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The electric synaptic efficacy, in terms of extracellular electrical potentials, and the intracellular postsynaptic efficacy, in terms of inositol phosphate (IP) accumulation, were evaluated in rat hippocampal slices exposed for a brief period (10 min) to a high concentration of calcium (+2.7 mM). In addition, the effects of N -methyl- d -asparate (NMDA) ionotropic and metabotropic glutamate receptor (mGluR) antagonists on the induction and the establishment or maintenance of enhanced synaptic efficacy of CA1 pyramidal neurons due to high-calcium exposure were also tested. Elevation of the calcium concentration from 1.3–4 mM in the medium bathing hippocampal slices produced a long-lasting (60 over 90 min) increase in the slope of the CA1 somatic excitatory postsynaptic potential and the amplitude of the population spike (PS). Slice perfusion with NMDA antagonists cyclazocine and cis-4-phosphonomethyl-2-piperidine-carboxylic acid (CGS 19755) or with mGluR antagonists l -2-amino-3-phosphonopropionic acid (AP3) or alpha-methyl-4-carboxyphenyl-glycine (all 0.1 mM), during the 10-min period of exposure to high-calcium prevented the induction of such changes. By contrast, slice perfusion with the same concentration of CGS 19755 or l -AP3 did not affect the already established long-lasting increase in amplitude of CA1 PS induced by high-calcium. Moreover, high-calcium failed to produce any significant modification of the basal IP accumulation or of the IP accumulation elicited by mGluR agonist 1S,3R-trans-amino cyclo-pentane-1,3-dicarboxylic acid (ACPD). In conclusion, the results confirm that high-calcium induces a long-lasting increase in synaptic efficacy in rat hippocampal slices. Both NMDA ionotropic and mGluR receptors are involved in the induction, but not in the maintenance, of this phenomenon. In line with these data no modifications of basal or ACPD-induced phosphoinositide hydrolysis have been found during the maintenance stage.

Expression of Ca(2+)-induced CA1 long-term potentiation (LTP) was analysed in hippocampal slices obtained from (1) 3-month-old and (2) 18-20-month-old Sprague-Dawley rats selected for their performances in the Morris water maze task. In all slices, a transient (10 min) increase of extracellular Ca2+ concentration (4 mM) caused a long-lasting enhancement of potentials evoked by electrical stimulation of radiatum fibers. However, a significant difference was found in the degree of potentiation among groups. In particular, increases of the CA1 response amplitudes were significantly lower in old rats impaired in spatial learning than in young at 30 (P < 0.05), 60, 90 and 120 min (P < 0.01) after restoring the normal Ca2+ concentration. On the contrary, no differences were observed between young animals and the old ones with good performances in spatial learning. The data suggest that amplitude of CA1 Ca(2+)-induced LTP in old rats is related to spatial learning abilities.

The influence of the anticonvulsant felbamate has been tested on in vitro excitotoxicity induced by treatment of hippocampal slices with elevated concentrations of NMDA, AMPA and kainic acid. For comparison, the effects of the glutamate antagonist 7-chlorokynurenic acid and of the anticonvulsants pentobarbitone and lamotrigine, were also studied. Slice perfusion with 50 microM NMDA or 25 microM AMPA or 12 microM kainic acid produced within 30 min a disappearance or a pronounced irreversible amplitude reduction of the CA1 electrical synaptic responses. Slice perfusion with 1.2-1.6 mM felbamate or 100 microM lamotrigine significantly decreased the incidence of the irreversible disappearance of the CA1 electrical response induced by kainic acid. On the contrary, slice perfusion with the same concentrations of the drugs did not affect the irreversible disappearance of the CA1 electrical response induced by NMDA or AMPA. By contrast, slice perfusion with 100 microM of 7-chlorokynurenic acid significantly prevented the neurotoxic effects induced by both NMDA and kainic acid, while 100 microM of pentobarbitone failed to affect kainic acid-induced neurotoxicity. The different profile of neuroprotection elicited by felbamate with respect to reference drugs indicates that a different mechanism of action than antagonism of NMDA response or potentiation of GABA response underlies the neuroprotectant effects of felbamate.

The in vitro antiepileptic activity of the novel anticonvulsant drug felbamate was tested in rat hippocampal slices on the CA1 epileptiform bursting induced by different chemical epileptogenic agents. The effects of felbamate were compared with those of the anticonvulsant drugs diphenylhydantoin and pentobarbitone and with the effects of excitatory amino acid antagonists acting at both N-methyl-D-aspartate (NMDA) and non-NMDA receptors. Like the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX), felbamate at a minimum effective concentration of 1 mM induced a significant (P < 0.01) reduction of the duration of the CA1 epileptiform bursting due to the K+ channel blocker, 4-aminopyridine, and the excitatory amino acids, kainate and quisqualate. Like the NMDA receptor antagonist ketamine, felbamate (1.6 mM) significantly (P < 0.01) decreased the duration of the CA1 epileptiform bursting caused by 'Mg(2+)-free' solutions. Conversely, felbamate (1.6 mM), CNQX (100 microM) and ketamine (100 microM) failed to affect the epileptiform bursting induced by the GABA antagonist penicillin. Pentobarbitone (100 microM) significantly (P < 0.01) decreased the duration of the CA1 epileptiform bursting caused by 'Mg(2+)-free' solutions, 4-aminopyridine or penicillin, while diphenylhydantoin (up to concentrations of 100 microM) failed to have an effect. The results indicate that felbamate displays a unique profile of in vitro antiepileptic effects as a broad spectrum antagonist of excitatory amino acid transmission.

