Antidepressant-type effect of the NK3 tachykinin receptor agonist aminosenktide in mouse lines differing in endogenous opioid system activity.

The influence of the tachykinin NK3 receptor agonist, aminosenktide on the immobility in the forced swimming test was studied in mouse lines selectively bred for divergent magnitudes of stress-induced analgesia. The high analgesia (HA) line is known to display enhanced, and the low analgesia (LA) line displays reduced activity of the opioid system. Aminosenktide at doses of 125 microg/kg or 250 microg/kg intraperitoneally (IP) reduced, in naltrexone-reversible manner, the immobility more of opioid receptor-dense HA than of unselected mice, but was ineffective in the opioid receptor-deficient LA line. The effect of aminosenktide was quite similar to the antiimmobility action of desipramine (10 mg/kg IP), a prototypic antidepressant agent. None of the compounds increased animals' locomotion as found with an open field test; therefore their antiimmobility effect cannot be attributed to a change in general motility. The results claim that aminosenktide causes an antidepressant effect, and endogenous opioids are involved in this process.

Effects of a methanolic extract and a hyperforin-enriched CO2 extract of Hypericum perforatum on alcohol intake in rats.

Hypericum perforatum extracts (HPE) inhibit ethanol intake in rats. Hypericin and hyperforin have been proposed as major active principles of HPE. The present study compared the effect on ethanol intake in alcohol-preferring rats of two Hypericum perforatum extracts: a methanolic extract containing 0.3% hypericin and 3.8% hyperforin (HPE1) and a CO2 extract (HPE2) with 24.33% hyperforin and very low hypericin content. Freely feeding and drinking rats were offered 10% ethanol 2 h/day and HPE were given intragastrically 1 h before access to ethanol. Both extracts dose-dependently reduced ethanol intake, HPE2 being about eight times more potent than HPE1. Food and water intakes were not affected by doses that reduced ethanol intake. HPE2, unlike HPE1, reduced blood-alcohol levels (BAL) at doses of > or = 31.2 mg/kg, whereas the dose of 15.6 mg/kg, which reduced ethanol intake, did not significantly modify BAL; blood-acetaldehyde levels were never increased. As previously observed for HPE1, intracerebroventricular pretreatment with 5,7-dihydroxytryptamine (150 microg/rat) did not affect attenuation of ethanol intake induced by HPE2, but reduced its effect in the forced swimming test (FST). Intraperitoneal pretreatment with the sigma-1 receptor antagonist NE-100 (0.25 mg/kg) did not affect inhibition of ethanol intake induced by HPE1 (250 mg/kg) or HPE2 (125 mg/kg), but abolished the effect of both extracts in the FST. In conclusion, the present results indicate that HPE2 inhibits ethanol intake more potently than HPE1; the higher potency of HPE2 parallels the hyperforin content, suggesting that hyperforin may have an important role in reducing ethanol intake. Moreover, different neurochemical mechanisms are apparently responsible for the reduction of ethanol intake and for the antidepressant-like effect of HPE.

The psychopharmacology of tachykinin NK-3 receptors in laboratory animals.

The present article reviews the studies so far published on the psychopharmacological effects mediated by tachykinin NK-3 receptors in laboratory animals. Central administration of NK-3 receptor agonists has been reported to attenuate alcohol intake in alcohol-preferring rats and to evoke conditioned place preference. These findings suggest that NK-3 receptors may affect reward processes to drugs of abuse. Anxiolytic-like and antidepressant-like effects have been previously reported for NK-1 receptor antagonists, and anxiolytic-like effects for NK-2 receptor antagonists. More recently, it has been shown that NK-3 receptor agonists have anxiolytic-like and antidepressant-like effects in mice and rats, while an NK-3 receptor antagonist was reported to be anxiogenic in mice. These findings indicate that different TK receptor subtypes may be involved in anxiolytic-like and antidepressant-like effects in laboratory animals and raise interest for the possible role of NK-3 receptors in the control of anxiety and depression in man.

Nociceptin/orphanin FQ and drugs of abuse.

