Ralph L. Cooper

Vasopressin and conditioned flavor aversion in aged rats

The effect of lysine vasopressin on the performance of young-adult and old rats subjected to a conditioned flavor aversion procedure was studied. Young rats maintained an aversion to a 0.1% saccharin solution significantly longer than did older rats. Treatment with lysine vasopressin ( 1 microgram/kg) during the recovery period prolonged the aversion in both age groups. A single injection of lysine vasopressin prior to the aversion procedure significantly reduced the age difference in extinction. These observations support the hypothesis that age-dependent changes in endogenous vasopressin synthesis or secretion underlie some of the behavioral deficits observed in old animals.

Induced Ovulation in Aged Female Rats by L-dopa Implants into the Medial Preoptic Area

Direct placement of L-dopa into the medial preoptic area (MPOA) of aged pseudopregnant or constant vaginal estrous female rats resulted in a reinitiation of vaginal cycles and ovulation. Similar treatment with L-dopa in the dorsomedial septum or cortex was ineffective. Direct placement of leucine into any of the three brain regions did not have an effect on ovarian function. Intermittent treatment with L-dopa to MPOA was found to reinstate and maintain vaginal cycles in constant estrous females only when administered on the day of vaginal estrus of successive cycles. These findings support the hypothesis that age-dependent disturbances in ovarian function may be initiated by changes in neurotransmitter metabolism within the central nervous system.

Sexual behavior in aged, noncycling female rats

Abstract Sexual behavior of 19 month old, noncycling, female rats was evaluated for a period of 8 days. The sexual behavior of 11 aged females revealing constant vaginal cornification (CVC) for 30 days prior to, and during the observation period was variable. Eight of the CVC females showed consistently high lordosis quotients (LQ), whereas 3 showed no lordosis. A significant negative correlation was found between food intake and LQ over the 8 day period. In 8 other aged females, the vaginal smear was characterized by a mixture of both leucocytes and cornified cells, each day, for a period of 30 days prior to, and during the observation period. Lordosis behavior was absent in all females revealing this mixed type (MX) smear when they were tested. At random times after the test period, 3 CVC and 2 MX females showed a vaginal cycle. As the vaginal cycle was observed each female was again tested for sexual behavior. All 5 females were highly receptive when placed with the male during the evening of vaginal proestrus, but not at other times. It is concluded that despite disruptions of regular ovarian cyclicity, aged female rats are still capable of showing a lordosis response.

Sexual receptivity in aged female rats ☆: Behavioral evidence for increased sensitivity to estrogen

Abstract Lordosis behavior and behavioral patterns indicative of sexual receptivity or nonreceptivity were evaluated in 3- and 25-month-old female rats. Intact, 25-month-old females revealing a pattern of prolonged vaginal cornification (PVC) were highly receptive, whereas 25-month-old pseudopregnant (PL) females were nonreceptive. These measures did not differ as a result of previous sexual experience (i.e., sexually naive vs retired breeders). Following ovariectomy, sexual behavior persisted significantly longer in 25-month-old PVC females than in 3-month-old females ovariectomized during vaginal proestrus. No difference was observed in the rate at which the vaginal smears of 25-month-old PVC and young ovariectomized females became leukocytic. When tested 5, 19, and 20 days after ovariectomy, sexual behavior was absent in all females. Following treatment with estradiol benzoate (0.5 or 1.0 μg/kg), the latency for the reappearance of sexual behavior in 25-month-old females was significantly shorter than that in similarly treated 3-month-old females. This was the case regardless of prior ovarian condition (PVC or PL) and breeding experience. In addition, the mean lordosis quotient (LQ) of 25-month-old females receiving either dose of EB was significantly greater than that of similarly treated 3-month-old females on at least 5 days of a 10-day treatment period. These results are discussed in terms of possible age-related changes in central and peripheral estrogen metabolism.

Effects of septal lesions on the courtship behavior of male ring doves (Streptopelia risoria)

Abstract Male ring doves exhibit several androgen-dependent behavior patterns. Preliminary studies indicated that one of these, the nest-soliciting display, was selectively increased following septal lesions. In the present study castrated male ring doves received a septal lesion followed by daily intramuscular injections of 30 μg testosterone propionate (TP). Although one of the androgen-dependent displays, the bow-coo, was unaffected by the lesions, nest soliciting was significantly elevated during the period of hormone treatment. The restoration of nest-soliciting behavior in the males with septal lesions was even more rapid than that of unlesioned males receiving 200 μg TP/day, although after 12 days of treatment the performances of the latter came to approximate those of the males bearing septal lesions. Males that had received lesions in brain areas other than the septum were no more responsive to 30 μg of TP than were nonlesioned males receiving similar hormone treatment. It is suggested that the influence of the septum differs among the various androgen-dependent displays.

