M.B. Waller

Effect of low dose ethanol on spontaneous motor activity in alcohol-preferring and -nonpreferring lines of rats ☆

To determine if behavioral arousal may be associated with ethanol preference, the effects of low to moderate doses of ethanol on spontaneous motor activity (SMA) were studied in the selectively bred alcohol-preferring (P) and -nonpreferring (NP) lines of rats as well as in the Maudsley Reactive (MR/N) and Nonreactive (MNR/N) strains. Alcohol-naive rats had food and water available ad lib, but food was removed 24 hr before and during activity testing. After an intraperitoneal injection of saline (5 ml) or ethanol (0.12 to 1.5 g/kg), SMA was monitored every three min for 30 min in an electronic activity monitor. The P and MR/N rats exhibited increased SMA after doses of 0.12 and 0.25 g/kg. Both the NP and MNR/N rats failed to show increased SMA at any ethanol dose. Moderate doses of ethanol, 1.0 and 1.5 g/kg, consistently depressed SMA in all lines/strains. In 24 hr-fasted rats, increased SMA occurred within 6-12 min after injection, but free-fed rats exhibited increased SMA 12-24 min after an ethanol dose of 0.25 g/kg. Free-choice drinking scores (10% ethanol (v/v) versus water) for the P, MR/N, MNR/N and NP rats were 6.6 +/- 0.5, 4.9 +/- 0.8, 2.2 +/- 0.7 and 1.4 +/- 0.3 g ethanol/kg body wt/day (mean +/- SEM), respectively. The data indicate a positive relationship between ethanol preference and ethanol-induced motor stimulation and suggest that hyperactivity may be an expression of the positive reinforcing effect of ethanol for alcohol-preferring rats.

Induction of dependence on ethanol by free-choice drinking in alcohol-preferring rats

Studies were performed to examine whether chronic voluntary consumption of ethanol by the selectively-bred, alcohol-preferring P-rats produces physical dependence. Body weight reduction, food restriction and flavoring the 10% ethanol solution increased ethanol consumption from 7 to 14 g ethanol/kg body weight/day when water was freely available. Under similar conditions, consumption by selectively-bred, alcohol-nonpreferring NP-rats increased from 1 to 12 g/kg/day. Removal of ethanol after eight weeks induced physical signs of withdrawal in both lines of animals. In two subsequent studies, P-rats were given food, water and unflavored 10% ethanol ad lib for 15 and 20 weeks; ethanol consumption was 7.2 and 5.6 g/kg/day, respectively. Upon removal of ethanol, manifestations of withdrawal, scored blind in one experiment, developed in 85% of the animals and persisted for 72 hours. Importantly, none in the control groups of P and NP rats given water only exhibited these signs. The ethanol withdrawn groups were hyperactive in both the open-field and the head-poke apparatus. These results indicate that sufficient ethanol was voluntarily consumed by the selectively-bred alcohol-preferring P-rats under free-feeding conditions to produce physical dependence.

Effects of scheduled access on ethanol intake by the alcohol-preferring (P) line of rats.

The effects of scheduling the availability of ethanol on its voluntary consumption by the selectively bred alcohol-preferring P rats were examined under three conditions: unrestricted 24 hr/day access (Condition A), access limited to a continuous 4 hr/day (Condition B), and access limited to 1 hr every 3 hr, 4 times/day (Condition C). Food and water were always available. Daily alcohol intakes (mean +/- SEM) with Conditions A, B and C were 6.9 +/- 0.2, 2.1 +/- 0.2 and 4.4 +/- 0.2 g/kg, respectively, while the intake per hour of availability increased from 0.3 +/- 0.03 under Condition A to 1.1 +/- 0.4 g/kg under condition C. The amount of ethanol consumed per drinking episode under Conditions A, B and C were 1.1 +/- 0.1, 2.1 +/- 0.2 and 1.1 +/- 0.03 g/kg, respectively. Mean blood alcohol concentrations (BACs), determined periodically during the dark cycle of Condition A and five minutes after drinking episodes under Conditions B and C, were 59 +/- 10, 61 +/- 7 and 62 +/- 7 mg%, respectively. When unlimited access was reinstated after Condition C, daily alcohol consumption returned to a level similar to that under the initial Condition A (7.2 +/- 0.5 g/kg). When the ethanol concentration was increased from 5 to 20% (v/v) under Condition C, the amount of ethanol consumed per episode at 5% was significantly less than at the 10, 15 and 20% concentrations, and the volume consumed was significantly lower at the 20% concentration than at the 5, 10 and 15% concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Different sensitivities to ethanol in alcohol-preferring and -nonpreferring rats☆

