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R Samanin

Publications and source records attributed to R Samanin.

At least 73 records · Page 4Linked to original sources

Expression of GAP-43 in the granule cells of rat hippocampus after seizure-induced sprouting of mossy fibres: in situ hybridization and immunocytochemical studies.

The axonal growth-associated protein GAP-43 is believed to play some role in the synaptic remodelling that takes place in the hippocampus of adult rats after certain experimental lesions. GAP-43 mRNA is highly expressed in adult CA3 pyramidal cells but almost absent in the dentate granule cells. We analysed whether the sprouting of granule cell axons, the mossy fibres of the hippocampus, caused by kainic acid-induced seizures in adult rats was associated with any induction of GAP-43 mRNA in granule cells and with any changes in the immunostaining pattern of GAP-43 in the hippocampus. Increased GAP-43 mRNA expression was found to be induced in granule cells 18, 24 and 30 h after a systemic injection of kainic acid which induced generalized seizures in adult rats, and returned to control levels by 48 h post-treatment. No effect was observed in other regions of the hippocampus. However, when kainic acid was injected into 15-day-old rats, which responded with generalized seizures but no sprouting of mossy fibres, there was no induction of GAP-43 mRNA in the granule cells, suggesting a close relation between GAP-43 expression and sprouting of these cells. Seven days after kainic acid injections, GAP-43 immunostaining was decreased in the inner molecular layer of the dentate gyrus except for a thin supragranular band, whereas 30 days after treatment all animals showed increased GAP-43 immunoreactivity in the whole inner molecular layer.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Potential antidepressant properties of SR 57746A, a novel compound with selectivity and high affinity for 5-HT1A receptors.

SR 57746A, 4-(3-trifluoromethylphenyl)-N-[2-(naphth-2-yl)ethyl]-1,2,3,6- tetrahydropyridine HCl, was studied for its specific 5-HT1A receptor agonist action and antidepressant-like effects in the rat. The compound showed a high affinity for 5-HT1A specific binding sites in the rat hippocampus (IC50 3 nM), moderate affinity (10(-7)-10(-6) M) for dopamine D2 receptor, 5-HT uptake, 5-HT2 and alpha 1-adrenoceptor binding sites and practically no effect on binding sites of monoamine, GABAA, benzodiazepine and histamine receptors. It inhibited forskolin-stimulated adenylate cyclase activity in rat hippocampal membranes at concentrations of 10(-6) and 10(-5) M. The effect of 10(-6) M SR 57746A on forskolin-stimulated adenylate cyclase activity was completely antagonized by 10(-6) M (-)-propranolol. Administered per os as a three-dose course to rats, SR 57746A significantly increased struggling in the forced swimming test at doses from 0.3 to 3 mg/kg. Single doses had no such effect. The effect of a three-dose course with 1 mg/kg SR 57746A on rats' struggling was antagonized by pretreatment with 5 mg/kg i.p. metergoline, a non-selective 5-HT receptor antagonist, and by 20 mg/kg i.p. (-)-propranolol, an antagonist at 5-HT1 receptors. Three oral doses of 100 mg/kg parachlorophenylalanine, an inhibitor of 5-HT synthesis, and 100 mg/kg i.p. (+/-)-sulpiride, an antagonist at dopamine D2 receptors, also antagonized the effect of SR 57746A in the forced swimming test. The results show that SR 57746A has selectivity and high affinity for 5-HT1A receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenylyl Cyclases↗

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.

5,7-Dihydroxytryptamine↗

Evidence that extracellular concentrations of dopamine are regulated by noradrenergic neurons in the frontal cortex of rats.