Catecholaminergic-serotonergic balance in the CNS and reproductive cycling in aging rats

Treatment with the serotonin (5-HT) reuptake inhibitor zimelidine, 20 mg/kg/24 hr, SC, for 14 days increased the duration of vaginal cycles in 3 month-old Long Evans hooded rats. It induced persistent vaginal estrus in 12 of 16 ten-month-old animals, and blocked reinitiation of vaginal cycles by L-dopa in 10 of 10 twenty-month-old rats. A single injection of zimelidine at 1400 hr did not alter the vaginal smear pattern of young or middle-aged cycling females or old constant estrus females. Also, a single dose of zimelidine at 1400 hr on the day of vaginal proestrus had no effect on serum LH values in young females. The serotonergic neurotoxin 5,7-dihydroxytryptamine, 4 micrograms, injected into the ventral and dorsal raphe areas (after desipramine, 25 mg/kg IP) reinitiated vaginal cycling in 8 of 13 twenty-month-old rats. These results suggest that age-dependent changes in serotonin metabolism may contribute to the age-dependent changes in luteinizing hormone secretion which eventually lead to the cessation of ovarian function in the rat and that alterations in serotonin function are an important component of the mechanism by which treatments with catecholamine precursors reinstate ovarian function in the old female rat.

Effect of luteinizing hormone-releasing hormone antiserum on sexual behavior in the female rat

Various components of sexual receptivity were measured in ovariectomized, estrone-primed female rats following direct placement of luteinizing hormone releasing hormone (LH-RH) or a LH-RH antiserum into the medial preoptic area. Two hours after treatment with LH-RH antiserum, rats showed a significant increase in lordosis behavior indicative of increased sexual receptivity. When tested 3 and 7 hours after treatment, both LH-RH antiserum and LH-RH-treated rats displayed increased lordosis behavior. Similar treatment with a specific peripheral LH-RH agonist and antagonist had no effect on sexual behavior. Proceptive behavior was absent or minimal in all groups and therefore was not affected by the different treatments. Similarly, there was no difference in the rejection quotients of the females representing the various treatment groups. These results demonstrate that the same behavioral response can be observed in animals treated centrally with LH-RH and a highly specific LH-RH antiserum. Similar treatments with a specific peripheral LH-RH agonist or antagonist were without effect. These results suggest that the characteristics of LH-RH recognition sites in the brain are different from those in the pituitary.

Pattern of food intake and body weight gain in aged, noncycling female rats.

Food intake and body weight were observed in middle-aged, noncycling female rats. The body weight of female rats showing constant vaginal cornification showed no change between the ages of 13.0 and 18.5 months. The body weight of recurrently pseudopregnant and ovariectomized females showed significant increases during the 5.5-month observation period. The mean daily food intake of the recurrently pseudopregnant and ovariectomized females was also significantly greater than that of the constant vaginal estrous group. It is hypothesized that the hormone-sensitive neural structures regulating food intake remain functional and that differential patterns of food intake and body weight gain in the aged female are a consequence of the disturbed ovarian function.

Age-dependent changes in hippocampal theta

The hippocampal theta rhythm in rats exhibited an age-dependent slowing in modal frequency. However, the theta rhythm of young rats with chronic respiratory infections showed a similar slowing. Respiratory disease-free hamsters also exhibited an age-dependent slowing of modal frequencies. These findings emphasize that the health status of the animal must be examined carefully in order to establish an age-dependent slowing in hippocampal rhythm.

Synergistic effects of estrogen and serotonin-receptor agonists on the development of pituitary tumors in aging rats.

The purpose of this study was to determine if pituitary 5-HT levels change as a function of age or endocrine state, and further if such changes are associated with pituitary pathology. Middle-aged constant estrous (CE) rats had larger (p less than 0.05) pituitary glands containing more (p less than 0.05) serotonin (5-HT) than those from young females or comparably aged, irregularly cycling rats. Ovariectomy lowered pituitary 5-HT content in middle aged CE rats. In contrast, pituitary weight and 5-HT content were increased in young rats of both sexes bearing subcutaneous, steroid-containing capsules that produced elevated levels of serum estradiol 17 beta. However, exogenous estrogen failed to raise pituitary 5-HT concentrations since pituitary weight increased more than 5-HT levels, even though the total amount of amine was significantly increased (p less than 0.05) compared with controls. These findings suggest that pituitary 5-HT increases during aging regardless of ovarian status and in addition, that total 5-HT content of the gland is increased further in hyperestrogenic states such as CE. Since pituitary adenomas occur more frequently in aged CE rats than in diestrous females or males, it was of interest to determine if 5-HT contributes to the tumorigenic effect of estrogen. Thus, the 5-HT receptor agonists zimelidine or quipazine were administered to ovariectomized rats bearing estrogen containing capsules. Rats treated with drugs had larger pituitaries containing more tumors than those receiving the steroid alone. However, these effects were dependent upon estrogen since pituitary pathology did not increase when ovariectomized rats were given 5-HT neuroleptics without the steroid.(ABSTRACT TRUNCATED AT 250 WORDS)