Effects Of Ethanol In Rats Research Articles

Effect of Naloxone on Behavioral Changes Induced by Subchronic Administration of Ethanol in Rats

Endogenous opioid peptides appear to be involved in acute behavioral effects induced by single doses of ethanol. However, its role in repeated ethanol exposure has not been studied. In the present study ethanol was given to rats at the doses of 2 and 4 g/kg by a stomach gauge for 15 days, and its effects on spontaneous motility, open-field activity, and active avoidance behavior recorded on the 3rd, the 6th and the 15th days. Then the effect of naloxone (0.5 and 2 mg/kg by intraperitoneal route) was tested against a challenge ethanol dose, administrated by oral route, on the 16th day. Control animals received tap water and saline instead of ethanol or naloxone, respectively. Both doses of ethanol induced a decrease in spontaneous motility that was antagonized by naloxone. Open-field ambulations were increased by the high dose of ethanol, low-dose lacking effect; naloxone did not modify these ethanol effects. The low dose of ethanol shortened latency time in shuttlebox, the high dose causing escape and freezing responses; none of these effects were modified by naloxone. Therefore, endogenous opioid peptides appear to play a limited role in the chronic effects of ethanol in rats; particularly its effects in tests inducing an increase in the level of anxiety were resistant to naloxone.

Prior Repeated Exposure to a 5-HT 3 Receptor Agonist Does Not Alter the Ethanol-Induced Conditioned Taste Aversion in Rats

Several reports have indicated that the brain serotonergic 5-HT 3 receptors are involved in at least some central effects of ethanol in rats. However, using an operant drug discrimination procedure, we have shown that these receptors are not primarily involved in the discriminative stimulus effects of ethanol. The aim of the present study was to further elucidate the role of 5-HT 3 receptors in the formation of the ethanol-cueing effects in rats. To this purpose, a crossfamiliarization conditioned taste aversion (CF-CTA) procedure was used. Four daily injections of 1.5 g/kg ethanol (10% v/v) resulted in a significant attenuation of the subsequent ethanol-induced CTA. In contrast, four daily injections of the 5-HT 3 receptor agonist, 1-( m-chlorophenyl)-biguanide (mCPBG; 50 μg per rat, ICV) did not alter the subsequent ethanol-induced CTA. The 50 μg dose of mCPBG produced a marked CTA in a control experiment. These results taken together with some previous findings from our laboratory suggest that the brain 5-HT 3 receptors do not play any crucial role in the mediation of the discriminative stimulus effects of ethanol.

Nefazodone attenuates the behavioral and neurochemical effects of ethanol

This study evaluated the influence of nefazodone, a combined 5-HT 2A receptor antagonist and 5-HT reuptake inhibitor, on the behavioral and neurochemical effects of ethanol in nonselected male Wistar rats. In microdialysis experiments, ethanol (2.5 g/kg, IP) increased extracellular accumbal dopamine levels by 36% ( p = 0.0073) compared to baseline levels, and elevated the maximal DOPAC and HVA levels by 26% ( p = 0.0093) and 52% ( p = 0.0010), respectively. Nefazodone (50 mg/kg, SC) per se increased accumbal dopamine levels by 28% ( p = 0.0199), but, when injected 40 min before ethanol, reduced the ethanol-induced elevation of accumbal dopamine overflow ( p = 0.0132) and decreased the ethanol-induced HVA levels ( p = 0.0159). In an ethanol(6% v/v)/water free-choice paradigm, nefazodone (50 mg/kg, SC) decreased ethanol intake by 51% ( p = 0.0251) and preference by 22% ( p = 0.0251) in high- but not low-preferring rats from a nonselected Wistar strain. These results show that nefazodone modulates the mesolimbic dopamine system in a dopamine activity-dependent manner, and influences the neurochemical and behavioral effects of ethanol in the rat.

