Reversal of visual attention dysfunction after AMPA lesions of the nucleus basalis magnocellularis (NBM) by the cholinesterase inhibitor donepezil and by a 5-HT1A receptor antagonist WAY 100635.

RATIONALE: Degeneration of the cholinergic magnocellular neurons in the basal forebrain and their cortical projections is a major feature of the neuropathology of Alzheimer's disease (AD). In addition to memory dysfunction, attentional functions are also impaired in AD. OBJECTIVE: We investigated the extent to which the cholinesterase inhibitor donepezil reversed the attentional performance deficit in nucleus basalis magnocellularis (NBM) lesioned rats. We also examined the effects of a selective and potent 5-HT(1A) receptor antagonist, WAY 100635, on the attentional deficit of NBM lesioned rats. METHODS: We injected alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) into the NBM to selectively destroy cholinergic neurons projecting to the neocortex. Attentional functions were examined using the 5-CSRT task, in which hungry rats were required to locate brief visual targets presented randomly in one of five locations in a specially designed chamber. RESULTS. AMPA lesions of the NBM caused marked reductions in choline acetyltransferase activity (ChAT) ranging from 30 to 46% in medial areas of the cortex (medial-frontal and cingulate) and from 58 to 72% in more lateral areas (anterior-dorso-lateral and parietal). AMPA lesioned rats made fewer correct responses (choice accuracy), longer latency to correct response and an increase in the number of premature and perseverative responses. These impairments showed some recovery over the next 12 weeks. Reducing the duration of the visual stimulus reinstated the impairments in choice accuracy. The anticholinesterase inhibitor donepezil at 1.0 mg/kg but not 0.5 mg/kg reversed the impairments in choice accuracy and correct response latency. The premature and perseverative over-responding of AMPA lesioned rats remained unchanged. A dose of 0.1 mg/kg WAY 100635 to AMPA-lesioned rats improved their choice accuracy but did not shorten correct response latencies. The number of premature responses was reduced by WAY 100635 but perseverative over-responding was not affected. CONCLUSIONS: The attentional impairments induced due to cortical cholinergic dysfunction may be ameliorated by cholinergic treatments such as cholinesterase inhibitors. In addition, 5-HT(1A) receptors and the cortical cholinergic system exert balanced opposition in regulating attentional performance in the rat. Blockade of 5-HT(1A) receptors may be useful to treat some aspects of attentional dysfunction in AD.

Stimulation of 5-HT(1A) receptors in the dorsal raphe ameliorates the impairment of spatial learning caused by intrahippocampal 7-chloro-kynurenic acid in naive and pretrained rats.

OBJECTIVE: The present study investigated the effect of stimulating 5-HT(1A) receptors in the dorsal raphe on the impairment of spatial learning caused by intrahippocampal 7-chloro-kynurenic acid (7-Cl-Kyn) in naive rats and in rats familiar with the general requirements of the task. METHODS: A week after implantation of cannulae to give access to the dorsal raphe (DR) and the CA1 region of the dorsal hippocampus, rats started their 5 days acquisition training on a two-platform spatial discrimination task in a water maze. On each acquisition day, WAY 100635 and 8-OH-DPAT alone or in combination were injected into the dorsal raphe (DR) 5 min before intrahippocampal injections of 7-Cl-Kyn which was given 10 min before the training session. Similar experiments were conducted in rats that had been familiarized with the general requirements of the task by pretraining them in the water maze in the absence of distal cues. RESULTS: 7-Cl-Kyn (3 microg/microl), injected bilaterally in the CA1 region of the dorsal hippocampus, impaired choice accuracy with no significant effect on choice latency. Rats treated with 7-Cl-Kyn tended to spend more time swimming close to the pool walls and made more errors of omission than controls in the first two sessions. Administered into the DR, the 5-HT1A receptor agonist 8-OH-DPAT (1 microg/0.5 microl) had no effect on any parameter of rats' performance but antagonized the impairment of choice accuracy caused by intrahippocampal 7-Cl-Kyn. Injected into the DR, 1 microg/0.5 microl WAY 100635, a 5-HT(1A) receptor antagonist, had no effect on rats' performance or on the impairment caused by intrahippocampal 7-Cl-Kyn, but antagonized the effect of 8-OH-DPAT on the 7-Cl-Kyn-induced deficit. The non-mnemonic behavioral disturbances shown by naive rats treated with 7-Cl-Kyn were greatly reduced in pretrained rats which, nevertheless, showed a marked impairment of choice accuracy similar to that of naive rats. As in previous experiments, administration of 1 microg/0.5 microl 8-OH-DPAT in the dorsal raphe antagonized the impairment of choice accuracy caused by intrahippocampal 7-Cl-Kyn without any effect on other parameters of rats' performance. CONCLUSIONS: The results show that stimulation of presynaptic 5-HT(1A) receptors in the dorsal raphe counteracts the deficit in spatial learning caused by a reduced NMDA-mediated excitatory input on pyramidal cells in the hippocampus. The possible mechanisms and the importance of these findings for the symptomatic treatment of memory disorders in man are discussed.

