Residual learning deficit after heavy exposure to cannabis or alcohol in rats

Cholinergic system and memory in the rat: effects of chronic ethanol, embryonic basal forebrain brain transplants and excitotoxic lesions of cholinergic basal forebrain projection system

Oral administration of ethanol (20% v/v) to male Sprague-Dawley rats for different periods of time up to 28 weeks resulted in profound reductions of acetylcholine content, in vitro synthesis and release of acetylcholine, choline uptake, activities of choline acetyltransferase, acetylcholinesterase and pyruvate decarboxylase, content of noradrenaline, serotonin and, to a lesser extent, dopamine throughout the brain. Changes were fully and partially reversible by a 4 weeks' ethanol-free period following a treatment of 8 and 18 weeks, respectively. They remained persistent, however, after 28 weeks of treatment. Performance in an eight arm-radial maze revealed a severe impairment in both spatial and non-spatial reference and working memory. A similar pattern of memory impairment was obtained after ibotenate lesion of the cholinergic basal forebrain projection system. In order to test whether this memory impairment depends on cholinergic deafferentation of the cortex, cholinergic-rich fetal basal forebrain cell suspensions were transplanted into cortex, hippocampus or both these sites in ethanol treated rats. Cholinergic-rich transplants, but not cholinergic-poor transplants, were effective in ameliorating impaired memory function and measures of cholinergic activity in the basal forebrain projection system. The behavioural efficacy of the basal forebrain grafts was well correlated with measures of both transplant volume and the degree to which they restored acetylcholine content at the transplant site; these transplants had no effect, however, on brain monoamine levels. The effects of the cholinergic-rich transplants into cortical and hippocampal sites were additive in their amelioration of performance in the radial maze. Similarly, ibotenate lesions of the sites of origin of the cholinergic projections to neocortex (in the region of the nucleus basalis magnocellularis) and hippocampus (the medial septal areas and nucleus of the diagonal band), respectively, were additive in their deleterious effects on maze performance. There were no qualitative differences in the susceptibility of the four different types of memory performance measured (spatial and non-spatial reference and working memory) to the effects of ethanol, ibotenate lesions of the cholinergic projection system, or cholinergic-rich brain tissue transplants. Thus, overall, the results indicate that the forebrain cholinergic system acts as a whole, without major functional differences between the projections originating in the medial septal area/diagonal band complex and the basal nucleus, and that it discharges a very general function in cognitive processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Repeated withdrawal from ethanol on radial arm acquisition in rats

Male rats were treated with ethanol (8.0-12.0 g/kg/day) for four 2 week periods interrupted every 2 weeks by a 2 week period of no drug treatment. Thus they experienced withdrawal from ethanol four times. Other rats were treated with ethanol for 8 weeks with no interruptions, to control for the total dose and duration of drug treatment. Acquisition of an eight-arm radial maze response when daily ethanol treatment was ended, was not affected by either the experience of four withdrawals from ethanol or by 8 weeks of ethanol treatment. The lack of withdrawal-induced impairment can be attributed to a lack of sensitivity in the maze task to possible withdrawal-induced deficits and to an insufficient duration of ethanol dependence.

Residual effects of chronic cannabis treatment on behavior in mature rats

Mature rats (starting weight at least 270 g) were treated daily with cannabis extract (daily THC dose 20 mg/kg) for 3 months. After a 1- to 4-month drug-free period, residual effects on a variety of behaviors were studied. No residual effects were found in learning of an eight-arm radial maze task, nor on a differential reinforcement of low-rate responding (DRL-20) task, nor on open field activity. On the other hand, two-way shuttle box avoidance learning was facilitated by previous cannabis treatment, since cannabis-treated rats exhibited shorter mean latencies to avoid footshock than vehicle controls. The findings indicate greater vulnerability of immature organisms (previous studies) than mature organisms (the present study) to long-term effects of chronic cannabis administration.

Residual effects of prolonged cannabis treatment on shuttle-box avoidance in the rat

Chronic oral administration of cannabis extract to rats was examined for its residual effects on shuttle-box avoidance learning. In experiment 1 avoidance learning was assessed in rats that had been tested previously on other behavioral tests. Chronic treatment (3 months) facilitated the learning of shuttle-box avoidance in cannabis-treated animals relative to vehicle controls. In experiment 2 very similar results were obtained in naive rats. These and other residual effects of chronic cannabis treatment are similar to the effects of hippocampal lesions.