Nociceptin/orphanin FQ (NC) binds with high affinity to the opioid receptor-like1 (ORL1) receptor. NC has been reported to block opioid-induced supraspinal analgesia, and it has been proposed that it may represent a functional antiopioid peptide in the control of brain nociceptive processes. The wide distribution of NC and of its receptors in the central nervous system suggests, however, that it may be involved in the control of a variety of biologic functions. Increasing evidence indicates that it may influence the rewarding and reinforcing properties of drugs of abuse. NC has been shown to abolish the rewarding properties of ethanol and morphine in the place conditioning paradigm, to reduce ethanol consumption in alcohol-preferring rats and to inhibit stress-induced alcohol-seeking behavior. These findings suggest that drugs directed at central NC receptors may represent an interesting approach to the treatment of ethanol and opiate abuse.

Effects of Hypericum perforatum extract on ethanol intake, and on behavioral despair: a search for the neurochemical systems involved.

The present study investigated the possible involvement of sigma receptors and of serotonergic mechanisms in the effects of Hypericum perforatum extract (HPE) on immobility time in the forced swimming test (FST) and on ethanol intake in Marchigian Sardinian alcohol-preferring rats. The HPE employed was a dry extract containing 0.3% hypericin and 3.8% hyperforin. Intraperitoneal pretreatment with 20 mg/kg of the sigma receptor antagonist rimcazole (RIM), 30 min prior to HPE, completely suppressed the antiimmobility effect of HPE (3 intragastric injections of 250 mg/kg). Intracerebroventricular pretreatment with 5, 7-dihydroxytryptamine (5,7-DHT), which produced a marked depletion of brain serotonin, reduced the antiimmobility effect, although this reduction was not as pronounced as that of RIM. On the other hand, the inhibitory effect of HPE on 10% ethanol intake was modified neither by 5,7-DHT nor by RIM pretreatment. These results suggest that the antidepressant-like effect of HPE in the FST may be mediated by interaction with sigma receptors and to some extent by increased serotonergic neurotransmission. On the other hand, these mechanisms appear to be unimportant for the effect of HPE on ethanol intake.

Hyperphagic effect of novel compounds with high affinity for imidazoline I(2) binding sites.

Previous studies have suggested that imidazoline I(2) receptors play a role in feeding control in rats. The effect of subcutaneous (s.c.) injections of four novel imidazoline I(2) ligands, 2-naphthalen-2yl-4,5-dihydro-1H-imidazole hydrochloride (benazoline), 2-styryl-4,5-dihydro-1H-imidazole oxalate (tracizoline), o-nitro-tracizoline and o-methyl-tracizoline (metrazoline) on food intake during the light phase was now evaluated in freely feeding male Wistar rats. Their effect was compared to that of idazoxan, a high-affinity ligand at imidazoline I(2) binding sites, but also a potent alpha(2)-adrenoceptor antagonist. Compared to idazoxan, metrazoline exhibits a higher pK(i) for imidazoline I(2) binding sites in rat liver, while the other compounds have a slightly lower pK(i); on the other hand, the novel compounds have much lower affinity than idazoxan at alpha(2)-adrenoceptors. Idazoxan stimulated drinking at a dose as low as 1 mg/kg, and evoked feeding at a higher dose (30 mg/kg). The selective alpha(2)-adrenoceptor antagonist 2-methoxy-idazoxan (RX821002), with negligible affinity at imidazoline I(2) binding sites, significantly increased drinking but failed to stimulate feeding at doses of 10-50 mg/kg. Metrazoline induced hyperphagia and water drinking at doses of 50 mg/kg or higher. Its dipsogenic effect was secondary to the hyperphagic effect, since it was not observed in rats without access to food. Benazoline significantly increased feeding only in response to 30 mg/kg, but its effect was less pronounced than that of metrazoline. Tracizoline and o-nitro-tracizoline were inactive. Following injection into the lateral cerebroventricle at doses up to 100 microgram/rat, and into the third or fourth brain ventricle at doses up to 50 microgram/rat, neither idazoxan nor metrazoline induced hyperphagia. The present results support the idea that imidazoline I(2) ligands influence feeding in rats, and suggest that their site of action is not in the central nervous system. The finding that idazoxan elicits a more potent hyperphagic effect than metrazoline and benazoline, although its affinity for imidazoline I(2) binding sites is lower than that of metrazoline and similar to that of benazoline, raises the question whether its hyperphagic effect might also be due to interaction with other receptors.

Antidepressant-like effect of ethanol revealed in the forced swimming test in Sardinian alcohol-preferring rats.