Chronic treatment with desipramine facilitates its effect on extracellular noradrenaline in the rat hippocampus: studies on the role of presynaptic alpha2-adrenoceptors.

Adaptive phenomena such as desensitization of autoreceptors are considered an important factor in the achievement of therapeutic efficacy of antidepressant drugs after chronic treatment. We have studied whether a chronic treatment with desipramine had a greater effect than a single dose on the extracellular concentrations of noradrenaline in the dorsal hippocampus. Administration of 10 mg/kg i.p. desipramine once daily for 14 days significantly raised the basal extracellular noradrenaline in the dorsal hippocampus 24 h but not 48 h after the last drug injection. A challenge dose of desipramine increased extracellular noradrenaline in rats treated chronically with vehicle and desipramine. The effect was significantly higher in rats treated chronically with desipramine 48 h but not 24 h after the last injection. An intraperitoneal administration of the alpha2-adrenoceptor agonist clonidine at the dose of 10 microg/kg significantly reduced extracellular noradrenaline in the control group but not in animals chronically treated with desipramine whereas 30 microg/kg clonidine produced a similar decrease in both groups. Three concentrations of clonidine (0.05, 0.5 and 1 microM) infused into the hippocampus significantly reduced extracellular noradrenaline to a similar extent in rats chronically treated with saline or desipramine. Fourty-eight hours after the last injection of the chronic treatment, [3H]RX-821002 binding to alpha2-adrenoceptors in the rat locus coeruleus measured by autoradiography was not significantly modified. A slight (17%) but significant decrease of neuronal uptake of [3H]noradrenaline was found in synaptosome preparations from dorsal hippocampus of rats chronically treated with desipramine, but this was likely due to a decrease in affinity. The results suggest that a repeated treatment with desipramine (10 mg/kg i.p. once daily for 14 days) facilitates its effect on extracellular noradrenaline in the dorsal hippocampus and induces adaptive changes probably involving desensitization of alpha2-adrenoceptors, with no changes in their density, on noradrenergic neurons in the locus coeruleus.

Chronic treatment with reboxetine by osmotic pumps facilitates its effect on extracellular noradrenaline and may desensitize alpha(2)-adrenoceptors in the prefrontal cortex.

1. This study investigated the effect of acute (2 days) and chronic (14 days) treatment with a selective inhibitor of noradrenaline uptake, reboxetine (10 mg kg(-1) day(-1)) by osmotic pumps, on extracellular noradrenaline and the sensitivity of alpha(2)-adrenoceptors in the prefrontal cortex of rats. 2. The effect of continuous infusion of reboxetine for 14 days on cortical extracellular noradrenaline was significantly higher (599% of vehicle levels) than after 2 days (263% of vehicle levels). 3. Brain concentrations of reboxetine after 2 and 14 days of infusion were 37.9+/-17.8 and 37.1+/-7.7 ng g(-1), respectively. 4. Reboxetine infused for 2 and 14 days significantly increased extracellular dopamine in the prefrontal cortex, to a similar extent (257 and 342% of vehicle levels, respectively), whereas extracellular 5-HT was not modified by either treatment. 5. Clonidine (10 and 30 microg kg(-1) i.p.) reduced cortical extracellular noradrenaline similarly in animals treated with reboxetine or vehicle for 2 days whereas the effects in rats infused with reboxetine for 14 days were markedly less than in vehicle-treated animals. 6. Clonidine (0.05 and 0.2 microM), infused through the dialysis probe into the prefrontal cortex, reduced cortical extracellular noradrenaline much less in rats treated with reboxetine for 14 days than in vehicle-treated animals. 7. Reboxetine's effect on extracellular noradrenaline in the prefrontal cortex was greater after chronic treatment and could be associated with desensitization of terminal alpha(2)-adrenoceptors that normally serve to inhibit noradrenaline release.

Low doses of 8-OH-DPAT prevent the impairment of spatial learning caused by intrahippocampal scopolamine through 5-HT(1A) receptors in the dorsal raphe.

