RESUMEN
The present study has employed in vitro receptor autoradiography with (S)-[(3)H]-5-fluorowillardiine (10 nM) to visualise the presence of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) binding sites in the brain stems of adult (16-18 weeks) normotensive (Wistar-Kyoto (WKY) and Don Ryu (DRY)) and Spontaneously Hypertensive (SHR) rats. Similar topographic distribution and density of (S)-[(3)H]-5-fluorowillardiine binding was observed in the nucleus tractus solitarius (NTS) of all three strains. Specific (S)-[(3)H]-5-fluorowillardiine binding sites were also visualised in sections of nodose ganglion from adult WKY rats, demonstrating that vagal afferent perikarya possess AMPA binding sites. However, while unilateral vagal deafferentation did not result in a significant decrease in binding site density in the caudal half of the rat NTS, the visualisation of AMPA binding sites on the nodose ganglion is consistent with the existence of a population of binding sites on vagal afferent terminals. In the caudal half of the rat NTS, AMPA binding sites appear to be predominantly postsynaptic in nature.
Asunto(s)
Tronco Encefálico/metabolismo , Hipertensión/metabolismo , Ácido alfa-Amino-3-hidroxi-5-metil-4-isoxazol Propiónico/metabolismo , Alanina/análogos & derivados , Alanina/metabolismo , Animales , Sitios de Unión/fisiología , Desnervación , Masculino , Neuronas Aferentes/metabolismo , Ganglio Nudoso/metabolismo , Pirimidinas/metabolismo , Ratas , Ratas Endogámicas SHR , Ratas Endogámicas WKY , Valores de Referencia , Núcleo Solitario/metabolismo , Distribución Tisular/fisiología , Nervio Vago/citología , Nervio Vago/metabolismoRESUMEN
In vivo microdialysis was used to measure release of endogenous l-glutamate and l-aspartate in the nucleus tractus solitarius of the anaesthetised rat evoked by baroreceptor loading. Aortic constriction, the method of loading, elicited a reproducible increase in extracellular levels of l-glutamate to 322+/-139% of basal levels, which could be attenuated by concomitant local administration of the nicotinic acetylcholine receptor antagonist mecamylamine (100 microM).
Asunto(s)
Ácido Aspártico/metabolismo , Ácido Glutámico/metabolismo , Receptores Nicotínicos/fisiología , Núcleo Solitario/metabolismo , Animales , Masculino , Mecamilamina/farmacología , Microdiálisis , Antagonistas Nicotínicos/farmacología , Presorreceptores/fisiología , Ratas , Ratas Endogámicas WKYRESUMEN
The nucleus tractus solitarius is a key brain centre involved in the regulation of numerous autonomic functions. The present study has employed in vitro autoradiography and in vivo microdialysis to investigate the presence and function of nicotinic acetylcholine receptors located in the medial nucleus tractus solitarius of the rat. Autoradiography using [125I]alpha-bungarotoxin (0.5 nM) enabled visualization of binding sites on sections of rat and monkey brainstem. Specific binding was highest in the medial nucleus tractus solitarius. The presence of binding sites was also apparent on sections of rat nodose ganglia/vagus nerve and human inferior vagal ganglia. Subsequent to unilateral ligation of the vagus nerve in the rat, an accumulation of binding sites was visualized adjacent to the ligature. Unilateral nodose ganglionectomy in the rat caused an approximate 97% reduction in [125I]alpha-bungarotoxin binding site density in the medial nucleus tractus solitarius from 814 +/- 183 to 27 +/- 2 d.p.m./mm2. Microdialysis results indicated that local administration of nicotine (1 mM) into the nucleus tractus solitarius of the rat resulted in increases of extracellular L-glutamate of 146 +/- 9% of basal levels. This effect was not reproducible following a second stimulation and was also blocked by prior and co-administration of the nicotinic acetylcholine receptor antagonist mecamylamine (100 microM). Extracellular levels of L-aspartate exhibited a similar pattern although results were not significant. Taken together, these results are supportive of the presence of a population of [125I]alpha-bungarotoxin binding sites located presynaptically with respect to vagal afferent terminals in the medial nucleus tractus solitarius of the rat. It is possible that these binding sites are the site of action of locally administered nicotine on extracellular levels of L-glutamate, the favoured neurotransmitter at primary baroreceptor afferent fibres. These data are discussed in relation to the functional pharmacology of acetylcholine and nicotinic acetylcholine receptors in this region of the brain.