RATIONALE: A large body of evidence indicates high comorbidity between depression and alcohol abuse. The self-medication hypothesis proposes that depressed subjects may abuse ethanol because it reduces the symptoms of depression. The present study evaluated whether ethanol may exert an antidepressant-like action in genetically selected alcohol-preferring rats, either Sardinian alcohol-preferring (sP) or Marchigian Sardinian alcohol-preferring (msP) rats, and for comparison in Sardinian alcohol-non-preferring (sNP) rats. METHODS: The forced swimming test (FST) was used to evaluate the antidepressant-like action of ethanol; in this test the effect of ethanol ingestion on the immobility time was determined. RESULTS: Ethanol-naive sP rats exhibited a longer period of immobility in comparison to sNP rats. Both in ethanol-naive sP and msP rats, voluntary ethanol drinking reduced the immobility time. A similar effect was obtained when repeated (five or nine) intragastric administrations of 0.7 g/kg ethanol were given during the 24 h prior to the test in msP and in sP, but not in sNP rats. Desipramine, like ethanol, sharply reduced immobility at doses of 5 or 20 mg/kg, given 3 times in the 24 h before the test in msP rats. The reduced immobility induced by ethanol in msP rats was apparently not the consequence of a general motor activation, because 9 IG administrations of ethanol, 0.7 g/kg, failed to alter locomotor activity in the open field test. Moreover, blood alcohol levels and rectal temperature of msP, sP and sNP after IG ethanol administration were not statistically different. CONCLUSIONS: The present results provide evidence for an antidepressant-like action of ethanol in sP and msP rats and suggest that this action may contribute to sustain their high ethanol drinking.

Ethanol induces conditioned place preference in genetically selected alcohol-preferring rats.

The study of the biological mechanisms of ethanol reward has greatly suffered from problems to obtain ethanol-induced conditioned place preference (CPP) in rats. In the present study, CPP was obtained in genetically selected Marchigian Sardinian alcohol-preferring (msP) rats, derived from Sardinian alcohol-preferring rats, following intragastric (IG) ethanol administration by means of a permanent IG catheter, but not after intraperitoneal (IP) injection or IG gavage. Rats with permanent IG catheter, received IG administration of 0.35, 0.7, 1.5 or 2.8 g/kg ethanol, as a 10% v/v solution. In ethanol-experienced rats 0.7 or 1.5, but not 0.35 or 2.8 g/kg ethanol significantly increased in comparison to controls the time spent in the ethanol-associated previously non-preferred compartment, which became preferred in the post-conditioning test. In ethanol-naive rats, only 0.7 g/kg ethanol significantly increased the time spent in the ethanol-associated compartment. On the other hand, no effect was observed in alcohol-experienced rats following IG gavage, or IP injection of 0.35, 0.7 or 1.5 g/kg ethanol. The present results provide evidence that ethanol possesses postingestive rewarding properties in msP rats, and that it can reliably induce CPP in them, provided that an appropriate method of administration is adopted.

Effect of nociceptin on alcohol intake in alcohol-preferring rats.

The present study investigated the effect of nociceptin (NC), the endogenous ligand of the opioid-like orphan receptor ORL1, on ethanol intake in genetically selected Marchigian Sardinian alcohol-preferring (msP) rats. Acute intracerebroventricular (i.c.v.) injection of 250 or 500 ng/rat of NC, just before access to 10% ethanol (offered 2 h/day), significantly increased ethanol intake. Subchronic (7 days) i.c.v. injection of 500 ng/rat of NC, given just before access to 10% ethanol (for 30 min/day), resulted in a progressive decrease in ethanol consumption. After the end of NC treatment, rats progressively recovered their usual ethanol intake. When NC, 500 or 1000 ng/rat, was tested versus the effect of ethanol in the place conditioning paradigm, NC significantly reduced the increase in time spent in the ethanol-paired compartment after conditioning. This finding suggests that NC reduces the rewarding properties of ethanol in msP rats; thus, they may respond to the acute NC administration by increasing their ethanol intake in an attempt to achieve the usual reinforcing effect of ethanol, whereas subchronic NC treatment may result in extinction of ethanol drinking. The results of the present study suggest that the brain NC mechanisms may represent an interesting target of pharmacological interventions for the treatment of alcoholism.

Mechanism of action for reduction of ethanol intake in rats by the tachykinin NK-3 receptor agonist aminosenktide.

