Hormonal control of odor preferences and urine-marking in male and female rats

Gonadectomized male and female rats show no preferences for the odors of conspecifics of the opposite sex and no urine-marking. Castrated males given testosterone propionate (TP) injections showed preferences for female odors over no odor as did males given estradiol benzoate (EB). Males given EB plus progesterone (P), P only, or oil (controls) showed no preferences for female odors. No group of ovariectomized females (TP, EB, EB+P, or oil injected) showed a preference for male odors over no odor. Males given TP, EB, or EB+P injections showed an increase in urine-marking while males given P or oil showed no marking. Females given TP injections showed an increase in marking but those given EB, EB+P or oil showed no marking. These results are discussed in relation to studies on the hormonal control of scent-marking in gerbils and sexual behaviour in rats.     

Rewarding properties of social interactions in adolescent and adult male and female rats: impact of social versus isolate housing of subjects and partners

Social interactions have been shown to be rewarding for adolescent and adult rats; however, there has been little emphasis on comparing the strength of the rewarding value of social stimuli across ontogeny. Since age differences in social interactions may vary with sex or housing circumstances, the present study assessed social conditioned place preference (CPP) in adolescent and adult male and female Sprague-Dawley rats housed either socially or in isolation and conditioned with either group-housed or isolate-housed partners. Isolated animals of both sexes and ages demonstrated social CPP, with the strongest preference emerging in adolescent males. Social CPP was not evident in group-housed adults whereas group-housed adolescents developed a preference for the compartment previously paired with similarly housed partners; however, when socially housed adolescents were conditioned with isolated partners, social CPP did not emerge. Age differences in social CPP may reflect age-related neural alterations in brain systems implicated in regulation of social behavior.     

Comparison of Bricanyl® Turbuhaler and Berotec® dry powder inhaler

Terbutaline (Bricanyl) 0.5 mg t.i.d. administered via Turbuhaler was compared with fenoterol (Berotec) 0.2 mg t.i.d. administered via Inhalator Ingelheim in 36 asthmatic children aged 7-12 years. The study was of an open crossover design with two randomly allocated treatment periods, each lasting 2 weeks. Forced expiratory volume in 1 s (FEV1) and forced vital capacity (FVC) were measured at clinic visits before study start and at the end of each treatment period. The patients recorded peak expiratory flow (PEF) before and after inhaler use, morning and evening. They also recorded asthma symptoms and number of extra inhalations. At the end of the study, children and parents were asked for inhaler preference. No differences between the treatments were found concerning the results of the lung function measurements at the clinic or at the PEF measurements at home. No differences were found between the treatments as regards asthma symptoms or number of extra inhalations. Two patients experienced mild side effects during fenoterol treatment, none during terbutaline treatment. Treatment with terbutaline in Turbuhaler was preferred by a majority of children and parents. In conclusion, in this group of asthmatic children, treatment with terbutaline administered via Turbuhaler was as efficacious as treatment with fenoterol administered via Inhalator Ingelheim. There was a clear preference in favour of the Turbuhaler.     

Limb preference after unilateral pyramidotomy in adult and neonatal rats

As previously reported, unilateral pyramidotomy in newborn rats results in the development of an aberrant ipsilateral corticospinal tract that originates from the intact side. In the present study, limb preference after unilateral pyramidotomy in adult and neonatal rats was examined in search of differences that might correlate with this aberrant tract. However, no significant differences were observed between the two groups. Postoperatively, adult animals preferred the limb corresponding to the intact corticospinal tract in spite of a pre- and postoperative testing bias toward the opposite limb. Similarly, the animals that sustained neonatal lesion followed by testing at maturity also preferred the limb corresponding to the normal crossed corticospinal tract.     

Effect of insulin on sex differences in the intake of glucose solutions in rats

Adult male and female Wistar rats maintained on ad lib diet were given a choice between tap water and a solution of glucose in the concentration of either 5 or 12%. Both sexes exhibited a marked preference for glucose solutions. With the 5% solution the volume intake was similar in both sexes and the total calorie intake was normal. With the 12% solution the volume intake was higher in females than in males, while in both sexes the total calorie intake was increased to a similar (maximum acceptable) level. Treatment with Protamine Zinc Insulin (PZI) in a daily dose of 40 U/kg b.w. markedly increased the intake of the 5% solution in both sexes, but significantly more in females than in males, thus revealing sex differences which were not manifest in untreated rats. PZI treatment had little effect on 12% glucose solution intake, presumably because with this solution the total calorie intake was increased to a maximum already in untreated rats.     

Taste preferences in a free-choice situation following electrical stimulation and lesion of septal area in rats

In the present study, electrical stimulation of medical or laternal septal areas and total or restricted lesions of these were conducted to observe the effect on ingestion of primary taste solutions in a free-choice situation. Stimulation induced a specific decrease in the intake of NaCl solution and had no effect on saccharin, acetic acid and quinine solutions and water. Total septal lesion or restricted lesions of medial or lateral septal areas induced hyperdipsia in rats. The lesioned rats, in a free-choice situation preferred NaCl, saccharin, as well as acetic acid solutions. This increase in acetic acid intake after lesion suggests that sour taste is also affected. Furthermore, there was no consumption of quinine solution before and after the lesion. This might be due to the presence of sweet tasting saccharin solution in this free-choice situation. These results indicate that the septal area causes aversion to NaCl intake, probably by inhibiting lateral hypothalamic neurons responsible for NaCl ingestion. The consumption of large quantities of saccharin, NaCl and acetic acid after the septal lesion suggests that the rats become overresponsive to taste factors in a free-choice situation.     

