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Effects of a range of dopamine receptor agonists and antagonists on ethanol intake in the rat.

The aim of this study was to assess the effects of a range of dopaminergic agents on consumption of an ethanol solution (10% ethanol, 3% glucose) in rats. A two-bottle, free-choice paradigm was used following induction of ethanol consumption and preference in standard laboratory rats. The model used provides a robust and reliable level of ethanol oral administration in normal laboratory rats. Both ethanol intake and preference were reduced by a dopamine D1 receptor partial agonist, SFK 38393 ((+/-)-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol hydrochloride), in a dose-dependent manner. The dopamine D2/D3 receptor agonist 7-OH-DPAT ((+/-)-7-hydroxy-N,N-(di-n-propyl-2-aminotetralin)) at the lowest dose of 0.01 mg/kg increased both ethanol intake and preference. At higher doses (0.03-0.1 mg/kg) no significant effects were found. The dopamine D1 receptor antagonist SCH 23390 (R-(+)-7-chloro-2,3,4,5-tetrahydro-3-methyl-1-phenyl-1H-3-benzazepine-8- ol), dopamine D2/D3 receptor antagonist raclopride and 5-HT2/D2 receptor antagonist risperidone did not affect ethanol consumption, although all at high doses induced a significant decrease in water intake, indicating a non-specific decrease in consummatory behavior with these compounds. These results suggest the involvement of the dopaminergic system in ethanol intake and ethanol reinforcement with dopamine D1 and D2/D3 receptors playing opposing roles. Blockade of dopamine D2 receptors had no selective effect on ethanol consumption and ethanol preference.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗

Chronic mild stress has no effect on responding by rats for sucrose under a progressive ratio schedule.

Exposure of rats to chronic unpredictable mild stress (CMS) has been shown to produce a syndrome in which a wide range of consummatory behaviors are attenuated, resembling a state of anhedonia, which may be reversed by treatment with antidepressant drugs. The aim of the present study was to determine whether CMS would also affect a rat's motivation to respond for a sucrose solution, as assessed by its performance under a progressive ratio (PR) schedule of reinforcement. Control studies demonstrated that break points in nonstressed rats were sensitive to both the concentration of sucrose solution used, as well as the period of food and water deprivation used prior to testing. Exposure of rats to CMS had no effect upon break points when responding under a progressive ratio schedule for either a 1% or 7% sucrose solution, although subjects did display the typical reduction in consumption of a freely consumed 1% sucrose solution. These results are not readily understood within the theoretical framework of the CMS model of anhedonia and imply instead that both the neural and psychological correlates of motivation may be less susceptible to modulation by the effects of CMS than the free consumption of sweet solutions.

Animals↗

Competition in size-structured populations: mechanisms inducing cohort formation and population cycles.

In this paper we investigate the consequences of size-dependent competition among the individuals of a consumer population by analyzing the dynamic properties of a physiologically structured population model. Only 2 size-classes of individuals are distinguished: juveniles and adults. Juveniles and adults both feed on one and the same resource and hence interact by means of exploitative competition. Juvenile individuals allocate all assimilated energy into development and mature on reaching a fixed developmental threshold. The combination of this fixed threshold and the resource-dependent developmental rate, implies that the juvenile delay between birth and the onset of reproduction may vary in time. Adult individuals allocate all assimilated energy to reproduction. Mortality of both juveniles and adults is assumed to be inversely proportional to the amount of energy assimilated. In this setting we study how the dynamics of the population are influenced by the relative foraging capabilities of juveniles and adults. In line with results that we previously obtained in size-structured consumer-resource models with pulsed reproduction, population cycles primarily occur when either juveniles or adults have a distinct competitive advantage. When adults have a larger per capita feeding rate and are hence competitively superior to juveniles, population oscillations occur that are primarily induced by the fact that the duration of the juvenile period changes with changing food conditions. These cycles do not occur when the juvenile delay is a fixed parameter. When juveniles are competitively superior, two different types of population fluctuations can occur: (1) rapid, low-amplitude fluctuations having a period of half the juvenile delay and (2) slow, large-amplitude fluctuations characterized by a period, which is roughly equal to the juvenile delay. The analysis of simplified versions of the structured model indicates that these two types of oscillations also occur if mortality and/or development is independent of food density, i.e. in a situation with a constant juvenile developmental delay and a constant, food-independent background mortality. Thus, the oscillations that occur when juveniles are more competitive are induced by the juvenile delay per se. When juveniles exert a larger foraging pressure on the shared resource, maturation implies an increase not only in adult density, but also in food density and consequently fecundity. Our analysis suggests that this correlation in time between adult density and fecundity is crucial for the occurrence of population cycles when juveniles are competitively superior.

