Biomedical subjects

Y P Tang

Publications and source records attributed to Y P Tang.

7 recordsLinked to original sources

PubMed1992

Photoperiod modulates pubertal shifts in behavioral responsiveness to testosterone.

This study examined the effect of photoperiod on pubertal maturation of steroid-dependent reproductive behaviors in male European ferrets (Mustela putorius furo). In the first experiment, levels of neck gripping, mounting, and pelvic thrusting in gonadally intact prepubertal (PRE) ferrets were compared with those of adults that had undergone puberty either while housed in short days (8 hr light/16 hr darkness per day; SD), or after transfer from SD to long days (18 hr light/6 hr darkness per day; LD) at 12 weeks of age. Both LD and SD adults demonstrated significantly greater amounts of neck gripping and mounting than PRE males. In addition, a significantly greater proportion of adults in both SD and LD displayed at least one incidence of the three behaviors compared to PRE ferrets. There were no statistically significant differences in behavior of the gonadally intact LD and SD adults. In the second experiment, dose-response curves for behavioral responses to subcutaneous injections of 0, 0.5, 1.25, 2.5, 5, and 10 mg/kg testosterone propionate (TP) in oil were generated in castrated PRE, SD, and LD males. The lowest dose of TP elicited significantly greater amounts of all three behaviors in LD adults than in PRE ferrets. In addition, levels of mounting and thrusting elicited by the lowest dose of TP were significantly greater in LD adults than in SD adults. These data indicate that pubertal activation of male sexual behavior in male ferrets is accompanied by a pubertal increase in responsiveness to the behavioral effects of testosterone. Furthermore, the degree of behavioral responsiveness of adult ferrets to testosterone is modulated by environmental photoperiod experienced during reproductive maturation.

Animals↗

PubMed1991

Testosterone in MPOA elicits behavioral but not neuroendocrine responses in ferrets.

The amount of time male ferrets were engaged in neck gripping, mounting, and thrusting was quantified in 30-min tests with a receptive female before and after castration. Bilateral cannulae containing a total of approximately 2 mg testosterone propionate (TP) in cocoa butter were then stereotaxically aimed at the medial preoptic area (MPOA). Tests for sexual behavior were conducted on days 3, 7, 14, and 21 postimplantation. Ferrets were histologically categorized as either 1) Miss (implants not in MPOA), 2) Unilateral implant in MPOA, or 3) Bilateral implants in MPOA. The mean amount of time spent neck gripping, mounting, and thrusting increased significantly over castrate levels on postimplantation day 14 in the Bilateral group, but not in the Miss or Unilateral groups. In all groups, mean plasma testosterone concentrations were below or near the lower limit of detectability on the day before TP implantation and on postimplantation test days. In the same plasma samples, luteinizing hormone concentrations were within the normal range of castrated ferrets, and did not significantly decline after TP implantation. These results suggest that the MPOA is a neural site for androgen activation of certain components of reproductive behavior but not for negative feedback on gonadotropin secretion in male ferrets.

Animals↗

PubMed1988

Differential effects of testosterone, 5 alpha-dihydrotestosterone and oestradiol-17 beta on plasma concentrations of LH in castrated ferrets.

The biological activity of testosterone often depends on the conversion of testosterone within the target cell to an androgenic or oestrogenic metabolite. The purpose of this study was to compare the relative ability of testosterone and two of its metabolites, dihydrotestosterone (DHT) and oestradiol, to suppress LH secretion in castrated male ferrets. Castrated ferrets were treated with five different doses of steroid by implanting various numbers of s.c. silicone elastomer capsules packed with either testosterone, DHT or oestradiol. The lowest dose of oestradiol (0.1 mm capsule length/100 g body weight, mean estimated total release rate of 25 ng/day) significantly suppressed plasma concentrations of LH in castrated ferrets. Higher amounts of DHT (2.5 mm capsule length/100 g body weight, mean estimated total release rate of 88 ng/day) were required for a significant reduction in plasma concentrations of LH. Concentrations of LH were also significantly lowered by testosterone when administered at a 2.5 mm capsule length/100 g body weight; however, estimated total release rate was 312 ng/day from these capsules. The fact that oestradiol was more effective than DHT, and that DHT was more effective than testosterone in inhibiting LH secretion in castrated ferrets, suggests that in gonadally intact ferrets, testosterone may be converted to DHT or oestradiol within target cells that mediate steroid negative feedback on LH secretion.