Intracerebroventricular (i.c.v.) injection of tachykinin (TK) NK-3 receptor agonists inhibits alcohol intake in genetically selected alcohol-preferring rats. The present study investigated the mechanism of action by which the selective TK NK-3 receptor agonist aminosenktide (NH2-SENK) attenuates ethanol intake in Marchigian Sardinian alcohol-preferring (msP) rats. The effect of NH2-SENK was studied by i.c.v. injection in the conditioned taste aversion (CTA) and in the conditioned place preference (CPP) paradigms; moreover, the effect of NH2-SENK on blood alcohol levels (BAL) following intragastric ethanol administration was investigated. The i.c.v. dose of 125 ng/rat of NH2-SENK, that markedly reduces ethanol intake, did not modify BAL, nor did it increase the CTA induced by intraperitoneal injection of ethanol, 1 g/kg body weight. These findings suggest that the effect of NH2-SENK on alcohol consumption is not related to modification of the pharmacokinetics of ethanol, nor to increase of the aversive properties of ethanol. On the other hand, the same i.c.v. dose of NH2-SENK evoked a pronounced and statistically significant CPP. This finding indicates that the TK NK-3 receptor agonist NH2-SENK possesses rewarding properties in msP rats and suggests that its inhibitory effect on ethanol consumption may be due to substitution of the rewarding properties of ethanol, thus making its consumption redundant.

Effect of lesions of the nucleus basalis magnocellularis and of treatment with posatirelin on cholinergic neurotransmission enzymes in the rat cerebral cortex.

The effect of 4 and 8 weeks of treatment with the thyrotropin releasing hormone (TRH), analogue posatirelin (L-6-ketopiperidine-2-carbonyl-L-leucyl-proline amide), on the changes of cholinergic neurotransmission enzymes, choline acetyltransferase (ChAT) and acetylcholinesterase (AChE), caused by lesions of the nucleus basalis magnocellularis (NBM), was investigated in the rat frontal cortex. ChAT and AChE were demonstrated with immunohistochemical and histochemical techniques, respectively associated with image analysis and microdensitometry. Monolateral and bilateral lesions of NBM area caused a significant loss of ChAT-immunoreactive nerve cell bodies in the NBM, as well as a remarkable decrease of ChAT-immunoreactive fibres and of AChE reactivity in the frontal cortex ipsilateral to the lesion or of both sides, respectively. The number of ChAT-immunoreactive nerve cell bodies in the lesioned NBM was higher in posatirelin-treated rats for 8 weeks in comparison with control NBM-lesioned rats. Moreover, the compound increased the number of ChAT-immunoreactive fibres in the frontal cortex of monolaterally and bilaterally NBM-lesioned rats at 8 weeks after lesion, but was without effect on these fibres in sham-operated rats. The same is true for AChE reactivity, developed in the neuropil of the frontal cortex, which was restored in part by an 8-week treatment with posatirelin in NBM-lesioned rats. These findings suggest that treatment with posatirelin rescues cholinergic neurons of the NBM and cholinergic projections to the cerebral cortex affected by lesioning of the NBM. The functional relevance of these observations and their possible applications should be evaluated in future studies.

Sensitivity of brain sites to the inhibitory effect on alcohol intake of the tachykinin aminosenktide.

The present study evaluated the sensitivity of several brain sites to the inhibitory effect of the tachykinin (TK) NK-3 receptor agonist aminosenktide (NH2-SENK) on 10% ethanol intake in genetically selected Marchigian Sardinian alcohol-preferring rats. Attention was focused on limbic structures involved in alcohol-seeking behavior and endowed with TK NK-3 receptors. NH2-SENK was bilaterally injected into the shell of the nucleus accumbens (NACC), the medial amygdala (AMY), the dorsal hippocampus (HIPP), the ventral tegmental area (VTA), the bed nucleus of the stria terminalis (BNST), the lateral hypothalamus (LH), and the nucleus basalis magnocellularis (NBM). NH2-SENK (injected up to 25-75 ng/site) into the NACC, AMY, HIPP, and VTA did not significantly modify ethanol intake. Injection of NH2-SENK into the BNST reduced ethanol intake at doses of 25 ng/site or higher, but the same doses also reduced water intake in water-deprived rats and food intake in food-deprived rats. Injection of NH2-SENK into the LH or the NBM at doses of 0.5, 5, or 25 ng/site inhibited 10% ethanol intake even at the lowest dose tested without affecting either food or water consumption in deprived animals. Present results indicate that the LH and the NBM are highly sensitive to the inhibitory effect of the TK NK-3 receptor agonist NH2-SENK on ethanol intake. TK peptides have been shown to evoke conditioned place preference following injection in the LH or the NBM, suggesting that in these brain sites the effect of TK agonists on ethanol intake might be due to interference with reward processes.