The neurotoxicity of ethanol

Alterations in nervous system functioning following acute and chronic ethanol exposure have been studied in a great number of experimental investigations. Results from many of these investigations can be difficult to interpret, particularly since a variety of techniques and exposure models are employed. This review emphasizes those studies which, in the opinion of the author, fit into a pattern where results from studying one function of the nervous system is in accordance with results from studying another. Thus, the fluidizing effect of ethanol on the neuronal membrane - an effect which ethanol shares with anaesthetics - leads to a change in protein function which in turn affects ion transport such as Na+ and Ca++ across the membrane due to changes in the ion channels. Cation influx is probably directly coupled to neurotransmitter release which is in agreement with the finding that ethanol exposure results in inhibition of Na+ and Ca++ current as well as acetylcholine release. The sensitization of the dopaminergic system after ethanol exposure may also be related to the changes in cation flux, and the changes in this system probably play a crucial rôle in the development of tolerance and withdrawal symptoms. Other aspects such as impairment of protein synthesis, altered GABA function of impairment of neuron excitability and conduction are more difficult to place in proper perspective. The rôle of acetaldehyde in acute as well as chronic ethanol intoxication also remains a controversy. These may, however, be secondary phenomena to primary changes in different part of the nervous system not necessarily important in the clinical situation. Behavioural and anatomical studies particularly from recent years have shown that experimental animals develop memory disturbances following chronic exposure even when kept on sufficient diet. These findings argue strongly for a direct toxic effect of ethanol, and are furthermore compatible with behavioural changes in chronic alcoholics, dominated by memory impairment. Since it has been argued that the cholinergic system plays a significant rôle for memory function, a possible explanation for some of the psychological and anatomical deficits caused by ethanol is thus the changes in the function of the cholinergic system particularly in the hippocampal regions.

Behavioral effects of prolonged administration of delta 9-tetrahydrocannabinol in the rat

Rats treated chronically with delta 9-tetrahydrocannabinol (THC, daily oral dose 20 mg/kg) were examined for residual effects on a variety of behaviors following a 1-4-month drug-free period. Learning a 12-arm radial maze and a differential reinforcement of low-rate responding (DRL-20) task was significantly retarded in THC-treated animals, although performance reached control levels by the end of testing. Learning two-way shuttle box avoidance was slightly facilitated in the drug-treated subjects. In open field tests THC-treated rats displayed an initial hypoactivity, followed by hyperactivity, but these changes were not significant. Most of the effects of THC resemble, but are weaker than those of chronic treatment with cannabis extract in a dose containing the same amount of THC. The findings are discussed in terms of the role of other constituents of cannabis that may add to, or potentiate the effects of THC itself.

Electrophysiological analysis of synaptic distribution in CA1 of rat hippocampus after chronic ethanol exposure

This study investigated the long-lasting effects of chronic ethanol consumption on the distribution of Schaffer collateral-commissural (SCH/COM) afferents within stratum radiatum of rat hippocampal CA1. Experimental animals were fed an ethanol-containing liquid diet for 20 weeks but were withdrawn from the special diet for at least 8 weeks prior to acute electrophysiological recordings. Field potential laminar analyses were performed by stepping the recording electrode in 25 microns increments through CA1 and sampling evoked potentials at each point. One-dimensional current-source density (CSD) was calculated from the field potential laminar profiles to enhance spatial resolution of current sources and sinks. Stimulation of the SCH/COM afferents elicits short-latency, negative field potentials throughout the synaptic terminal zone (stratum radiatum). CSD analysis in normal animals revealed that the synaptic currents generated in stratum radiatum concentrate into bimodal yet overlapping components, peaking 71.3 microns and 228.3 microns from the pyramidal cell layer. Chronic ethanol treatment produced: (1) a 13.2% shrinkage of the overall extent of current sinks in stratum radiatum; (2) a 37.4% reduction in the spatial extent of the sink proximal to the cell layer; and (3) an increase in the amplitude of the more distal sink. We tentatively propose the proximal and distal sinks to reflect a separation of the COM and SCH afferents, respectively. Chronic ethanol thus appeared to have selectively produced persistent damage to the COM-CA1 pathway.

Residual effects of prolonged cannabis administration on exploration and DRL performance in rats

Chronic oral administration of cannabis extract to rats (daily delta 9-tetrahydrocannabinol dose 20 mg/kg) was examined for its residual effect on open field activity and DRL (differential reinforcement of low-rat responding) performance, following a 2-3 month drug-free period. Locomotor activity during the latter part of an open field test was markedly increased in rats previously treated for either 6 months or 3 months with the drug. The same treatments also produced a significant impairment on a DRL-20 task relative to control subjects' performance. These and other findings (impaired maze learning and facilitated two-way shuttle box avoidance) might mean that cannabis produces long-lasting hippocampal dysfunction in rats.