Experiments were performed to confirm that noradrenergic terminals regulate extracellular concentrations of dopamine (DA) in the frontal cortex of rats. The effects of 20 mg/kg 1-[2-[bis(4-fluorphenyl)methoxy]-ethyl]-4-(3- phenylpropyl)piperazine (GBR 12909), a selective inhibitor of DA uptake, and 2.5 mg/kg desipramine (DMI) on the extracellular concentrations of DA in the frontal cortex and striatum were studied in rats given 6-hydroxydopamine (6 micrograms/microliters) bilaterally into the locus coeruleus to destroy noradrenergic terminals. GBR 12909 increased dialysate DA similarly in the striatum of vehicle and 6-hydroxydopamine-treated rats, whereas in the frontal cortex it raised DA concentrations only in lesioned animals. DMI raised extracellular DA concentrations in the frontal cortex but not in the striatum of controls. The effect of DMI on cortical DA was abolished by the 6-hydroxydopamine lesion. GBR 12909, at a subcutaneous dose of 20 mg/kg, further increased cortical dialysate DA in rats given DMI intraperitoneally at 20 mg/kg or through the probe at 10(-5) mol/L. The data support the hypothesis of an important regulation of the extracellular concentrations of DA in the frontal cortex by noradrenergic terminals.

Animals↗

Electrical kindling of the hippocampus is associated with functional activation of neuropeptide Y-containing neurons.

The release of neuropeptide Y (NPY) was measured from hippocampal slices of rats at stage 2 (preconvulsive stage) and stage 5 (full seizure expression) of electrical kindling of the dorsal hippocampus (upper blade of the dentate gyrus). Spontaneous release in naive rats (9.0 +/- 0.8 fmol/ml every 10 min) was independent of external Ca2+ but was reduced by 38 +/- 3.6% (P < 0.05) during 20 min incubation with 5 microM tetrodotoxin. Spontaneous efflux in naive rats did not differ from that in shams (implanted with electrodes but not stimulated) or in rats kindled to stage 2 and stage 5. Twenty-five, 50 and 100 mM KCl induced a concentration-dependent release of NPY (P < 0.05 and P < 0.01 at 25 and 50-100 mM respectively) from slices of shams. The effect of 100 mM KCl was reduced by 94 +/- 1% (P < 0.01) in the absence of Ca2+. Two days after the last stage 2 stimulation and 1 week after the last stage 5 seizure, NPY release was significantly larger than in shams at all KCl concentrations in the stimulated and contralateral hippocampus (P < 0.05 and P < 0.01). Forty-eight hours after one single after-discharge and 1 month after the last stage 5 seizure, 50 mM KCl induced a significantly larger release of NPY in the stimulated and contralateral hippocampus (P < 0.01 and P < 0.05), although the effect was less than during kindling.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗

Increased expression of preproneuropeptide Y and preprosomatostatin mRNA in striatum after selective serotoninergic lesions in rats.

The levels of neuropeptide Y and somatostatin may change when serotoninergic neurotransmission is altered in different brain regions. To assess whether serotonin regulates the synthesis of these peptides, we measured the levels of preproneuropeptide Y (ppNPY) and preprosomatostatin (ppSOM) mRNA in different brain regions after intracerebroventricular injection of 5,7-dihydroxytryptamine (5,7-DHT), a selective serotonin neurotoxin. The mRNA of these peptides significantly increased in the striatum but not in hippocampus and frontal cortex. It thus appears that serotonin has an inhibitory effect on the biosynthesis of neuropeptide Y and somatostatin in striatum whereas it probably acts by stimulating the release of these peptides in hippocampus and frontal cortex.

5,7-Dihydroxytryptamine↗

Increased expression of GAP-43, somatostatin and neuropeptide Y mRNA in the hippocampus during development of hippocampal kindling in rats.