The Effects of Naloxone on Expression and Acquisition of Ethanol Place Conditioning in Rats

Naloxone has been shown to facilitate extinction of ethanol-induced conditioned place preference (CPP) in mice. The present-study extended these findings by examining naloxone’s effect on the expression (Experiment 1) and acquisition (Experiment 2) of place conditioning with ethanol in rats. In Experiment 1, after place conditioning with ethanol (1.8 g/kg, IP), groups N0, N1.5, and N10 received 0, 1.5, or 10 mg/kg naloxone before testing. As expected, ethanol produced a robust conditioned place aversion (CPA). However, naloxone had no effect on expression of CPA. In contrast to studies with mice, the endogenous opioid system does not appear to be involved in the conditioned motivational effects of ethanol in rats. In Experiment 2, groups SE1 and SE2, NS(1.5), NE(1.5), and NE(10), received ethanol alone (1.2 g/kg), naloxone alone (1.5 mg/kg), naloxone 1.5 mg/kg plus ethanol, and naloxone 10 mg/kg plus ethanol during acquisition, respectively. All naloxone-treated groups exhibited CPA. Moreover, group NE(1.5) showed a stronger CPA than group NS(1.5). The CPA produced by coadministration of naloxone and ethanol was attributed to naloxone’s effects on the neural processes underlying ethanol’s unconditioned aversive effects, or to other nonspecific effects on ethanol’s motivational properties.

Cardiovascular Effects of Ethanol in Rats Selectively Bred for High or Low Sensitivity to the Hypnotic Effects of Ethanol

The cardiovascular effects of acute ethanol administration were studied in rats selectively bred for high (HAS) or low sensitivity (LAS) to the acute hypnotic effect of ethanol. In chronically cannulated, conscious animals, the intravenous administration of 1 g/kg of ethanol caused moderate hypotension and tachycardia in both HAS and LAS rats. The phenylephrine-induced reflex bradycardia and the baroreflex slope were significantly reduced by ethanol only in HAS and not in LAS rats. In urethane-anesthetized HAS rats, the baroreflex inhibitory action of ethanol was present under control conditions, but it was absent after depletion of endogenous GABA by treatment of the rats with 100 mg/kg of 3-mercaptopropionate. These findings confirm the role of endogenous GABA in the baroreflex inhibitory action of ethanol, and are compatible with the documented differential sensitivity of the GABAA, receptor complex to ethanol in HAS and LAS rats.

Disruption of tolerance to the ataxic effect of ethanol by an extraneous stimulus

According to a conditioning analysis, pharmacological conditional responses (CRs) contribute to tolerance. We previously reported (24) that, as expected on the basis of this model, tolerance to the hypothermic effect of ethanol is attenuated by “external inhibition,” for instance, by presentation of a novel stimulus (a strobe). However, results of more recent research (2,12,13) indicate that novel stimuli augment the hypothermic effect of ethanol in rats receiving the drug for the first time. It is possible, therefore, that a novel stimulus apparently attenuates ethanol tolerance because it augments ethanol-hypothermia, rather than because it functions as an external inhibitor. Two experiments were designed to evaluate external inhibition of tolerance to another effect of ethanol—ataxia. Although the initial ataxic effect of the drug (unlike the hypothermic effect) is not enhanced by a novel stimulus, the stimulus reinstated ethanol-induced ataxia in tolerant rats. The results demonstrate external inhibition of ethanol tolerance in a preparation not confounded by the effects of the novel stimulus on initial responding to ethanol.

Place conditioning with alcohol in alcohol-preferring and -nonpreferring rats

A place-conditioning procedure was used to examine the effect of selective breeding for ethanol preference on sensitivity to the rewarding and/or aversive effects of ethanol. On 4 alternate days, groups of seven to eight alcohol-preferring (P) and alcohol-nonpreferring (NP) rats received IP injections of 0.0 (saline controls), 0.5, 1.0, or 1.5 g ethanol/kg body wt. immediately before 15-min confinement in a novel environment. On the 4 intervening days the same rats received saline injections before 15 min confinement in a different environment. On day 9, a 15-min choice test was given with no injections, in which the rats could move freely between the ethanol and the saline-paired environments. Dose-dependent avoidance of the ethanol-paired environment was observed in both lines of rats (1.0 and 1.5 g/kg), but the magnitude of the avoidance was less in the P relative to the NP rats, indicating that ethanol was less aversive for the P rats. No evidence for a place preference was observed in either line with any of the ethanol doses. An innate reduced sensitivity to the aversive effects of ethanol in rats of the P line and/or an enhanced sensitivity to the aversive effects of ethanol in rats of the NP line may contribute to the different levels of oral ethanol self-administration observed in these selectively bred rat lines.