Animals↗

Autonomic and vasomotor regulation.

The cerebellum not only modulates the systemic circulation, but also profoundly influences cerebral blood flow (rCBF) and metabolism (rCGU), and initiates long-term protection of the brain from ischemia. Electrical stimulation of the rostral ventral pole of the fastigial nucleus (FN), elevates arterial pressure (AP), releases vasoactive hormones, elicits consummatory behavioral and other autonomic events and site specifically elevates rCBF independently of changes in rCGU. Cerebral vasodilation results from the antidromic excitation of axons of brain stem neurons which innervate cerebellum and, through their collaterals, neurons in the rostral ventrolateral reticular nucleus (RVL). RVL neurons initiate cerebral vasodilation over polysynaptic vasodilator pathways which engage a population of vasodilator neurons in the cerebral cortex. In contrast, intrinsic neurons of FN, when excited, elicit widespread reductions in rCGU and, secondarily, rCBF, along with sympathetic inhibition. Electrical stimulation of FN can reduce the volume of a focal cerebral infarction produced by occlusion of the middle cerebral artery by 50%. This central neurogenic neuroprotection is long lasting (weeks) and is not due to changes in rCBF or rCGU. Rather, it appears to reflect alterations in neuronal excitability and/or downregulation of inflammatory responses in cerebral vessels. The FN, therefore, appears to be involved in widespread autonomic, metabolic, and behavioral control, independent of motor control. The findings imply that the FN receives inputs from neurons, probably widely represented in the central autonomic core, which may provide continuing information processing of autonomic and behavioral states. The cerebellum may also widely modulate the state of cortical reactivity to ischemia, hypoxia, and possibly other neurodegenerative events.

Animals↗

Multiple ejaculations and chronic fluoxetine: effects on male rat copulatory behavior.

Male rats were treated with fluoxetine (FLX) or vehicle daily for 14 days and copulatory behavior tested on day 15. Rats were either mated to three ejaculations or to sexual exhaustion. Both standard measures and the mount bout analysis were used to evaluate the effects of the chronic FLX on male rat copulatory behavior. Only 56.25% of the animals treated with FLX achieved three ejaculations. FLX inhibited the consumatory aspect of male sexual behavior, especially the ability to achieve three ejaculations, but there was no effect on the propensity of the male to pursue the female. These differences were observed for the first three ejaculations. Analysis of the last three ejaculations in those animals that mated to exhaustion did not reveal an effect of FLX. The behavioral pattern of FLX-treated animals during the first three ejaculations resembled that observed during the last three ejaculatory series in the vehicle-treated animals that mated to exhaustion. The results are discussed in terms of the serotonergic effects on male rat sexual behavior.

Animals↗

A sucrose-based maintenance diet increases sensitivity to appetite suppressant effects of naloxone.

Rats maintained under restricted access to food (but at 100% free-feeding weights) received one of two diets in their home cages: a palatable sucrose-based diet, or regular chow (grain based diet), and could respond for either sucrose- or grain-based reinforcers under an FR 40 reinforcement schedule (crossover design). Naloxone (0, 0.1, 0.3, 1.0, and 3.0 mg/kg) was more potent in reducing operant-chamber responding in rats maintained on a sucrose-based diet in their home cages than those fed a grain-based diet, regardless of the type of pellets available in the operant chambers. Whereas naloxone decreased response rate over the session, it had no effect on initiation of responding. Results support the hypothesis that opioids are involved in the maintenance, but not the initiation of consummatory behavior. Furthermore, increased potency of naloxone following chronic ingestion of palatable food is similar to that observed following chronic opiate administration, suggesting a relationship between palatability and opioids.

Animals↗

Measuring hedonic impact in animals and infants: microstructure of affective taste reactivity patterns.

The hedonic impact of taste is reflected in affective facial reactions made by human infants, other primates, and even rats. Originally studied in human infants, affective reactions to taste have also been used by affective neuroscience to identify hedonic brain systems in studies of animals (via application of neural stimulation, pharmacological activation, and neural lesion manipulations). The chief limitation of measuring affective reactions is that it is difficult for experimenters to know how to interpret them, and therefore how to interpret changes produced by brain manipulations. This paper notes guidelines to interpretation. It examines the phylogenetic continuity between humans, other primates, and rats in terms of the microstructure of taste-elicited affective reactions. It reviews evidence that affective taste reactivity patterns truly reflect a 'core hedonic process' of palatability or affect, rather than being an ingestion measure, consummatory behavior measure, or a sensory reflex measure. It reviews affective neuroscience studies of taste reactivity that have identified true hedonic brain substrates, and discriminated them from false hedonic brain substrates. It considers the neural bases of incentive 'wanting' versus 'liking'. Finally, it notes the difference between human subjective affective ratings of pleasure and 'core hedonic processes' reflected by behavioral affective reactions.