1. We studied the effects of low doses of 8-OH-DPAT, a 5-HT(1A) receptor agonist, on the impairment of spatial learning caused by scopolamine injected into the CA1 region of the dorsal hippocampus of rats performing a two-platform spatial discrimination task. 2. Bilateral injections of 4 microg (in 1 microl) of scopolamine into the CA1 region of the dorsal hippocampus 10 min before each training session impaired choice accuracy with no effect on choice latency and errors of omission. 3. Administered subcutaneously 20 min before each training session, 8-OH-DPAT 10 and 30 (but not 3) microg kg(-1) did not modify choice accuracy but prevented the impairment by intrahippocampal scopolamine. 4. Injection of 1.0 microg (in 0.5 microl) of WAY 100635, a 5-HT(1A) receptor antagonist, into the dorsal raphe 5 min before scopolamine had no effect on choice accuracy and latency or errors of omission and did not modify the effect of scopolamine, but completely antagonized the effect of 10 and 30 microg kg(-1) 8-OH-DPAT on scopolamine-induced impairment of choice accuracy. 5. The results confirm previous findings that stimulation of presynaptic 5-HT(1A) receptors in the dorsal raphe attenuates the deficit of spatial learning caused by blockade of cholinergic excitatory input on hippocampal pyramidal cells. 6. Drugs that stimulate presynaptic 5-HT(1A) receptors such as 5-HT(1A) receptor partial agonists may be useful in the symptomatic treatment of human memory disturbances associated with loss of cholinergic innervation to the hippocampus.

Alnespirone and buspirone have anxiolytic-like effects in a conflict procedure in rats by stimulating 5-HT(1A) receptors.

We studied the anxiolytic-like activity of alnespirone and buspirone, two 5-HT(1A) receptor agonists, in a modified Geller-Seifter conflict model, and examined the role of 5-HT(1A) receptors by studying whether WAY-100635, a selective antagonist at these receptors, blocked their effects. Administered s.c. 30 minutes before testing, 0.5 and 1mg/kg alnespirone significantly increased punished responding, whereas lower doses (0.125 and 0.25 mg/kg) had no effect. At 1mg/kg, alnespirone significantly reduced the rates of unpunished responding. One dose of buspirone (1mg/kg) significantly increased punished responding and reduced unpunished responding. Lower doses were ineffective. Administered s.c. 40 minutes before testing, WAY-100635 had no effect on any parameter but completely antagonized the effects of alnespirone (1mg/kg) and buspirone (1mg/kg) on punished responding. The ability of buspirone to reduce unpunished responding was not antagonized by WAY-100635, probably reflecting a sedative effect of buspirone due to dopamine D2 receptor blockade. The results suggest that alnespirone and buspirone have anxiolytic-like activity in a conflict procedure by stimulating 5-HT(1A) receptors, presumably at a presynaptic level. Like buspirone, alnespirone may have useful effects in the treatment of anxiety disorders.

The 5-HT(1A) receptor agonist 8-OH-DPAT reduces rats' accuracy of attentional performance and enhances impulsive responding in a five-choice serial reaction time task: role of presynaptic 5-HT(1A) receptors.

RATIONALE: Whilst several studies have investigated the role of serotonergic receptor subtypes in learning and memory, relatively few studies have examined their role in attentional processes. OBJECTIVE: The present study investigated the role of pre- and postsynaptic 5-HT1A receptors on rats' attentional performance in the five-choice serial reaction time task (5-CSRT). METHODS: Hungry rats were trained in the 5-CSRT task to detect brief (0.5 s) flashes of light presented randomly in one of five locations with a fixed intertrial interval of 5 s paced by the rat. We studied the effects of 8-OH-DPAT, a 5-HT1A receptor agonist, at various subcutaneous (SC) doses (10-100 microg/kg) on measures of rats' discriminative accuracy (the index of attentional functioning) and various behavioural indices of response control and motivation. Manipulations of basic task parameters, intracerebroventricular (ICV) injections of 5,7-dihydroxytryptamine (5,7-DHT) to deplete forebrain 5-HT and treatments with a selective 5-HT1A receptor antagonist WAY 100635 were made in order to determine the behavioural and neural specificity of the effects of 8-OH-DPAT. RESULTS: A dose of 100 microg/kg, but not lower doses, significantly reduced choice accuracy and increased errors of omission, latencies to respond correctly and to collect food reward and premature responses. All these effects were completely blocked by WAY 100635, injected SC 5 min before 8-OH-DPAT at doses from 10-100 microg/kg. WAY 100635 by itself had no effect in the task. Dimming the visual stimuli to one-third of the usual brightness did not modify the effect of 8-OH-DPAT on choice accuracy. Prolonging the stimuli from 0.5 to 1.0 s reversed 8-OH-DPAT's effect on choice accuracy but did not modify the other effects on rats' performance. An ICV injection of 150 microg 5,7-DHT, which depleted forebrain serotonin by 90%, reversed 8-OH-DPAT's effect on choice accuracy but did not modify the effects on errors of omission and latency to make correct responses. Similar effects were found by infusing 1.0 microg/0.5 microl WAY 100635 in the dorsal raphe 5 min before 8-OH-DPAT. 8-OH-DPAT increased the latency to collect the reinforcement; this effect was attenuated by ICV 5,7-DHT and completely antagonized by WAY 100635 in the dorsal raphe. Rats treated with 5,7-DHT or 8-OH-DPAT showed more premature responses and these effects were markedly reduced by the combined treatment. CONCLUSIONS: The results suggest that stimulation of presynaptic 5-HT1A receptors is involved in the ability of 8-OH-DPAT to cause attentional dysfunction and enhance impulsivity while slowing of responding and increase in errors of omission mainly depend on stimulation of post-synaptic 5-HT1A receptors.

