Immediate and delayed voluntary ethanol effects on motor performance, learning and inhibition in rats

Effects of moderate chronic ethanol consumption on hippocampal nicotinic receptors and associative learning

A number of studies have reported that ethanol exposure induces changes in different brain systems. The hippocampus is a brain region that is very vulnerable to ethanol exposition, which functionally results in impairment of learning and memory processes reported in heavy drinkers. Hippocampal nicotinic receptors are involved in learning and memory. In this study, we determined the effects of ethanol on the main hippocampal subtypes of neural nicotinic receptors (alpha7 and alpha4beta2) in rats non-selected for alcohol consumption, in order to check for possible changes on these receptors that could be linked with alterations in learning acquisition. Binding assays were carried out with [3H]methyllycaconitine ([3H]MLA) to study the alpha7 and [3H]nicotine to study alpha4beta2 receptors. Auto-shaping, continuous ratio and extinction procedures were used as behavioral tests. The results show that moderate chronic ethanol consumption for 10 weeks produces: (a) a decrease of both hippocampal nicotinic receptor subtypes without alterations in affinity; (b) no differences in behavioral performance between control rats and ethanol-drinking rats in auto-shaping and continuous ratio; (c) an improvement of performance of extinction paradigm. These results indicate that chronic ethanol consumption, at moderate levels, induces changes in hippocampal nicotinic receptors but does not impair acquisition and performance of new associative learning and even improves some kind of paradigms. These results may have implications in the biochemical basis of interactions between alcohol and nicotine and the effects of these drugs on behavior.

Intrahippocampal allopregnanolone decreases voluntary chronic alcohol consumption in non-selected rats

We have recently shown that 0.2 microg of the neurosteroid allopregnanolone (AlloP) administered to the hippocampus induced an anxiolytic-like profile and also reduced alcohol withdrawal symptoms in voluntary and chronic alcohol-drinking rats. The aim of the present work was to study whether the administration of this dose of AlloP could affect alcohol consumption in non-selected rats that have been voluntarily ingesting high doses of alcohol for long periods of time in a limited access procedure. We used a free-choice drinking procedure that involved providing the rats with an alcoholic solution (10% ethanol) at an early age. Alcohol and control rats were assigned randomly to three groups that received an intrahippocampal (dorsal CA1) injection before the period of alcohol consumption after a long history of chronic alcohol intake. The injection groups were AlloP (0.2 microg, 1.26 microM), pregnenolone sulfate (PregS) (5 ng, 24 microM) or vehicle. Blood alcohol concentrations (BAC) were assessed before testing the effects of injections on alcohol consumption. Although AlloP did not eliminate alcohol ingestion, it significantly decreased alcohol consumption. The intrahippocampal administration of PregS, at the dose tested, did not effectively modify alcohol consumption levels. These results indicate that the positive modulation of hippocampal GABA(A) receptors induced by neurosteroids can be an important neurobiological target for reducing chronic alcohol consumption.

Comparison between multiple behavioral effects of peripheral ethanol administration in rats: Sedation, ataxia, and bradykinesia

