Comparative Pharmacokinetics and Local Tolerance of Tenofovir Alafenamide (TAF) From Subcutaneous Implant in Rabbits, Dogs, and Macaques.

The administration of antiretrovirals (ARVs) for HIV pre-exposure prophylaxis (PrEP) is highly efficacious and may benefit from new long-acting (LA) drug delivery approaches. This paper describes a subcutaneous, reservoir-style implant for the LA delivery of tenofovir alafenamide (TAF) and documents the preclinical assessment of implant safety and pharmacokinetics (PK) in New Zealand White (NZW) rabbits (3 groups of n = 5), beagle dogs (2 groups of n = 6), and rhesus macaques (2 groups of n = 3). Placebo implants were placed in rabbits (n = 10) and dogs (n = 12). Implant parameters, including selection of the TAF form, choice of excipient, and PCL formulation were tuned to achieve targeted concentrations of the active anabolite of TAF, tenofovir diphosphate (TFV-DP), within peripheral blood mononuclear cells (PBMCs) and mucosal tissues relevant to HIV transmission. Sustained concentrations of TFV-DP in PBMCs over 100 fmol/106 cells were achieved in all animal species indicating that the implants effectively delivered TAF for 3-6 months. Unlike placebo implants without TAF, all active implants resulted in local adverse events (AEs) proximal to the implant ranging in severity from mild to moderate and included dermal inflammation and necrosis across all species. Despite these AEs, the implant performed as designed and achieved a constant drug release profile, supporting the continued development of this drug delivery platform.

Intragastric self-infusion of ethanol by ethanol-preferring and -nonpreferring lines of rats.

An ethanol-preferring line of rats, developed by selective breeding, consumed as much as 9.4 +/- 1.7 grams of ethanol per kilogram of body weight per day through intragastric self-infusions, yielding blood ethanol concentrations of 92 to 415 milligrams per 100 milliliters. By contrast, the ethanol- nonpreferring line self-administered only 0.7 +/- 0.2 gram per kilogram per day. These findings indicate that the reinforcing effect of ethanol is postabsorptive and is not mediated by the drug's smell or taste. Hence the ethanol-preferring line of rats may be suitable animal model of alcoholism.

The potential for CYP2D6 inhibition screening using a novel scintillation proximity assay-based approach.

High throughput inhibition screens for human cytochrome P450s (CYPs) are being used in preclinical drug metabolism to support drug discovery programs. The versatility of scintillation proximity assay (SPA) technology has enabled the development of a homogeneous high throughput assay for cytochrome P450 2D6 (CYP2D6) inhibition screen using [O-methyl-(14)C]dextromethorphan as substrate. The basis of the assay was the trapping of the O-demethylation product, [(14)C]HCHO, on SPA beads. Enzyme kinetics parameters V(max) and apparent K(m), determined using pooled human liver microsomes and microsomes from baculovirus cells coexpressing human CYP2D6 and NADPH-cytochrome P450 reductase, were 245 pmol [(14)C]HCHO/min/mg protein and 11 microM, and 27 pmol [(14)C]HCHO/min/pmol and 1.6 microM, respectively. In incubations containing either pooled microsomes or recombinant CYP2D6, [(14)C]dextromethorphan O-demethylase activity was inhibited in the presence of quinidine (IC(50) = 1.0 microM and 20 nM, respectively). By comparison, inhibitors selective for other CYP isoforms were relatively weak (IC(50) > 25 microM). In agreement, a selective CYP2D6 inhibitory monoclonal antibody caused greater than 90% inhibition of [(14)C]dextromethorphan O-demethylase activity in human liver microsomes, whereas CYP2C9/19- and CYP3A4/5-selective antibodies elicited a minimal inhibitory effect. SPA-based [(14)C]dextromethorphan O-demethylase activity was also shown to correlate (r(2) = 0.6) with dextromethorphan O-demethylase measured by high-performance liquid chromatography in a bank of human liver microsomes (N = 15 different organ donors). In a series of known CYP2D6 inhibitors/substrates, the SPA-based assay resolved potent inhibitors (IC(50) < 2 microM) from weak inhibitors (IC(50) >or= 20 microM). It is concluded that the SPA-based assay described herein is suitable for CYP2D6 inhibition screening using either native human liver microsomes or cDNA-expressed CYP2D6.

