Complex plastic changes in the neuropeptide Y system during ethanol intoxication and withdrawal in the rat brain

Previous studies show that chronic ethanol treatment induces prominent changes in brain neuropeptide Y (NPY). The purpose of the present study was to explore ethanol effects at a deeper NPY-system level, measuring expression of NPY and its receptors (Y1, Y2, Y5) as well as NPY receptor binding and NPY-stimulated [(35)S]GTPgammaS functional binding. Rats received intragastric ethanol repeatedly for 4 days, and the NPY system was studied in the hippocampal dentate gyrus (DG), CA3, CA1, and piriform cortex (PirCx) and neocortex (NeoCx) during intoxication, peak withdrawal (16 hr), late withdrawal (3 days), and 1 week after last ethanol administration. NPY mRNA levels decreased during intoxication and at 16 hr in hippocampal regions but increased in the PirCx and NeoCx at 16 hr. NPY mRNA levels were increased at 3 days and returned to control levels in most regions at 1 week. Substantial changes also occurred at the receptor level. Thus Y1, Y2, and Y5 mRNA labelling decreased at 16 hr in most regions, returning to control levels at 3 days, except for PirCx Y2 mRNA, which increased at 3 days and 1 week. Conversely, increases in NPY receptor binding occurred in hippocampal regions during intoxication and in functional binding in the DG and NeoCx during intoxication and at 16 hr and in PirCx during intoxication and at 1 week. Thus this study shows that ethanol intoxication and withdrawal induce complex plastic changes in the NPY system, with decreased/increased gene expression or binding occurring in a time- and region-specific manner. These changes may play an important role in mediating ethanol-induced changes in neuronal excitability.

Irreversibility of kindled alcohol-withdrawal behaviour in rats

In order to investigate whether alcohol-withdrawal kindling is an irreversible process, male Wistar rats were exposed to 12 episodes, each consisting of 2 days of severe alcohol intoxication and 5 days of alcohol withdrawal. Spontaneous withdrawal seizures were found in 15% of the animals during episodes 10-12. After an alcohol-free period of 26 days, the animals were subjected to three more episodes of alcohol dependence (i.e. episodes 13-15) in which 12% of the animals developed spontaneous withdrawal seizures. Based on several statistical tests, we concluded that there was no true difference between the seizure activity in episodes 10-12 and episodes 13-15, indicating that alcohol-withdrawal kindling is a long-lasting and perhaps irreversible process. In a second experiment, an alcohol-withdrawal kindled group was first exposed to seven episodes of alcohol dependence. A diazepam group went through the same alcohol regimen, but each withdrawal reaction was blocked by diazepam treatment. Finally, a single episode group was included which was fed isocalorically with the kindled animals. After an alcohol-free period of 11 days, all three groups were subjected to 4 days of severe alcohol intoxication. During the subsequent withdrawal reaction seizures were observed in 22-26% of the animals with no significant differences across the groups. These results call for a modification of the kindling hypothesis of alcohol withdrawal and suggest that kindling-induced alterations may be overlooked if convulsive behaviour is tested during a relatively strong withdrawal reaction.

Electrical amygdala kindling in alcohol-withdrawal kindled rats

Repeated alcohol withdrawal has been shown to kindle seizure activity. The purpose of the present investigation was to study electrical amygdala kindling in rats previously exposed to alcohol-withdrawal kindling. In three independent experiments, male Wistar rats were subjected to multiple episodes each consisting of 2 days of severe alcohol intoxication and 5 days of alcohol withdrawal. In the first experiment, the alcohol-withdrawal kindled animals were divided into two groups depending on whether spontaneous alcohol-withdrawal seizures were observed in episodes 10-13. In the second and third experiments, the alcohol-withdrawal kindled animals were compared to a group in which alcohol-withdrawal kindling was prevented by diazepam treatment during the withdrawal reactions in order to discriminate between the effect of withdrawal and intoxication. Electrical kindling was initiated 28-35 days after the last alcohol dose by exposing the animals to daily electrical stimulations of the right amygdala. The results showed that amygdala kindling was facilitated in alcohol-withdrawal kindled animals which showed spontaneous withdrawal seizure activity, compared with animals exposed to multiple episodes of alcohol withdrawal which did not develop withdrawal seizures or with animals exposed to a single episode of alcohol intoxication. When compared to the control group, the alcohol-withdrawal kindled group with seizures also kindled at a faster rate, but the difference did not reach statistical significance and therefore the results must be regarded as preliminary at present.