Although low doses of systemic ethanol stimulate locomotion in mice, in rats the typical response to peripheral ethanol administration is a dose-dependent suppression of motor activity. In the present study, male rats received acute doses of ethanol IP (0.0, 0.25, 0.5, 1.0 or 2.0 g/kg) and were tested on several behavioral tasks related to the motor suppressive or sedative effects of the drug. This research design allowed for comparisons between the effects of ethanol on different behavioral tasks in order to determine which tasks were most sensitive to the drug (i.e., which tasks would yield deficits that appear at lower doses). In the first two experiments, rats were evaluated on a sedation rating scale, and ataxia/motor incoordination was assessed using the rotarod apparatus. Administration of 2.0 g/kg ethanol produced sedation as measured by the sedation scale, and also impaired performance on the rotarod. In a third experiment, ethanol reduced locomotion in the stabilimeter at several doses and times after IP injection, with 0.25 g/kg being the lowest dose that produced a significant decrease in locomotion. Finally, experiment four studied the effects of ethanol on operant lever pressing reinforced on a fixed ratio 5 (FR5) schedule for food reinforcement. Data showed suppressive effects on lever pressing at doses of 1.0, and 2.0 g/kg ethanol. Analysis of the interresponse time distribution showed that ethanol produced a modest slowing of operant responding, as well as fragmentation of the temporal pattern of responding and increases in pausing. Taken together, these results indicate that rats can demonstrate reduced locomotion and slowing of operant responding at doses lower than those that result in sedation or ataxia as measured by the rotarod. The detection of subtle changes in different motor test across a broad range of ethanol doses is important for understanding ethanol effects in other cognitive, motivational or sensory processes.

Effects of Intrahippocampal Nicotine and Neurosteroid Administration on Withdrawal in Voluntary and Chronic Alcohol-Drinking Rats

BACKGROUND

Previous studies have shown that 4.6 mug of nicotine administered to the hippocampus can deteriorate learning acquisition in alcohol-drinking rats. The aim of the present study was to research whether this nicotine dose can alter the alcohol withdrawal syndrome and whether the two neurosteroids, allopregnanolone (AlloP) and pregnenolone sulfate (PregS), at doses previously reported as anxiolytic and promnesic, respectively, can modulate these effects.

METHODS

We used a free-choice drinking procedure that involved providing the rats with an alcoholic solution (10% ethanol) at an early age. Alcohol and control rats were assigned randomly to six groups that received two consecutive intrahippocampal (dorsal CA1) injections once per week during three consecutive weeks after one hour of ethanol drinking. The first injection was nicotine (4.6 microg, 20 mM) or saline and the second injection was PregS (5 ng, 24 microM), AlloP (0.2 microg, 1.26 microM) or saline. Blood alcohol concentrations were assessed one week before the withdrawal testing. Locomotor activity and audiogenic seizures were tested during withdrawal after 110 days of voluntary ethanol consumption. Rats were injected immediately before the withdrawal testing.

RESULTS

AlloP induced a decrease in horizontal and vertical activities, suggesting that the dose tested has sedative effects. AlloP reversed the seizures induced by ethanol withdrawal and also the spontaneous audiogenic seizures induced by the acoustic stimulation in control rats. Moreover, AlloP decreased other alcohol withdrawal signs, such as tail stiffening and body rigidity. Intrahippocampal administration of nicotine or PregS, at the doses tested, did not effectively modify the expression of audiogenic seizures induced by alcohol withdrawal.

CONCLUSIONS

These results show that hippocampal GABAergic activity and AlloP have an important role in preventing convulsive behavior. The results also highlight the therapeutic potential of AlloP for reducing the alcohol withdrawal syndrome.

Intrahippocampal nicotine and neurosteroids effects on the anxiety-like behaviour in voluntary and chronic alcohol-drinking rats

Considerable evidence suggests that the anxiolytic effects of ethanol may be one of the factors that promotes alcohol consumption. The present study aimed to characterize the effects of intrahippocampal administrations of nicotine and the two neurosteroids pregnenolone sulphate (PregS) and allopregnanolone (AlloP) on anxiety-like behaviours in alcohol-drinking rats. A long-lasting free-choice drinking procedure with an early availability (from weaning) of an alcoholic solution (10% (v/v) ethanol, 3% (w/v) glucose in distilled water) was used. After 80 days of consumption, alcohol-drinking and control rats were deprived of food and assigned at random to six groups. After 100 days of consumption, each group received two consecutive intrahippocampal (dorsal CA1) injections. First injection: nicotine (4.6 microg, 20 mM) or saline; second injection: PregS (5 ng, 24 microM), AlloP (0.2 microg, 1.26 microM) or saline. Following the injections, novelty-directed activity (open field, OF), and motor coordination (80 degrees inclined screen) were tested. Blood alcohol concentrations (BACs) were assessed. Anxiolytic-like effects of voluntary ethanol consumption and intrahippocampal AlloP administration were observed. Alcohol intake increased the novelty-induced ambulation and exploration of central areas, and decreased defecation. The high exploration levels induced by AlloP decreased significantly over sessions, indicating a rapid habituation to the environmental conditions. Motor coordination was deteriorated by ethanol consumption. These results demonstrate the effects of chronic alcohol intake and neurosteroid administration on anxiety-related behaviours, and suggest an important role of the hippocampal GABA(A) receptor in these behaviours.