Operant Ethanol‐Reinforced Behavior in P, NP, HAD, and LAD Rats Bred for High Versus Low Ethanol Preference

These studies examined the reinforcing effects of ethanol in rats selectively bred for high versus low ethanol drinking in a two-bottle choice preference task, namely the Preferring (P), Non-Preferring (NP), High Alcohol Drinking (HAD), and Low Alcohol Drinking (LAD) rats. The results substantiate findings suggesting that genetic factors are significant in determining whether ethanol will come to serve as a reinforcer. P rats exhibited high levels of responding for ethanol compared with the water vehicle, NP and HAD rats exhibited more moderate levels of responding for ethanol, and the behavior of LAD rats suggested that ethanol served only inconsistently as a reinforcer for these rats. Overall, the results suggest the existence of distinct, biologically influenced components of ethanol drinking behavior. Preference appears to measure an inherent facilitative factor allowing animals to initiate ethanol drinking. The operant chamber paradigm appears to measure factors related to whether and to what extent ethanol will serve as a positive reinforcer following conditioned exposure to the drug. Although preferring animals generally find ethanol reinforcing there seems to be little quantitative relationship between degree of preference and whether ethanol will serve as a reinforcer. Lack of preference does not seem to be predictive of lack of reinforcement. Thus, it appears that preference for ethanol and reinforcement from ethanol are somewhat overlapping, but distinct factors that contribute to ethanol drinking. These results suggest the existence of multiple components of behavior mediated by multiple mechanisms that contribute to ethanol drinking.

Differential development of acute tolerance to the motor impairment and anticonvulsant effects of ethanol.

The development of acute tolerance to the motor impairment and anticonvulsant effects of ethanol was examined. Acute tolerance to the motor impairment effect of ethanol was shown by a decrease in the degree of intoxication, as measured on the moving belt task, at higher blood ethanol levels ranging from 206 to 256 mg/dl. There was no evidence of acute tolerance to the anticonvulsant effect of ethanol in rats tested over the same time period. These results indicate that, like chronic tolerance, acute tolerance to ethanol develops at different rates for different effects of the drug. The fact that chronic tolerance to the anticonvulsant effect of ethanol has been well documented raises doubts about the assumption that similar physiological changes underlie acute and chronic tolerance to a drug effect, and support the idea that the relationship between acute and chronic tolerance is more complex than previously thought.

Relationship between A 1 adenosine receptors and protein kinase C activity in the control of purine release from rat cultured astrocytes

We reported that inhibition of central sympathetic pools of imidazoline I1 receptors abolishes the hypotensive effect of ethanol in rats with glycerol-induced acute renal failure (ARF). This study investigated whether adenosine receptors modulate the ethanol-I1-receptor interaction. The effect of selective blockade of adenosine A1, A2A, or A2B receptors on hemodynamic responses to ethanol in the absence and presence of the I1-receptor agonist moxonidine was determined in ARF rats. Ethanol (1 g/kg i.v.) decreased and increased blood pressure (BP) and heart rate (HR), respectively. Pretreatment with moxonidine abolished the hypotensive but not the tachycardic effect of ethanol. The hypotensive effect of ethanol remained unaltered after selective blockade of A1, A2A, or A2B receptors with 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) and 8-(3-chlorostyryl) caffeine (CSC) and alloxazine, respectively. Neither was ethanol hypotension affected after inhibition of adenosine uptake by dipyridamole (DPY). Alternatively, the ability of moxonidine to abolish ethanol hypotension was still evident in presence of alloxazine whereas it disappeared or weakened in rats pretreated with CSC and DPCPX, respectively. These findings implicate adenosine A2A receptors in the moxonidine-evoked inhibition of the hypotensive action of ethanol. A modulatory role for adenosine A1 site in the ethanol-I1-receptor interaction is also possible through as yet unidentified mechanism.

Failure of the partial inverse benzodiazepine agonist Ro15-4513 to block the lethal effects of ethanol in rats

The partial inverse benzodiazepine agonist Ro15-4513 has been found to antagonize some of the behavioral and physiological effects of low to moderate doses of ethanol. In the present study, pretreating rats with Ro15-4513 (1, 3, 10, and 30 mg/kg) at doses equal to or greater than those used in prior investigations failed to block the lethal effects of intraperitoneal injections of ethanol at a dose of 5.4 g/kg. These results suggest that the lethal actions of ethanol may involve a mechanism that is not blocked by Ro15-4513, which is known to selectively antagonize ethanol-stimulated chloride uptake via the GABA-coupled chloride ion channel.