Characterization of the ethanol-like discriminative stimulus effects of 5-HT receptor agonists as a function of ethanol training dose.

A drug discrimination procedure was used to characterize the ethanol-like effects of a variety of 5-HT1 agonists. Previous studies found that the degree of substitution of the 5-HT1B/2C agonist TFMPP (m-trifluoromethylphenylpiperazine) depended on the training dose of ethanol. The present studies extend this initial finding to four additional 5-HT agonists with different selectivity for 5-HT1A, 5-HT1B, or 5-HT2C receptors: CGS 12066B (7-trifluoromethyl-4(4-methyl-1-piperazinyl)-pyrrolo[1,2a]quinoxaline maleate), mCPP [1-(3-chlorophenyl)piperazine diHCl], RU 24969 [5-methoxy-3(1,2,3,4-tetrahydro-4-pyridinyl]-1H-indole succinate and 8-OH DPAT [(+/-)-8-hydroxy-2-(di-n-propylamino)tetralin HBr]. Separate groups of rats were trained to discriminate 1.0 g/kg (n = 7), 1.5 g/kg (n = 6) or 2.0 g/kg (n = 8) ethanol from water. Following training, three to five doses of each 5-HT agonist were tested twice in each rat. The most selective 5-HT1B agonist tested, CGS 12066B (3-17 mg/kg; IP), completely substituted for the 1.0 g/kg ethanol, but not for 1.5 or 2.0 g/kg ethanol. Likewise, the 5-HT1B/2C agonist mCPP (0.56-1.7 mg/kg; IP) completely substituted only in the 1.0 g/kg ethanol training group. The 5-HT1A/1B agonist RU 24969 (0.1-3.0 mg/kg; IP) substituted for all training doses of ethanol, although in a lower proportion of the rats tested in the 2.0 g/kg ethanol training group. Finally, the 5-HT1A agonist 8-OH DPAT (0.1-1.0 mg/kg, IP) did not substitute completely for any ethanol training dose. The results consistently show that agonists with 5-HT1B activity produce discriminative stimulus effects similar to low and intermediate, but not high, ethanol training doses.

TC-2559: a novel orally active ligand selective at neuronal acetylcholine receptors.

TC-2559 [(E)-N-Methyl-4-[3-(5-ethoxypyridin)yl]-3-buten-1-amine] is a novel nicotinic agonist markedly more selective than recently reported novel nicotinic receptor ligands (selectivity ratio for central nervous system (CNS) to peripheral nervous system (PNS)>4000). TC-2559 competes effectively with [3H]-nicotine binding (K(i)=5 nM) but not with [125I]-bungarotoxin (>50,000 nM). Dopamine release from striatal synaptosomes and ion flux from thalamic synaptosomes indicate that TC-2559 is potent and efficacious in the activation of CNS receptors and significantly reduced glutamate-induced neurotoxicity in vitro. TC-2559 has no detectable effects on muscle and ganglion-type nicotinic acetylcholine receptors at concentrations up to 1 mM. TC-2559 significantly attenuates scopolamine-induced cognitive deficits in a step-through passive avoidance task. Acute and repeated oral dosing of TC-2559 enhances performance in a radial arm maze task. In contrast to the effects of equimolar concentrations of (-) nicotine, TC-2559 does not induce hypothermia and locomotor activity is not enhanced following repeated daily administration of 14 days. TC-2559 has a markedly enhanced CNS-PNS selectivity ratio and an intra-CNS selectivity as evidenced by the improved cognition without increased locomotor activity. The in vitro and in vivo studies in the present study suggest that TC-2559 has the desired profile to be further evaluated as a potential therapeutic agent for neurodegenerative diseases.