Asunto(s)
Tronco Encefálico/metabolismo , Bungarotoxinas/metabolismo , Ganglio Nudoso/metabolismo , Receptores Nicotínicos/análisis , Núcleo Solitario/metabolismo , Adulto , Anciano , Animales , Autorradiografía , Femenino , Humanos , Radioisótopos de Yodo , Macaca fascicularis , Masculino , Microdiálisis , Persona de Mediana Edad , Ratas , Ratas Endogámicas WKY , Receptores Nicotínicos/metabolismo , VagotomíaRESUMEN
1. In the present study, in vitro electrophysiology and receptor autoradiography were used to determine whether rat vagal afferent neurones possess gamma-aminobutyric acid (GABA)A receptors. 2. GABA (1-100 microM) and isoguvacine (3-100 microM) caused a concentration-dependent depolarization of the rat isolated nodose ganglion preparation at room temperature. When applied to the tissue 20 min before the agonist, SR95531 (3 microM) and bicuculline (3 microM) caused a parallel shift to the right of the GABA and isoguvacine concentration-response curves, yielding shifts of 81 fold and 117 fold for SR95531 and 4 fold and 12 fold for bicuculline, respectively. 3. Baclofen (10 nM-100 microM) was unable to elicit a depolarization of the rat isolated nodose ganglion preparation at either room temperature or at 36 degrees C, whilst 5-aminovaleric acid (10 microM), a GABAB receptor antagonist, was unable to antagonize significantly the GABA-induced depolarization at either room temperature or at 36 degrees C. 4. [3H]-SR95531 (7.2 nM), a GABAA receptor-selective antagonist, bound topographically to sections of rat brainstem. Specific binding was highest in the medial nucleus tractus solitarius (NTS) and dorsal motor nucleus of the vagus nerve (DMVN). Binding was also observed in certain medullary reticular nuclei, in particular the parvocellular reticular nucleus. 5. Unilateral nodose ganglionectomy caused a reduction in GABAA binding site density in the medial NTS from 93 +/- 7 to 68 +/- 6 d.p.m./mm2. This procedure also caused a reduction in GABAA binding site density in the side of the NTS contralateral to the lesion, from 151 +/- 12 to 93 +/- 7 d.p.m./mm2. Sham surgery had no effect on the binding of [3H]-SR95531 in rat brainstem. 6. The present data provide evidence for the presence of GABAA receptors located on the soma and central terminals of rat vagal afferent neurones. Additionally, a population of GABAA receptors is evidenced postsynaptically in the rat NTS with respect to vagal afferent terminals. These data are discussed in relation to the functional pharmacology of GABA in this region of the NTS.
Asunto(s)
Neuronas Aferentes/fisiología , Receptores de GABA-A/fisiología , Nervio Vago/fisiología , 2-Amino-5-fosfonovalerato/farmacología , Animales , Autorradiografía , Bicuculina/farmacología , Tronco Encefálico/citología , Tronco Encefálico/efectos de los fármacos , Tronco Encefálico/metabolismo , Desnervación , Electrofisiología , Antagonistas de Aminoácidos Excitadores/farmacología , Agonistas del GABA/farmacología , Antagonistas del GABA/farmacología , Procesamiento de Imagen Asistido por Computador , Técnicas In Vitro , Ácidos Isonicotínicos/farmacología , Masculino , Neuronas Aferentes/efectos de los fármacos , Ganglio Nudoso/citología , Ganglio Nudoso/efectos de los fármacos , Ganglio Nudoso/fisiología , Terminales Presinápticos/efectos de los fármacos , Terminales Presinápticos/fisiología , Piridazinas/farmacología , Ratas , Ratas Endogámicas WKY , Receptores de GABA-A/efectos de los fármacos , Nervio Vago/citología , Nervio Vago/efectos de los fármacosRESUMEN
In vivo microdialysis was employed to measure release of endogenous L-glutamate (GLU) and L-aspartate (ASP) in the medial nucleus tractus solitarius of urethane anaesthetised rats. Basal extracellular levels of these amino acids were stable following a 90 min equilibration period (6.3 +/- 0.24 and 3.4 +/- 0.6 pmol/20 microliters sample of GLU and ASP, respectively). Basal levels of endogenous extracellular GLU and ASP were increased over 2-fold and 3-fold, respectively, following local administration of the selective 5-hydroxytryptamine (5-HT3) receptor agonist phenylbiguanide (300 microM). Intracerebral administration of the selective 5-HT3 receptor antagonist ondansetron (30 microM) blocked the effect of phenylbiguanide on GLU release whilst the effect on ASP was variable and complex. These data suggest that 5-HT3 receptor activation in the rat nucleus tractus solitarius can affect excitatory amino acid neurotransmission in this region of the medulla oblongata.