Learning impairment in the radial-arm maze following prolonged cannabis treatment in rats

Chronic oral administration of cannabis extract to rats (daily delta 9-tetrahydrocannabinol dose 20 mg/kg) was examined in three experiments for its residual effect on radial-arm maze learning following a 1-month drug-free period. Learning a simple eight-arm maze was significantly impaired in rats treated for either 6 months (Experiment I) or 3 months (Experiment II) with the drug. In Experiment III, animals that received the extract for 3 months exhibited significant learning deficits on a much more difficult 12-arm radial maze. The results demonstrate that the deleterious effects of cannabis on radial-arm maze learning are probably due to a tendency toward increased vigilance and perseveration, possibly combined with an impaired utilization of spatial cues.

Augmentation of short-term plasticity in CA1 of rat hippocampus after chronic ethanol treatment

The neurotoxic effects of chronic ethanol exposure were investigated in rat hippocampus by electrophysiological analysis of the Schaffer collateral-commissural input to stratum radiatum of CA1. Experimental animals were fed an ethanol-containing liquid diet for 20 weeks but were withdrawn from the special diet at least eight weeks prior to acute electrophysiological recordings. Ethanol treatment had no effect on input-output relationships for either the population EPSP or the population spike (PS). During paired-pulse stimulation, the ethanol group exhibited a greater facilitation of the test pulse PS relative to the control group, although potentiation of the EPSP was unchanged. In addition, the ethanol group showed a trend toward greater facilitation of the PS during 5 and 10 Hz tetani. No differences between groups were observed in the magnitude or duration of the long-term potentiation produced by 5, 10 or 100 Hz stimulus trains. Ethanol treatment did significantly reduce the transient spike depression after low frequency stimulation. This pattern of results is similar to that found for treatments which reduce hippocampal recurrent inhibition. Thus, chronic ethanol treatment may produce a lasting disruption of intrinsic inhibitory neurotransmission in the rat hippocampus.

Reversal of ethanol tolerance and cross-tolerance to pentobarbital in the rat

Adult male Wistar rats were fed nutritionally adequate liquid diets providing 35% of the total calories as ethanol, while pair-fed controls received the corresponding diet with ethanol replaced by an equicaloric concentration of sucrose. After 2, 4, 6, 8, 10 and 14 weeks of chronic ethanol treatment, separate groups of rats were injected with a test dose of either ethanol (3 g/kg) or pentobarbital (40 mg/kg). Rectal temperatures were determined prior to and at 30, 60, 90 and 120 min after injection. The fall in rectal temperature after a test dose of ethanol or pentobarbital was significantly lower at 2 and 4 weeks in ethanol-treated rats than in pair-fed controls. After 6 and 8 weeks of chronic ethanol treatment, the fall in temperature after the same test doses was still less in ethanol-treated rats than in controls. However, at 10 and 14 weeks the fall in temperature was virtually identical in the two groups. A similar pattern of results was obtained when ethanol-induced sleep was compared in ethanol-treated rats and control rats. These intriguing results challenge the generally believed concept that tolerance and cross-tolerance, once produced, are sustained with chronic treatment, and may raise the possibility that such processes are reversible even during chronic treatment, at least under certain regimens.

Impairment of acquisition of a DRL schedule following prolonged ethanol consumption

Two groups of male hooded rats (N = 9) were given either ethanol or sucrose solutions as their only source of fluid for six months. Thirty days after the ethanol treatment, the rats were reduced to 85% of their free-feeding weights and allowed to obtain 45 mg of food pellets on an FR 1 schedule fof five consecutive days. Subsequently, the rats were tested on four DRL schedules (6. 12, 18, 24 sec). There was no difference between the two groups on FR 1 or DRL 6 sec schedules; however, when the DRL interval was lengthened to 12, 18, and 24 sec, the ethanol group required more sessions than the sucrose group to reach criterion performance. After increases in the DRL interval, the modal interresponse time of the ethanol group shifted more slowly than that of the sucrose group.

Adolescent drug abuse and the development of behavior

Extensive research has revealed that illicit drug use often commences during adolescence, a critical period of physical and psychological development, and it is my intent to selectively focus upon some of the potentially significant interactions between illicit drug abuse and the development of behavior during the adolescent period.

Alterations of macromolecule biosynthesis after chronic administration of opiates and ethanol

The literature concerning the effects of opiates, alcohol and barbiturates on RNA and protein metabolism is reviewed. Recent findings from this laboratory suggest that chronic morphine treatment increases the template activity of chromatin from oligodendroglial nuclei while chronic ethanol treatment decreases this activity. In addition, chronic morphine treatment stimulates protein synthesis in cell free systems and may increase the synthesis of discrete synaptic membrane proteins. Results from other laboratories suggest a general decrease in macromolecule biosynthesis with long term ethanol consumption. These results are discussed in terms of the possible roles of protein synthesis in the effects of chronic opiate and ethanol administration.