The sensitivity of the P and NP rats to ethanol was determined by the jumping test [23]. Proper interpretation of this test requires knowledge of the regional differences in the distribution of ethanol as a function of time after ethanol injection. Ethanol concentration in brain was higher than those in tail blood and skeletal muscle within the initial 30 min following the intraperitoneal injection of ethanol and was also higher than that in cerebral blood in the first 15 min. However, after 60 min, ethanol concentrations in brain and tail blood were identical. After ethanol injection (2 g/kg), the P rats jumped 88, 78, 85, 54 and 19% higher than the NP rats at 30, 60, 120, 180 and 240 min, respectively. The tail blood ethanol concentrations did not differ between the P and NP rats after 60 min. The P rats also jumped higher than the NP rats after injection of 1.5 and 2.5 g/kg ethanol. These results indicate that the P rats are innately less sensitive to the effects of ethanol than the NP rats.

Progress toward a voluntary oral consumption model of alcoholism

With the goal of obtaining a suitable animal model for voluntary oral consumption of ethanol, the investigators selectively bred lines of alcohol-preferring and alcohol-nonpreferring rats, with preference considered as a function of the concentration of ethanol ingested. Studies with these animals showed that drinking is voluntary and not contingent on caloric restriction; that they will work to obtain ethanol even when food and water are freely available, and in so doing, show psychological or behavioral tolerance; that the amount of ethanol voluntarily consumed approaches their apparent maximum capacity for ethanol elimination. This amount of ethanol was capable of altering brain neurotransmitter content, thus exerting a CNS pharmocologic effect. In addition, the rats will bar-press for intravenous administration of ethanol, and with prolonged, free-choice consumption, ethanol intake increases to as much as 12 g per kg body weight per day without producing behavioral deficits, suggesting the development of tolerance.

Initial sensitivity and acute tolerance to ethanol in the P and NP lines of rats

We recently reported that selectively bred, alcohol-preferring (P) and alcohol-nonpreferring (NP) rats differ in sensitivity to a single sedative-hypnotic dose of ethanol, as measured by performance in the jump test. The present study examines the contributions of initial sensitivity and acute tolerance development to this difference. Initial sensitivity, assessed by brain alcohol content upon loss of the aerial righting reflex, was not significantly different between P and NP groups given 3 g ethanol/kg body weight intraperitoneally. Acute tolerance was indexed from blood alcohol concentrations (BAC) upon recovery of jumping performance following two successive ethanol doses. Practiced P and NP rats were required to jump 35 cm to a descending platform following the IP injection of 2.0 g ethanol/kg. The NP group took significantly longer (74 min) than the P (33 min) group whereupon BAC1 of NP rats (234 mg%) was significantly lower than that of P rats (250 mg%). A second injection (1.0 g/kg) was given immediately after the animals reached the 35 cm criterion. Again, NP rats took significantly longer (124 min) than P rats (52 min) to jump 35 cm and BAC2 of NP animals was lower (295 mg%) than that of P rats (343 mg%). The difference between BAC2 and BAC1, the measure of tolerance development, was significantly larger for P rats (90 mg%) than for NP rats (61 mg%). No significant differences in blood ethanol elimination were observed between the groups. The data indicate no difference in initial sensitivity between P and NP animals but that P rats develop acute tolerance more rapidly and/or to a greater degree than do NP rats. The results are consistent with a relationship in these selectively bred lines of rats between alcohol preference and the development of acute tolerance.

Monoamine uptake inhibitors attenuate ethanol intake in alcohol-preferring (P) rats ☆

The P line of alcohol-preferring rats drink pharmacologically significant amounts of ethanol when given free choice between a 10 percent ethanol solution and water. Serotonin (5-HT) uptake inhibitors and desipramine, a norepinephrine (NE) uptake inhibitor, were found to significantly reduce their ethanol consumption for up to 24 hours after intraperitoneal injection. To determine if this effect of 5-HT uptake inhibitors could be altered by receptor antagonists, some of which are short acting, P rats were trained to drink ethanol by free choice during scheduled availability, with ethanol being presented one hour every four hours during the light cycle. The majority of the ethanol was consumed during the first hour of availability, and the ethanol intake was significantly reduced by the 5-HT uptake inhibitors, fluoxetine and fluvoxamine. Pretreatment with antagonists for 5-HT1, 5-HT2 and alpha- and beta-NE receptor systems failed to alter the fluvoxamine attenuation of ethanol intake. The mechanism by which 5-HT uptake inhibitors alter ethanol preference remains unclear.