Affect↗

Hypocretin receptor protein and mRNA expression in the dorsolateral pons of rats.

The hypocretins (also known as orexins) are hypothalamic peptides that have been implicated in feeding and sleep regulation. Previous reports have described the distribution of the mRNAs encoding two hypocretin receptors (HCRT-R), but the pattern of protein expression has not been investigated. Here we examine the distribution of the mRNA and protein for the HCRT receptor 1 (HCRT-R1) and HCRT receptor 2 (HCRT-R2) in the pontine brainstem and demonstrate that they are present in many pontine nuclei including those associated with REM sleep. Immunohistochemistry indicates that one or both of the receptor subtypes are expressed in the dorsal raphe, the lateral dorsal tegmental (LDT), the pedunculo pontine (PPT), the locus coeruleus (LC), the locus subcoeruleus, pontis oralis, Barrington's, the trigeminal complex (mesencephalic trigeminal and motor nucleus of the trigeminal nerve), the dorsal tegmental nucleus of Gudden (DTG), the ventral cochlear nucleus (VCA), trapezoid nucleus (TZ), pontine raphe nucleus and the pontine reticular formation. These regions have been shown to be involved in mastication, bladder control, gastrointestinal function and in arousal. Given these projection sites and the functions associated with these sites, we suggest that HCRT may play a role in maintaining alertness and vigilance while the animal is engaged in consummatory behavior.

Animals↗

Hippocampal network patterns of activity in the mouse.

Genetic engineering of the mouse brain allows investigators to address novel hypotheses in vivo. Because of the paucity of information on the network patterns of the mouse hippocampus, we investigated the electrical patterns in the behaving animal using multisite silicon probes and wire tetrodes. Theta (6-9 Hz) and gamma (40-100 Hz) oscillations were present during exploration and rapid eye movement sleep. Gamma power and theta power were comodulated and gamma power varied as a function of the theta cycle. Pyramidal cells and putative interneurons were phase-locked to theta oscillations. During immobility, consummatory behaviors and slow-wave sleep, sharp waves were present in cornu ammonis region CA1 of the hippocampus stratum radiatum associated with 140-200-Hz "ripples" in the pyramidal cell layer and population burst of CA1 neurons. In the hilus, large-amplitude "dentate spikes" occurred in association with increased discharge of hilar neurons. The amplitude of field patterns was larger in the mouse than in the rat, likely reflecting the higher neuron density in a smaller brain. We suggest that the main hippocampal network patterns are mediated by similar pathways and mechanisms in mouse and rat.

Animals↗

Effects of prenatal ethanol exposure and postnatal handling on conditioned taste aversion.

Studies have shown that animals prenatally exposed to ethanol (E) exhibit deficits in conditioned taste aversion as well as displaying hypothalamic-pituitary-adrenal (HPA) hyperresponsiveness during exposure to stressors. In contrast, postnatal handling has been shown to attenuate both emotional and HPA reactivity under certain conditions. The present study tested the hypothesis that handling could attenuate adverse effects of prenatal ethanol exposure on consummatory behavior and HPA activity in a conditioned taste aversion task. We found that both prenatal ethanol exposure and handling independently increased saccharin consumption over 5 days of pretoxicosis exposure, suggesting that neophobia decreased at a faster rate in these animals. When conditioned aversion was assessed in handled animals under nondeprived conditions, E animals showed increased consumption compared to controls. Furthermore, across prenatal groups, lower corticosterone (CORT) levels were found in handled compared to nonhandled animals during reexposure under food-deprived conditions, emphasizing the importance of assessing both behavior and HPA function when examining an animal's response to a task and indicating that handling may not be effective at attenuating some deficits in E animals.

Animals↗

Relation of drinking and eating to masculinity and femininity.

The relationship between desirable and undesirable aspects of masculinity and femininity and drinking and eating was investigated. A sample of 144 university women in Australia completed questionnaires that assessed masculinity and femininity, reported drinking, alcohol dependence, eating restraint, frequency of dieting, and overeating. Evidence of a common underlying dimension linking aspects of problem drinking and overeating to undesirable masculine characteristics was found. The results are consistent with the view that women engage in excessive consummatory behaviors such as binging to deal with their gender-role conflict.

Adult↗

Alcohol withdrawal increases neuropeptide Y immunoreactivity in rat brain.