Animals↗

PubMed1987

Stress and corticotropin-releasing factor potentiate center region activity of mice in an open field.

The effects of corticotropin-releasing factor (CRF) and previously published effect of stress on the locomotor activity of mice in different regions of an open field were compared. Intracerebroventricular (ICV) administration of 0.2 microgram CRF, like stress, significantly increased center region activity; this effect was reversed by the benzodiazepine diazepam (DZP) at a dose of DZP having no significant effect alone. A dose of DZP that antagonized CRF-potentiated center region activity did not block amphetamine-stimulated center area activity. These results suggest that CRF may normally be responsible for many behavioral changes during conditions of stress.

Amphetamine↗

PubMed1987

Differential biochemical mechanisms mediate locomotor stimulation effects by caffeine and nicotine in rats.

Effects of caffeine and the interactive effects of caffeine and nicotine on locomotor activity in rats were examined in the present study. Other than confirming previous reports that both drugs enhanced locomotion, we have also found that their effects on activity were additive. Meanwhile, results of various biochemical measures have revealed that at the minimum effective doses of caffeine and nicotine which facilitated locomotor activity, only one biochemical system was preferentially influenced by either drug alone. The most significant findings were that caffeine stimulated the release of catecholamines and nicotine decreased the concentrations of tyrosine and tryptophan in brain. The combined effects of caffeine and nicotine on these brain amines were not different from those of each drug alone. Together with the report that caffeine and nicotine had differential actions on different activity measures, the present results support the hypothesis that caffeine and nicotine affect locomotor activity via different neurochemical mechanisms.

Animals↗

PubMed1987

Gabaergic interneurons in the dorsal raphe mediate the effects of apomorphine on serotonergic system.

Apomorphine (APO) has been shown to elevate the concentrations of serotonin (5-HT) and its major metabolite 5-hydroxyindoleacetic acid (5-HIAA) in the mesostriatal but not the mesolimbic serotonergic systems. We have previously demonstrated that the serotonergic actions of APO were secondary to dopamine (DA) autoreceptor stimulation in the substantia nigra. Using picrotoxin as a pharmacological tool, we have presently found that these effects of APO were also indirectly mediated through gamma-aminobutyric acid (GABA) neurons. In examination of the exact anatomical locus of GABA neurons responsible for the observed effects of APO, the results indicate that bilateral lateral habenular lesions did not block the effects of APO on 5-HT neurons, while direct picrotoxin infusion to the dorsal raphe, at a dose having no significant influence by itself, antagonized APO's actions. Together with the anatomical, biochemical and histofluorescent findings, it is suggested that APO influences dorsal raphe 5-HT by stimulation of DA autoreceptors in the substantia nigra; therefore, inhibition of DA neuron activity and the nigro-raphe pathway. Normally, DA probably exerts an excitatory influence on gabaergic interneurons in the dorsal raphe, and these inhibitory interneurons then synapse on 5-HT neurons in the same area. Activation of 5-HT neurons were explained by a disinhibitory effect as a result of reduced release of GABA due to feedback inhibition of DA neuron firing following APO activation of DA autoreceptors in the substantia nigra. The striatal presynaptic and postsynaptic DA receptors, however, do not appear to mediate the above effects of APO.

Animals↗

PubMedDate not supplied

LHRH in the ferret: pubertal decrease in the number of immunopositive arcuate neurons.

This study correlated a region-specific change in the number of luteinizing hormone-releasing hormone-immunopositive (LHRH+) neurons with pubertal development in male ferrets. There were 50% fewer LHRH+ cell bodies in the arcuate nucleus of peri- and postpubertal ferrets than in prepubertal ferrets; this significant decrease represented a 15% reduction in the overall number of LHRH+ neurons. Intracerebroventricular colchicine did not reveal additional numbers of LHRH+ neurons in the arcuate nucleus, indicating that the pubertal decrease in arcuate LHRH+ cell bodies was not due to rapid transport of peptide. These results suggest that LHRH of arcuate origin may inhibit release of LHRH via ultrashortloop negative feedback in prepubertal ferrets. Cessation of peptide production in half of the arcuate LHRH neurons at puberty could result in a reduction in this inhibitory signal that permits the pubertal increase in LHRH/LH release. Alternatively, LHRH of arcuate origin may have a nonpituitary role. In either case, these data provide evidence for heterogeneity of function among LHRH+ neurons.

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