Assessment of the mixed discriminative stimulus effects of ethanol in a three-choice ethanol-dizocilpine-water discrimination in rats.

Previous drug discrimination studies have elucidated the importance of the NMDA, GABA(A) and 5-HT(1) receptor systems in mediating the discriminative stimulus effects of ethanol. The present study used a three-choice drug discrimination paradigm in an attempt to determine whether the salient NMDA antagonistic effects were separable from other stimulus effects of ethanol. Adult Long-Evans rats (n = 7) were trained to discriminate ethanol (1.5g/kg, intragastric (i.g.)), the uncompetitive NMDA antagonist dizocilpine (0.17mg/kg, i.g.) or water (3.5ml, i.g.) under a food-reinforced fixed-ratio 15 (FR15) schedule of reinforcement. Following training, substitution tests were conducted with the GABA(A)/benzodiazepine (GABA(A)/BDZ) positive modulator pentobarbital (PB, 5.6-17mg/kg, i.g.), the uncompetitive NMDA antagonist phenycldine (PCP, 0.1-5.6mg/kg, i.p.) and the 5-HT(1) agonist RU 24969 (0.1-3.0mg/kg, i.p.). Complete substitution of PCP (ED(50), 0.9mg/kg) for dizocilpine was found in all animals. Conversely, PB (ED(50), 10mg/kg) substituted fully for ethanol in five of seven animals, whereas RU 24969 (ED(50), 1.4mg/kg) completely substituted for ethanol in only three of seven animals tested. The result demonstrate that a three-choice discrimination using dizocilpine, ethanol and water as training conditions can be established in rats. By contrasting the discriminative stimulus effects of an uncompetitive NMDA antagonist to ethanol, the ethanol-like effects of pentobarbital and RU 24969 are attenuated compared to previous studies of two-choice ethanol water discrimination.

Urinary metabolites of the antiprotozoal agent cis-3a,4,5,6,7,7a- hexahydro-3-(1-methyl-5-nitro-1H-imidazol-2-yl)-1,2-benzisoxazole in the rat.

1H-NMR and MS were employed to identify 13 rat urinary metabolites of 14C-labeled cis-3a,4,5,6,7,7a- hexahydro-3-(1-methyl-5-nitro-1H-imidazol-2-yl)-1,2-benzisoxazole (MK-0436). The major free (unconjugated) metabolite was cis-3a,4,5,6,7, 7a-hexahydro-3-carboxamido-1,2-benzisoxazole; it was also the second most abundant metabolite released during hydrolysis of the conjugated fraction. All other identified metabolites were hydroxylated analogues substituted at C(4)-C(7a) of the cyclohexane ring. the 4-equatorial,5-axial,7a-triol was the second most abundant metabolite excreted in an unconjugated form. Four monohydroxy (5-axial, 6-axial, 6-equatorial, 7-equatorial) metabolites of the drug were identified; they were found in the conjugated fraction only and were released by hydrolysis. The 5-axial hydroxy compound is the major conjugated metabolite and is overall the most abundant of all the metabolites. Six dihydroxy metabolites were identified: one was found exclusively in the free state, three as conjugates only (including the 7-axial,7a-diol, which is the major dihydroxy species), and two both free and conjugated. A second triol was found both free and conjugated.

Effects of acute ethanol administration on monoamine and metabolite content in forebrain regions of ethanol-tolerant and -nontolerant alcohol-preferring (P) rats.