Asunto(s)
Aminoácidos Excitadores/metabolismo , Receptores de Serotonina/metabolismo , Núcleo Solitario/metabolismo , Animales , Ácido Aspártico/metabolismo , Biguanidas/farmacología , Aminoácidos Excitadores/farmacología , Ácido Glutámico/metabolismo , Hipoglucemiantes/farmacología , Técnicas In Vitro , Masculino , Microdiálisis , Ondansetrón/farmacología , Ratas , Ratas Endogámicas WKY , Núcleo Solitario/efectos de los fármacosRESUMEN
1-(2-Methoxyphenyl)-4-[(phthalimido)butyl] piperazine (NAN-190) and 8-[4-[4-(2-pyrimidinyl)-1-piperazinyl]butyl]-8-azaspiro[4.5] decane-7,9-dione (buspirone) are 5-HT1A receptor partial agonists which decrease 5-hydroxytryptamine (5-HT) release in vivo. In order to assess whether these ligands decrease 5-HT release by stimulating 5-HT1A receptors we examined the ability of the selective 5-HT1A receptor antagonist N-tert-butyl 3-4-(2-methoxyphenyl) piperazin-1-yl-2-phenylpropanamide dihydrochloride (WAY-100135) to block their inhibitory effects on 5-HT. NAN-190 (0.1 mg/kg s.c.) and buspirone (1.0 mg/kg s.c.) significantly decreased extracellular levels of 5-HT in hippocampal dialysates. WAY-100135 (10.0 mg/kg s.c.) attenuated the effect of buspirone but had no significant effect on the NAN-190-induced decreased in 5-HT release. These data demonstrate that buspirone is an agonist at the somatodendritic 5-HT1A receptor but that the inhibitory effects of NAN-190 on 5-HT release may be mediated via a mechanism other than, or in addition to, 5-HT1A receptor agonism.
Asunto(s)
Buspirona/farmacología , Hipocampo/metabolismo , Piperazinas/farmacología , Antagonistas de la Serotonina/farmacología , Agonistas de Receptores de Serotonina/farmacología , Serotonina/metabolismo , Animales , Interacciones Farmacológicas , Espacio Extracelular/efectos de los fármacos , Espacio Extracelular/metabolismo , Hipocampo/efectos de los fármacos , Inyecciones Subcutáneas , Masculino , Ratas , Ratas Sprague-Dawley , Técnicas EstereotáxicasRESUMEN
SDZ 216,525 has been proposed to be a silent 5-HT1A receptor antagonist. The present study examined the potential intrinsic agonist action of SDZ 216,525 using two in vivo models of somatodendritic 5-HT1A autoreceptor function: 5-HT release using microdialysis and feeding behaviour of satiated animals. SDZ 216,525 (1 mg/kg s.c.) and the alpha 1-adrenoceptor antagonist prazosin (1 mg/kg s.c.) significantly decreased hippocampal 5-HT release. In addition, SDZ 216,525 (3 and 10 mg/kg s.c.) and prazosin (3 and 10 mg/kg s.c.) significantly increased food intake in satiated rats. The selective 5-HT1A receptor antagonist (RS)-WAY100135 (10 mg/kg s.c.) which has been demonstrated to block the effects of 8-OH-DPAT on 5-HT release and food intake had no significant effect on the response induced by SDZ 216,525. In contrast, the non-selective 5-HT1A receptor antagonist (-)-pindolol (8 mg/kg s.c.) attenuated both SDZ 216,525 responses. The decrease in hippocampal 5-HT release and increase in food intake induced by SDZ 216,525 suggest that the compound may be a 5-HT1A receptor partial agonist. However, the failure of the 5-HT1A receptor antagonist (RS)-WAY100135 to block the SDZ 216,525 responses suggests that SDZ 216,525 decreases 5-HT release and increases food intake by a mechanism other than 5-HT1A receptor agonism. The high affinity of SDZ 216,525 for the alpha 1-adrenoceptor, and the ability of prazosin to decrease 5-HT release and increase food intake, suggest that the effects of SDZ 216,525 may be mediated via an alpha 1-adrenoceptor antagonist action.