JL13, a pyridobenzoxazepine compound with potential atypical antipsychotic activity, increases extracellular dopamine in the prefrontal cortex, but not in the striatum and the nucleus accumbens of rats.

In behavioral and receptor binding studies, 5-(4-methylpiperazin-1-yl)-8-chloro-pyridol[2,3b] [1,5]benzoxazepine (JL13) shows an atypical antipsychotic profile. We used microdialysis in awake rats to study the effects of various intraperitoneal doses of JL13 on extracellular concentrations of dopamine in the prefrontal cortex, nucleus accumbens and striatum. JL13 at 20 mg/kg and 40 mg/kg dose-dependently raised extracellular dopamine (234% and 434% of basal levels at peak, respectively) in the prefrontal cortex whereas lower doses (5 mg/kg and 10 mg/kg) had no effect. Extracellular concentrations of dihydroxyphenylacetic acid and homovanillic acid were also significantly increased in the prefrontal cortex of rats given 40 mg/kg JL13 (310% and 230% of basal levels, respectively). At 20 mg/kg and 40 mg/kg JL13 did not affect the extracellular concentrations of dopamine and its metabolites in the striatum and nucleus accumbens. The mechanisms by which JL13 increases cortical dopamine release and the significance for potential antipsychotic efficacy are discussed.

Modulatory role of neuropeptides in seizures induced in rats by stimulation of glutamate receptors.

Stimulation of glutamate receptors has been reported to modulate the expression of neuropeptides and their receptors in neurons. On the other hand, neuropeptides are known to regulate the presynaptic glutamate release and neuronal responses to excitatory neurotransmission. This evidence indicates a functional interaction between glutamatergic and neuropeptidergic transmission in the central nervous system (CNS). In this report, we provide pharmacologic evidence in experimental models of seizures, suggesting that somatostatin (SRIF) and neuropeptide Y (NPY) are endogenous modulators of glutamate-mediated hyperexcitability in the CNS. Electroencephalographic (EEG) and behavioral seizures were induced in rats by intrahippocampal or systemic injection of kainic acid, a glutamate analog. The number of EEG seizures and their total duration were inhibited significantly by intracerebral application of a SRIF(1) receptor agonist. Similarly, kainate seizures were reduced by N[-2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl-D-arginamide++ +] (BIBP 3226), a NPY Y(1) receptor antagonist. Enhanced seizure susceptibility to pentylentetrazol, ensuing in rats after a systemic administration of kainic acid, was reduced significantly by intracerebral application of RC 160, a SRIF(1) receptor agonist, or NPY 13-36, a Y(2)/Y(5) receptor agonist. This evidence suggests that neuropeptide analogs may be of value for controlling seizures and possibly in other pathologic conditions associated with excessive glutamate function.

Roles of 5-HT(1A) receptors in the dorsal raphe and dorsal hippocampus in anxiety assessed by the behavioral effects of 8-OH-DPAT and S 15535 in a modified Geller-Seifter conflict model.