The intraperitoneal injection of d-amphetamine (5 mg/kg i.p.), preceded (10 min before) by intrastriatal injection of an adenosine A2 receptor agonist (CGS 21680, 5-10 micrograms) or followed (5 min later) by an intrastriatal adenosine A1 receptor agonist (N6-cyclopentyladenosine, CPA, 30 micrograms), induced ipsilateral rotations in rats. The opposite effect (contralateral rotations) was observed with adenosine receptor antagonists (A2 antagonist, 3,7-dimethyl-1-propargylxanthine, DMPX, 10 micrograms; A1 antagonist, 8-cyclopentyl-1,3-dimethylxanthine, CPT, 2.5 micrograms). These results confirm that both adenosine A2 and A1 receptors modulate striatal dopaminergic neurotransmission.

Induction of post-tetanic potentiation (PTP) and long-term potentiation (LTP) was analyzed in hippocampal slices obtained from (i) young (6 months old) rats of different strains (Sprague-Dawley, SD; spontaneously hypertensive rats, SHR; and Wistar-Kyoto, WKY), and (ii) from aged (20–24 months old) SD and Fischer 344 (F 344) rats, each group showing a different performance in the Morris maze test. After the application of an electrical tetanus (1 s, 100 Hz, 50 μA) in the stratum moleculare, a significant difference was found in the percent of induction of the dentate PTP in hippocampal slices obtained from rats of different strains and ages. In particular, the induction of the dentate PTP was significantly (P < 0.01) higher in slices obtained from young SD or spontaneously SHR rats, having the better performance in the Morris maze than in slices obtained from old SD or F 344 rats or young WKY rats which had poorer performances in the Morris maze. On the contrary, no significant differences were found in the percent of induction of the LTP in the dentate area of hippocampal slices obtained from rats of different strains and ages. Moreover, after the application of an electrical tetanus (1 s, 100 Hz, 50 μA) in the stratum radiatum, no significant differences were found in the percent of induction of both PTP and LTP in the CA1 area of hippocampal slices obtained from rats of different strains and ages. The data show that the induction of hippocampal dentate high-frequency PTP is reduced not only in old rats but also in some peculiar strains of rats with impaired behavioral capability in the Morris maze.

Induction of posttetanic potentiation (PTP) and long-term potentiation (LTP) was analyzed in hippocampal slices obtained from a) young 6-month-old Sprague-Dawley (SD) rats, all of them performing well in the Morris Maze, and b) aged SD 20-month-old and Fischer 344 24-month-old rats showing different degrees of ability in the same test. After the application of an electrical tetanus 1 s, 100 Hz, 50 microA in the stratum radiatum, no significant differences were found in the percent of induction of both PTP and LTP in the CA1 area of hippocampal slices obtained from rats of different strains and ages. After the application of an electrical tetanus 1 s, 100 Hz, 50 microA in the stratum moleculare, a significant difference was found in the percent of dentate PTP induction in hippocampal slices obtained from rats of different ages. Specifically, dentate PTP induction was significantly (p0.01) higher in slices obtained from young SD rats, and from old SD rats with a better performance in the Morris maze, escape latency less than 10 s and 150 cm, than in slices obtained from old SD or Fischer 344 rats that had shown poor performance in the Morris Maze. On the contrary, no significant differences were found in the percent of dentate LTP in hippocampal slices obtained from rats of different strains and ages. The data demonstrate that the induction of hippocampal dentate high-frequency PTP is selectively reduced in old rats with impaired Morris Maze performance.

The effects of various calcium antagonists, acting at the different neuronal calcium channels, were studied towards two models of in vitro neuronal injury in rat hippocampal slices. In particular, the influence of the drugs were tested on the electrical failure induced by treatment of hippocampal slices with hypoxia or high concentrations of the excitatory amino acid N-methyl-D-aspartate (NMDA). The L-type calcium antagonists, nifedipine (100 microM) and diltiazem (100 microM) or the T-type calcium antagonist amiloride (100 microM) failed to significantly affect the recovery from the CA1 electrical failure induced by both hypoxia or NMDA (50 microM). The N-type calcium antagonists, omega-conotoxin GVIA (0.5 microM) and neomycin (300 microM) significantly (P0.01) increased the probability of the recovery of the CA1 population spike after hypoxia but not after NMDA (50 microM). The glutamate antagonist dizocilipine (50 microM), tested for comparison, significantly (P0.01) increased the probability of the recovery of the CA1 population spike after hypoxia and NMDA (50 microM). The results suggest an involvement of calcium channels especially of N-type in the genesis of hypoxic but not NMDA neuronal injury.

1. 1. The effects of the non-opioid antitussives caramiphen and carbetapentane and of the anticonvulsants 5,5-diphenylhydantoin and MK 801 were tested towards hypoxia-induced electrical changes in rat hippocampal slices. 2. 2. The incidence of appearance of hypoxia-induced epileptiform bursting was significantly decreased (P < 0.05) by carbetapentane (50–100 μM), caramiphen (50–100 μM), 5,5-diphenylhydantoin (25–50 μM), and the glutamate antagonist dizocilpine (MK 801, 25–50 μM). 3. 3. The incidence of reappearance of the CA1 population spike after hypoxia was significantly increased (P < 0.05) by carbentapentane (50–100 μM), caramiphen (50–100 μM), 5,5-diphenylhydantoin (25–50 μM), and MK 801 (25–50 μM). 4. 4. The results suggest a useful role for non-opioid antitussives and some anticonvulsants in the treatment of hypoxia-induced functional disturbances.