The contents of dopamine (DA), serotonin (5-HT) and their metabolites in the frontal cortex, anterior striatum, nucleus accumbens and hypothalamus of alcohol-tolerant and -nontolerant rats of the alcohol-preferring P line were determined one hour after the IP administration of 2.5 g ethanol/kg body wt. Compared with saline-injected controls, nontolerant P-rats injected with ethanol had (a) 60% higher levels of 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the frontal cortex; (b) 30-60% higher levels of DOPAC and HVA in the anterior striatum and nucleus accumbens; and (c) 20% higher levels of 5-HIAA in all three forebrain regions. In the tolerant group, the effects of IP ethanol on DOPAC and HVA were markedly attenuated or completely eliminated in these three forebrain regions. However, in the case of 5-HIAA, an attenuated response was observed only in the nucleus accumbens of the tolerant group. The IP administration of ethanol had little effect on the contents of DA or 5-HT in any of these three forebrain regions, with the exception that 5-HT levels were elevated in the anterior striatum of both the tolerant and nontolerant groups. In the hypothalamus, there were no significant differences for the contents of DA, 5-HT or their metabolites between the nontolerant or tolerant P rats after IP ethanol. The data indicate that both acute ethanol administration and chronic alcohol intake by the P line of rats alters certain DA and 5-HT systems that may be involved in the brain reward circuitry and in DA pathways involved in motor functions.

Metabolic mapping of the effects of chronic voluntary ethanol consumption in rats.

The 2-[14C]deoxyglucose method was used to examine the effects of chronic, voluntary ethanol consumption on rates of local cerebral glucose utilization (LCGU). LCGU was measured in male Long-Evans rats immediately following the completion of a 60-min schedule-induced polydipsia drinking session. Three groups of animals were examined: animals with a history of ethanol consumption that received ethanol on the test day (ethanol-ethanol), animals with a similar ethanol history that were presented with water on the test day (ethanol-water), and a control group that received water throughout the experiment (water-water). Ethanol consumption on the test day resulted in a highly discrete pattern of metabolic changes, with significant decreases in glucose utilization in the hippocampal complex, habenula, anterior ventral thalamus, and mammillary bodies, whereas increases were observed in the nucleus accumbens and locus coeruleus. Rates of LCGU in the ethanol-water group were increased throughout all regions of the central nervous system examined, indicating that the long-term consumption of moderate ethanol doses that do not produce physical dependence can cause significant changes in functional brain activity.

Persistence of tolerance to a single dose of ethanol in the selectively-bred alcohol-preferring P rat.

The persistence of tolerance to a single dose of ethanol was examined in the selectively-bred alcohol-preferring P line of rats. Tolerance was measured by a test that required trained rats to jump onto a descending platform to avoid footshock. On day 0, each trained rat received a single IP injection of 2.5 g ethanol/kg body weight and was tested every 15 minutes for recovery to a criterion of 75% of pre-alcohol training performance. The second ethanol injection of 2.5 g/kg and testing were carried out seven days later for one group (n = 12), and 14 days later for another group (n = 12). Tolerance was assessed by the differences in time required to recover to criterion performance and blood alcohol concentrations (BACs) at time of recovery on day 0 vs. day 7 and day 14. The mean recovery times and BACs on day 0 were 156 +/- 5 minutes and 222 +/- 6 mg%, respectively. The group injected on day 7 exhibited shorter recovery times of 113 +/- 4 minutes and higher BACs at recovery of 261 +/- 4 mg%, while the group injected on day 14 did not show any significant differences from the values obtained on day 0. In a second experiment, the persistence of tolerance in P rats was compared with that of rats from the alcohol-nonpreferring NP line and of stock Wistar rats (n = 6/group). All rats were trained and tested for recovery to criterion after 2.5 g ethanol/kg on day 0 as described for the first experiment. The rats were then injected with ethanol and tested for tolerance on three subsequent occasions.(ABSTRACT TRUNCATED AT 250 WORDS)

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)

High-throughput simultaneous determination of the HIV protease inhibitors indinavir and L-756423 in human plasma using semi-automated 96-well solid phase extraction and LC-MS/MS.

