Acute effects of ethanol on ingestive behavior in rats

Alcohol and oxytocin: Scrutinizing the relationship

The initial enthusiasm towards oxytocin (OXT) as a potential treatment for alcohol use disorder has been recently tempered by recognizing existing gaps in literature and the recent appearance of a relatively small number of clinical studies with negative outcomes. On the other hand, several new studies continue to support the OXT system's potential for such treatment. In this review, we thoroughly analyze existing literature assessing both alcohol's effects on the OXT system and OXT's effects on alcohol-related behaviors. Both rodent and clinical research is discussed. We identify areas that have been studied extensively and those that have been undeservingly understudied. OXT's potential effects on tolerance, withdrawal, craving, anxiety and social behaviors, and how these processes ultimately affect alcohol consumption, are critically explored. We conclude that while OXT can affect alcohol consumption in males and females, more comprehensive studies on OXT's effects on alcohol-related tolerance, withdrawal, craving, anxiety and social affiliations in subjects of both sexes and across several levels of analyses are needed.

The osmoresponsiveness of oxytocin and vasopressin neurones: Mechanisms, allostasis and evolution

In the rat supraoptic nucleus, every oxytocin cell projects to the posterior pituitary, and is involved both in reflex milk ejection during lactation and in regulating uterine contractions during parturition. All are also osmosensitive, regulating natriuresis. All are also regulated by signals that control appetite, including the neural and hormonal signals that arise from the gut after food intake and from the sites of energy storage. All are also involved in sexual behaviour, anxiety-related behaviours and social behaviours. The challenge is to understand how a single population of neurones can coherently regulate such a diverse set of functions and adapt to changing physiological states. Their multiple functions arise from complex intrinsic properties that confer sensitivity to a wide range of internal and environmental signals. Many of these properties have a distant evolutionary origin in multifunctional, multisensory neurones of Urbilateria, the hypothesised common ancestor of vertebrates, insects and worms. Their properties allow different patterns of oxytocin release into the circulation from their axon terminals in the posterior pituitary into other brain areas from axonal projections, as well as independent release from their dendrites.

Implication of coronin 7 in body weight regulation in humans, mice and flies

Background

Obesity is a growing global concern with strong associations with cardiovascular disease, cancer and type-2 diabetes. Although various genome-wide association studies have identified more than 40 genes associated with obesity, these genes cannot fully explain the heritability of obesity, suggesting there may be other contributing factors, including epigenetic effects.

Results

We performed genome wide DNA methylation profiling comparing normal-weight and obese 9–13 year old children to investigate possible epigenetic changes correlated with obesity. Of note, obese children had significantly lower methylation levels at a CpG site located near coronin 7 (CORO7), which encodes a tryptophan-aspartic acid dipeptide (WD)-repeat containing protein most likely involved in Golgi complex morphology and function. Anatomical profiling of coronin 7 (Coro7) mRNA expression in mice revealed that it is highly expressed in appetite and energy balance regulating regions, including the hypothalamus, striatum and locus coeruleus, the main noradrenergic brain site. Interestingly, we found that food deprivation in mice downregulates hypothalamic Coro7 mRNA levels, and injecting ethanol, an appetite stimulant, increased the number of Coro7 expressing cells in the locus coeruleus. Finally, by employing the genetically-tractable Drosophila melanogaster model we were able to demonstrate an evolutionarily conserved metabolic function for the CORO7 homologue pod1. Knocking down the pod1 in the Drosophila adult nervous system increased their resistance to starvation. Furthermore, feeding flies a high-calorie diet significantly increased pod1 expression.

Conclusion

We conclude that coronin 7 is involved in the regulation of energy homeostasis and this role stems, to some degree, from the effect on feeding for calories and reward.

