Effect of acute and chronic administration of buspirone on serotonin and benzodiazepine receptor subtypes in the rat brain: an autoradiographic study.

The affinity of buspirone and its main metabolite 1-(2-pyrimidinyl)piperazine (PmP) for serotonin1 (5-HT1) and benzodiazepine receptors was first evaluated by computerized receptor autoradiography. The results confirmed that buspirone is a selective 5-HT1A ligand, since it inhibited the binding of [3H]5-HT with lower IC50 values (about 100 nM) in regions of the brain of the rat where this receptor subtype is predominant (such as hippocampal areas). Larger IC50 values than 3 microM were found in areas of the brain richer in 5-HT1 receptors, other than the 5-HT1A subtype (e.g. striatum, substantia nigra and the ventricles). The PmP was not selective, inhibiting the binding of [3H]5-HT with similar affinity (about 4-10 microM) in all the regions of the brain examined. Neither buspirone nor PmP, up to 100 microM, were active on benzodiazepine receptors. The autoradiographic technique was therefore used to evaluate the effects of acute (10 mg/kg, p.o., 1 hr before killing) and chronic (10 mg/kg, i.p., twice a day for 21 days, 24 hr washout) treatment with buspirone in male rats. Acute treatment reduced the binding of [3H]5-HT in all the regions of the brain studied, including those with low levels of 5-HT1A receptors, indicating the occupancy of 5-HT1 receptors by either buspirone or its metabolite. The binding of [3H]flunitrazepam was decreased (16%) only in the substantia nigra.(ABSTRACT TRUNCATED AT 250 WORDS)

Adaptive changes in the NMDA receptor complex in rat hippocampus after chronic treatment with CGP 39551.

Chronic treatment of adult rats with DL-(E)-2-amino-4-methyl-5-phosphono-3-pentenoic carboxyethylester (CGP 39551) (30 mg/kg orally for 12 days) induced a significant increase, 72 h after the last dose, in the N-methyl-D-aspartate (NMDA)-sensitive [3H]glutamate binding in the hippocampal pyramidal layer (stratum oriens CA1, CA3: +51% on average; stratum radiatum CA1, CA3: +40% on average; stratum pyramidale CA1: +20%, CA3: +55%) and in the dentate gyrus (+43%) compared to vehicle-injected animals, as assessed by quantitative receptor autoradiography. Similar results were obtained using the NMDA receptor antagonist, [3H]DL-(E)-2-amino-4-propyl-5-phosphono-3-pentenoic acid (CGP 39653). Saturation experiments showed that the increase in [3H]CGP 39653 binding was due to the maximum number of receptors, without changes in affinity. The same regimen did not alter [3H]N-(1-[2-thienyl]-cyclohexyl)-3,4-piperidine (TCP) binding to the ion channel coupled to the receptor but prevented D-serine (5 microM)-induced enhancement of [3H]glutamate binding. NMDA (3-300 microM) enhanced [3H]noradrenaline release from hippocampal slices, and 7-Cl-kynurenic acid (5-100 microM) and (+)-5-methyl-10,11-dihydro-5H-dibenzo-[a,d]cyclo-hepten-5,10-imine maleate (MK 801) (0.03-0.3 microM), antagonists at the glycine site and ion channel respectively, antagonized this effect to the same extent in CGP 39551-treated rats and controls. Chronic CGP 39551 did not affect the neurotoxic potency of quinolinic acid, a selective agonist at the NMDA receptor, injected in the hippocampus.(ABSTRACT TRUNCATED AT 250 WORDS)

Down-regulation of alpha 2-adrenoceptors involved in growth hormone control in the hypothalamus of infant rats receiving short-term clonidine administration.

In infant rats short-term administration of the alpha 2-adrenoceptor agonist, clonidine (CLO), induces refractoriness to the growth hormone (GH)-releasing effect of an acute CLO challenge. CLO reportedly stimulates GH release via increased release of GH-releasing hormone (GHRH) from the hypothalamus. Based on these premises, in this study we investigated the possibility that repeated CLO administration may induce down-regulation of hypothalamic alpha 2-adrenoceptors, involved in GH control, thus prohibiting the GH-releasing effect of the drug. alpha 2-Adrenoceptor binding was determined in different brain regions of 10-day-old rats pretreated for 5 days with CLO (150 micrograms/kg, b.i.d.) and killed 14 h after last CLO administration. [3H]p-Aminoclonidine [( 3H]PAC) was used as the specific ligand of alpha 2-adrenoceptors. Treatment with CLO decreased by about 30% the maximum number of binding sites (Bmax) in areas of the mediobasal hypothalamus (MBH) involved in the stimulatory control of GH secretion, i.e. nucleus periventricularis arcuatus, nucleus ventromedialis hypothalami and nucleus lateralis hypothalami. Reduction of Bmax for [3H]PAC binding was observed also in the nucleus periventricularis hypothalami, an area involved in the inhibitory control of GH secretion and, among extrahypothalamic areas, only in the cortex piriformis. In no brain areas was the affinity constant (Kd) for [3H]PAC binding significantly changed after CLO pretreatment. Binding studies performed with a specific ligand of alpha 1-adrenoceptors, [3H]prazosin, showed that the effect of CLO was specific since no changes in the Bmax or Kd were present in either hypothalamic or extrahypothalamic regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Does GFAP mRNA and mitochondrial benzodiazepine receptor binding detect serotonergic neuronal degeneration in rat?