The expression and distribution of the mRNA coding for the growth-associated protein-43 (GAP-43), a putative marker for neuritic growth, for preprosomatostatin and the preproneuropeptide Y (ppNPY) were analysed in the rat hippocampus during the development of hippocampal kindling by an in situ hybridization technique and computer-assisted grain counting in the cell. The levels of GAP-43 mRNA increased significantly in the CA3 pyramidal neurons and hilar polymorphic neurons of the dentate gyrus 2 days after stage 2 of kindling (preconvulsive stage) but not stage 5 (full seizure expression) in the stimulated hippocampus. The distribution of GAP-43 mRNA was the same in the hippocampus of kindled rats as in sham-stimulated animals. Preprosomatostatin mRNA and ppNPY mRNA contents rose significantly in the hilar polymorphic neurons of the dentate gyrus of the stimulated and contralateral hippocampus at both stages of kindling, with the greatest effect at stage 5. In addition, the number of ppNPY mRNA neurons in the fascia dentata was significantly higher in kindled rats than in controls, but there were no differences in the number of preprosomatostatin mRNA-positive cells. Preprosomatostatin and ppNPY mRNAs were also increased in the neurons of the stratum oriens of the CA1-CA3 subfield of fully kindled animals, whereas at stage 2 only neurons of the CA1 stratum oriens showed a significant increase of preprosomatostatin mRNA. No changes in preprosomatostatin and ppNPY mRNA expression were observed in the various regions of the hippocampus after a single afterdischarge or 1 month after stage 5.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

Clonidine-induced place preference is mediated by alpha 2-adrenoceptors outside the locus coeruleus.

Clonidine, administered intraperitoneally at doses of 0.05 and 0.5 mg/kg, produced a conditioned place preference when paired with the less preferred compartment. No preference for either compartment was found when a balanced conditioning place preference paradigm was used. Infusion of 6 micrograms/microliters 6-hydroxydopamine in the locus coeruleus, which markedly depleted noradrenaline in terminal regions, did not modify the effect of 0.05 and 0.5 mg clonidine on place preference. The effect of 0.5 mg/kg was prevented by 1 mg/kg idazoxan, an alpha 2-adrenoceptor antagonist, but not by 3 mg/kg prazosin, which blocks alpha 1-adrenoceptors. Idazoxan by itself (at doses from 0.3 to 3 mg/kg) induced a conditioned place preference when paired with the less preferred side. The results suggest that clonidine has motivational properties which serve to attenuate the aversiveness of the less preferred side in a conditioned place preference paradigm. Stimulation of alpha 2-adrenoceptors postsynaptic to noradrenaline-containing neurons seems to be involved.

Adrenergic alpha-Antagonists↗

Distribution of GAP-43 mRNA in the adult rat brain.

Regional distribution of gene expression of the axonal growth-associated protein, GAP-43, was studied in adult rat brains by in situ hybridization autoradiography to determine the features of mature neuronal populations that synthesize GAP-43 protein. Such synthesis appears to correlate with axonal growth during maturation and regrowth after axotomy. In most adult neurons, the sharp decline in GAP-43 gene expression implies a reduced capacity for axonal growth. Neurons capable of extending axonal knobs in the absence of injury may indicate a "plasticity" underlying dynamic processes of interaction between neurons and their synaptic targets. Antisense and sense (control) riboprobes were used on serial sections in the three principal axes, and the magnitude of hybridization signal was examined to determine regional patterns. GAP-43 mRNA levels are pronounced in diverse neuronal groups including the locus coeruleus, raphé nn., dopaminergic nigral and ventral tegmental nn., mitral cells, hippocampal CA3, inferior olivary n., vagal motor n. and other parasympathetic preganglionic neurons, select thalamic midline and intralaminar nn., several specific nn. of the hypothalamus and basal forebrain, the granular layer of cerebellar cortex, the infragranular neocortex, and the granular olfactory paleocortex; there is a substantial range in the magnitude of expression. Regions revealing minimal signal include most thalamic sensory relay nuclei, the granule neurons of the olfactory bulb and dentate gyrus, and the caudate and putamen. Possible concomitants of GAP-43 expression include regulation of ion flux and neurotransmitter release. Those neurons with long, extensively dispersed and numerous synaptic connections display the strongest signals and may possess the greatest propensity for continuous growth and turnover of their axon terminals, in contrast to short-axon and specific projection neurons exhibiting minimal levels. These data may enable inferring which populations display normal or experimentally induced axonal growth.