8-OH-DPAT [8-hydroxy-2-(di-N-propylamino)tetralin], a 5-HT(1A) receptor agonist, and S 15535 (4-benzodioxan-5-yl)1-(indan-2-yl)piperazine, a partial agonist at 5-HT(1A) receptors, were administered into the dorsal raphe nucleus and dorsal hippocampus and their behavioral effects were assessed in a modified Geller-Seifter conflict model. Injected into the dorsal raphe nucleus 8-OH-DPAT, 1 microg but not 0.04 or 0.2 microg 0.5 microl(-1), and S 15535, 2.5 microg but not 0.1 or 0.5 microg 0.5 microl(-1), significantly increased punished responding with no effect on rates of unpunished or time-out responding. WAY 100635, a selective 5-HT(1A) receptor antagonist, injected subcutaneously at 0. 3 mg kg(-1) 30 min before 1 microg 8-OH-DPAT or 2.5 microg S 15535 in the dorsal raphe, completely antagonized their effects on punished responding. At doses ranging from 1 to 10 microg microl(-1) injected into the CA1 region of the dorsal hippocampus neither 8-OH-DPAT nor S 15535 modified punished responding or the rates of time-out. At the highest doses, 8-OH-DPAT significantly reduced unpunished responding whereas S 15535 had the opposite effect. The results suggest that stimulation of 5-HT(1A) receptors in the dorsal raphe nucleus has anxiolytic-like effects whereas stimulation of postsynaptic receptors in the dorsal hippocampus has no anxiolytic or anxiogenic effects, at least judging from changes in rates of punished responding. These results are compatible with the hypothesis that 5-HT(1A) receptor agonists and partial agonists attenuate anxiety by reducing serotonergic transmission in brain areas innervated by the dorsal raphe nucleus.

Differential expression of S100beta and glial fibrillary acidic protein in the hippocampus after kainic acid-induced lesions and mossy fiber sprouting in adult rat.

The expression of S100beta and glial fibrillary acidic protein (GFAP) was analyzed following bilateral injection of kainic acid (KA), a glutamate derivative, into the CA3 region of the adult rat hippocampus. This treatment produces a progressive degeneration of the pyramidal neurons of the hippocampus while sparing the granule cells of the dentate gyrus which undergo sprouting of their axons in the supragranular layer. Messenger RNA and protein levels were measured, by Northern blot and ELISA, in the hippocampus of lesioned and sham-operated rats 1, 7, and 30 days after KA injection. A significant increase of GFAP and its mRNA was demonstrated at each time point, whereas S100beta mRNA levels were significantly enhanced only 30 days after the KA injection and the levels of S100beta protein remained unchanged at all time points. However, when analyzed by immunohistochemistry the S100beta showed clear changes in its expression and distribution depending on the region considered. One month after KA injection, S100beta immunoreactivity was considerably reduced in the stratum radiatum of CA3 region, but there was increased S100beta immunoreactivity in the stratum moleculare. In particular, a notable band of S100beta positive, hypertrophic astrocytes appeared in the supragranular layer of the dentate gyrus where the sprouting of mossy fiber collaterals was detected by Timm's staining. These data show for the first time that an increase in S100beta expression in subpopulations of reactive astrocytes may be involved in the structural reorganization of the hippocampus following KA-induced neurodegeneration.

S 15535, a benzodioxopiperazine acting as presynaptic agonist and postsynaptic 5-HT1A receptor antagonist, prevents the impairment of spatial learning caused by intrahippocampal scopolamine.

1 The effect of S 15535 (4-benzodioxan-5-yl)1-(indan-2-yl)piperazine), an agonist at presynaptic and antagonist at postsynaptic 5-HT1A receptors, on the impairment of spatial learning caused by intrahippocampal scopolamine in a two-platform spatial discrimination task was studied. 2 Scopolamine (4.0 microg microl-1), injected bilaterally into the CA1 region of the dorsal hippocampus 10 min before each training session, impaired choice accuracy with no effect on choice latency and errors of omission. 3 Administered subcutaneously 30 min before each training session, S 15535 1.0 (but not 0.3) mg kg-1 did not modify choice accuracy but prevented its impairment by intrahippocampal scopolamine. 4 WAY 100635, a 5-HT1A receptor antagonist, injected into the dorsal raphe at 1.0 microg 0.5 microl-1 5 min before scopolamine, had no effect on choice accuracy and latency or errors of omission and did not modify the effect of scopolamine but completely antagonized the effect of S 15535 (1.0 mg kg-1) on scopolamine-induced impairment of choice accuracy. 5 The results confirm a previous report (Carli et al., 1998) that stimulation of presynaptic 5-HT1A receptors in the dorsal raphe counteracts the deficit caused by intrahippocampal scopolamine, probably by facilitating the transfer of facilitatory information from the entorhinal cortex to the hippocampus. 6 Drugs that stimulate action on presynaptic 5-HT1A receptors, such as S 15535 and other partial 5-HT1A receptors agonists, may be useful in the symptomatic treatment of human memory disturbances associated with loss of cholinergic innervation to the hippocampus.