Serotonin1A receptor autoradiography during alcohol-withdrawal kindling

A series of autoradiography experiments were conducted in order to test the theory that the serotonin (5-HT) receptor subtype 5-HT(1a) is involved in alcohol-withdrawal kindled convulsive behaviour. Alcohol-withdrawal kindling was performed by subjecting male Wistar rats to multiple episodes consisting of 2 days of alcohol intoxication and 5 days of alcohol withdrawal. In the first episode alcohol intoxication led to focal downregulation of [3H]-8-hydroxy-2-(di-n-propylamino)tetralin ([3H]-8-OH-DPAT) binding sites in septum and subregions of frontal cortex, hippocampus, and entorhinal cortex. This alcohol-induced response was blunted in both alcohol-withdrawal kindled animals and in animals exposed to repeated alcohol dependence in which the previous withdrawal reactions were blocked by diazepam administration. A paradoxical upregulation of [3H]-8-OH-DPAT binding sites was found in septum and subregions of frontal cortex, hippocampus, and entorhinal cortex in control animals which were fed isocalorically with the alcohol-withdrawal kindled animals and subsequently exposed to 2 days of alcohol intoxication. It was concluded that the alterations in the alcohol induced 5-HT(1a) receptor regulation after multiple episodes of alcohol dependence were not caused by alcohol-withdrawal kindling processes per se, but were due to both alcohol specific and alcohol non-specific effects.

Glutamate and benzodiazepine receptor autoradiography in rat brain after repetition of alcohol dependence

During repeated alcohol withdrawal, convulsive withdrawal behavior has been shown to be increased in a kindling-like manner in both clinical and experimental studies. In the present experiment, quantitative autoradiography was used to investigate binding of tritiated ligands to glutamate receptor subtypes and the benzodiazepine/GABA (BZ/GABA) receptor complex in rats exposed to 14 episodes of alcohol withdrawal. Seizures were detected in 25% of the animals during withdrawal episode 10-13. Repeated alcohol withdrawal resulted in a decrease in the number of [3H]-alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid ([3H]-AMPA) binding sites in striatum and sub-regions of the entorhinal cortex, the cerebellum and the hippocampus, while the [3H]-flunitrazepam binding was down-regulated in the frontal cortex. There was no differences between the controls and the multiple withdrawal animals regarding the [3H]-dizocilpine ([3H]-MK801) binding and the [3H]-kainic acid binding. However, within the latter group, those animals in which withdrawal seizures were observed had increased [3H]-MK801 binding sites in focal regions of entorhinal cortex and hippocampus, compared to those in which seizures were not observed. The decreased AMPA binding suggested impaired glutamate neurotransmission. As such, this receptor probably did not contribute to alcohol withdrawal kindling, but rather was involved in seizure protective mechanisms during this process.

No loss of somatostatin-immunoreactive neurons in the hippocampal dentate hilus of alcohol-withdrawal-kindled rats

The neuropeptide somatostatin has been suggested to play a role in seizure genesis, electrical kindling and the neurotoxic effects of alcohol. The purpose of the present experiment was to study somatostatin-immunoreactive (SS-IR) neurons in hippocampus during alcohol-withdrawal kindling. Alcohol-withdrawal kindling was performed by subjecting male Wistar rats to seven weekly episodes consisting of 2 days of severe alcohol intoxication and 5 days of alcohol withdrawal. Then the kindled animals (multiple withdrawal group) and a single withdrawal group, which was fed isocalorically with the kindled animals during episodes 1-7, were exposed to 4 days of severe alcohol intoxication (episode 8). During the following withdrawal, the seizure activity was observed 9-15 h after last alcohol dose, in order to subdivide the animals from these two groups into groups with and without seizures. Subsequently, SS-IR neurons were visualized immunocytochemically and counted in the hilus of the dentate gyrus (hippocampus). The number of SS-IR neurons per unit area of the hilus was neither affected by a single nor by multiple episodes of alcohol withdrawal. We therefore concluded that a loss of these neurons is not involved in the development of alcohol-withdrawal-kindled seizures.