Ro 15-4513 does not antagonize the discriminative stimulus- or rate-depressant effects of ethanol in rats

Female rats, trained to discriminate between IP administered 1.2 g/kg ethanol (ETOH) and the saline vehicle (12 ml/kg), did not press the nondrug associated lever in tests with ETOH (0.9 and 1.2 g/kg) plus the purported amethystic imidazo benzodiazepine Ro 15-4513 (3 and 10 mg/kg) as examined at two intervals after ETOH administrations viz. 7.5 and 15 min. The two doses of Ro 15-4513 were administered 5 min prior to ETOH. Response times were increased in tests with the combination. ETOH in expired air was not different in the two drug conditions, i.e., ETOH singly and together with Ro 15-4513, irrespective of the dose combinations examined. Rats trained to press a bar (FR-10 operant behavior) for sweetened water disclosed increases in the time used to obtain the reinforcer after treatments with ETOH and Ro 15-4513. Thus, Ro 15-4513 did not seem to reverse any of the behaviors examined in this study.

Intra‐Accumbens trh prolongs maintenance of tolerance to hypothermic effect of ethanol in rats

AbstractTolerance to the hypothermic effect of ethanol (Et–OH) developed in male Wistar rats treated daily with 5 g/kg of 20 per cent ET–OH v/v i.g. for 6 days. On Day 6 Et–OH treatment was discontinued and the animals were divided into two groups injected into the nucleus accumbens septi (NAS), either with pGlu‐His‐Pro‐NH2 (TRH) or saline. The peptide was injected via permanently implanted cannulae in doses of 10 or 30 m̈g in 0.5 m̈l on each side once daily. The effect of such treatment on the maintenance of Et–OH tolerance was assessed by measuring the temperature decrement in response to a challenge dose of Et–OH (5 g/kg i.p.) given on Day 10. It was found that in saline‐treated rats the initial tolerance declined. TRH‐injected groups exhibited constantly low response to hypothermic action of Et–OH. In a control experiment TRH was shown to have no effect on the body temperature after intra‐accumbens application in Et–OH‐naive rats.

Antagonism of the stimulant and depressant effects of ethanol in rats by naloxone.

The action of naloxone (0.5 and 2 mg/kg IP) on the behavioural effects of a low (2 g/kg PO) and a high dose (4 g/kg PO) of ethanol was studied in rats. Ethanol at the low dose increased spontaneous motility, enhancing open-field external ambulations and reducing shuttle-box latency. All these effects were antagonized by naloxone. Ethanol at the high dose produced by hypomotility, decreasing open-field external ambulations and impairing shuttle-box performance. In this case, naloxone also reduced the ethanol effect, but its action was less consistent. Therefore, although mechanisms other than a specific opioid receptor blockade by naloxone must be considered, an involvement of opioid peptides in the effects of ethanol cannot be discounted.

Vasopressin-Like peptides retain ethanol tolerance in the absence of changes in serotonin synthesis in limbic structures

Central tolerance to the effects of ethanol in rats can be prolonged beyond its normal time of disappearance by administration of vasopressin (AVP) or desgycinamide-arginine-vasopressin (DGAVP) after ethanol withdrawal. While the mechanism underlying this effect is unknown, we have reported that specific depletion of hippocampal serotonin (5-HT) prevents the prolongation of tolerance by DGAVP. The present study explored possible presynaptic interactions between DGAVP and 5-HT terminals in the hippocampus, in relation to tolerance retention. When administered acutely, DGAVP had no effect on the rates of hippocampal or septal 5-HT synthesis in naive rats, as assessed by the NSD 1015 method. Moreover, chronic DGAVP treatment that maintained tolerance did not change the in vivo rate of 5-HT synthesis in the hippocampus or septum. Similarly, no significant differences were found in the levels of hippocampal 5-HT or 5-HIAA levels were slightly but significantly lower in ethanol-DGAVP than in ethanol-saline rats. In vitro studies revealed, on the other hand, that addition of AVP to the incubation medium failed to affect the spontaneous and stimulated release of endogenous 5-HT from hippocampal slices. While the lack of changes in hippocampal 5-HT synthesis argues against a presynaptic DGAVP- 5-HT interaction, the possibility remains of a peptide modulation of 5-HT postsynaptic actions.