Animals↗

Tianeptine raises dopamine and blocks stress-induced noradrenaline release in the rat frontal cortex.

The effects of various doses of tianeptine on extracellular concentrations of dopamine were studied in the frontal cortex and nucleus accumbens of the rat. At 5 and 10 mg/kg intraperitoneally, tianeptine raised extracellular dopamine in the nucleus accumbens but only the higher dose caused a significant increase in the frontal cortex. At 10 mg/kg tianeptine significantly raised the concentrations of dihydroxyphenylacetic acid and homovanillic acid in both brain regions. In another experiment, 10 and 20 mg/kg tianeptine did not modify the extracellular concentrations of noradrenaline in the frontal cortex but dose dependently blocked the increase in extracellular noradrenaline caused by restraint stress.

3,4-Dihydroxyphenylacetic Acid↗

Stimulation of hippocampal 5-HT1A receptors causes amnesia and anxiolytic-like but not antidepressant-like effects in the rat.

Administration of 2 and 5 but not 0.4 microgram/microliter 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) into the CA1 region of the dorsal hippocampus 10 min before the acquisition trial in a passive avoidance task significantly reduced retention latencies 24 h later. The effect of 5 micrograms 8-OH-DPAT on retention latencies was completely antagonized by 1 microgram/microliter spiroxatrine, a 5-HT1A receptor antagonist, infused into the dorsal hippocampus 5 min before 8-OH-DPAT. Administered 5 min after the acquisition trial, 5 micrograms/microliters 8-OH-DPAT had no effect on retention latencies 24 h later. Administration of 5 micrograms/microliters 8-OH-DPAT into the dorsal hippocampus did not significantly change the thresholds for responses to the same electrical stimuli used in the passive avoidance task and had no antidepressant-like effect in the forced swimming test. The dose of 5 micrograms/microliters 8-OH-DPAT administered into the dorsal hippocampus caused anxiolytic-like effects assessed by stress-induced deficit in open field locomotor activity. The results suggest that stimulation of 5-HT1A receptors in the dorsal hippocampus impairs rats' performance in a passive avoidance task by interfering with memory processes or by attenuating the emotional impact of the shock through an anxiolytic action.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

The hypophagic effect of restraint stress in rats can be mediated by 5-HT2 receptors in the paraventricular nucleus of the hypothalamus.

Ritanserin (0.5 and 1 mg/kg) and ketanserin (2.5 mg/kg), two antagonists with high affinity for 5-HT2 receptors, attenuated restraint stress-induced hypophagia in rats. Two injections of the 5-HT2 receptor antagonist cinanserin (30 nmol/0.5 microliter) in the paraventricular nucleus of the hypothalamus completely reversed the effect of stress on food intake. (+/-)Cyanopindolol (3 and 8 mg/kg), an antagonist at 5-HT1A and 5-HT1B receptors, had no effect whereas 8-hydroxy-2-di-n-propylamino)tetralin (30-300 micrograms/kg), an agonist at 5-HT1A receptors, significantly attenuated the hypophagia. The results suggest that restraint stress-induced hypophagia is mediated by 5-HT2 receptors in the paraventricular nucleus of the hypothalamus. The potential utility of this model in anorexia nervosa is discussed.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

Anti-somatostatin antibody enhances the rate of hippocampal kindling in rats.

A somatostatin-specific antibody (Ab) (1:250) was continuously infused into the stimulated dorsal hippocampus of rats from 4 days before to 26 days after the beginning of kindling or until the first stage 5. Controls received boiled Ab. The number of stimulations to the first stage 5 were reduced by 41 +/- 4% (P < 0.01, Student's t-test) in animals infused with the Ab compared to controls. The cumulative after-discharge in the stimulated hippocampus was slightly, although not significantly, reduced. Kindling was not affected when the Ab was infused only during the first 10 stimulations (stage 2). Histological analysis showed no neurotoxic effects in the hippocampus as a consequence of Ab infusion.

