The orexin-1 receptor antagonist SB-334867 decreases anxiety-like behavior and c-Fos expression in the hypothalamus of rats exposed to cat odor.

Increasing evidence suggests that the orexin system is involved in modulating anxiety, and we have recently shown that cat odor-induced anxiety in rats is attenuated by the orexin receptor antagonist SB-334867. In the current experiment, c-Fos expression was used to map changes in neuronal activation following SB-334867 administration in the cat odor anxiety model. Male Wistar rats were exposed to cat odor with or without SB-334867 pre-treatment (10 mg/kg, i.p.). A naïve control group not exposed to cat odor was also used. Following cat odor exposure, brains were processed for c-Fos expression. Vehicle-treated rats showed an increase in anxiety-like behaviors (increased hiding and decreased approach toward the cat odor), and increased c-Fos expression in the posteroventral medial amygdala (MePV), paraventricular hypothalamus (PVN) and dorsal premammillary nucleus (PMd). In rats pretreated with SB-334867, approach scores increased and c-Fos expression decreased in the PVN and PMd. These results provide both behavioral and neuroanatomical evidence for the attenuation of cat odor-induced anxiety in rats via the orexin system.

High ambient temperature increases 3,4-methylenedioxymethamphetamine (MDMA, "ecstasy")-induced Fos expression in a region-specific manner.

3,4-Methylenedioxymethamphetamine (MDMA, "Ecstasy") is a popular drug that is often taken under hot conditions at dance clubs. High ambient temperature increases MDMA-induced hyperthermia and recent studies suggest that high temperatures may also enhance the rewarding and prosocial effects of MDMA in rats. The present study investigated whether ambient temperature influences MDMA-induced expression of Fos, a marker of neural activation. Male Wistar rats received either MDMA (10 mg/kg i.p.) or saline, and were placed in test chambers for 2 h at either 19 or 30 degrees C. MDMA caused significant hyperthermia at 30 degrees C and a modest hypothermia at 19 degrees C. The 30 degrees C ambient temperature had little effect on Fos expression in vehicle-treated rats. However MDMA-induced Fos expression was augmented in 15 of 30 brain regions at the high temperature. These regions included (1) sites associated with thermoregulation such as the median preoptic nucleus, dorsomedial hypothalamus and raphe pallidus, (2) the supraoptic nucleus, a region important for osmoregulation and a key mediator of oxytocin and vasopressin release, (3) the medial and central nuclei of the amygdala, important in the regulation of social and emotional behaviors, and (4) the shell of the nucleus accumbens and (anterior) ventral tegmental area, regions associated with the reinforcing effects of MDMA. MDMA-induced Fos expression was unaffected by ambient temperature at many other sites, and was diminished at high temperature at one site (the islands of Calleja), suggesting that the effect of temperature on MDMA-induced Fos expression was not a general pharmacokinetic effect. Overall, these results indicate that high temperatures accentuate key neural effects of MDMA and this may help explain the widespread use of the drug under hot conditions at dance parties as well as the more hazardous nature of MDMA taken under such conditions.

Regional expression of c-fos in rat brain following stimulation of the ventral tegmental area.

This study has investigated the effect of stimulating the region of origin of the mesolimbic dopaminergic system, the ventral tegmental area (VTA), with the substance P analogue DiMe-C7 on the regional expression of c-fos in the rat forebrain. We have previously shown this treatment produced a prolonged increase in blood pressure and heart rate which was mediated by both dopaminergic mechanisms and vasopressin release. Stimulation of the VTA resulted in increased levels of c-Fos immunostaining in several target regions of the mesolimbic dopaminergic system (such as the frontal cortex, olfactory tubercle, islands of Calleja and amygdala), with the notable exception of the nucleus accumbens. A marked increase in c-fos expression was also found in the supraoptic nucleus but not the paraventricular nucleus in the hypothalamus. These results support a role for a number of target areas of the mesolimbic dopaminergic system and vasopressin release in the increase in blood pressure and heart rate produced by stimulation of the VTA.

Short-term effects of high dose oral medroxyprogesterone acetate on bone density in premenopausal women.

Despite the widespread use of the C21 progestin medroxyprogesterone acetate (MPA) in hormone replacement therapy and gynecological practice, its effects on bone density are uncertain, with contradictory reports in the literature. We have examined the short term changes in bone density at the lumbar spine (a predominantly trabecular site) and the femoral neck (a predominantly cortical site) in 13 premanopausal women prescribed high dose MPA (50 mg/day) for gynecological disorders and in 12 control subjects. Compared to basal values, lumbar spine bone mineral density (measured by dual energy x-ray absorptiometry) fell progressively by a mean 2.4% at 6 months and 4.1% at 12 months (both P < 0.01); in five subjects who continued the drug, it had fallen by a mean 5.9% at 20 months (P < 0.002). The spinal bone loss in the MPA users was significantly greater than that in controls (P < 0.005 at 6 months; P < 0.01 at 12 months) and occurred despite a significant gain in body weight in the women using MPA (median, 3.5 kg at 6 months; P < 0.01). In four subjects in whom bone density was measured 6 months after cessation of MPA, spinal bone density showed significant recovery (mean increment, 2.8%; P < 0.025). Femoral neck bone density measurements did not differ between the groups. MPA induced amenorrhea in all subjects who continued with it beyond 6 months, and the amenorrheic subjects were estrogen deficient (median plasma estradiol, 70 pmol/L). We conclude that, when given in doses sufficient to induce hypogonadism, MPA use is associated with significant early loss of trabecular bone, which is probably the consequence of estrogen deficiency.

An in vivo model for the rapid assessment of the local effects of parathyroid hormone on bone histomorphometry.

The process of bone remodelling is likely to be controlled to a large extent by factors acting locally in a paracrine or autocrine manner, along with some systemic control. In our laboratory we routinely use an in vivo model in which the local effects of factors on bone histomorphometry can be determined. The factor under investigation is injected just above the periosteum of the right hemicalvaria in the adult male mouse. These subcutaneous injections are given daily over a 1-week period and the animals sacrificed at intervals after the last injection. With appropriate staining techniques it is possible to determine the effects of a particular agent on osteoblast and osteoclast numbers; the area of total bone, mineralized bone, osteoid and periosteum; osteoblast, osteoclast and eroded surfaces, and thus to infer the rate of bone formation and bone resorption in the right hemicalvaria compared to the uninjected left hemicalvaria and to vehicle-injected control animals. All these parameters are measured using a bone-dedicated image analyzer. Utilizing this in vivo model, we and others have studied a number of bone-active factors. We report the effects of parathyroid hormone, as well as reviewing results of our studies of leukemia inhibitory factor, amylin, calcitonin and calcitonin gene-related peptide in the model. The results obtained are similar to those found in most other animal models and in man. In conclusion, we describe an in vivo model whereby bone-active factors, injected locally, can be rapidly assessed.