Biochemical and behavioral effects of acute ethanol in rats at different environmental temperatures.

The role of ethanol-induced hypothermia on some selected biochemical and behavioral parameters was evaluated. Rats were kept from 1 h before to 1 h after injection (saline or ethanol 2 g/kg, 20% solution IP) in an environment chamber at either 22 degrees C or 35 degrees C, and then tested behaviorally or sacrificed. Exposure of rats to a warm environment (35 degrees C) prevented the ethanol-induced hypothermia found in rats kept at 22 degrees C. Ethanol-treated rats kept at 35 degrees C had an attenuated increase in levels of free fatty acids and of corticosterone in plasma, suggesting that part of the ethanol-induced response may result from hypothermia rather than from ethanol itself. In addition, tyrosine levels were unexpectedly increased by 18% in intoxicated animals kept at 35 degrees C. By contrast, gross motor activity tested 1 h after injection was depressed more in animals kept at 35 degrees C than in those kept at 22 degrees C, and swim performance was impaired more at 5-20 min after treatment in animals not showing hypothermia. The greater behavioral impairment was not due to any debilitating effects of the warm environment since the saline control animals showed comparable activity to that of rats kept at 22 degrees C. We conclude that ethanol-induced hypothermia may influence and interact with other actions of ethanol.

Conditioning and extinction of tolerance to the hypothermic effect of ethanol in rats.

The contribution of classical conditioning to tolerance to the hypothermic effect of ethanol was examined. During the tolerance acquisition phase, rats were exposed at 4-day intervals to a distinctive set of environmental cues paired with injections of ethanol (1.4 g/kg, ip). Interspersed between these drug trials were exposures to an alternate set of cues paired with injections of saline. In addition, three groups experienced different amounts of stimulation and activity during drug exposure in order to determine whether "behavioral augmentation" of tolerance would occur. In subsequent tests, the rats were tolerant only in the presence of cues previously paired with ethanol. Moreover, this environmentally specific tolerance was associated with a conditioned hyperthermic response to placebo (saline) injections in the drug environment. An extinction procedure designed to weaken tolerance mediated by classical conditioning was also found to be effective. Evidence for conditioned tolerance was weakest in animals experiencing low levels of activity during the initial drug exposure periods.

Cholinergic mediation of motor effects of ethanol in rats

The role of cholinergic neurons in the motor depressant effects of ethanol was examined. Choline chloride pretreatment (30–90 mg/kg i.p.) potentiated the hypomotility produced by 2 g/kg of ethanol. Physostigmine pretreatment (0.2 mg/kg, i.p.) also enhanced the motor depression produced by ethanol. Conversely, in animals pretreated with scopolamine (0.25 and 0.5 mg/kg) the depressant effect of ethanol was less. The potentiation produced by choline was not associated with changes in levels of ethanol in blood. It is concluded that cholinergic neurons are involved in the motor activity changes produced by ethanol. Such a mechanism may operate in conjunction with the dopaminergic neuronal system.

Decreased intoxicating effect of ethanol in rats after 6-hydroxydopamine-induced degeneration of ascending dopamine pathways

Selective lesion of ascending dopamine pathways was made by injecting the neurotoxin 6-OHDA (8 μg/4 μl) bilaterally close to the nigro-striatal dopamine pathway of 18 male Long Evans rats. Similar injections of the vehicle were given to 10 control rats. Two months after the operation intoxication was measured in a tilting-plane test after an injection of ethanol (2 g/kg, IP). Ethanol impaired the performance of the 6-OHDA-treated rats significantly less than that of the controls. This finding suggests a role for the central dopamine neurons in the intoxicating effect of ethanol.

Effect of lysine on toxicity and depressant effects of ethanol in rats

When l-lysine was administered prior to toxic doses of ethanol, the LD50 for ethanol was slightly increased after both po and ip administration. The onset of ethanol-induced sleeping time was prolonged while the duration was reduced by pretreatment with l-lysine.