Prior repeated exposure to a 5-HT3 receptor agonist does not alter the ethanol-induced conditioned taste aversion in rats.

Several reports have indicated that the brain serotonergic 5-HT3 receptors are involved in at least some central effects of ethanol in rats. However, using an operant drug discrimination procedure, we have shown that these receptors are not primarily involved in the discriminative stimulus effects of ethanol. The aim of the present study was to further elucidate the role of 5-HT3 receptors in the formation of the ethanol-cueing effects in rats. To this purpose, a crossfamiliarization conditioned taste aversion (CF-CTA) procedure was used. Four daily injections of 1.5 g/kg ethanol (10% v/v) resulted in a significant attenuation of the subsequent ethanol-induced CTA. In contrast, four daily injections of the 5-HT3 receptor agonist, 1-(m-chlorophenyl)-biguanide (mCPBG; 50 microg per rat, i.c.v.) did not alter the subsequent ethanol-induced CTA. The 50 microg dose of mCPBG produced a marked CTA in a control experiment. These results taken together with some previous findings from our laboratory suggest that the brain 5-HT3 receptors do not play any crucial role in the mediation of the discriminative stimulus effects of ethanol.

Blockade of pre- and post-synaptic 5-HT1A receptors does not modify the effect of fluoxetine or 5-hydroxytryptophan on ethanol and food intake in rats.

Selective serotonin reuptake inhibitors (SSRIs) or serotonin precursors inhibit ethanol and food intake by increasing the synaptic availability of 5-HT in the central nervous system. However, these agents can also increase 5-HT levels at somatodendritic 5-HT1A autoreceptors, with negative effects on serotonergic transmission. (+)WAY100135 [N-ter-butyl 3-4-(2-methoxy-phenyl) piperazin-1-yl-2-phenylpropanamide dihydrochloride] is a selective antagonist both at pre- and post-synaptic 5-HT1A receptors. The present study investigated the effect on ethanol and food intake of (+)WAY100135, given alone or coadministered with the SSRI fluoxetine or the 5-HT precursor 5-hydroxytryptophan (5-HTP) in genetically selected alcohol-preferring rats. Blockade of presynaptic 5-HT1A receptors after injection of (+)WAY100135, 0.1 or 1 microgram/rat, into the dorsal raphe did not significantly modify ethanol, food or total fluid intake. The same doses of (+)WAY100135 did not modify the inhibition of ethanol and food intake induced by intraperitoneal (i.p.) injection of fluoxetine, 5 mg/kg. Subcutaneous (s.c.) administration of (+)WAY100135 (1 or 10 mg/kg) did not affect the 3-h, or the overnight intake of ethanol, food or total fluids. Given together with i.p. fluoxetine (5 mg/kg) or s.c. 5-HTP (100 mg/kg plus carbidopa. 12.5 mg/kg), the same s.c. doses of (+)WAY100135 did not modify their inhibitory effect on ethanol and food consumption. Present findings suggest that blockade either of pre- or of pre- and postsynaptic 5-HT1A receptors does not potentiate the inhibitory effect of fluoxetine or 5-HTP on ethanol and food intake.

Further evidence that the tachykinin PG-KII is a potent agonist at central NK-3, but not NK-1, receptors.

Intracerebroventricular (i.c.v.) injection of tachykinins (TKs) inhibits ethanol intake and angiotensin II-induced water intake; the effects are apparently mediated by NK-3 and NK-1 receptors, respectively. The present study evaluated the effect of the TK PG-KII, a novel kassinin-like peptide isolated from the skin of the Australian frog Pseudophryne güntheri, in these in vivo tests for central activity. PG-KII, given by i.c.v. injection, potently inhibited alcohol intake in genetically selected alcohol-preferring rats, being about 3 times more potent than the selective NK-3 receptor agonist NH2-SENK. The dose of 100 ng/rat, that markedly inhibited ethanol intake, did not inhibit food intake and prandial drinking in food deprived rats, providing evidence that the effect of PG-KII on ethanol intake is behaviorally selective. The effect on ethanol intake was inhibited by i.c.v. injection of the NK-3 receptor antagonist R820, but was not modified by the NK-1 receptor antagonist SR 140333. PG-KII inhibited drinking induced by angiotensin II only at doses of 300 or 1000 ng/rat, being about 5 times less potent than the selective NK-1 receptor agonist [Sar9, Met(O2)11] substance P. These doses of PG-KII produced also marked increase in competing behaviors, such as grooming and locomotion. The dose of 1000 ng/rat evoked a general inhibition of the ingestive behavior, reducing also food intake. The i.c.v. injection of the NK-1 receptor antagonist SR 140,333 only slightly inhibited the effect of PG-KII on angiotensin II-induced drinking, while it markedly reduced that of [Sar9, Met(O2)11] substance P. These findings, in accordance with those of previous studies, indicate that PG-KII is endowed with marked activity at central NK-3 receptors, and low activity at NK-1 receptors.