A method for the simultaneous determination of the HIV protease inhibitors indinavir and L-756423, in human plasma has been developed. Plasma samples (0.5 ml) were extracted using a 3M Empore 96-well plate in the mixed phase cation exchange (MPC) format. The extraction method was automated through the application of both the Packard 204DT and TOMTEC Quadra 96 work stations, and the resulting extracts were analyzed using a PE-Sciex API-3000 LC-MS/MS with a heated nebulizer interface (500 degrees C). The assay was linear in the concentration range 1-2500 ng/ml for indinavir and 5 2500 ng/ml for L-756423 when 0.5-ml aliquots of plasma were extracted. Recoveries of indinavir and L-756423 were greater than 76 and 80%, respectively, over the calibration curve range when using the described sample preparation method. Within-batch precision and accuracy for the quantitation of indinavir over the range 1-2500 ng/ml were 5.4% R.S.D. or less and within 4.0%, respectively. Within-batch precision and accuracy for the quantitation of L-756423 over the range 5-2500 ng/ml were 5.3% R.S.D. or less and within 3.4%, respectively. Interbatch variability for the analysis of indinavir QC samples at low (3 ng/ml), middle (250 ng/ml) and high (2250 ng/ml) were 3.2, 2.9, and 1.9%, respectively. Interbatch variability for the analysis of L-756423 QC samples at low (15 ng/ml), middle (250 ng/ml) and high (2250 ng/ml) concentration were 2.0, 2.5, and 3.3%, respectively. The validated assay was used in support of human clinical trials.

Operant responding for oral ethanol in the alcohol-preferring P and alcohol-nonpreferring NP lines of rats.

Rats of the P (n = 4) and NP (n = 5) lines were housed in operant chambers with food available ad lib, but all liquid was obtained by responding on either of two levers according to a FR5 schedule. Presses on one lever produced water from an automated dipper, while the other lever gave access to a dipper containing ethanol in concentrations ranging from 2 to 30% (v/v). P rats worked to obtain the ethanol at all concentrations offered and preferred the ethanol over water. The highest ethanol intake averaged 7.7 +/- 0.5 g/kg body weight/day at the 15% concentration and at least 5.8 +/- 0.9 g/kg/day for the 20-30% range. The NP rats responded more for the 2 and 5% concentrations of ethanol than for water, but responded predominantly for water when the ethanol concentrations were 10% and higher. In a second experiment, NP rats drank water rather than 10% ethanol by free-choice, even though the ethanol was mixed with a preferred flavor and the water with a nonpreferred flavor. The findings indicate that ethanol is rewarding to P rats in concentrations up to 30% (v/v) but is not rewarding to NP rats when the concentration is 10% and above.

Persistence of tolerance in the P line of alcohol-preferring rats does not require performance while intoxicated.

Persistence of tolerance was measured seven days after a single ethanol injection (2.5 g/kg b. wt.) in the alcohol-preferring P line of rats with and without testing in a shock-motivated jump task during the initial ethanol exposure. P rats were trained to jump 50 cm to avoid shock and were assigned to one of three groups. On day 0, group E/J (n = 8) was injected with ethanol and tested on the jump task until recovery to criterion (37.5 cm), while group S/J (n = 21) was injected with saline and was tested yoked to an E/J rat. Rats in the E/NJ group (n = 19) received ethanol but were not tested on day 0. Seven days later, all rats received 2.5 g ethanol/kg and were tested to criterion. Recovery times on day 7 were significantly longer (p less than 0.05) for rats in the S/J group (169 +/- 7 min) than for the E/J (141 +/- 11 min) and E/NJ (145 +/- 6 min) rats. Blood ethanol concentrations at recovery for the E/NJ group were higher than the S/J group on day 7 and higher than the E/J group on day 0 (p less than 0.05). The results indicate that the persistence of tolerance manifested by the P rats is an inherited behavioral trait that requires only ethanol exposure.

Effects of fluoxetine and desipramine on palatability-induced ethanol consumption in the alcohol-nonpreferring (NP) line of rats.

