Norman T. Adler

Genital Sensory Field: Enlargement by Estrogen Treatment in Female Rats

Recordings of neuronal activity in the pudendal, genitofemoral, and pelvic nerves indicate that the sensory fields of these three nerves are the perineum, the caudal abdomen, and the vagino-cervical area and rectum, respectively. The sensory field of the pudendal nerve was significantly larger in estrogen-treated ovariectomized female rats than in uninjected controls. This effect of estrogen was not mediated by pudendal efferents.

The Role of the Female During Copulation in Wild and Domestic Norway Rats (Rattus Norvegicus)

The copulatory behavior of both wild and domestic strains of Rattus norvegicus was observed via continuous video monitoring as it spontaneously occurred in the large seminatural environment and under standard laboratory conditions. A factorial design demonstrated that the female Norway rat has the major role determining the amount and timing of copulation once mating begins. Copulation between wild pairs was characterized by fewer ejaculatory series than domestic pairs. The first ejaculatory series of wild pairs contained more intromissions at longer intervals. Domestic pairs had the same total number of intromissions in a copulatory session, but spread over multiple ejaculatory series with few intromissions at short intervals in the first series. The characteristic differences between the copulatory patterns of wild and domestic pairs was determined by the females strain condition and was either statistically independent or opposite to the males strain condition. Specifically, the population pattern of a wild female was characterized by fewer ejaculatory series and more intromissions at longer intervals before the first ejaculation than the pattern of a domestic female. These differences between wild and domestic populations were produced by differences in the rate of active solicitations for an intromission by individual females : the solicitation occurred virtually in a one-to-one correspondence with an intromission. There were no gross anatomical differences between the vaginal size and placement of the two strains. The female solicitation is a distinct and quantifiable behavior not found in the standard testing cage: its occurrence depends on a larger and more complex environment. In addition, copulation in the larger seminatural environment is characterized by fewer intromissions in each ejaculatory series of a session at longer copulatory intervals. The role of the female is discussed both in terms of the individual interactions which underlie it and in terms of its physiological functions for successful reproduction in the rat. Copulation with a wild male is characterized by longer intervals between the intromissions of the first ejaculatory series than with a domestic male. The wild condition of both the pair and the female showed the opposite effect. This difference is evaluated in terms of the different mating strategies for the two sexes on a population level and in terms of the individual interactions that allow a compromise for successful reproduction of the pair.

Systematic interrelationship of mating, vaginal plug position, and sperm transport in the rat

Abstract A quantitative means of evaluating the position of the vaginal plug in the vagina of the female rat was developed. Using this technique we demonstrated a systematic relationship between the position of the vaginal plug in the vagina, and sperm transport. The more fully the perimeter of the rostral end of the vaginal plug lodged in the vaginal-cervical junction, the greater was the transport of sperm from the vagina to the uterus. Secondly, males which maintained pelvic contact with the female for more than one sec after the final ejaculatory thrust deposited vaginal plugs which tended to fill three-fourths to the entire circumference of the vaginal-cervical junction. Males which maintained pelvic contact with the female for less than one sec after the final ejaculatory thrust deposited vaginal plugs which tended to fill one-half or less of the circumference of the vaginal-cervical junction. The protracted pelvic thrust shown by most males at ejaculation may cause the vaginal plug to lodge tightly in the vaginal-cervical junction.

Computer assisted analysis of 2-DG autoradiographs.

A computerized image processing system is described that assists the neurobiologists in analyzing data from 2-DG autoradiography by providing for: (1) Rapid fine-scale digitization of gray levels using a TV camera (2) The recognition of and verification of subtle differences in optical density with the aid of color windows (3) the superimposition of the autoradiographic image upon the histological image, so that the activity seen in the autoradiograph can be accurately assigned to anatomically defined structures (4) The production of numerical data suitable for statistical analysis and line drawings suitable for black on white publication (5) The relating of local gray level to a norm for the image as a whole, so as to remove the variability introduced by variations in section thickness, in the amount of 2-DG seen by the brain during incorporation, in level of anesthesia, etc. If the localized darkening in autoradiographic images is being used as an index of localized functional activity rather than as a measure of metabolism, normalization obviates the need to obtain arterial blood samples. These routines permit anatomically accurate numerical analysis of autoradiographs without any constraints on the experimental situation.

Copulatory Behavior Can Inhibit Pregnancy in Female Rats

If female rats received genital stimulation soon enough after their male partners had ejaculated, sperm transport and subsequent pregnancy were inhibited. Manual stimulation by the experimenter or five intromissions by a male rat were sufficient stimuli to reduce the number of sperm found in the uterus and to reduce the number of uterine implantation sites.

