Spiroxatrine augments fluoxetine-induced reduction of ethanol intake by the P line of rats

Rat animal models for screening medications to treat alcohol use disorders

The purpose of this review is to present animal research models that can be used to screen and/or repurpose medications for the treatment of alcohol abuse and dependence. The focus will be on rats and in particular selectively bred rats. Brief introductions discuss various aspects of the clinical picture, which provide characteristics of individuals with alcohol use disorders (AUDs) to model in animals. Following this, multiple selectively bred rat lines will be described and evaluated in the context of animal models used to screen medications to treat AUDs. Next, common behavioral tests for drug efficacy will be discussed particularly as they relate to stages in the addiction cycle. Tables highlighting studies that have tested the effects of compounds using the respective techniques are included. Wherever possible the Tables are organized chronologically in ascending order to describe changes in the focus of research on AUDs over time. In general, high ethanol-consuming selectively bred rats have been used to test a wide range of compounds. Older studies usually followed neurobiological findings in the selected lines that supported an association with a propensity for high ethanol intake. Most of these tests evaluated the compound's effects on the maintenance of ethanol drinking. Very few compounds have been tested during ethanol-seeking and/or relapse and fewer still have assessed their effects during the acquisition of AUDs. Overall, while a substantial number of neurotransmitter and neuromodulatory system targets have been assessed; the roles of sex- and age-of-animal, as well as the acquisition of AUDs, ethanol-seeking and relapse continue to be factors and behaviors needing further study. This article is part of the Special Issue entitled "Alcoholism".

Effects of the 5-HT1A receptor agonist ipsapirone on operant self-administration of ethanol in the rat

Although the serotonin (5-HT)1A receptor agonist ipsapirone reduces ethanol intake in a variety of animal models of alcoholism, such effects have only been reported in models based on nonoperant behavior (e.g., two-bottle choice procedures). It was the aim of the present study to characterize the effects of ipsapirone in an operant model of alcohol self-administration. Rats were trained during daily 30-min sessions to respond for oral delivery of an ethanol solution (10% w/v) or water in a two-lever, fixed-ratio:1, saccharin-fading procedure. After establishment of stable responding, ipsapirone (0, 2.5-20 mg/kg, intraperitoneal) was tested in combination with different ethanol unit doses (0, 1.25-20%). Ethanol-reinforced responding was related to the ethanol unit dose in an inverted U-shaped manner. Ipsapirone dose-dependently decreased the number of ethanol- and water-reinforced lever responses, irrespective of the ethanol unit dose, and failed to affect ethanol preference. As there was only a minor difference between the minimal effective dose which reduced operant responding for ethanol and water (i.e., 10 and 20 mg/kg, respectively), and there was no evidence for a drug-induced left- or rightward shift of the ethanol unit dose-response curve, the effects of ipsapirone are considered to be nonselective. It is suggested that the ethanol intake-reducing effects of ipsapirone are not the result of a drug-induced interference (either of an attenuating, or potentiating, nature) with the positive reinforcing stimulus properties of alcohol.

Serotonin and alcohol intake, abuse, and dependence: findings of animal studies

Despite a relatively large body of literature on the role of the neurotransmitter serotonin (5-hydroxytryptamine, or 5-HT) in the regulation of alcohol intake, the functional significance of serotonergic neurotransmission and its relationship to alcohol intake, abuse, and dependence remains to be fully elucidated. In part two of this review, the experimental (animal) data is summarized along two lines: the effects of serotonergic manipulations on the intake of alcohol, and the effects of acute and chronic alcohol intake, as well as the withdrawal of chronic alcohol, on the serotonergic system. It is concluded that serotonin mediates ethanol intake as a part of its larger role in behavior modulation, such that increases in serotonergic functioning decrease ethanol intake, and decreased serotonergic functioning increases ethanol intake. Ethanol produces transient increases in serotonergic functioning that activate the mesolimbic dopaminergic reward system. The results are discussed in light of recent theories describing the regulatory role of serotonin in general behavior.