Mongolian gerbils (Meriones unguiculatus) are genetically predisposed to seizures, for which an involvement of hippocampal hyperexcitability and disinhibition has been suggested. The response in vitro of the hippocampal synaptic circuit upon exposure to an elevated extracellular calcium concentration is well known in the rat, and its dependence on inhibitory and excitatory transmission has been thoroughly studied. The purpose of the present investigation was to compare the influence of elevated extracellular calcium on inhibitory and excitatory transmission in the dentate area and the CA1 field of gerbil and rat hippocampal slices. Elevated calcium induced in the CA1 area of both animal species a long-term potentiation (LTP)-like response. Upon calcium exposure in the dentate area a decrease in population spike amplitude occurred in both gerbil and rat slices, indicating a similar degree of synaptic inhibition in the two species. However, in contrast to the effects known in the rat, elevated extracellular calcium failed to enhance the excitatory postsynaptic potential in the gerbil dentate area. This difference may depend on the species-specific, selective presence of the calcium-binding protein parvalbumin in perforant path terminals of the gerbil, which may be relevant to the susceptibility to seizures of this animal species.

Omega-conotoxin (1 and 2 micrograms/10 microliter i.c.v.), a N-type calcium channel blocker, and amiloride (7.5 and 15 micrograms/10 microliter i.c.v.), a T-type calcium antagonist, significantly prevented the EEG and behavioural effects induced by phencyclidine (PCP, 5 mg/kg i.p.) in rats. In accordance with previous studies showing the significant influence of L-type calcium blockers in the same model, these results confirm that the modulation of calcium currents plays a key role in the expression of PCP-induced effects.

Muscarinic cholinoceptor subtypes (M1 and M2) were studied in membrane particles of the rat frontoparietal cortex 72 h and 1, 2, 3, and 4 weeks after ipsilateral lesioning of the nucleus basalis magnocellularis (NBM). The affinity of the ligand used to characterize muscarinic cholinoceptors, 3H-quinuclidinyl benzilate did not significantly change in lesioned compared with sham-operated rats as well as the density of high affinity (M1) sites. Low affinity muscarinic cholinoceptors (M2 sites) were significantly decreased in NBM-lesioned rats 72 h and 1 week after lesioning. The density of M2 sites did not significantly differ in lesioned rats 2 or 3 weeks after NBM lesioning, but increased, in comparison with sham-operation 4 weeks after NBM lesioning. These findings suggest that frontoparietal M2 muscarinic cholinoceptors, which probably have a presynaptic localization, are sensitive to NBM lesions. Their changes at different times after NBM lesioning suggest the occurrence of loss, compensation and upregulation of cholinergic projections arising to the neocortex from the NBM.

Phencyclidine (PCP), a drug inducing schizophrenia-like symptoms in humans, is reported to be a noncompetitive antagonist at the N-methyl-d-aspartate (NMDA) subtype of excitatory amino acid receptors. In rats, PCP produces three dose-dependent stages of EEG patterns: 1) increase of cortical desynchronization duration; 2) increase of the amplitude of the high-frequency (20–30 Hz) low-voltage (30–50 µV) cortical background activity; 3) appearance of cortical slow (2–3 Hz) wavesharp wave complexes. These EEG changes are accompanied by stimulatory-depressive effects such as stereotypy (circling, head weaving) and ataxia. In the present study, the EEG and behavioural effects induced by systemic administration of the NMDA antagonists dizocilpine (MK 801), dextromethorphan (DM), [+ -alpha-(4-chlorophenyl)-4-[(phenyl)methyl-1-piperidine ethanol] (SL 82.0715), (+)3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid (CPP), cis-4-phosphonomethyl-2-piperidine-carboxylic acid (CGS 19755) have been compared to those of PCP in rats. The rank of potency for inducing PCP-like EEG stages 1–3 was as follows: MK 801 > PCP > CGS 19755 > CPP. These drugs also induced PCP-like behavioural effects. On the contrary, DM and SL 82.0715, administered up to the dose of 100 mg/kg IP, failed to induce PCP-like behavioural effects and elicited only the stage 1 of PCP-like EEG. These results strongly suggest the involvement of NMDA neurotransmission in the behavioural and EEG effects of PCP.

We have recently demonstrated that monolateral lesions of the Nucleus Basalis Magnocellularis (NBM), which is a nucleus sending cholinergic projections to the fronto-parietal cortex, cause a loss in the intensity of Timm staining in the intrahippocampal pathway of mossy fibres (MF). Moreover, these lesions induce ultrastructural changes consistent with the occurrence of degeneration of presynaptic buttons of MF. The present study was designed to quantify the effects of NBM lesioning on the morphology of the presynaptic buttons of MF. Moreover the effects of 4-week choline alfoscerate (alphaGFC) treatment on the density of Timm staining and on the ultrastructure of presynaptic buttons of MF were assessed, alphaGFC, which was given at an oral daily dose of 100 mg/kg, is a precursor in the biosynthesis of several brain phospholipids which increases the availability of choline in the nervous tissue. Monolateral lesions of NBM cause, 4 weeks after lesioning, a significant decrease in the intensity of Timm staining in the MF area accompanied by a loss of about 23% of presynaptic buttons of MF. Moreover about 40% of presynaptic buttons of MF show an impaired morphology. alphaGFC administration restored the intensity of Timm staining in the MF area. In alphaGFC-treated rats, the loss of presynaptic buttons and the number of impaired buttons were reduced to about 12% and 27%, respectively in comparison with non-treated animals. These results confirm and extend our previous observations indicative of the occurrence of transneuronal degenerations in the MF of the hippocampus after monolateral NBM lesioning. Moreover these findings show that alphaGFC treatment is able to counter in part these degenerative changes.