Effect of treatment with the neuroactive peptide posatirelin on microanatomical changes of frontal cortex and hippocampus caused by lesions of the locus coeruleus.

The influence of monolateral and bilateral lesions of the Locus coeruleus (LC) on the number of nerve cell and glial fibrillary acidic protein (GFAP)-immunoreactive astrocyte profiles, on silver-gold impregnated fibres and on tyrosine hydroxylase (TH) immunoreactivity was assessed in the rat frontal cortex and hippocampus. The influence of treatment for 4 and 8 weeks with a 10 mg/kg/day dose of the neuroactive peptide posatirelin on the above parameters was also investigated. Lesions of the LC decreased the number of nerve cell profiles in the frontal cortex 8 weeks after lesioning and were without effect on nerve cell profiles in the frontal cortex 4 weeks after lesioning and in the hippocampus at both 4 and 8 weeks after LC lesioning. Glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes were not affected by lesions of LC. Silver-gold impregnated fibres were decreased in the frontal cortex but not in the hippocampus of LC-lesioned rats at 8 weeks after lesioning. TH immunoreactivity, which was localized in nerve fibre-like structures both in the frontal cortex and in the hippocampus was decreased in the frontal cortex and in the hippocampus from the 4th week after LC lesioning. Treatment with posatirelin was without effect on the number of nerve cell and of GFAP-immunoreactive astrocyte profiles at both 4 and 8 weeks after LC lesioning, with the exception of nerve cells of the frontal cortex in monolaterally-lesioned rats which were increased 8 weeks after lesioning. The compound increased silver-gold impregnated fibres in the frontal cortex of monolaterally lesioned rats after 8 weeks of treatment, but did not affect TH immunoreactivity both in the frontal cortex or in the hippocampus. The above results suggest that treatment with posatirelin exerts a neuroprotective effect on the frontal cortex consisting of the partial restoration of some microanatomical changes caused by lesions of LC. The possible significance of this effect is discussed.

Effect of the thyrotropin releasing hormone analogue posatirelin (RGH 2202) on microanatomical changes induced by lesions of the nucleus basalis magnocellularis in the rat.

The effect of 4 and 8 weeks treatment with 10 mg/kg/day of the thyrotropin releasing hormone analogue posatirelin (L-6-ketopiperidine-2-carbonyl-L-leucyl-proline amide) on microanatomical changes induced by monolateral and bilateral lesions of the nucleus basalis magnocellularis (NBM) were investigated. The following parameters were assessed in the frontal cortex and hippocampus of NBM-lesioned and sham-operated rats: 1) number of nerve cell and glial fibrillary acidic protein (GFAP)-immunoreactive astrocyte profiles; 2) density of silver-gold impregnated fibres; 3) density of choline acetyltransferase (ChAT)-immunoreactive fibres; 4) intensity of acetylcholinesterase (AChE) staining. In NBM-lesioned untreated rats, no changes in the number of nerve cell or of astrocyte profiles were found either in the frontal cortex or in the hippocampus. The only exception was a decrease in the number of granule neuron profiles in the dentate gyrus at 8 weeks after lesioning. Silver-gold impregnated fibres, which express the width of interneuronal connections, were reduced in the hippocampus but not in the frontal cortex of NBM-lesioned rats. ChAT immunoreactivity and AChE reactivity, which were localised respectively in nerve fibre-like structures and in the neuropil, were decreased in the frontal cortex but not in the hippocampus from the fourth week after NBM lesioning. Lesions did not change the number of ChAT-immunoreactive nerve fibres or intensity of AChE staining in the hippocampus. Treatment with posatirelin was without effect on the number of nerve cell profiles or of GFAP-immunoreactive astrocytes both at 4 and 8 weeks after NBM lesioning. Treatment with the compound increased the number of silver-gold impregnated fibres in the hippocampus of NBM-lesioned rats and restored in part ChAT immunoreactivity and AChE reactivity in the frontal cortex. These effects were noticeable in NBM-lesioned rats after 8 weeks of treatment. The possible significance of the neuroprotective effect elicited by posatirelin treatment after lesions of the NBM is discussed.