Studies on the acute and chronic effects of reboxetine on extracellular noradrenaline and other monoamines in the rat brain.

1 The effect of reboxetine, a novel antidepressant drug that potently and selectively inhibits neuronal noradrenaline (NA) uptake, on brain extracellular monoamines was studied by microdialysis. 2 Fifteen mg kg-1 i.p. reboxetine raised extracellular NA in the frontal cortex (by 242%) and dorsal hippocampus (by 240%). 3 Idazoxan (1 mg kg-1 s.c.), given 60 min after 15 mg kg-1 reboxetine, markedly potentiated the effect on extracellular NA in the frontal cortex (by 1580%) and dorsal hippocampus (by 1360%), but had no effect by itself. 4 Twenty-four hours after the last injection of a chronic schedule (15 mg kg-1 i.p. once daily for 14 days) reboxetine had no effect on basal extracellular concentrations of NA in the dorsal hippocampus and a challenge dose of reboxetine (15 mg kg-1) raised extracellular NA similarly in rats treated chronically with reboxetine (by 353%) and saline (by 425%). 5 Ten and 20 microg kg-1 i.p. clonidine dose-dependently reduced hippocampal extracellular NA similarly in rats given chronic reboxetine (by 32% and 57%) and saline (by 42% and 56%). 6 Extracellular concentrations of dopamine and 5-HT in the striatum were similar in rats treated chronically with reboxetine and saline. A challenge dose of reboxetine (15 mg kg-1) had no effect on striatal extracellular dopamine and slightly increased striatal extracellular 5-HT to a similar extent in rats treated chronically with reboxetine (by 137%) and saline (by 142%). 7 The results suggest that combining reboxetine with an alpha2-adrenoceptor antagonist may facilitate its antidepressant activity. Repeated treatment confirmed that reboxetine is fairly selective for the noradrenergic system but provided no evidence of adaptive changes in that system that could facilitate its effect on extracellular NA.

Studies on the role of serotonin receptor subtypes in the effect of sibutramine in various feeding paradigms in rats.

The effect of the 5-hydroxytryptamine (5-HT) and noradrenaline (NA) reuptake inhibitor sibutramine was studied in food deprived, neuropeptide Y (NPY)- or muscimol-injected rats. Sibutramine dose-dependently reduced feeding caused by food-deprivation (ED50 = 5.1+/-0.8 mg kg(-1)) or by NPY injection into the paraventricular nucleus of the hypothalamus (ED50 = 6.0+/-0.5 mg kg(-1)). The increase in food intake caused by muscimol injected into the dorsal raphe was not modified by sibutramine (1-10 mg kg(-1)). The hypophagic effect of 5.1 mg kg(-1) sibutramine in food-deprived rats was studied in rats pretreated with different serotonin receptor antagonists. Metergoline (non-selective, 0.3 and 1.0 mg kg(-1)), ritanserin (5-HT2A/2C, 0.5 and 1.0 mg kg(-1)) and GR127935 (5-HT1B/1D), 0.5 and 1.0 mg kg(-1)) did not modify the hypophagic effect of sibutramine, while SB206553 (5-HT2B/2C, 5 and 10 mg kg(-1)) slightly but significantly reduced it (Fint(2.53) = 3.4; P<0.05). The reduction in food intake caused by 6.0 mg kg(-1) sibutramine in NPY-injected rats was not modified by GR127935 (1.0 mg kg(-1)). The results suggest that, with the possible exception of a partial involvement of 5-HT2B/2C receptors in sibutramine's hypophagia in food-deprived rats, 5-HT1 and 5-HT2 receptor subtypes do not play an important role in the hypophagic effect of sibutramine, at least in the first 2 h after injection.

Fluoxetine increases extracellular dopamine in the prefrontal cortex by a mechanism not dependent on serotonin: a comparison with citalopram.

Fluoxetine at 10 and 25 mg/kg increased (167 and 205%, respectively) the extracellular dopamine concentration in the prefrontal cortex, whereas 25 (but not 10) mg/kg citalopram raised (216%) dialysate dopamine. No compound modified dialysate dopamine in the nucleus accumbens. The effect of 25 mg/kg of both compounds on cortical extracellular dopamine was not significantly affected by 300 mg/kg p-chlorophenylalanine (PCPA) (fluoxetine, saline, 235%; PCPA, 230%; citalopram, saline, 179%; PCPA, 181%). PCPA depleted tissue and dialysate serotonin by approximately 90 and 50%, respectively, and prevented the effect of fluoxetine and citalopram on dialysate serotonin (fluoxetine, saline, 246%; PCPA, 110%; citalopram, saline, 155%; PCPA, 96%). Citalopram significantly raised extracellular serotonin from 0.1 to 100 microM (251-520%), whereas only 10 and 100 microM increased dialysate dopamine (143-231%). Fluoxetine similarly increased extracellular serotonin (98-336%) and dopamine (117-318%). PCPA significantly reduced basal serotonin and the effects of 100 microM fluoxetine (saline, 272%; PCPA, 203%) and citalopram (saline, 345%; PCPA, 258%) on dialysate serotonin but did not modify their effect on dopamine (fluoxetine, saline, 220%; PCPA, 202%; citalopram, saline, 191%; PCPA, 211%). The results clearly show that the effects of fluoxetine and of high concentrations of citalopram on extracellular dopamine do not depend on their effects on serotonin.