The effects of cis-3,4 dichloro-N-2-(1-pyrrolidinyl)cyclo-hexyl-benzamide (U-54494A), an anticonvulsant related to kappa opioids, were studied in vitro on the extracellular electrical activity of the CA1 region of slices of hippocampus in the rat. The effects of U-54494A were compared to those of the kappa opioid agonist trans-3,4 dichloro-N-2-(1-pyrrolidinyl)cyclo-hexyl benzeneacetamide methane sulphonate (U-50488H). Both U-54494A and U-50488H, in concentrations of 50 and 100 microM, respectively, reduced the magnitude of the orthodromically evoked CA1 population spikes after electrical stimulation of the stratum radiatum (100-200 microA, 70 microseconds, 0.1 Hz). Naltrexone (25 microM), or the selective kappa opiate receptor antagonist, 1-cyclopenthyl-5-(1,2,3,4,5,6-hexahydroxy-3,6,11-trimethyl-2 -6-methano-3- benzazocin)-3-pentatone methane sulphonate (WIN 44441-3) (25 microM), prevented the depressant activity of U-54494A (200 microM) on the CA1 population spikes. High calcium (+3mM) solutions prevented the depressant activity of increasing concentrations of both U-54494A and U-50488H on the amplitude of CA1 population spikes. Up to 200 microM, both drugs were ineffective in depressing the epileptiform bursting in CA1, due to 1 mM penicillin or to perfusion of the slice in absence of magnesium ions. The results demonstrate: (1) the inability of U-54494A to show antagonistic activity in two in vitro models of interictal epilepsy; (2) a depressant effect of U-54494A on basal synaptic transmission in the CA1 region of the hippocampus, which may be related to an influence on transneuronal calcium currents and which may be involved in the reported antagonism of ictal epileptic seizures by drugs.

1. 1. In in vivo and in vitro studies in rats, the effects of dextromethorphan (DM), dextrorphan (DX), and levorphanol (LV) were compared with those induced by kappa and sigma opiate agonists. 2. 2. In rat hippocampal slices all the morphinans were able to pertubate the CA1 hippocampal synaptic transmission, while only DX and LV affected the N- methyl- d -aspartate excitability through a possible interaction at sigma opiate receptors. 3. 3. On the other hand EEG studies show that only DX appears to act as a full agonist at sigma opiate receptors. 4. 4. Present data demonstrate diversified electrophysiological properties of morphinans both in in vitro and in vivo studies.

The existence of possible right-left asymmetries in sulfide-silver stainable fibre systems in the rat frontal, parietal and occipital cortices was assessed using the neo-Timm histochemical technique associated with microdensitometry. In the cerebral cortex sulfide-silver stainable fibres are localized in the neuropil of laminae I-III and V. The density of sulfide-silver stainable fibres which is parallel to the density of zinc-containing presynaptic structures, was the highest in the right frontal cortex and the lowest in the right occipital cortex. In the frontal cortex sulfide-silver staining is stronger in the right hemisphere than in the left (P

1. 1. The influence of the change of potassium and calcium concentrations in the medium bathing hippocampal slices has been tested on the purinergic drug effects. 2. 2. The depressive effects of purinergic agonists were antagonized by 50% by doubling the potassium concentrations, while they were not affected by doubling calcium concentrations. 3. 3. The data demonstrate a direct intrinsic activity of potassium ions, and suggest a possible direct interaction between adenosine receptors and potassium transneuronal fluxes.

A behavioural study on the effects of D1 and D2 dopamine receptor antagonists (SCH 23390 and sulpiride respectively) and of an A1 adenosine receptor agonist (N6-L-phenylisopropyladenosine, L-PIA) against phencyclidine (PCP)-induced effects was assessed in adult male rabbits. SCH 23390 (0.003-0.01 mg/kg i.v.) and sulpiride (12.5 mg/kg i.v.) were able to significantly prevent PCP-induced stereotypy. Ataxia was reduced by SCH 23390 (0.003 mg/kg i.v.), while it was potentiated by sulpiride (12.5 mg/kg i.v.). Given alone at 12.5 mg/kg, sulpiride induced some EEG and behavioural effects in rabbits, while SCH 23390 (0.003 and 0.01 mg/kg) did not. L-PIA prevented both PCP-induced stereotypy and ataxia at the dose (0.1 mg/kg i.v.) devoid of behavioural or EEG effects by itself. Our results suggest that D1 dopamine receptors might play a more important role than D2 receptors in the expression of PCP-induced behaviour. They also propose that A1 adenosine receptors might be involved (e.g. via an influence on the dopamine release) in the behavioural effects of PCP.

Although biochemical and behavioural studies have shown right-left differences in several areas of the rat limbic system, some anatomical studies reported no significant right-left differences in several morphological parameters of the hippocampus. The purpose of the present study was to determine whether there are asymmetries in the micro-anatomy of the rat hippocampus by examining the intensity of Timm staining in various hippocampal fields and the area occupied by mossy fibres by the use of combined microdensitometric and quantitative image analysis techniques. Timm staining demonstrates the distribution of intrahippocampal association pathways because it is a histochemical marker of zinc and other heavy transition metals. There were no right-left differences in the density of Timm staining at the level of the dentate gyrus, in the dendritic layer of CA1 and CA2 fields, in the mossy fibre area or in the subiculum. These findings provide further evidence of a lack of morphological asymmetry in the rat hippocampus.

Biochemical and behavioral studies demonstrated lateralized differences in several areas of the rat limbic system. However, no significant right-left differences in several morphological parameters of the hippocampus were reported in some anatomical studies. To evaluate further possible asymmetries in microanatomy of the rat hippocampus the intensity of Timmstaining in different hippocampal fields and the area occupied by mossy fibres were assessed using combined microdensitometric and quantitative image analysis techniques. Timmstaining is a sensitive marker for the histochemical detection of zinc and other heavy transition metals and it is considered to be related to the distribution of intrahippocampal association pathways. No right-left differences were seen in the density of Timm-staining at the level of the dentate gyrus and in the dendritic layer of CA1 and Ca2 fields, in the mossy fibre area or in the subiculum. These findings support the view of lack of morphologic asymmetry in the rat hippocampus.