Brain levels of amines and amino acids in taste aversion-prone and -resistant rats

Possible biological contributions to taste aversion (TA) conditionability were explored by comparing whole-brain levels of five neurotransmitter amines and 14 common amino acids within TA-prone (TAP) and TA-resistant (TAR) rats. The selectively bred strains had been developed via 22 generations of bidirectional nonsibling matings based on susceptibility to cyclophosphamide-induced conditioned TAs. The target substances were separated by HPLC and were measured by electrochemical or fluorometric procedures. The TAP brains had higher levels of serotonin (5-HT) and lower levels of norepinephrine (NE) than TAR brains. No strain differences were found with respect to dihydroxyphenylalanine (DOPAC), dopamine (DA), or 5-hydroxyindoleacetic acid (5-HIAA). Among amino acids, TAP rats had lower levels of lysine than TARs: no other differences were detected. Therefore, higher levels of 5-HT and lower levels of NE and lysine were associated with enhanced TA conditionability. The 5-HT and NE results extend prior indications of their central neurotransmitter TA involvements. The functional role of lysine in TA or other brain functions remains obscure.

Ipsapirone and 8-OH-DPAT reduce ethanol preference in rats: involvement of presynaptic 5-HT1A receptors

The selective serotonin(5-HT)1A receptor agonists 8-OH-DPAT and ipsapirone were tested in selectively inbred Wistar rats, with high preference [70-90%: defined as the ratio of ethanol (EtOH) to total fluid intake] for EtOH (10% v/v) over water in a two-bottle free choice situation. Rats were injected shortly before the overnight test session (8:00 P.M.-8:00 A.M.). EtOH and water consumption were determined in 20-min intervals; food consumption after the session. 8-OH-DPAT (ED50: 2.4 mg/kg, SC) and ipsapirone (ED50: 12.5 mg/kg, SC) reduced EtOH preference in a dose-dependent manner. In addition, 8-OH-DPAT increased total fluid intake, whereas ipsapirone enhanced total food intake. The EtOH preference reduction was time-dependent and reached a maximum within the second 4 h after application of 8-OH-DPAT (-73%) and ipsapirone (-72%). The preference reducing effect of ipsapirone (20 mg/kg, PO) was completely blocked by the nonselective 5-HT1A antagonist spiperone (0.05 mg/kg, SC). Local application of 8-OH-DPAT (10 micrograms, 0.5 microliters) into the dorsal raphe nucleus (DRN, a brain area rich in somatodendritic 5-HT1A autoreceptors), reduced the EtOH preference significantly as compared to the saline injection in the same animal (-12%, 8:00-12:00 P.M.). Only marginal effects on ingestion behavior were observed after microinjection into the nucleus accumbens. Reduction of brain 5-HT levels by pretreatment with the 5-HT synthesis inhibitor pCPA (2 x 150 mg/kg, IP) resulted in a short lasting, marked reduction (-54%) and a long lasting, small attenuation of the EtOH preference. Total food consumption was strongly decreased but returned soon to normal; total fluid intake was only slightly decreased. The EtOH preference reducing effect of ipsapirone (5 and 20 mg/kg, SC) was attenuated in pCPA-pretreated rats. The present data suggest that 5-HT1A receptor ligands reduce EtOH preference via stimulation of 5-HT1A receptors in the DRN. The possibility of additional mechanism(s) is discussed.

Serotonin, dopamine and GABA involvement in alcohol drinking of selectively bred rats

Neurochemical and neuropharmacological studies were undertaken to assess the involvement of CNS serotonin (5-HT), dopamine (DA) and GABA systems in regulating the alcohol-drinking behavior of two lines of rats selectively bred for their high alcohol-seeking behavior, namely the alcohol-preferring P line and the high alcohol-drinking HAD line of rats. Neurochemical data indicate that high alcohol-seeking behavior (when compared with data from rats with low alcohol-seeking characteristics) is associated with: a) lower (10-20%; p less than 0.05) contents of 5-HT in certain limbic regions (e.g., nucleus accumbens, frontal cortex, hypothalamus and hippocampus); b) a lower (10-15%; p less than 0.05) content of DA in the nucleus accumbens; c) higher (20-35%; p less than 0.05) densities of 5-HT1A binding sites in some limbic regions (e.g., medial nucleus accumbens, medial prefrontal cortex and ventral hippocampus); and d) a greater (20-50%) density of GABA axon terminals in the nucleus accumbens. Furthermore, the acute administration of high doses of ethanol appears to increase the activity of the 5-HT and DA projections to the nucleus accumbens of the P line of rats (as indicated by the 20-30% elevated tissue levels of 5-HT and DA metabolites following IP ethanol administration); neuronal tolerance to alcohol appears to develop in both these monoamine pathways, as suggested by an attenuated effect on metabolite levels by a challenge dose of ethanol given to P rats that had been chronically drinking alcohol.(ABSTRACT TRUNCATED AT 250 WORDS)