WAY 100635, a 5-HT1A receptor antagonist, prevents the impairment of spatial learning caused by blockade of hippocampal NMDA receptors.

We studied the effect of WAY 100635, a 5-HT1A receptor antagonist, on the impairment of spatial learning caused by intrahippocampal injection of 3-((R)-2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP), a competitive NMDA receptor antagonist, in a two-platform spatial discrimination task. CPP, 3 and 10 ng/microl, administered bilaterally into the CA1 region of the dorsal hippocampus 10 min before each training session, dose-dependently reduced choice accuracy in the two-platform spatial discrimination task with little or no effect on choice latency and errors of omission. A volume of 10 ng/microl intrahippocampal CPP did not affect choice accuracy or latency of a non-spatial visual discrimination task. Subcutaneous doses of 0.3 and 1 mg/kg WAY 100635 did not modify the choice accuracy, but prevented the impairment caused by 10 ng/microl intrahippocampal CPP. A dose of 20 ng/microl WAY 100635 into the dorsal hippocampus prevented the deficit caused by 10 ng/microl CPP administered in the same region. The results suggest that blockade of 5-HT1A receptors can compensate the loss of NMDA-mediated excitatory input to pyramidal cells in the hippocampus. These findings may have clinical relevance for the symptomatic treatment of memory disorders associated with reduced glutamate transmission mediated by NMDA receptors.

Brain-derived neurotrophic factor immunoreactivity in the limbic system of rats after acute seizures and during spontaneous convulsions: temporal evolution of changes as compared to neuropeptide Y.

Seizures increase the synthesis of brain-derived neurotrophic factor in forebrain areas, suggesting this neurotrophin has biological actions in epileptic tissue. The understanding of these actions requires information on the sites and extent of brain-derived neurotrophic factor production in areas involved in seizures onset and their spread. In this study, we investigated by immunocytochemistry the changes in brain-derived neurotrophic factor in the hippocampus, entorhinal and perirhinal cortices of rats at increasing times after acute seizures eventually leading to spontaneous convulsions. We also tested the hypothesis that seizure-induced changes in brain-derived neurotrophic factor induce later modifications in neuropeptide Y expression by comparing, in each instance, their immunoreactive patterns. As early as 100 min after seizure induction, brain-derived neurotrophic factor immunoreactivity increased in CA1 pyramidal and granule neurons and in cells of layers II-III of the entorhinal cortex. At later times, immunoreactivity progressively decreased in somata while increasing in fibres in the hippocampus, the subicular complex and in specific layers of the entorhinal and perirhinal cortices. Changes in neuropeptide Y immunoreactivity were superimposed upon and closely followed those of brain-derived neurotrophic factor. One week after seizure induction, brain-derived neurotrophic factor and neuropeptide Y immunoreactivities were similar to controls in 50% of rats. In rats experiencing spontaneous convulsions, brain-derived neurotrophic factor and neuropeptide Y immunoreactivity was strongly enhanced in fibres in the hippocampus/parahippocampal gyrus and in the temporal cortex. In the dentate gyrus, changes in immunoreactivity depended on sprouting of mossy fibres as assessed by growth-associated protein-43-immunoreactivity. These modifications were inhibited by repeated anticonvulsant treatment with phenobarbital. The dynamic and temporally-linked alterations in brain-derived neurotrophic factor and neuropeptide Y in brain regions critically involved in epileptogenesis suggest a functional link between these two substances in the regulation of network excitability.

Citalopram-induced hypophagia is enhanced by blockade of 5-HT(1A) receptors: role of 5-HT(2C) receptors.