The influence of intracaudate administration of N-methyl-D-aspartic acid (NMDA) and of the competitive NMDA receptor antagonist, DL-2-amino-5-phosphonovaleric acid (AP-5) was studied on thyrotropin-releasing hormone (TRH)-induced scratching in rabbits. NMDA (28 nmol) significantly increased the latency of TRH-induced scratching but did not modify the duration of this behaviour. Conversely, AP-5 (0.5 mumol) significantly potentiated scratching duration. Since TRH-induced scratching has been reported to be a dopamine-dependent behaviour, these results suggest that NMDA receptor ligands modulate dopaminergic neurotransmission.

The effects of the 21-aminosteroids, U-74500A and U-78517F (drugs endowed with lipid peroxidation inhibitor properties) were tested on hypoxia-induced functional failure in rat hippocampal slices. For comparison, the effects of the non-competitive N-methyl-D-aspartate antagonist, dizocilpine (MK-801) were studied. Perfusion of slices with 50 microM of MK-801 or with 50-100 microM of U-78517F, but not with 100-200 microM of U-74500A, significantly (P < 0.01) increased the incidence of reappearance of the CA1 population spikes after reoxygenation in rat hippocampal slices subjected to a 45-min hypoxic period followed by a 45-min reoxygenation period. Perfusion of slices with 12.5 microM of MK-801 plus 12.5 microM of U-78517F significantly (P < 0.05) increased the incidence of reappearance of the CA1 population spikes after reoxygenation with respect to perfusion of slices with 12.5 microM of U-78517F alone or with 12.5 microM of MK-801 alone. The results show that 21-aminosteroids have protective effects against hypoxia-induced functional failure in rat hippocampal slices. In addition, the data show that, under the same experimental conditions, the NMDA receptor antagonist, MK-801, was also able to improve hypoxia-induced functional failure. On the whole, the results suggest that the hypoxia-induced functional electrical failure might depend on both release of excitatory amino acids and oxygen free-radical-mediated membrane lipid peroxidation.

1. The effects of the mixed A1 and A2 adenosine receptor agonist N6-L-phenyl-isopropyladenosine (L-PIA) were tested on ischaemia-induced hippocampal neuronal injury in gerbils subjected to 5-min bilateral carotid occlusion. For comparison, the effects of the selective A2 adenosine receptor agonist, CGS 21680 were tested. 2. Five-min bilateral carotid occlusion produced within 1 week an irreversible suppression of the CA1, but not of the dentate extracellular electrical somatic responses, in 30% of gerbil hippocampal slices with respect to controls. In addition, a significant reduction occurred in the density of CA1 hippocampal pyramidal neurones but not of dentate granule cells with respect to controls. 3. Injection 1 h before or after bilateral carotid occlusion of L-PIA (0.8-1.5 mg kg-1, i.p.) but not of CGS 21680 (5 mg kg-1, i.p.), significantly prevented the irreversible disappearance of the CA1 extracellular electrical somatic responses with respect to controls. In addition, the CA1 pyramidal neuronal loss was also prevented. 4. The results show that activation of A1 adenosine receptors is able to prevent or block the electrophysiological and morphological correlates of hippocampal neuronal injury after global ischaemia in the gerbil, suggesting that adenosine receptor agonists might have a useful role in the treatment of neuronal functional and anatomical injury due to ischaemia.

The influence of adenosine A1 (N6-cyclopentyladenosine, CPA) and A2 (2-[4-(2-carboxylethyl)phenethylamino]-5'-N-ethylcarboxamido -adenosine hydrochloride, CGS 21680) receptor agonists on SKF 38393-induced electroencephalographic (EEG) arousal was studied in rabbits. While CPA (0.1 mg/kg i.v.) significantly prevented the EEG effects of SKF 38393, CGS 21680 (0.2 mg/kg i.v.) did not affect them. These results demonstrate that adenosine A1 receptors can modulate dopamine D1 receptor-induced EEG arousal and show, for the first time, that adenosine-dopamine interactions are involved in brain functions other than motor activity.

The putative dopamine D 3 receptor agonist, (±) 7-OH-di-n-propylaminotetralin (± 7-OH-DPAT), induced depressant effects on rabbit EEG at the dose of 1 mg kg i.v. Bromocriptine, a preferential dopamine D 2 receptor agonist, induced EEG activation at the dose of 0.5 mg kg i.v. Although the lack of very selective ligands makes it difficult to discriminate between D 2 - and D 3 - dependent effects, these findings suggest that -unlike D 2 receptors-dopamine D 3 receptors may mediate depressant effects on the electrocorticogram.

The effect of unilateral or bilateral lesions of the nucleus basalis magnocellularis (NBM) on the dentate gyrus of the hippocampus were assessed using microanatomical and electrophysiological techniques. NBM is the main cholinergic basal forebrain nucleus that supplies the fronto-parietal cortex. Lesions were induced using the neurotoxin ibotenic acid or a radio-frequency system and did not affect glutamic acid decarboxylase activity both in the frontal cortex and in the hippocampus. At 4 weeks after lesioning, a loss of choline acetyltransferase (ChAT) activity and of ChAT-immunoreactive fibres was observed in the frontal cortex but not in the hippocampus and no changes in the density of granule neurons of the dentate gyrus or in the hippocampal long-term potentiation (LTP) were noticeable. At 8 weeks after lesioning the loss of both ChAT activity and of ChAT-immunoreactive fibres persisted in the frontal cortex of NBM-lesioned rats. Moreover, at this time a significant decrease in the density of granule neurons in the dentate gyrus accompanied by a reduced probability of dentate LTP induction were observed in both ibotenic acid- and radio-frequency-lesioned rats. These findings have shown that although NBM does not send direct cholinergic projections to the hippocampus, lesions of this cholinergic nucleus are accompanied by delayed neurodegenerative changes involving the dentate gyrus. This suggests the occurrence of indirect connections between NBM and the hippocampus, the functional relevance of which should be explored.