Three groups of NP rats (n = 5/group) received food, water and one of 3 Polycose solutions ad lib. One group received a solution containing 3% (w/v) Polycose, 0.125% (w/v) saccharin, 0.5% (w/v) NaCl (3% POL solution) to which ethanol was gradually added over three weeks until the concentration of 10% (v/v) ethanol (E) was reached (3% POL + E group). Alcohol ingestion by the 3% POL + E group reached an average of 9 g of ethanol/kg b. wt./day; the rats attained average blood alcohol concentrations of 61 +/- 8 mg%. One control group (3% POL) was given the same solution as above but without ethanol. The second control group (17% POL) had access to a 17.6% Polycose solution supplemented with 0.125% saccharin and 0.5% NaCl and was isocaloric to the 3% POL + E solution. Although the three groups differed significantly in the amounts of food and Polycose solutions consumed, their total caloric intakes were equivalent. The IP administration of the serotonin (5-HT) uptake inhibitor fluoxetine (5 and 10 mg/kg) significantly reduced drinking of the group receiving the 3% POL + E solution by 23% and 67%, respectively, but did not alter intakes of the Polycose solutions by the 3% or 17% POL control groups. The IP administration of the norepinephrine (NE) uptake inhibitor desipramine (5 and 10 mg/kg) significantly reduced intake of the Polycose solution by the 17% POL group by 52 and 83%, respectively, but only the 10 mg/kg dose attenuated drinking of the solutions by the 3% POL and 3% POL + E groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of alcohol-preferring (P) and nonpreferring (NP) rats on tests of anxiety and for the anxiolytic effects of ethanol.

Rats of the selectively bred alcohol-preferring P and alcohol-nonpreferring NP lines were evaluated using three different behavioral measures of anxiety. Compared with NP rats, P rats (1) showed greater footshock-induced suppression of operant responding in an approach-avoidance conflict test; (2) spent less time in the open arms of an elevated plus maze; and (3) took longer in a passive avoidance test to step down from a platform to a grid floor where footshock was received 24 hours earlier. These findings indicate a greater degree of anxiety in the P than in the NP line of rats in these situations. Pretreatment with intraperitoneal (IP) ethanol (0.5-1.0 g/kg) injections produced anticonflict or anxiolytic effects in P but not in NP rats. However, the anticonflict effects of ethanol were small relative to those produced by chlordiazepoxide (CDP, 7.5 mg/kg) in both lines. The results demonstrate that selective breeding for divergent oral ethanol preference has produced associated differences between the P and NP lines of rats in behavioral tests of anxiety and in the anxiolytic effects of ethanol.

Ethanol self-infusion into the ventral tegmental area by alcohol-preferring rats.

The ventral tegmental area (VTA) and its projections have been implicated in the reinforcing effects of drugs of abuse. Selectively bred alcohol-preferring (P) and alcohol-nonpreferring (NP) lines of rats were used to evaluate the reinforcing actions of ethanol in the VTA using intracranial self-administration (ICSA) operant procedures. P rats self-administered nanoliter quantities of 50-200 mg% ethanol in artificial CSF directly into the VTA whereas NP rats had low levels of responding at these ethanol concentrations. Responses on the active lever were 50-fold higher for the P compared with the NP rats for the self-infusion of 150 mg% ethanol. NP rats responded at the same level on the active and inactive levers at all ethanol concentrations and had low responses/session (3 to 15 total responses) at all concentrations. Further, operant responding on the active lever was reduced when artificial CSF alone was substituted for 100 mg% ethanol, and responding on the active lever was reinstated when ethanol was returned. For one group of rats, an illuminated house light served as a discriminative stimulus, which signalled the availability of ICSA, while a cue light was paired with the onset of ethanol infusion. Extinction in the presence of these stimuli required 6-7 sessions. However, only 2-3 extinction sessions were necessary for another group trained without stimulus cues, suggesting that cues paired with the ICSA of ethanol can acquire conditioned reinforcing properties. The findings indicate that ethanol can act as a reinforcer when administered directly into the VTA.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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)