Intracerebroventricularly (ICV) injected 5,7-dihydroxytryptamine (5,7-DHT), which reduced by 70-90% forebrain serotonin levels, significantly raised glial fibrillary acidic protein (GFAP) mRNA levels in the hippocampus and nucleus raphe dorsalis 5 days but not 15 days after the lesion. A significant increase of mitochondrial benzodiazepine receptors (MBR), measured by binding autoradiography of 3H-PK 11195, was found in the nucleus raphe dorsalis 5 and 15 days after the ICV 5,7-DHT and also in the hippocampus, ventral tegmental area, and substantia nigra at 15 days. No significant effect was observed in the striatum and cortex for either GFAP mRNA or MBR binding. Unlike the ICV route, bilateral injection of 5,7-DHT into the medial forebrain bundle, which caused a 65-90% reduction of serotonin levels in different forebrain regions, significantly raised GFAP mRNA and MBR binding only at the site of injection with no effect in hippocampus, striatum, and cortex. MBR binding slightly increased in the nucleus raphe dorsalis 15 days after the lesion. High doses of d-fenfluramine (10 mg/kg intraperitoneally twice daily for 4 days) caused 80-90% reduction of serotonin levels 5 days after the last injection but did not change the GFAP mRNA or the MBR binding in any of the brain regions considered. These findings suggest that the effect of 5,7-DHT on microglial and glial markers is probably related to a nonspecific interaction with other neuronal systems besides the serotonin or to direct interaction with glial cells; the use of these parameters for detecting selective degeneration of serotonin axons presents some obvious limitations.

GABAA receptor impairment in the genetic absence epilepsy rats from Strasbourg (GAERS): an immunocytochemical and receptor binding autoradiographic study.

Some aspects of the GABA and cholinergic systems have been investigated in the cortex and thalamus of GAERS Wistar rats, a model of petit-mal epilepsy, and in a non-epileptic control strain. GABA and its synthetic enzyme, glutamic acid decarboxylase (GAD), were located by immunocytochemistry; the GABAA receptors were evaluated by autoradiography of GABA-enhanced 3H-flunitrazepam binding and by immunocytochemistry using specific antibodies against the beta 2-beta 3 subunits of GABAA receptor protein. GABA and GAD immunocytochemistry did not show up any difference in density or distribution of immunoreactive elements (fibers, terminals and neurons) between epileptic and control animals, but autoradiographic and immunocytochemical studies showed a decreased enhancement of 3H-flunitrazepam binding and of beta 2-beta 3 subunits of GABAA receptor in the sensorimotor cortex and anterior thalamic areas of the epileptic strain. No differences were found in benzodiazepine receptors in the two strains. GABAB receptors were measured as 3H-baclofen binding in a crude synaptic membrane preparation and there was no difference between epileptic and control animals. Choline acetyltransferase, the synthetic enzyme for acetylcholine, and muscarinic receptor subtypes (M1 and M2), visualized respectively by an immunocytochemical procedure and binding autoradiography, did not differ in epileptic and normal rats. The data suggest an impairment of the 'GABAA system' in restricted brain regions of epileptic rats, due to a reduction of receptor beta 2-beta 3 subunits and coupling to benzodiazepine receptors despite the normal synthesis and location of the neurotransmitter.

Modulation of [3H]-glutamate binding by serotonin in the rat hippocampus: an autoradiographic study.

Serotonin (5-HT) added in vitro (10 microM) increased [3H]-glutamate specific binding in the rat hippocampus, reaching statistical significance in layers rich in N-Methyl-D-Aspartate sensitive glutamate receptors. This effect was explained by a significant increase in the apparent affinity of [3H]-glutamate when 5-HT is added in vitro. Two days after lesion of serotonergic afferents to the hippocampus with 5,7-Dihydroxytryptamine [3H]-glutamate binding was significantly decreased in the CA3 region and stratum lacunosum moleculare of the hippocampus, this reduction being reversed by in vitro addition of 10 microM 5-HT. The decrease observed is due to a significant reduction of quisqualate-insensitive (radiatum CA3) and kainate receptors (strata oriens, radiatum, pyramidal of CA3). Five days after lesion [3H]-glutamate binding increased significantly in the CA3 region of the hippocampus but was not different from sham animals in the other hippocampal layers. Two weeks after lesion [3H]-glutamate binding to quisqualate-insensitive receptors was increased in all the hippocampal layers, while kainate and quisqualate-sensitive receptors were not affected. These data are consistent with the possibility that 5-HT is a direct positive modulator of glutamate receptor subtypes.

A case of truncus arteriosus type II.

A case of truncus arteriosus type II is reported. Truncus arterious is an uncommon congenital cardiac defect where a single great vessel exits the heart. Truncus arteriosus is usually fatal, if untreated. This defect occurs when the conus arteriosus and the truncus divide erroneously in the embryo. Palliative surgery in truncus arteriosus has been unsuccessful. Pulmonary banding has been tried and was ineffective and usually fatal. We operated on a nine-month-old (6200 g) male infant with a type II (Edwards-Collett) defect and a large ventricular septal defect. The pulmonary artery average pressure was 51 mmHg. We performed a cardiopulmonary bypass in the usual manner. Pulmonary arteries were resected from the truncal root, and primary end-to-end anastomosis of the truncal root to the ascending aorta was performed. Right ventricle to pulmonary artery continuity was provided using a valveless Gore-Tex graft. We lost our patient due to intractable pulmonary hypertension on the first postoperative day.

Transient global amnesia: case-reports.

We report the clinical and paraclinical data concerning 53 cases of transient global amnesia.