Stimulation of tachykinin NK-3 receptors in the nucleus basalis magnocellularis reduces alcohol intake in rats.

Injections in the nucleus basalis magnocellularis (NBM) of the tachykinin (TK) NK-3 receptor agonist [Asp5,6,MePhe8]substance P(5-11), also referred to as amino-senktide (NH2-SENK), markedly reduced alcohol intake in genetically selected alcohol-preferring rats, offered 10% ethanol 2 h/day. The threshold dose in the NBM was 0.5 ng/site, while neither 1 nor 10 ng/rat of NH2-SENK inhibited alcohol intake following administration into the lateral ventricle. Injection of NH2-SENK, 25 ng/site, in the NBM did not modify water or food intake in water deprived rats, providing evidence for the behavioral selectivity of the effect on ethanol intake. The selective TK NK-3 receptor antagonist, R-820, injected in the NBM at the dose of 1000 ng/site 5 min before NH2-SENK 5 ng/site, significantly reduced the effect of NH2-SENK. The selective TK NK-1 receptor agonist [Sar9,Met(O2)11]substance P inhibited alcohol intake following injection in the NBM only at 25 ng/site; but the same dose induced marked grooming and inhibited also water intake in water deprived rats. The present results confirm that TK NK-3, but not NK-1, receptor agonists selectively inhibit ethanol intake in alcohol-preferring rats and suggest that the NBM is a site of action for their effect.

Possible mechanism of action for the attenuation of ethanol intake induced by ritanserin in rats.

The 5-HT2 receptor antagonist, ritanserin, reduces alcohol intake in rats and the nucleus accumbens (NAC) has been proposed as a site of action for the drug. Recent microdialysis studies have shown that acute subcutaneous (SC) administration of ritanserin increases extracellular 5-HT levels in the NAC. The present study evaluated, in genetically heterogeneous rats with developed preference for 3% ethanol, whether the attenuation of ethanol intake induced by ritanserin might be related to its effect on the synaptic availability of 5-HT in the NAC. Damaging 5-HTergic neurons by intracerebroventricular infusion of 5,7-dihydroxytryptamine (5,7-DHT) abolished the effect of ritanserin on ethanol consumption. Injections of the 5-HT3 receptor antagonist MDL 72222 into the NAC significantly reduced the inhibitory effect of SC injection of ritanserin, 1 mg/kg, and completely abolished the effect of ritanserin, 0.1 mg/kg. Subcutaneous injections of MDL 72222, 0.3 mg/kg 3 times/day, suppressed the effect of SC ritanserin, 0.1 mg/kg. The present findings, together with those of previous experiments showing that the tryptophan hydroxylase inhibitor p-chlorophenylalanine abolishes the effect of ritanserin, support the hypothesis that its effect on ethanol intake may be due to increased synaptic availability of 5-HT into the NAC.

The 5-HT4 receptor antagonist, GR113808, reduces ethanol intake in alcohol-preferring rats.

The present study evaluated the effect of the selective 5-HT4 receptor antagonist, GR113808, on ethanol intake in alcohol-preferring rats. Rats were offered 10% ethanol 2 h/day. In the first experiment, rats had food and water ad lib and 10% ethanol was offered from 1800 to 2000 h. In the second experiment, food was freely available, 10% ethanol was offered 2 h/day, from 1800 to 2000 h, and water was offered for 4 h, from 1800 to 2200 h. In both experiments GR113808 was subcutaneously injected at doses of 1, 3, or 10 mg/kg for 4 consecutive days, 5 min before access to ethanol. From the first day of administration, GR113808 significantly reduced the volitional ethanol intake in water sated rats at the three doses tested. In water-deprived rats, it reduced ethanol intake at 3 and 10 mg/kg, without modifying total fluid and food intake. In both experiments the effect of GR113808 remained rather stable during the 4 days of administration. The present findings, showing that the 5-HT4 receptor antagonist, GR113808, selectively reduces ethanol intake in alcohol-preferring rats, suggest that 5-HT4 receptors may play a role in alcohol intake control.