Animals↗

Role of serotonin receptors in the effect of sertraline on feeding behaviour.

The effect of sertraline, a serotonin (5-HT) uptake inhibitor, on 1 h food intake of food-deprived rats was studied in male rats treated intraperitoneally with 1 and 2.5 mg/kg metergoline, a 5-HT1 and 5-HT2 receptor antagonist, 0.5 mg/kg GR 38032F, a 5-HT3 receptor antagonist, or intracerebroventricularly with 6-hydroxy-dopamine to destroy catecholamine-containing neurons. The feeding-suppressant effect of 10 mg/kg sertraline was not significantly modified by any treatment. At 1 and 2.5 mg/kg metergoline did not significantly modify the reduction in total intake and meal size induced by sertraline in slightly-deprived rats whereas at 1 mg/kg the 5-HT receptor antagonist completely blocked the effect of 1.5 mg/kg d-fenfluramine, a 5-HT releaser and uptake inhibitor. In a runway test, metergoline at 1 but not 2.5 mg/kg significantly attenuated the effect of 10 mg/kg sertraline on starting speed in the first and second trial blocks. Both doses tended to attenuate the effect of sertraline on running speed but the interaction was not significant. The reduction in food intake induced by sertraline was antagonized only by 1 mg/kg metergoline in the last trial block. The bulk of these findings argues against an important role of 5-HT receptors in the effect of sertraline on feeding behaviour.

1-Naphthylamine↗

Effect of d-fenfluramine and 5,7-dihydroxytryptamine on the levels of tryptophan hydroxylase and its mRNA in rat brain.

Repeated high doses of d-fenfluramine (dF; 10 mg/kg, i.p. twice daily for 4 days) markedly reduced serotonin (5-HT) concentrations in the hippocampus and striatum of rat brain up to 1 month after treatment, while tryptophan hydroxylase (TPH) levels were reduced only in the hippocampus 5 days after injection. Unlike dF, an intracerebroventricular (i.c.v.) injection of 5,7-dihydroxytryptamine (5,7-DHT 150 micrograms/20 microliters) induced a marked and long-lasting reduction of 5-HT and TPH in both brain regions. Thirty days after injection, 5,7-DHT, but not dF, markedly reduced the number of labelled neurons in the dorsal and ventral regions of the nucleus raphe dorsalis (NRD) and raised the levels of TPH mRNA in the spared neurons at all times examined. TPH mRNA levels were raised 5 and 15 days after dF treatment in the NDR suggesting that changes in the TPH gene expression or transcript stability result following 5-HT depletion. These data are in agreement with the suggestion that 5,7-DHT damages 5-HT nerve terminals and perikarya, but leave unanswered the question of the mechanism of the long-lasting reduction of 5-HT levels caused by high, repeated doses of dF.

5,7-Dihydroxytryptamine↗

Extracellular somatostatin measured by microdialysis in the hippocampus of freely moving rats: evidence for neuronal release.