The effects of monolateral lesioning of the nucleus basalis magnocellularis (NBM) and of choline alphoscerate treatment on histochemically reactive vesicular zinc stores were assessed in the rat brain using the sulphide-silver histochemical technique. Histochemically reactive zinc stores are located primarily within association fibres of the neuropil of the cerebral cortex as well as in the mossy fibres of the hippocampus. The density of cortical and hippocampal sulphide-silver positive fibres, which might have a role in cognitive and mnemonic processes, parallels the density of zinc-containing presynaptic buttons. Unilateral lesions of NBM caused a remarkable decrease of sulphide-silver positive fibres from the 4th week after lesioning in the neuropil of the ipsilateral fronto-parietal cortex and from the 3rd week in the mossy fibres of the ipsilateral hippocampus. Treatment with choline alphoscerate, which is a precursor in the biosynthesis of brain phospholipids that increases the bioavailability of acetylcholine in the nervous tissue, restored, in part, the density and pattern of sulphide-silver positive fibres in the fronto-parietal cortex and in the hippocampus. The data suggest that, analogously to reports from Alzheimer's disease patients, lesions of the NBM cause a decrease of zinc stores in the rat brain. Choline alphoscerate treatment is able to counter the expression of this phenomenon which accompanies experimental lesions of the NBM.

BEHAVIOURAL and biochemical evidence for the existence of a powerful specific postsynaptic interaction between adenosine A 1 and dopamine D 1 receptors in the mammalian brain was found. Behavioural data showed that A 1 receptor stimulation induced a decrease in the D 1 -induced motor activation in reserpinized mice and a decrease in the D 1 -dependent oral dyskinesia in rabbits. Biochemical data suggested that A 1 receptor stimulation could produce a GTP-independent uncoupling of the rat striatal D 1 receptor to the G protein. The A 1 -D 1 receptor-receptor interaction might represent an important additional mechanism of action responsible for the motor depressant effects of adenosine agonists and for the motor stimulant effects of adenosine antagonists, like the methylxanthines caffeine and theophyllin

The induction of hippocampal frequency-potentiation (i.e. post-tetanic potentiation (PTP) and long-term potentiation (LTP) was analyzed in rat hippocampal slices obtained from animals showing impaired place learning in the Morris water maze as a consequence of bilateral striatal injection of quinolinic acid. Vehicle-injected animals, showing normal performances in the Morris water maze, behaved as controls. After the application of an electrical tetanus (1 s, 100 Hz, 50 microA) in the stratum radiatum, no significant differences were found in the percent of induction of both PTP and LTP in the CA1 area of hippocampal slices obtained from lesioned and sham-operated rats. After the application of an electrical tetanus (1 s, 100 Hz 50 microA) in the stratum moleculare, a significant difference was found in the percent of dentate PTP induction in hippocampal slices obtained from lesioned and sham-operated rats. Specifically, dentate PTP induction was significantly (P < 0.01) higher in slices obtained from sham-operated rats with a good performance in the Morris water maze than in slices obtained from striatally lesioned rats, which had shown poor performance in the Morris water maze. On the contrary, no significant differences were found in the percent of dentate LTP in hippocampal slices obtained from rats of the two groups. The data demonstrate that the impairment of the place learning in striatally lesioned rats is associated with a selective reduction of hippocampal dentate frequency-potentiation.

The influence of bilateral intrastriatal injection of quinolinic acid (QA, 300 nmol) was studied in male Wistar rats. Behavioral and electrophysiological experiments were conducted in 15 lesioned plus 15 vehicle-injected (control) animals. With respect to control animals, QA-lesioned rats showed marked, statistically significant alterations from both the behavioral (greater motor activation in response to d-amphetamine, place-learning deficit in the Morris water maze), and the electroencephalographic (reduced voltage amplitude and EEG power at the level of frontal cortex) points of view. In addition, a significant loss in body weight and a marked striatal gliosis (GFAP staining) were observed in lesioned rats. Conversely, QA-lesioned rats did not show modifications in posttetanic potentiation (P.T.P.) or long-term potentiation (L.T.P.) in CA1 hippocampal area. The present results confirm that QA lesions of rat striatum may be regarded as a suitable model of Huntington's disease (HD).

In the present paper, the influence of the adenosine receptor agonist N6-(l-2-phenylisopropyl)adenosine (L-PIA) and of the adenosine receptor antagonist caffeine on the epileptiform and neurotoxic effects of N-methyl-d-aspartate (NMDA) has been tested in rat hippocampal slices. Slice superfusion with 1 microM NMDA changed within 30 min the control CA1 field potentials into an epileptiform bursting in all experiments. Slice superfusion with 0.5-1 microM L-PIA or 50-100 microM caffeine plus 1 microM NMDA inhibited or potentiated, respectively, the CA1 epileptiform bursting duration with respect to a slice superfusion with 1 microM NMDA alone. Slice superfusion with 50-100 microM NMDA induced within a few minutes the appearance of short-lived (1-2 min) additional epileptiform population spikes, followed by an irreversible disappearance of the CA1 population spike. Slice superfusion with 50 microM of the NMDA antagonist dizocilpine (MK801) plus 50-100 microM NMDA prevented in all experiments the irreversible disappearance of the CA1 population spike with respect to a slice superfusion with 50-100 microM alone. Neither in a slice superfusion with 0.5-1 microM L-PIA plus 50-100 microM NMDA nor in a slice superfusion with 50-100 microM caffeine plus 50-100 microM NMDA did this effect occur. The results demonstrate that adenosine receptor ligands modulate the epileptiform but not the neurotoxic effects of NMDA.

