Biomedical subjects

Ann S Clark

Publications and source records attributed to Ann S Clark.

4 recordsLinked to original sources

PubMed2003

The display of sexual behaviors by female rats administered ICI 182,780.

ICI 182,780 (ICI) is a pure antiestrogen that when administered systemically does not cross the blood-brain barrier, thus its actions are limited to the periphery. Four experiments were conducted to test the effects of ICI on the display of sexual behaviors in ovariectomized rats. Experiment 1 examined the effects of three doses of ICI (250, 500, and 750 micro g/rat) on sexual receptivity and paced mating behavior in rats primed with estradiol benzoate (EB) in combination with progesterone (P). Experiments 2 and 3 compared the display of sexual behaviors in rats primed with EB+P or EB alone and administered either 250 micro g ICI (Experiment 2) or 500 micro g ICI (Experiment 3). Experiment 4 tested the effects of ICI (250 and 500 micro g) on the expression of estrogen-induced progestin receptors in the uterus. ICI did not affect the display of sexual receptivity in any experiment. In rats primed with EB+P, paced mating behavior was altered by the 500 and 750 micro g, but not the 250 micro g, doses of ICI. The lowest (250 micro g) dose of ICI did alter paced mating behavior in rats primed with EB alone. The effects of ICI on paced mating behavior were manifested by a substantial lengthening of contact-return latencies following intromissions and ejaculations. The percentage of exits were not affected by ICI. Estrogen stimulation of uterine weight and induction of uterine progestin receptors was suppressed by ICI (250 and 500 micro g). ICI effects on paced mating behavior in hormone-primed female rats are likely to reflect antiestrogenic actions in the periphery, including interference with the estrogen induction of progestin receptors.

Animals↗

PubMed2003

Chronic administration of anabolic steroids disrupts pubertal onset and estrous cyclicity in rats.

Use of anabolic-androgenic steroids (AASs) is becoming increasingly popular among adolescent girls, yet the effects of AASs on female physiology and development are not well understood. The present study compared the effects of chronic exposure to three individual AASs, stanozolol (0.05-5 mg/kg), 17alpha-methyltestosterone (0.5-5 mg/kg), and methandrostenolone (0.5-5 mg/kg) on the onset of puberty and estrous cyclicity in the rat. Female rats received daily injections of AASs for 30 days (Postnatal Day [PN] 21-51). Rats receiving the highest dose of each of the AASs (5 mg/kg) displayed vaginal opening at a younger age than rats receiving the oil vehicle. The day of first vaginal estrus was delayed in rats receiving stanozolol (5 mg/kg) or 17alpha-methyltestosterone (0.5-5 mg/kg) but not in rats receiving methandrostenolone. At the highest dose (5 mg/kg), each of the AASs reduced the incidence of regular estrous cyclicity during the treatment period. Concurrent administration (on PN21-51) of the androgen receptor antagonist, flutamide (10 mg/kg, twice daily), reversed the effects of 17alpha-methyltestosterone (5 mg/kg) on vaginal opening. Flutamide administration also eliminated the effects of stanozolol (5 mg/kg) and 17alpha-methyltestosterone (5 mg/kg) on the day of first vaginal estrus. In contrast, rats receiving flutamide and methandrostenolone (5 mg/kg) exhibited first vaginal estrus earlier than controls. The present results indicate that chronic exposure to AASs during development has deleterious effects on the female neuroendocrine axis and that these effects appear be mediated via multiple mechanisms.

Anabolic Agents↗

PubMed2002

Hippocampal spatial representations require vestibular input.

The hippocampal formation is essential for forming declarative representations of the relationships among multiple stimuli. The rodent hippocampal formation, including the entorhinal cortex and subicular complex, is critical for spatial memory. Two classes of hippocampal neurons fire in relation to spatial features. Place cells collectively map spatial locations, with each cell firing only when the animal occupies that cell's "place field," a particular subregion of the larger environment. Head direction (HD) cells encode directional heading, with each HD cell firing when the rat's head is oriented in that cell's particular "preferred firing direction." Both landmarks and internal cues (e.g., vestibular, motor efference copy) influence place and HD cell activity. However, as is the case for navigation, landmarks are believed to exert greater influence over place and HD cell activity. Here we show that temporary inactivation of the vestibular system led to the disruption of location-specific firing in hippocampal place cells and direction-specific discharge of postsubicular HD cells, without altering motor function. Place and HD cell activity recovered over a time course similar to that of the restoration of vestibular function. These results indicate that vestibular signals provide an important influence over the expression of hippocampal spatial representations, and may explain the navigational deficits of humans with vestibular dysfunction.

Animals↗

PubMed2002

Effects of ibotenic acid lesions of the nucleus accumbens on paced mating behavior in the female rat.

The present study investigated the role of the nucleus accumbens (NAcc) in paced mating behavior in female rats. A sexually receptive female rat will approach and withdraw from a sexually active male, thereby controlling the timing of the receipt of sexual stimulation (e.g., mounts, intromissions, ejaculations). In this study, ibotenic acid lesions in the NAcc core increased the likelihood that a female rat would withdraw from a male rat after a mount but did not affect contact return latency or sexual receptivity. Ibotenic acid lesions in the NAcc shell did not affect paced mating behavior or sexual receptivity. The results suggest that the NAcc core plays a role in suppressing withdrawal behavior in response to less intense mating stimulation.

Animals↗