BACKGROUND: Neuropeptide Y (NPY) is widely expressed in the brain and is known to affect consummatory behaviors including drinking alcohol as well as to play a role in seizures. We investigated the effects of a 4 day binge ethanol treatment model that is known to induce physical dependence and withdrawal seizures to determine the effects of ethanol dependence and withdrawal on NPY expression. METHODS: Male Sprague Dawley rats were treated with ethanol or control nutritionally complete diets by intragastric treatment three times per day for 2 or 4 days with an average daily dose of approximately 8 g/kg ethanol per day. Ethanol-fed rats treated for 4 days and then withdrawn for 24, 72, and 168 hr also were studied. Brains were perfused and sectioned for immunohistochemistry for NPY, phospho-cyclic adenosine monophosphate responsive element binding (pCREB), and other proteins. RESULTS: NPY immunoreactivity (NPY-IR) was found in several brain regions, with the hippocampus and cerebral cortex showing the most pronounced changes. NPY-IR was reduced by ethanol treatment in hippocampus and cortex, although at 72 hr of withdrawal there was a dramatic increase in NPY-IR in the hilus of the dentate gyrus and in CA3 and CA2 fields of hippocampus. Ethanol withdrawal seizures occurred around 12 to 24 hr of withdrawal, preceding the changes in NPY-IR at 72 hr. pCREB immunoreactivity (pCREB-IR) tended to decrease during ethanol treatment but showed a dramatic increase in dentate gyrus at 72 hr of withdrawal. Parvalbumin immunoreactivity indicated that some of the pCREB-IR and NPY-IR were within inhibitory interneuron basket cells of the hippocampal hilus. NPY-IR returned to control levels by 168 hr of withdrawal. CONCLUSIONS: These studies suggest that hippocampal NPY is reduced during the development of ethanol dependence. Ethanol withdrawal seizures precede a dramatic increase in hippocampal NPY-IR. Previous studies have suggested that NPY in the hippocampus reduces seizure activity and that NPY is induced by seizure activity. Thus, the increase in NPY-IR at 72 hr of withdrawal after binge ethanol treatment may be protective against prolonged withdrawal seizure activity.

Animals↗

Ethanol consumption following acute treatment with methysergide, fluoxetine, fenfluramine, and their combination.

Methysergide (MS), a postsynaptic serotonin antagonist, was administered acutely in three experiments in relation to water or 5% ethanol solution intake of 24-hr, water-deprived male Sprague-Dawley rats. In the first experiment, MS significantly increased the consumption of ethanol at doses of 0.25, 2.0, and 4.0 mg/kg. Water intake was significantly increased by MS at the 2.0 mg/kg dose. In the second experiment, which was different from the first one in that MS was administered during the dark cycle, ethanol solution intake was again significantly increased at all three levels. In the third experiment, fenfluramine (FFL) and fluoxetine (FLU) were administered acutely (at 8 mg/kg) after MS (0.25 mg/kg) followed by measuring water or ethanol solution intake. FFL and FLU significantly decreased intake of both water and ethanol solution, a process that was significantly reversed by MS; to a greater degree for FLU (74%) than for FFL (57%). The successful use of MS in increasing ethanol intake in these studies may be due to the low doses used in comparison with earlier unsuccessful attempts. The procedure of treating 24-hr, water-deprived rats with acute doses of pre- and postsynaptic serotonin agonists and antagonists appears to be a useful model for further elucidation of their interaction in ethanol consummatory behavior.

Alcohol Drinking↗

Alcohol schema acquisition in preschoolers: differences between children of alcoholics and children of nonalcoholics.

Cognitive schemas provide the structure within which children organize their knowledge and beliefs about the use of alcohol. The development of schemas about alcohol should be affected both by age and parental patterns of alcohol use. We examined differences in alcohol schema development among 139 male children of alcoholics (COAs) and 82 controls [children of nonalcoholics (NCOAs)] utilizing the Appropriate Beverage Task as an indicator of these processes. Overall, the vast majority of the sample identified at least one alcoholic beverage from photographs, even at age 3. COAs were more likely to identify at least one alcoholic beverage. With age controlled, COAs were better able to identify specific alcoholic beverages and correctly identified a larger number of alcoholic beverages. There was a trend for these children of alcoholic men to attribute more alcoholic beverage use to male adults than NCOAs. Moreover, differences in these children's attributions of alcoholic consummatory behavior were predicted by their parents' current consumption levels. Results provide evidence that alcohol schemas are detectable in early childhood and are more common in children from alcoholic homes. Discussion focuses on the potential relevance of these risk attributes to the development of more fully formed alcohol expectancies and to the later emergence of alcohol-related difficulty.

Alcohol Drinking↗