The relationships between the in vivo epileptogenic effects of opiates and the in vitro electrophysiological activity of opiates, enkephalins and inhibitors of endogenous peptidase were analyzed in order to ascertain the effective functional role of the endogenous opiate peptidergic system in the control of neuronal excitability. Morphine, enkephalins and related drugs induced in rats and rabbits naloxone-sensitive non-convulsive hippocampal EEG epileptiform activity after systemic or central administration. Higher doses of morphine and related drugs induced naloxone-insensitive convulsive EEG epileptiform activity within all the brain after systemic or central administration. Morphine and enkephalins, selectively acting at mu opiate receptors (DAGO, morphiceptin), increased in rat hippocampal slices the excitability of CA1 pyramidal cells, an effects revealed by a naloxone-sensitive increase of the magnitude of the CA1 population spike and by the appearance of several additional epileptiform population spikes. Enkephalins, selectively acting at delta opiate receptors (DPDPE, deltorphin), produced a naloxone-sensitive increase of the magnitude of the CA1 population spike but failed to induce the appearance of several additional epileptiform population spikes. Enkephalinase inhibitors (thiorphan, SCH32615) failed to affect the basal CA1 electrical response, but potential the epileptiform activity induced by DAGO. Collectively, the data indicate that hippocampal mu opiate receptors mediate the excitatory-epileptogenic effects of opiates.

The effects of the non-opioid oral antitussives dextromethorphan (DM) and caramiphen (CP) were tested against the behavioural and EEG effects elicited by the N-methyl-D-aspartate (NMDA) antagonists dizocilpine (MK 801) and phencyclidine (PCP) in rats and mice. PCP (1.25-10 mg/kg i.p.) induced a dose-dependent increase/decrease of the locomotor/exploratory activity of mice. DM (25-50 mg/kg i.p.) and MK 801 (0.125-0.250 mg/kg i.p.) induced an increase of the locomotor/exploratory activity of mice, while CP (25-50 mg/kg i.p.) did not produce such an effect. CP (12.5 mg/kg i.p.) and DM (12.5 mg/kg i.p.) significantly potentiated the effects of PCP (1.25 mg/kg i.p.) and MK 801 (0.062 mg/kg i.p.) in the open field test in mice. In rats, PCP (1.25-10 mg/kg i.p.) induced three dose-dependent EEG stages: 1) increase of the cortical desynchronization periods; 2) increase of the amplitude of cortical background activity; 3) appearance of cortical slow wave-spike complexes. Even though DM (up to 100 mg/kg i.p.) only induced PCP-like EEG stage 1 by itself, and CP (up to 50 mg/kg i.p.) did not affect basal cortical EEG activity, these drugs, at the doses of 30-50 mg/kg i.p., potentiated all the EEG effects induced by PCP. These data support the view of an interaction between non-opioid antitussives and non-competitive NMDA antagonists.

The probability of hippocampal long-term potentiation induction in the mossy fiber CA3 and commissural/associational CA3 responses and the cortical levels of choline acethyltransferase (ChAT) activity were compared in right nucleus basalis magnocellularis (NBM)-lesioned rats. A 50% reduction in the right cortical ChAT activity was demonstrated 4 weeks after an ibotenic acid lesion of the NBM. No significative differences were found in the probability of LTP induction of right hippocampal slices in sham-operated rats from 10 to 40 days after the injection into the right NBM. On the contrary, a progressive and significative increase in the probability of LTP induction was shown in right hippocampal slices of NBM-lesioned rats from 10 to 40 days after the injection of ibotenic acid into the right NBM. The results demonstrated the appearance of a paradoxical increase of hippocampal synaptic plasticity when the cortical cholinergic biochemical alterations are still present. This finding might be responsible for a behavioural recovery, in NBM-lesioned rats.

The influence of verapamil and flunarizine on phencyclidine-induced effects has been studied in adult male rats. Both verapamil (25 and 100 micrograms/10 microliters, i.c.v.) and flunarizine (40 and 60 mg/kg, i.p.) significantly reduced behavioural (mean intensity of ataxia, mean duration of head weaving) and the EEG (increase in the mean voltage of background activity of the EEG) effects induced by phencyclidine 5 mg/kg (i.p.). It was reported previously that nimodipine and diltiazem significantly potentiate effects induced by phencyclidine. The contrasting results obtained with verapamil and flunarizine, suggest that these drugs may modulate effects induced by phencyclidine by acting at sites other than NMDA receptor-coupled "L"-type calcium channel.