Autoradiographic localization of kappa opiate receptors in CNS taste and feeding areas

Recent evidence suggests that kappa opiate receptors may play a key role in the regulation of appetite. Such evidence implies that kappa receptors might be localized within specific brain areas known to regulate ingestive behaviors. On the basis of this implication we employed an in vitro film autoradiographic technique using 3H-ethylketocyclazozine as ligand to identify putative kappa receptors within CNS "taste" nuclei and surrounding areas. Coronal cryostat sections of rat brain were incubated with ligand in the presence of D-Ala2, D-Leu5-enkephalin (DADLE) and morphine, apposed to LKB Ultrofilm for 60 days, processed and kappa receptor densities evaluated with the aid of a hand held photometer and video image analyzer. Highest kappa receptor densities were found within various gustatory and feeding sites including the rostral pole of the nucleus of the solitary tract, parabrachial nuclei, ventral posterior and medial portions of the thalamus, medial hypothalamus, medial nuclei of the amygdala and bed nucleus of the stria terminalis. Various other midline and medial limbic areas also showed significant kappa densities.     

Anatomical disassociation of amphetamine's rewarding and aversive effects: An intracranial microinjection study

Amphetamine has rewarding properties in some behavioral paradigms, such as self-administration and conditioned place preference (CPP), but an aversive component is also apparent when the drug is tested with the conditioned taste aversion (CTA) paradigm. The persent study was an attempt to determine the neuroanatomical substrates of the drug's rewarding and aversive effects. Previous evidence suggested that amphetamine's stimulation of activity in dopaminergic synapses is critical for both effects. Amphetamine was therefore micro-injected bilaterally (10 g/0.5 l per side) into six different dopaminergic sites, each in a different group of animals: the medial prefrontal cortex, nucleus accumbens, anteromedial caudate nucleus, lateroventral caudate nucleus, amygdala, and the region subjacent to the area postrema (AP region). The effects of these injections in both the taste and place conditioning paradigms were examined in separate experiments. Of the six sites, a significant CPP was observed only with accumbens injections and a significant CTA was observed only with AP region injections. It was concluded that the accumbens plays a primary role in mediating the rewarding effects of amphetamine and that the AP region plays a primary role in mediating the CTA. This constitutes an anatomical disassociation of amphetamine's rewarding and aversive effects. The differential associative bias of place-reward and taste-aversion learning apparent in the results is discussed. Offprint requests to: N.M. White     

Central mediation of the conditioned taste aversion induced in rats by harmaline

The assumption that drugs used as unconditioned stimuli in conditioned taste aversion (CTA) studies act centrally was tested by comparing the effects of systemic and intracerebral injections of harmaline hydrochloride (H) in 340 rats. Intraperitoneal injection of 5–20 mg/kg but not of 2.5 mg/kg H administered 5 min after 15-min saccharin (0.1%) drinking decreased saccharin-water preference in a two-choice retention test, performed 48 h later, from 55% to 20%. Since CTA was not diminished when H (10 mg/kg) was injected into rats anesthetised immediately after saccharin drinking by pentobarbital (40 mg/kg), H (1.7–50 g) was administered intracerebrally to anesthetised rats fixed in the stereotaxic apparatus. Injection of 3–6 g H into the inferior olive elicited CTA comparable to that of systemic injection of 10 mg/kg H. Injections of 6 and 50 g H into cerebellum and bulbar reticular formation elicited weaker CTA while neocortical, hypothalamic and mesencephalic applications were ineffective. CTA could also be elicited when 50 g but not 6 g H was injected into the inferior olive 1 or 2 h after saccharin drinking. This delay-dependent effect and failure of non-contingent H administration to change saccharin preference indicates that the H-induced CTA is not contaminated by a non-specific increase in neophobia. It is concluded that H probably elicits CTA by activation of caudal bulbar structures, including the nucleus of the solitary tract, area postrema and lateral reticular formation.     

Ghrelin and Glucagon-Like Peptide-1: A Gut-Brain Axis Battle for Food Reward

Eating behaviors are influenced by the reinforcing properties of foods that can favor decisions driven by reward incentives over metabolic needs. These food reward-motivated behaviors are modulated by gut-derived peptides such as ghrelin and glucagon-like peptide-1 (GLP-1) that are well-established to promote or reduce energy intake, respectively. In this review we highlight the antagonizing actions of ghrelin and GLP-1 on various behavioral constructs related to food reward/reinforcement, including reactivity to food cues, conditioned meal anticipation, effort-based food-motivated behaviors, and flavor-nutrient preference and aversion learning. We integrate physiological and behavioral neuroscience studies conducted in both rodents and human to illustrate translational findings of interest for the treatment of obesity or metabolic impairments. Collectively, the literature discussed herein highlights a model where ghrelin and GLP-1 regulate food reward-motivated behaviors via both competing and independent neurobiological and behavioral mechanisms.