Diazepam prevents progression of kindled alcohol withdrawal behaviour

The purpose of the present experiment was to study the "kindling" hypothesis of alcohol withdrawal stating that exposure to repeated episodes of alcohol withdrawal results in an increased severity of subsequent withdrawal reactions. Two groups of male Wistar rats were subjected to 13 episodes of 2 days severe alcohol intoxication and 5 days alcohol withdrawal. Animals in the control group (n = 80) developed clinical withdrawal signs following each intoxication episode. In the diazepam group (n = 80) the withdrawal reactions during episodes 1-9 were blocked by intraperitoneal diazepam administration (0-30 mg/kg) 8, 11 and 15 h into withdrawal. During episode 10-13 diazepam treatment was terminated and convulsive withdrawal behaviour was observed 9-15 h after last alcohol dose. The probability of seizure activity during these four withdrawal episodes was calculated as 0.239 and 0.066 in the control and the diazepam groups, respectively. Based on Monte Carlo simulation techniques, this difference was found to be statistically significant (P < 0.05). No differences in the non-convulsive alcohol withdrawal symptoms tremor, hyperactivity and rigidity were detected between controls and diazepam animals after diazepam treatment. It was concluded that the increased convulsive behaviour in the control group was caused by cumulated kindling-like cerebral alterations during the previous repeated alcohol withdrawal phases.

Long-term administration of m-chlorophenylpiperazine (mCPP) to rats induces changes in serotonin receptor binding, dopamine levels and locomotor activity without altering prolactin and corticosterone secretion

Meta-chlorophenylpiperazine (mCPP) is a serotonin (5-HT) agonist with antidepressant actions. In order to investigate the effects of chronic mCPP treatment the drug was administered to rats for 15 days (5 mg/kg twice daily). Controls were administered saline. Long-term mCPP treatment led to a 36% increase in [3H]8-hydroxy-2-(di-n-propylamino)tetralin ([3H]8-OH-DPAT) binding to 5-HT1a receptors in hippocampus and a 74% decrease in [3H]ketanserin binding to 5-HT2 receptors in cortex, while (-)[125I]iodocyanopindolol ([125I]CYP) binding to 5-HT1b receptors in hypothalamus and striatum was unchanged. In hypothalamus, chronic mCPP treatment decreased the levels of dopamine (DA) but not 5-HT. The usual suppression of locomotor activity induced by acute mCPP administration was less after long-term mCPP treatment. Brain and plasma levels of mCPP following an acute dose were not different between controls and rats previously administered mCPP, suggesting that altered rate of metabolism of the drug did not explain the tolerance to the mCPP-induced decrease in locomotor activity. mCPP-induced prolactin (PRL) and corticosterone release were not changed by previous long-term mCPP administration. Thus, chronic mCPP administration to rats induced alterations in density of 5-HT receptor subtypes, hypothalamic levels of DA and locomotor behavior.

Convulsive behaviour during alcohol dependence: discrimination between the role of intoxication and withdrawal

Male Wistar rats were subjected to repeated weekly episodes of 2 days severe alcohol intoxication (intragastric intubation) and 5 days of withdrawal. In half of the animals the withdrawal reaction was attenuated during the first nine weekly episodes by intragastric intubations with phenobarbital. During episodes 10-14 both phenobarbital treated and phenobarbital untreated animals were allowed to develop a withdrawal reaction; all animals were video-recorded during withdrawal and the records were rated blindly for the occurrence of convulsive seizures. The results were analyzed by step-wise logistic analysis of regression including phenobarbital treatment, alcohol dose and intoxication score as explanatory variables for the occurrence of convulsive seizures. The animals that had been in withdrawal during all episodes developed significantly more convulsive seizures compared with animals that had their first nine withdrawal episodes attenuated by phenobarbital. The development of withdrawal seizures depended on repeated episodes of withdrawal, whereas repeated alcohol intoxication per se did not explain the development of seizures. There were no differences between the groups in the severity of the non-convulsive signs of alcohol withdrawal. Thus the development of seizures and the non-convulsive signs of alcohol withdrawal may result from two pathogenetically different mechanisms: 1) seizures from a cumulative kindling-like effect over long time periods and 2) physical signs of alcohol withdrawal may reflect the degree of physical dependence during the most recent drinking bout.