The effects of dextrorphan (DX) and dextromethorphan (DM) were tested using the electroencephalogram (EEG) and behavioral effects induced by topical cortical application of penicillin in rabbits. For comparison, the influence of the NMDA antagonists, dizocilpine (MK 801) and 3-((+-(-)2-carboxypiperazine-4-yl)propyl-1-phosphonic acid (CPP), and of pentobarbitone was investigated. Intracortical injection of 500 IU of penicillin produced an EEG spiking followed by a repeated generalization of the electrical and behavioral symptoms. Within a few minutes, DX (5-15 mg/kg, IV) or pentobarbitone (5-10 mg/kg, IV) reduced dose dependently and significantly (p less than 0.01) the interictal and ictal EEG and behavioral effects elicited by cortical injection of 500 IU of penicillin. Higher doses of pentobarbitone (20 mg/kg, IV) but not of DX (20 mg/kg, IV) completely blocked the ictal behavioral and EEG effects elicited by cortical injection of 500 IU of penicillin. Within a few minutes, MK 801 (0.1-0.2 mg/kg, IV) or CPP (10-20 mg/kg, IV) reduced dose dependently and significantly (p less than 0.01) the ictal EEG and behavioral effects elicited by cortical injection of 500 IU of penicillin, while they did not affect the penicillin-induced interictal EEG changes. Higher doses of MK 801 (0.3 mg/kg, IV) completely blocked the ictal behavioral and EEG effects elicited by cortical injection of 500 IU of penicillin. Within a few minutes, DM (10-20 mg/kg, IV) blocked the behavioral effects, but failed to affect either the interictal or the ictal EEG effects induced by cortical injection of 500 IU of penicillin.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of adenosinergic antagonists caffeine and DPCPX, and of the adenosinergic agonists L-PIA, CPA and CGS 21680 were investigated on fully and partially reversible hypoxia-induced electrophysiological changes in rat hippocampal slices. The influence of a high potassium solution and of the N-methyl-D-aspartate antagonist dizocilpine (MK 801) was also tested. The latency to obtain a 50% decrease in the amplitude of the CA1 population spike (CA1 PS) during a short- (5-10 min) lasting hypoxic period was significantly increased (P less than 0.01) by slice perfusion with caffeine (50 microM), DPCPX (0.2 microM), and by increasing (from 3 to 4 mM) the potassium concentration in the medium bathing the hippocampal slices. The latency was significantly decreased (P less than 0.01) by slice perfusion with L-PIA (0.2 microM) and CPA (0.05 microM). It was not significantly modified by CGS 21680 (5 microM). The incidence of reappearance of the CA1 PS during reoxygenation after long- (45 min) lasting hypoxia was significantly increased (P less than 0.05) by slice perfusion with MK 801 (50 microM), while it was not significantly affected by slice perfusion with caffeine (50 microM) or DPCPX (0.2 microM) or L-PIA (0.2 microM) or CPA (0.05 microM) or CGS 21680 (5 microM). The results indicate a prevalent involvement of the A1 adenosine receptors in the early mechanisms underlying hypoxia-induced reversible changes. Adenosine seems to have a limited role in the late mechanisms occurring after a long-lasting hypoxic period.

1. The effects of BRL 34915 (cromakalim), a potassium channel opener, have been tested on the epileptiform activity elicited by high dose/concentrations of some calcium antagonists in in vivo (diltiazem) and in vitro (diltiazem and verapamil) experiments in rats. 2. Diltiazem (150-300 mg kg-1, i.p.) induced behavioural and electroencephalographic (EEG) seizures that were completely prevented by cromakalim (10 nmol/10 microliters, i.c.v.). Whereas, pentobarbitone (5-10 mg kg-1, i.p.) only prevented the behavioural component of the seizures. 3. In hippocampal slices, verapamil (1.5-2.0 mM) produced, within 30-60 min of perfusion, a CA1 epileptiform bursting in 80% of the experiments. This epileptiform activity was prevented by the cromakalim concentration (50 microM) that did not affect the control CA1 synaptic transmission per se. Pentobarbitone also prevented verapamil-induced epileptiform bursting only at the concentration (100 microM) that also reduced control CA1 synaptic transmission. 4. Diltiazem (1.5 mM) produced a biphasic excitatory-depressant effect within 60 min of perfusion. A CA1 epileptiform bursting appeared in 100% of the experiments within 30 min of perfusion. These excitatory effects were followed by a depression phase, characterized by a reduction of the magnitude of CA1 excitatory postsynaptic potentials (e.p.s.ps) and population spike. 5. The diltiazem-induced epileptiform bursting was prevented by cromakalim at a concentration (50 microM) that did not affect the control CA1 synaptic transmission per se. Pentobarbitone also prevented the diltiazem-induced epileptiform bursting only at a concentration (100 microM) that also reduced the control CA1 synaptic transmission. Both cromakalim (50 microM) and pentobarbitone (100 microM) failed to affect the depressant effects of diltiazem on CA1 hippocampal area. On the contrary, high (3.3mM) calcium solutions prevented both the excitatory and the depressant effects of 1.5 mm diltiazem within 60 min.6. These data indicate an involvement of potassium currents in the epileptiform activity elicited by high doses of diltiazem and verapamil.

The interactions between dopamine D1 and D2 receptors in the model of thyrotropin-releasing hormone (TRH)-induced behavioural excitation were assessed in adult male rabbits. As we had previously observed with the dopamine D1 receptor antagonist SCH 23390 (0.01 mg/kg i.v.), sulpiride (12 mg/kg i.v.), a dopamine D2 receptor antagonist, also significantly antagonized the scratching behaviour elicited by TRH (100 micrograms/10 microliters i.c.v.). Sulpiride (6 and 12 mg/kg i.v.) also induced marked grooming. SKF 38393 (10 mg/kg i.v.), a dopamine D1 receptor agonist, did not modify the TRH-induced scratching. However, LY 17155 (0.5 mg/kg i.v.), a dopamine D2 receptor agonist, significantly increased it. The potentiating effects of LY 171555 were completely antagonized by SCH 23390. These results demonstrate that a concomitant activation of both dopamine D1 and D2 receptors is required for the expression of TRH-induced scratching. They also suggest that scratching behaviour may be a D2-dependent, D1-enabled response. The involvement of dopamine D1 and D2 receptors on grooming behaviour is also discussed.