The selective 5-hydroxytryptamine reuptake inhibitor citalopram (10 and 20 mg kg(-1), i.p.) significantly reduced food intake in male rats (CD-COBS) habituated to eat their daily food during a 4-h period. The 5-HT1A receptor antagonist WAY100635 (0.3 mg kg(-1)) administered systemically did not modify feeding but significantly potentiated the reduction in food intake caused by 10 mg kg(-1) i.p. citalopram. The dose of 5 mg kg(-1) i.p. citalopram was not active in animals pretreated with vehicle but significantly reduced feeding in animals pretreated with WAY100635. WAY100635 (0.1 microg 0.5 microl(-1)) injected into the dorsal raphe significantly potentiated the hypophagic effect of 10 mg kg(-1) citalopram. WAY100635 (1.0 microg 0.5 microl(-1)) injected into the median raphe did not modify feeding or the hypophagic effect of 10 mg kg(-1) citalopram. The 5-HT2B/2C receptor antagonist SB206553 (10 mg kg(-1), p.o.) slightly reduced feeding by itself but partially antagonized the effect of WAY100635 administered systemically (0.3 mg kg(-1), s.c.) or into the dorsal raphe (0.1 microg 0.5 microl(-1)) in combination with 10 mg kg(-1) i.p. citalopram. The hypophagic effect of 10 mg kg(-1) i.p. citalopram alone was not significantly modified by SB206553. Brain concentrations of citalopram and its metabolite desmethylcitalopram in rats pretreated with SB206553, WAY100635 and their combination were comparable to those of vehicle-pretreated rats, 90 min after citalopram injection. The hypophagic effect of citalopram was potentiated by blocking 5-HT1A receptors. Only the effect of the WAY100635/citalopram combination seemed to be partially mediated by central 5-HT2C receptors.

Stimulation of 5-HT1A receptors in the dorsal raphe reverses the impairment of spatial learning caused by intrahippocampal scopolamine in rats.

This study investigated the effect of stimulating 5-HT1A receptors in the dorsal raphe on the impairment of learning caused by 4 microg/microL scopolamine injected in the CA1 region of the dorsal hippocampus in rats performing a two-platform spatial discrimination task. At 1 (but not 0.2) microg/0.5 microL administered in the dorsal raphe on each acquisition training day 5 min before bilateral intrahippocampal injection of 4 microg/microL scopolamine, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), a 5-HT1A receptor agonist, had no effect on choice accuracy and latency or errors of omission but completely antagonized the impairment of choice accuracy by intrahippocampal scopolamine. Administered into the dorsal raphe at 0.2 and 1 microg/0.5 microL, WAY 100635, a 5-HT1A receptor antagonist, had no effect on rats' performance or on the impairment caused by intrahippocampal scopolamine but dose-dependently antagonized the effect of 1 microg/0.5 microL 8-OH-DPAT on the scopolamine-induced deficit. The results show that stimulation of presynaptic 5-HT1A receptors in the dorsal raphe reverses the deficit caused by intrahippocampal scopolamine, probably by facilitating the transfer of facilitatory information from the entorhinal cortex to the hippocampus. Together with a previous study showing that blockade of postsynaptic hippocampal 5-HT1A receptors antagonized the effect of intrahippocampal scopolamine in the two-platform spatial discrimination task (Carli et al., 1995b), the results suggest that drugs with presynaptic stimulatory and postsynaptic blocking actions on 5-HT1A receptors, such as partial agonists at these receptors, may be useful in the symptomatic treatment of human memory disturbances associated with loss of cholinergic innervation to the hippocampus.

Anticonvulsant properties of BIBP3226, a non-peptide selective antagonist at neuropeptide Y Y1 receptors.

Several lines of evidence indicate that neuropeptide Y (NPY)-mediated neurotransmission in the hippocampus is altered by limbic seizures. The functional consequences of this change are still unresolved and clearly depend on the type of NPY receptors involved. We have investigated the role of NPY Y1 receptor subtypes, which are enriched in the dentate area of the hippocampus, on EEG seizures induced by a local injection of 0.04 microg kainic acid in rats. Intrahippocampal administration of 10 microg BIBP3226 (N2- (diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]D-arginamide), a non-peptide selective antagonist at the NPY Y1 receptors, increased threefold on average (P < 0.01) the time to onset of seizures and reduced the number of seizures and the total time in seizures three- and fourfold, respectively (P < 0.01). Its inactive S-enantiomer BIBP3435 was ineffective on seizure activity. One microgram [Leu31,Pro34]NPY, an agonist at Y1 receptors, did not modify per se the EEG sequelae induced by kainic acid but it antagonized the anticonvulsant effect of BIBP3226. These results indicate that NPY Y1 receptors in the hippocampus are involved in epileptic phenomena and suggest that selective Y1 receptor antagonists may be of value for attenuating limbic seizures.