Somatostatin administration alters taste preferences in the rat

A role for the neuropeptide somatostatin in the neurobiology of behaviors associated with substances abuse and affective disorders

In recent years, neuropeptides which display potent regulatory control of stress-related behaviors have been extensively demonstrated to play a critical role in regulating behaviors associated with substance abuse and affective disorders. Somatostatin (SST) is one neuropeptide known to significantly contribute to emotionality and stress behaviors. However, the role of SST in regulating behavior has received relatively little attention relative to other stress-involved peptides, such as neuropeptide Y or corticotrophin releasing factor. This review characterizes our current understanding of the role of SST and SST-expressing cells in general in modulating several behaviors intrinsically linked to substance abuse and affective disorders, specifically: anxiety and fear; stress and depression; feeding and drinking; and circadian rhythms. We further summarize evidence of a direct role for the SST system, and specifically somatostatin receptors 2 and 4, in substance abuse disorders. This article is part of the special issue on 'Neuropeptides'.

Roles of hormones in taste signaling

Proper nutrition, avoidance of ingesting substances that are harmful to the whole organism, and maintenance of energy homeostasis are crucial for living organisms. Additionally, mammals possess a sophisticated system to control the types and content of food that we swallow. Gustation is a vital sensory skill for determining which food stuffs to ingest and which to avoid, and for maintaining metabolic homeostasis. It is becoming apparent that there is a strong link between metabolic control and flavor perception. Although the gustatory system critically influences food preference, food intake, and metabolic homeostasis, the mechanisms for modulating taste sensitivity by metabolic hormones are just now being explored. It is likely that hormones produced in the tongue influence the amounts and types of food that we eat: the hormones that we associate with appetite control, glucose homeostasis and satiety, such as glucagon-like peptide-1, cholecystokinin, and neuropeptide Y are also produced locally in taste buds. In this report, we will provide an overview of the peptidergic endocrine hormone factors that are present or are known to have effects within the gustatory system, and we will discuss their roles, where known, in taste signaling.

Predator stress induces behavioral inhibition and amygdala somatostatin receptor 2 gene expression

Psychological stressors precipitate and maintain stress-induced psychopathology, and it is likely that altered amygdala function underlies some of the deleterious effects of psychological stress. To understand the mechanisms underlying the linkage between the response to psychological stressors and maladaptive or psychopathological responses, we have focused on amygdala responsivity in animal models employing species-specific psychological stressors. In the present study, we characterized the effects of a 15-min exposure to a natural predator, the ferret, on rat behavior and the expression of the somatostatin family of genes in the amygdala. We examined the somatostatin family of genes because substantial evidence shows that central somatostatin systems are altered in various neuropsychiatric illnesses. We report that rats respond to acute ferret exposure with a significant increase in fearful and anxious behaviors that is accompanied by robust amygdala activation and an increase in somatostatin receptor 2 (sst2) messenger RNA expression within the amygdala and anterior cingulate cortex. These studies are the first to show stress-induced changes in amygdala sst2 expression and may represent one mechanism by which psychological stress is linked to adaptive and maladaptive behavioral responses.

Embryo/fetal toxicity assessment of lasofoxifene, a selective estrogen receptor modulator (SERM), in rats and rabbits

BACKGROUND

The purpose of this study was to evaluate the effects of lasofoxifene, a selective estrogen receptor modulator (SERM), on rat and rabbit fetal development.

METHODS

Lasofoxifene was administered orally to rats (1, 10, 100 mg/kg) between gestation days (GD) 6-17, and in rabbits (0.1, 1, 3 mg/kg) between GD 6-18. Maternal body weight and food consumption were monitored throughout pregnancy. Fetuses were delivered by Cesarean section on GD 21 in rats, and GD 28 in rabbits, to evaluate fetal viability, weight, and morphology. Drug concentrations in maternal plasma were measured in a separate cohort of animals at several time points commencing on GD 17 (rats) and 18 (rabbits). On GD 18 (rat) and GD 19 (rabbit) drug concentrations were measured in maternal plasma and in fetal tissue 2 hr post dosing to determine the fetal to maternal drug ratio.

RESULTS

In rats, there were dose-related declines in maternal weight gain and food consumption. Post implantation loss was significantly increased at dosages of 10 and 100 mg/kg, and the number of viable fetuses was decreased at 100 mg/kg. The placental weights increased, whereas fetal weights decreased in a dose-dependent manner. Lasofoxifene-related teratologic findings were noted at 10 and 100 mg/kg and included imperforate anus with hypoplastic tails, dilatation of the ureters and renal pelvis, misaligned sternebrae, hypoflexion of hindpaw, wavy ribs, and absent ossification of sternebrae. In rabbits, neither maternal weight gain nor food consumption were affected during treatment. Between GD 26-28, there was a dose-dependent increased incidence of red discharge beneath the cages. At 1 and 3 mg/kg, resorptions and post-implantation loss increased. There were no significant external or visceral effects, but 3 mg/kg there was an increased incidence of supernumerary ribs. Although the maternal plasma Cmax and AUC(0-24) were dose-dependent, the exposures in the rat were many orders of magnitude greater than in the rabbit even for the same 1 mg/kg dose. The single time point fetal/maternal drug ratio was higher in the rat (1.3-0.78) than in the rabbit (0.21-0.16).

CONCLUSION

In general, both maternal and fetal effects of lasofoxifene were similar to those reported with other SERMs. Although the incidence or severity of these effects was, in some instances, greater in the rat than in the rabbit, the doses and the resultant maternal and fetal exposures were many orders of magnitude higher in the rat, suggesting the rabbit to be more sensitive to the toxicological effects of lasofoxifene.

Peptides that regulate food intake: somatostatin alters intake of amino acid-imbalanced diets and taste buds of tongue in rats

The present studies were designed to evaluate a potential dose-dependent effect of somatostatin (SRIF) administered peripherally on intake of either a low-protein basal diet or threonine-imbalanced diet (THR-IMB), on body weight gain (DeltaBW), gut motility, and on the histology of taste buds in rats. SRIF administration had a dual effect related to its concentration, increasing the intake of THR-IMB diet at low concentration and decreasing THR-IMB diet at high concentration. During the light phase, SRIF treatment increased the intake of THR-IMB diet, suggesting that the usual anorectic effect induced by intake of THR-IMB diet was attenuated. High-dosage SRIF decreases gastrointestinal motility, which, in turn, can decrease food intake and DeltaBW. The combination of THR-IMB diet regimen and SRIF treatment also induced significant modifications on the taste buds of the tongue. The feeding response to an amino acid-imbalanced diet includes a learned aversion to the diet, and animals may use taste in establishing that aversion. Modifications of taste buds of SRIF-treated rats eating THR-IMB diet might explain the increase of imbalanced diet intake if treated rats perceive this food as less aversive.

Effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides from 1994 through 1998

Effects of peptides on the central nervous system are presented in two ways so as to provide a cross-listing. In the first table, the peptides are listed alphabetically. In the second table, the central nervous system effects are arranged alphabetically. No longer can there be any doubt that peptides affect the central nervous system, sometimes in several ways.