Ethanol, saccharin, and quinine: early ontogeny of taste responsiveness and intake

BACKGROUND

Rat pups demonstrate high levels of immediate acceptance of ethanol during the first 2 weeks of postnatal life. Given that the taste of ethanol is most likely perceived by infant rats as a combination of sweet and bitter, high intake of ethanol early in ontogeny may be associated with age-related enhanced responsiveness to the sweet component of ethanol taste, as well as with ontogenetic decreases in sensitivity to its bitter component. Therefore, the present study compared responsiveness to ethanol and solutions with bitter (quinine) and sweet (saccharin) taste in terms of intake and palatability across the first 2 weeks of postnatal life.

METHODS

Characteristic patterns of responsiveness to 10% (v/v) ethanol, 0.1% saccharin, 0.2% quinine, and water in terms of taste reactivity and fluid intake were assessed in rat pups tested on postnatal day (P) 4, 9, or 12 using a new technique of on-line monitoring of fluid flow through a two-channel intraoral cannula. Taste reactivity included analysis of ingestive and aversive responses following six intraoral infusions of the test fluids. This taste reactivity probe was followed by the intake test, in which animals were allowed to voluntarily ingest fluids from an intraoral cannula.

RESULTS

Pups of all ages showed more appetitive responses to saccharin and ethanol than to water or quinine. No age-related differences were apparent in taste responsiveness to saccharin and ethanol. However, the age-related pattern of ethanol intake drastically differed from that of saccharin. Intake of saccharin increased from P4 to P9 and decreased substantially by P12, whereas intake of ethanol gradually increased from P4 to P12. Intake of ethanol was significantly lower than intake of saccharin on P9, whereas P12 pups took in more ethanol than saccharin.

CONCLUSION

The findings of the present study indicate ontogenetic dissociations between taste reactivity to ethanol and saccharin and intake of these solutions, and suggest that high acceptance of ethanol early in ontogeny may not be associated with its orosensory properties but rather with the pharmacological effects of ethanol.

Effects of intracerebroventricular ethanol on ingestive behavior and induction of c-Fos immunoreactivity in selected brain regions

The early changes in the central nervous system (CNS) following drinking of ethanol (ETOH) are poorly understood. It is known that chronic intracerebroventricular (ICV) administration of ethanol to rats induces preference for imbibed alcohol solutions. These results suggest that ICV ethanol could alter taste preference. In the present study, we tested whether ETOH[ICV] could induce a conditioned taste preference (CTP) or aversion (CTA) and alter c-Fos immunoreactivity (c-Fos-IR) in brain regions associated with feeding, aversion, and/or reward. Acute ETOH[ICV], as tested in the ETOH-naïve rat, did not induce CTA nor affect the amount of water imbibed by treated rats. The effects of ETOH[ICV] on intake and preference were determined using a novel palatable (i.e. sweet) noncaloric 0.1% saccharin solution. A single dose of ETOH[ICV] in the ETOH-nai;ve animal induced a CTP for saccharin. ETOH[ICV] significantly increased c-Fos-IR in a number of brain sites associated with feeding and reward including the bed nucleus of the stria terminalis, lateral dorsal area (BSTLD); nucleus accumbens, shell area (AcbSh); hypothalamic paraventricular nucleus (PVN); and lateral septum, ventral area (LSV). Thus, ETOH induced a CTP, not CTA, via central mechanisms; it increased c-Fos-IR in specific sites associated with feeding and reward.

Acute effects of ethanol on feeding behavior and leptin-induced STAT3 phosphorylation in rat hypothalamus

OBJECTIVE

Drinking ethanol stimulates the appetite, producing a positive energy balance. The mechanism by which ethanol regulates the appetite in the central nervous system, however, has not been fully understood. The aim of this study is to investigate the interaction of ethanol with the satiety effect of leptin, a hormone which suppresses the appetite in the hypothalamic region.

DESIGN

: Leptin (7.5 micro g) or the same dose of phosphate buffer saline (PBS) was administered into the third ventricle (i.c.v.), 30 min after an intraperitoneal injection (i.p.) of ethanol (0.5 g/kg body weight) or the same dose of PBS.

