRF and with neurochemical evidence indicating that CRF can affect the activity of LC-NE neurons. The results indicate that CRF may act in or close to the LC to induce release of hippocampal NE, but the delayed response to CRF compared with that to glutamate, suggests that CRF does not directly activate LC-NE neurons.
Asunto(s)
Hormona Liberadora de Corticotropina/farmacología , Hipocampo/metabolismo , Locus Coeruleus , Norepinefrina/metabolismo , Animales , Electrofisiología , Inyecciones , Masculino , Microdiálisis , Ratas , Ratas Sprague-DawleyRESUMEN
Previous studies have indicated that intracerebroventricular (i.c.v.) infusions of corticotropin-releasing factor (CRF) activate locus coeruleus (LC) noradrenergic neurons and increase the metabolism and extracellular concentrations of norepinephrine (NE) in several brain regions, suggesting increased release. To examine the temporal aspects and mechanism of the presumed release of NE, CRF was infused i.c.v. and the oxidation current was recorded using carbon fiber voltammetric electrodes placed in rat hippocampus or cortex. The CRF (1 microg, i.c.v.) caused a significant increase of oxidation current with a delay of approximately 5 min, and a peak at approximately 35 min. Similar responses were observed in the medial prefrontal cortex. The hippocampal response was markedly attenuated when CRF was infused into rats pretreated with DSP-4 to deplete NE, suggesting that the observed changes in current resulted from oxidation of NE. The increase of NE-like current did not occur when 25 microg alpha-helical CRF9-41 (ahCRF) was injected immediately before 1 microg CRF, suggesting that the response was mediated by cerebral CRF-receptors. Subcutaneous pretreatment with the ganglionic blocker, chlorisondamine, at a dose of 3 mg/kg had no effect on the voltammetric response to CRF, but a 6 mg/kg dose completely prevented the response. The beta-adrenoceptor antagonists, S-propranolol (5 mg/kg), nadolol (5 and 10 mg/kg), and timolol (5 mg/kg) attenuated the NE response to i.c.v. CRF to varying degrees. When chlorisondamine (3 microg) or nadolol (5 microg) were given i.c.v. before the CRF, the hippocampal responses were not blocked. These results suggest peripheral actions of ganglionic and beta-adrenergic blockers. We conclude that peripheral autonomic mechanisms, and probably both central and peripheral beta-adrenoceptors, contribute to the increased secretion of hippocampal NE in response to i.c.v. CRF.
Asunto(s)
Hormona Liberadora de Corticotropina/administración & dosificación , Espacio Extracelular/metabolismo , Hipocampo/metabolismo , Norepinefrina/metabolismo , Corteza Prefrontal/metabolismo , Antagonistas Adrenérgicos beta/farmacología , Animales , Bencilaminas/farmacología , Clorisondamina/farmacología , Hormona Liberadora de Corticotropina/farmacología , Conductividad Eléctrica , Electroquímica/métodos , Bloqueadores Ganglionares/farmacología , Hipocampo/fisiología , Inyecciones Intraventriculares , Masculino , Inhibidores de la Captación de Neurotransmisores/farmacología , Concentración Osmolar , Oxidación-Reducción , Corteza Prefrontal/fisiología , Ratas , Ratas Sprague-DawleyRESUMEN
Intravenous administration of sodium nitroprusside (NP) decreases blood pressure and activates noradrenergic neurons in the locus coeruleus (LC). Microdialysis studies have shown that NP infusion is accompanied by increased extracellular concentrations of norepinephrine (NE) in the medial prefrontal cortex. The present study used in vivo voltammetry to obtain a finer temporal analysis of the NP-induced changes in the extracellular concentrations of catecholamine-like compounds in the LC terminal fields in the rat medial prefrontal cortex. Intravenous infusion of rats with NP caused a rapid decrease in blood pressure that lasted for the duration of the infusion but rapidly reversed when the infusion was terminated. After a delay of between about 2 and 8 min (mean 5 min), there was an increase in extracellular concentrations of a NE-like substance. Presumed cortical release of NE lasted for several minutes but had almost returned to baseline by the time the NP infusion was terminated at 15 min. In many cases, the first peak was followed by a second one, usually of smaller amplitude but more prolonged than the first one. There was no clear response to the cessation of infusion of NP. The time course of the initial response is comparable to the previously reported electrophysiological response of LC-NE neurons to NP. In rats treated with DSP-4 to deplete cortical NE, blood pressure was reduced as in untreated rats, but no voltammetric response to NP infusion was observed. These results suggest that activation of the NE-LC neurons by NP results in a delayed synaptic release of NE in the cerebral cortex which attenuates within several minutes.
Asunto(s)
Antihipertensivos/farmacología , Catecolaminas/metabolismo , Corteza Cerebral/metabolismo , Nitroprusiato/farmacología , Animales , Presión Sanguínea/efectos de los fármacos , Corteza Cerebral/efectos de los fármacos , Electrofisiología , Inyecciones Intravenosas , Masculino , Norepinefrina/fisiología , Oxidación-Reducción , Ratas , Ratas Sprague-DawleyRESUMEN
Voltammetric probes were constructed from stainless steel and fused silica tubing sheathing carbon fibers. Electrochemical tests were carried out to compare these electrodes with commercially available glass-sealed IVEC-5 electrodes. Electrodes of both types displayed a similar declining baseline and calculated coefficients of stabilization (tangent of baseline during a stable period). There were no significant differences in sensitivity between the two designs of electrodes to norepinephrine (NE) and dopamine (DA). All tested electrodes showed linear current responses to increasing concentrations of NE and DA. Fused silica (FS type) electrodes are suitable for electrochemical measurements (in vivo voltammetry) and display characteristics similar to those of commercially available IVEC-5 glass-sealed carbon fiber microelectrodes. Manufacture of FS type electrodes in a biochemical laboratory is easy and does not require any special equipment (such as a micropipette puller) or glass-handling skills. An additional fused silica tube can be glued to the electrode for microinjections. The electrodes are very robust, easy to handle and can be mounted on the arms of standard stereotaxic instruments. The electrodes can be made long enough to reach the deepest parts of brain of large animals.