The multiplicity of biological oscillators in the control of circadian running activity in the rat

Abstract The purpose of this experiment was to determine the degree to which a circadian running activity could be controlled by multiple biological oscillators within a single organism. Twelve male rats, housed in running wheels, had access to food from noon to 1 p.m. daily. In addition to this noon or fixed feeding, the rats received a moving feeding during which they had access to food for 1 hr every 25 hr. These two circadian feedings had a continually shifting phase relationship to each other. The animals responded to this regime by displaying separate bursts of running activity which were in relative coordination. Each animals behavior shifted between the three following general patterns: (1) one cycle of activity, either before the fixed or the moving feed; (2) two bursts of activity, one before the fixed feeding and one preceding the moving feeding or (3) a burst of activity not entrained to either one of the feedings but rather free running between the two. When the animals were subsequently offered continuous access to food, 10 of the 12 rats maintained two bursts of activity.

Sex and sodium intake in the rat

Female rats drink more 3% NaCl solution than do males, both when they need sodium (need-induced sodium intake or sodium appetite) and when they do not (need-free sodium intake). The sexual dimorphism of sodium intake is a secondary sexual characteristic because after castration at 1 day of age male rats drank 3% NaCl in adulthood in a manner similar to that of females in both the need-free and need-induced state, and females given long-term, neonatal testosterone drank low, malelike volumes of 3% NaCl on a daily need-free basis, but their response to sodium depletion was unchanged. This sexual dimorphism of sodium intake seems to be governed by testosterone that has been converted in the brain to estrogen because treatment of Day 1 castrated females with a nonaromatizable androgen, dihydrotestosterone, did not change either their need-free or their need-induced 3% NaCl intake. Castration in adulthood of male and female rats did not change their sodium consumption. However, when castrated adults received testosterone, need-free intakes of NaCl were suppressed in both sexes, but the suppression of 3% NaCl intake occurred only while the steroid was present. Exogenous testosterone also lowered the need-induced sodium intake of adult castrated females. Thus, in castrated adults, need-free intake was actively suppressed by exogenous testosterone in both sexes, whereas need-induced intake of NaCl was suppressed only in females. These data indicate that sodium intake in the rat is a sexually dimorphic behavior that is organized neonatally and can be actively suppressed in adulthood by testosterone.

Variation in the size and sensitivity of a genital sensory field in relation to the estrous cycle in rats

Abstract In rats showing normal estrous cycles, the size and sensitivity of the pudendal nerves sensory field was determined by recording spike potentials from the pudendal nerve. The overall sensory field area was larger and more sensitive in estrous than in diestrous females. This indicates that the fields characteristics can change within 2 days (the interval between diestrus and estrus), perhaps as a result of the increased estrogen secretion that occurs around the time of mating. One effect of this increased estrogen secretion may be to sensitize and to enlarge the sensory field of the pudendal nerve. In a second experiment, we found that the genital area of the female which the males penis contacts during an intromittive mount corresponds closely to an area of high sensitivity within the sensory field of the pudendal nerve. We suggest that the male rats copulatory contact with this region of the females perineum may facilitate the intensity of her lordosis and/or her orienting for intromission.

Circadian activity rhythms in rats with midbrain raphe lesions.

The dorsal and median mesencephalic raphe nuclei provide a robust projection to the hypothalamic suprachiasmatic nucleus, the site of a putative neuronal circadian pacemaker. Although it has been suggested that the raphe may play a role in the circadian timing system, this role has not yet been specified. In the present report, we examined the circadian activity patterns of rats with large mid-brain lesions aimed at the median and dorsal raphe nuclei under conditions of light-dark entrainment, and while free-running in constant light and constant darkness. The results indicate that midbrain raphe lesions may interfere with the expression of free-running circadian activity rhythms.

Hormonal control of female sexual behavior in the rat

Abstract Graded amounts of estradiol benzoate (ranging from 0.48 to 500 μg/kg) were administered to ovariectomized, adrenalectomized female rats in order to analyze the effects of estrogen on the qualitative and quantitative aspects of female reproductive behavior in this species. The interaction of hormone dose and copulatory stimulation was also investigated. In this study, soliciting behavior and lordosis responses were broken down into subcategories. There were three main results. First, it was found that the responses were hierarchically arranged such that, with increasing doses of hormone, the common elements of sexual responding appeared in the same order across individual females. Second, the chronic endocrine background of the female influenced the degree of her receptivity following an acute injection of estrogen. Third, repeated elicitation of lordosis by copulatory stimulation facilitated the subsequent occurrence of lordosis.