MATERIALS

Adult male Sprague-Dawley rats weighing 290-320 g were used.

MEASUREMENTS

Food intake was measured 2, 12 and 24 h after leptin i.c.v. infusion. The tyrosine phosphorylation of signal transducer and activator transcription factor 3 (STAT3) in the hypothalamus was analyzed by Western blotting.

RESULTS

The cumulative food intakes in the saline/leptin group (saline i.p.+leptin i.c.v.) were markedly reduced to about 45% of the saline/PBS group (saline i.p.+PBS i.c.v.) at 2, 12 and 24 h time points (P<0.05, 0.001, and 0.005, respectively). As compared with the saline/leptin group, those of the ethanol/leptin group (ethanol i.p.+leptin i.c.v.) were significantly increased to the level seen in the saline/PBS group at 12 and 24 h time points (P<0.05, and P<0.005 vs the saline/leptin group, respectively). Ethanol administration resulted in about a 50% reduction of the leptin-induced STAT3 tyrosine phosphorylation seen in the hypothalamic protein as compared to that of the saline/leptin group.

CONCLUSION

These findings suggest that ethanol-induced enhancement of the appetite may, in part, result from leptin resistance transiently caused by ethanol to attenuate the leptin signal transduction.

Alcohol ingestion decreases both diurnal and nocturnal secretion of leptin in healthy individuals

OBJECTIVE

Neuropeptide Y (NPY) stimulates appetite and increases food intake. Leptin inhibits NPY. It is not known whether alcohol influences any of these factors, but it has been suggested that alcohol stimulates appetite in man. The primary objective of this investigation was to determine whether ingestion of ethanol inhibits leptin secretion in normal subjects.

SUBJECTS AND DESIGN

Fourteen healthy, non-obese subjects of both sexes (7 F/7 M) were included. They were divided into two groups (I and II; 8/6). All were investigated on two occasions. On one occasion alcohol was ingested, and on the other drinking water was given. The experiments took place in random order, one week apart. In group I two experiments (A = alcohol; B = water) were performed during the day. In group II the experiments were carried out during the night (C = alcohol; D = water). Each alcoholic drink contained 0.45 g ethanol/kg. The drinks were given at 08.00, 09.30 and 11.00 hours in experiments A and B, and at 18.00, 20.00 and 22.00 hours in experiments C and D. Venous blood samples were collected before, during and after the drinks over periods of 6 h in group I and 14 h in group II.

MEASUREMENTS

Serum concentrations of leptin, insulin-like growth factor 1 (IGF-1), IGF binding protein 1 (IGFBP-1), insulin, cortisol, testosterone, ethanol and plasma glucose were determined. RESULTS Group I serum leptin levels declined during the day in both men and women regardless of whether alcohol or water had been administered in the morning. Since leptin levels in general were markedly higher in women than in men, all leptin changes after water/alcohol were transformed to percentage changes to make them comparable between sexes. When the percentage leptin decline over a 6-h period (08.00-24.00 hours) was expressed by a decremental area under curve (AUC08-14), it became evident that alcohol inhibited leptin secretion, inasmuch as the leptin decremental area, obtained after alcohol, was significantly larger than the one obtained after water (124 +/- 17 vs. 57 +/- 8; P < 0.01). Similar insulin and glucose levels were obtained after alcohol and water. Group II serum leptin levels increased after both alcohol and water during the initial part of the night (18.00-20.00 hours). In this period alcohol inhibited the secretion of leptin as shown by the leptin incremental area (AUC18-24) which was 53 +/- 18 after alcohol and 113 +/- 15 after water (P < 0.01). As the ethanol concentration in serum began to fall, its inhibitory effect on leptin gradually disappeared, and when leptin AUCs representing the entire night were determined after alcohol and water, they were not significantly different. Similar insulin, glucose, testosterone, IGF-1 and cortisol levels were found after alcohol and water. The IGFBP-1 level increased, but not significantly so until 6 h after commencing the alcohol ingestion.