Intracerebral microdialysis combined with a sensitive and specific radioimmunoassay was used to monitor the neuronal release of somatostatin (somatostatin-like immunoreactivity, SLI) in the dorsal hippocampus of freely moving rats. The sensitivity of the radioimmunoassay was optimized to detect < 1 fmol/ml. The basal concentration of SLI in 20-min dialysate fractions (5 microliters/min) collected 24 h after probe implantation was stable over at least 200 min. The spontaneous efflux dropped by 54 +/- 6.4% (p < 0.05) when Ca2+ was omitted and 1 mM EGTA added to the Krebs-Ringer solution and by 65.5 +/- 3.2% (p < 0.05) in the presence of 1 microM tetrodotoxin. Depolarizing concentrations of the Na+ channel opener veratridine (6.25, 25, 100 microM) induced 11 +/- 2 (p < 0.05), 17 +/- 2 (p < 0.05), and 21 +/- 5 (p < 0.01) fold increase in SLI concentration, respectively, during the first 20 min of perfusion. The effect of 100 microM veratridine was blocked by coperfusion with 5 microM tetrodotoxin (p < 0.01) and reduced by 79% (p < 0.01) in the virtual absence of Ca2+. Neuronal depolarization by 20 min of perfusion with Krebs-Ringer solution containing 25 and 50 mM KCl and proportionally lowered Na+ increased the dialysate SLI 4.4 +/- 1 (p < 0.05) and 17 +/- 3 (p < 0.01) fold baseline, respectively. Ten micromolar ouabain, a blocker of Na+,K(+)-ATPase, increased the dialysate SLI 15-fold baseline, on average (p < 0.05), during 80 min of perfusion. The results demonstrate the suitability of brain microdialysis for monitoring the neuronal release of SLI and for studying its role in synaptic transmission.

Animals↗

Reciprocal interaction of 5-hydroxytryptamine and cholecystokinin in the control of feeding patterns in rats.

1. The effect of the CCKA receptor antagonist, devazepide (100 mg kg-1) on meal parameters during the initial phase of the dark period was studied in free-feeding rats by use of a procedure for continuously monitoring feeding patterns. 2. In a second experiment, the effect of devazepide on the reduction in meal parameters induced by the 5-hydroxytryptamine (5-HT) releaser and uptake inhibitor, (+)-fenfluramine (1.5 mg kg-1) in 4 h food-deprived rats was examined. 3. The hypophagic effect of an intraperitoneal injection of cholecystokinin (CCK-8, 4 micrograms kg-1) was studied in rats treated with the 5-HT receptor antagonist, metergoline (1 and 2 mg kg-1). 4. Devazepide increased the size of the first meal in free-feeding, but not in 4 h food-deprived rats and partially antagonized the effect of (+)-fenfluramine on the size and duration of the first meal. The reduction in eating rate induced by (+)-fenfluramine was not modified by devazepide. No changes in (+)-fenfluramine or (+)-norfenfluramine levels were found in the brain of rats treated with devazepide. 5. The effect of CCK-8 on meal size was completely antagonized by 2 mg kg-1 metergoline. A significant interaction was also found between 2 mg kg-1 metergoline and CCK-8 as regards their effect on the inter-meal interval. 6. The results suggest a reciprocal interaction between 5-HT and CCK-8 in enhancing the satiating effect of food in rats.

Animals↗

Neurochemical mechanism of action of anorectic drugs.

Studies with dexfenfluramine, an anorectic agent which releases 5-hydroxytryptamine (5-HT) from nerve terminals and inhibits its reuptake, have considerably increased our knowledge of the role of 5-HT in feeding control. 5-HT1B receptors mediate the satiating effect of dexfenfluramine, whereas the mechanism by which 5-HT uptake inhibitors such as fluoxetine and sertraline cause anorexia is not clear. Anorexia induced by (+)-amphetamine, phentermine, diethylpropion and phenylpropanolamine seems to be the result of their ability to increase the release of noradrenaline and/or dopamine from nerve terminals and inhibit their reuptake or, in the case of phenylpropanolamine, to stimulate directly alpha 1-adrenoceptors. It has been suggested that beta- and alpha 1-adrenoceptors and D1 dopamine receptors are involved in their effect on food intake. The difficulties of extrapolation across species limit our knowledge of the mechanism of the anorectic action in humans. Significant advances in the treatment of feeding pathology will be linked to identifying new receptor types and subtypes for neurotransmitters and quantifying and modelling eating disorders such as binge-eating and food craving.

Animals↗