The neurosteroid pregnenolone sulfate neutralized the learning impairment induced by intrahippocampal nicotine in alcohol-drinking rats

The effects of intrahippocampal administration of nicotine and the neurosteroids pregnenolone sulfate and allopregnanolone on acquiring the lever-press response and extinction in a Skinner box were examined using voluntary alcohol-drinking rats. A free-choice drinking procedure that implies early availability of the alcoholic solution (10% ethanol v/v+3% glucose w/v in distilled water) was used. Alcohol and control rats were deprived of food and assigned at random to six groups. Each group received two consecutive intrahippocampal (dorsal CA1) injections immediately after 1-h of drinking ethanol and before the free lever-press response shaping and extinction session. The groups were: saline-saline; saline-pregnenolone sulfate (5 ng, 24 microM); saline-allopregnanolone (0.2 microg, 1.26 microM); nicotine (4.6 microg, 20 mM)-saline; nicotine-pregnenolone sulfate; nicotine-allopregnanolone. Blood alcohol concentrations were assessed the day before conditioning. The combination of the oral self-administration of ethanol and the intrahippocampal injection of nicotine deteriorated the ability to acquire the lever-press response. This effect was neutralized by intrahippocampal pregnenolone sulfate (negative modulator of the GABA(A) receptor complex), and it was not affected by intrahippocampal allopregnanolone (positive GABA receptor complex A modulator). Pregnenolone sulfate and allopregnanolone had no effects per se on lever-press acquisition, neither in alcohol-drinking rats nor in controls. Alcohol consumption facilitated operant extinction just as anxiolytics that act as positive modulators of the GABA receptor complex A receptors do, possibly reducing the anxiety or aversion related to non-reinforcement. This effect was increased by intrahippocampal nicotine.

Tolerance and sensitization to the hypnotic effects of alcohol induced by chronic voluntary alcohol intake in rats

The effect of a chronic alcohol exposure on the development of tolerance to the depressive effects of alcohol were examined in male Wistar rats that voluntary self-administered alcohol. A free-choice drinking procedure based on the limited access paradigm and the addition of glucose that implies an early availability of the alcoholic solution was used (Alcoholism Primary Praecox procedure). Alcohol induced sleep time (3.5 g alcohol per kg i.p.) was measured at 90 days (after 2 months of alcohol consumption) or at 60 + 90 days old (1 or 2 months of alcohol consumption). The psychomotor performance was also evaluated by means of an 80 degrees inclined screen test. Subjects that had been tested for the hypnotic effects at both 60 and 90 days showed a higher intake of alcoholic solution than the animals only tested at 90 days. The same consumption increase was observed in the glucose group. No significant differences between groups were observed in the inclined screen test. Tolerance to the hypnotic effects of alcohol was observed at 90 days. On the other hand, no significant differences between alcohol and control groups (glucose or water) were observed in the sleep time at 60 days. In the alcohol-drinking rats tested for two trials (60 and 90 days), sensitization instead of tolerance to the second hypnotic alcohol injection was seen. Tolerance to the hypnotic effects of alcohol observed after chronic voluntary alcohol consumption may provide animal models of alcoholism based on limited access to sweetened alcoholic solutions with construct validity.