CONCLUSION

Ingestion of moderate amounts of alcohol has an inhibitory effect on leptin secretion in normal subjects. The effect may be direct rather than indirect, since several factors known to affect leptin are not influenced by alcohol. It is tempting to speculate that alcohol might serve as an appetizer by decreasing leptin secretion, but additional studies are necessary to prove that hypothesis since previous studies have shown that leptin has a long-term rather than an acute effect on hunger.

The neuroendocrinology of thirst and salt appetite: visceral sensory signals and mechanisms of central integration

This review examines recent advances in the study of the behavioral responses to deficits of body water and body sodium that in humans are accompanied by the sensations of thirst and salt appetite. Thirst and salt appetite are satisfied by ingesting water and salty substances. These behavioral responses to losses of body fluids, together with reflex endocrine and neural responses, are critical for reestablishing homeostasis. Like their endocrine and neural counterparts, these behaviors are under the control of both excitatory and inhibitory influences arising from changes in osmolality, endocrine factors such as angiotensin and aldosterone, and neural signals from low and high pressure baroreceptors. The excitatory and inhibitory influences reaching the brain require the integrative capacity of a neural network which includes the structures of the lamina terminalis, the amygdala, the perifornical area, and the paraventricular nucleus in the forebrain, and the lateral parabrachial nucleus (LPBN), the nucleus tractus solitarius (NTS), and the area postrema in the hindbrain. These regions are discussed in terms of their roles in receiving afferent sensory input and in processing information related to hydromineral balance. Osmoreceptors controlling thirst are located in systemic viscera and in central structures that lack the blood-brain barrier. Angiotensin and aldosterone act on and through structures of the lamina terminalis and the amygdala to stimulate thirst and sodium appetite under conditions of hypovolemia. The NTS and LPBN receive neural signals from baroreceptors and are responsible for inhibiting the ingestion of fluids under conditions of increased volume and pressure and for stimulating thirst under conditions of hypovolemia and hypotension. The interplay of multiple facilitory influences within the brain may take the form of interactions between descending angiotensinergic systems originating in the forebrain and ascending adrenergic systems emanating from the hindbrain. Oxytocin and serotonin are additional candidate neurochemicals with postulated inhibitory central actions and with essential roles in the overall integration of sensory input within the neural network devoted to maintaining hydromineral balance.

Central inhibition of salt appetite by oxytocin in rats

Considerable evidence indicates an important role of hormones in the stimulation of fluid consumption. For example, angiotensin II (Ang II), together with afferent neural input from cardiovascular baroreceptors, is well known to stimulate thirst and NaCl intake in rats. Conversely, numerous studies have demonstrated that central oxytocin (OT) provides a stimulus for inhibition of salt appetite. The latter conclusion is supported by the following observations in rats: (a) intracerebroventricular (i.c.v.) injection of OT inhibits salt appetite stimulated by subcutaneous colloid; (b) treatments that inhibit NaCl intake, such as acute hyperosmolality, stimulate pituitary secretion of OT (which is correlated with central release of OT in these studies), whereas treatments that decrease OT secretion, such as systemic injection of deoxycorticosterone and dietary sodium deprivation, potentiate Ang-II-induced NaCl intake; (c) systemic ethanol administration inhibits OT secretion and enhances Ang-II-induced salt appetite; (d) naloxone, which augments stimulated OT secretion, inhibits NaCl appetite induced by colloid treatment, an effect that is abolished by i.c.v. pretreatment with an OT receptor antagonist; and (e) destruction of central neurons bearing OT receptors increases Ang II-induced salt appetite. By mediating the inhibition of NaCl intake in rats, central OT complements the known peripheral effects of OT to facilitate renal sodium excretion.