Effects of fluoxetine on the intragastric self-administration of ethanol in the alcohol preferring P line of rats

Rats of the alcohol-preferring P line (n = 7) were trained to self-administer ethanol (20% v/v) and water via an intragastric IG catheter. Food was available ad lib. Ethanol intakes averaged approximately 5-6 g/kg body wt./day. Treatment with the serotonin (5-HT) uptake inhibitor fluoxetine (10 mg/kg/day; IG) for seven consecutive days produced a marked decrease in ethanol self-administration on the first day, which was sustained throughout the seven days of treatment to values as low as 1 g/kg/day. Concomitant with the decrease in ethanol intake, the self-infusion of water gradually increased during the period of fluoxetine treatment. Total caloric intake (ethanol plus food) was moderately reduced during fluoxetine treatment; the decrease in food consumption was consistent but not statistically significant. When fluoxetine treatment was terminated, ethanol self-administration quickly returned to the prefluoxetine levels, while water intake began to decrease. Since no ethanol was consumed orally, the IG ethanol was not self-administered for its taste or smell, but apparently for its postingestive pharmacological effects. The robust reduction of ethanol self-infusion that occurred with fluoxetine treatment suggests that the 5-HT systems are involved in the reinforcing effects of ethanol in the P line of rats.

Chronic ethanol tolerance through free-choice drinking in the P line of alcohol-preferring rats ☆

The objective of this study was to determine if the selectively bred P line of alcohol-preferring rats would develop behavioral (neuronal) tolerance with free-choice drinking of ethanol. Adult, male P rats were divided into four groups. One group (FCE) received food, water and a 10% (v/v) ethanol solution ad lib, while the control group (C) had only food and water. The other two groups received either a liquid diet containing 5% (v/v) ethanol (LDE) or a control liquid diet (LDC). All groups were kept on their respective feeding regimens for 14 days. The mean (+/- SEM) ethanol intakes for the FCE and LDE groups were 6.8 +/- 0.5 and 9.9 +/- 0.4 g ethanol/kg body wt./day, respectively. A shock-motivated jumping task was used to test for tolerance. Each rat received an IP injection of 2.5 g ethanol/kg and was tested every 15 minutes for recovery to a criterion of 75% of the performance level achieved with training. All rats were tested twice, once on the day before beginning their feeding regimens (day 0) and again 14 days later. Tolerance was assessed from differences in time of recovery to criterion performance and in blood alcohol concentrations (BACs) at recovery on day 0 vs. day 14. The mean recovery times for the C, FCE, LDC, and LDE groups on day 0 were 177 +/- 6, 170 +/- 6, 143 +/- 10 and 153 +/- 13 minutes, respectively, and the BACs were 219 +/- 6, 222 +/- 5, 220 +/- 19 and 214 +/- 6 mg%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of intravenous ethanol and of 4-methylpyrazole on alcohol drinking in alcohol-preferring rats

Studies were undertaken to determine if elevated blood alcohol concentrations (BAC), produced by intravenous (IV) infusion of ethanol or by intraperitoneal (IP) administration of 4-methylpyrazole (4-MP), could reduce the free-choice oral alcohol consumption of adult male alcohol-preferring rats (P-rats). The IV infusion of ethanol either on a 24 or 12 (dark) hourly dose schedule reduced the amount of ethanol voluntarily ingested. There was a significant (p less than 0.05) inverse correlation between the amount of ethanol consumed orally and the amount of ethanol infused. Daily fluid and caloric intakes were not compromised. When the amount of ethanol infused was 85% or more of the control oral intake, there was a significant correlation between ethanol intake and tail-blood alcohol levels, taken at 5 min (r = 0.98; p less than 0.05) and 55 min (r = 0.93, p less than 0.05) after the last dark cycle infusion. Below the preinfusion level of 85%, the BAC were variable and did not correlate well with total ethanol intake. After a single IP injection of 4-MP, 90 mg/kg body wt, BAC increased from 10 mg% to 50-65 mg% for 2-3 days. Concomitant with the rise in BAC, these animals decreased their drinking of 10% ethanol and proportionately increased their water intake. The present studies suggest that pharmacological factors, distinct from orosensory cues, are important in regulating voluntary ethanol drinking behavior in the P-rats.