Acidic phospholipids in synaptosomal plasma membranes during repeated episodes of physical ethanol dependence in the rat

The effects of repeated episodes of ethanol intoxication and the hyperexcitable state of withdrawal on the synaptosomal concentration of acidic phospholipids were studied in rats. There was no indication that cumulative changes in the synaptosomal acidic phospholipid composition in general occurred during multiple episodes of ethanol intoxication and withdrawal. There was, however, a statistically significant decrease in acidic phospholipid concentration (phosphatidylinositol; PI) in synaptosomal membranes from animals revealing spontaneous convulsive behaviour during ethanol withdrawal. Hypothetically this may reflect an inability to increase acidic phospholipid membrane content and thus to adaptively increase the seizure threshold during withdrawal.

Alterations in serotonin receptor subtypes in ethanol-dependent rats

Serotonin (5-HT) receptor subtypes were investigated during severe ethanol intoxication and withdrawal. Ethanol was administered intragastrically five times a day for 4 days (12 g/kg per day). 5-HT receptor subtypes were studied: (1) in severely intoxicated animals (mean blood ethanol concentration (BEC) = 4.7 g/l); (2) during the withdrawal reaction; and (3) in a control group. The maximal density of [3H] 8-hydroxy-2-(di-n- propylamino)tetralin [( 3H] 8-OH-DPAT) binding (Bmax) to 5-HT1a receptors was decreased by 25 and 17% in the hippocampus during chronic ethanol intoxication and withdrawal, respectively. [3H]Ketanserin binding to 5-HT2 receptors in the cortex, (-)[125I]-iodo-cyanopindolol [( 125I]CYP) binding to 5-HT1b receptors in the striatum and hypothalamus, and [3H] 8-OH-DPAT binding in the cortex were not affected by chronic ethanol administration. Previous in vitro experiments have shown that 5-HT1a receptors in the hippocampus are inhibitory. The down-regulation of these receptors may play a role in physical ethanol dependence, by inducing hyperexcitability of the hippocampus.

The GABA/benzodiazepine receptor chloride channel complex during repeated episodes of physical ethanol dependence in the rat

The GABA/benzodiazepine (BZ) receptor chloride channel complex was investigated during repeated episodes of ethanol intoxication and withdrawal in the rat; the intragastric intoxication technique was applied and the severity of intoxication, withdrawal and number of seizures were recorded. The following groups were studied after decapitation during withdrawal 10-16 h after the last ethanol feeding: A) isocalorically fed controls not receiving ethanol; B) isocalorical controls subjected to a single ethanol intoxication period; C) animals subjected to 15 intoxication-withdrawal episodes (spontaneous seizures); D) same as C, but without developing seizures. A radio receptor technique was applied in the characterization of the receptor complex comprising specific binding to the BZ-receptor, the chloride channel and the GABA receptor by 3H-diazepam, 35S-TBPS and 3H-muscimol, respectively. The allosteric couplings among the components of the receptor complex were studied by 3H-diazepam and 35S-TBPS binding enhancement tests involving muscimol, ZK 93423 and DMCM. Cortex, hippocampus and cerebellum were the brain regions studied. Except for a reduced specific binding of 3H-diazepam in cerebellum, there were no indications of changes in specific binding to any part of the receptor complex. The allosteric coupling of BZ and GABA receptors as well as chloride channel-BZ receptors were unchanged in all groups. It is notable that no changes at all could be related to number of intoxication-withdrawal episodes or to the development of seizures. Thus, the present study gave no indication that the GABA/benzodiazepine receptor chloride channel complex is directly involved in the augmentation of cerebral nervous system excitability (seizures) during repeated episodes of physical ethanol dependence.

The effect of phenobarbital and carbamazepine on the ethanol withdrawal reaction in the rat

The effects of phenobarbital (PB) and carbamazepine (CZ) on the ethanol withdrawal reaction in the rat were investigated in a blind study including an untreated control group. Physical ethanol dependence was established by intragastric intubation during a 4-day period. Both the degree of intoxication and the withdrawal reaction were assessed by standardised assessment instruments. Treatment with PB (40-60 mg/kg) and CZ (80-120 mg/kg) was initiated 10 h after the last ethanol dose and continued during the first 24 h of withdrawal. Serum concentrations of the drugs were measured. Both PB and CZ significantly reduced the ethanol withdrawal reaction compared to controls, and PB was significantly more effective than CZ. The degree of drug intoxication signs assessed by the same rating scale as the degree of ethanol intoxication indicated that maximum tolerable drug doses were used. PB probably exerts its treatment effect through the mechanism of cross dependence with ethanol, while CZ may exert a more specific effect on limbic structures responsible for central nervous system excitability.