Ronald J. Barfield

Intraspecific fighting during late pregnancy and lactation in rats and effects of litter removal.

Female rats (Experiment 1A) were tested for aggression against an adult male intruder in a home-cage test situation at several-day intervals from Day 18 of gestation through Day 21 of lactation. The peak frequencies of attacks and bites and the lowest latency to the first attack occurred on Day 9 of lactation, with concomitant increases in subordinate behaviors by the intruders occurring at that time. Virgin females (Experiment 1B) isolated for comparable periods of time in the test cage showed no differences in fighting levels as a function of length of residence in the home cage. Removal of the litter 4 hr prior to aggression testing on either Day 9 or 10 of lactation (Experiment 2) resulted in significant decreases in fighting levels by lactating females and in significant decreases in subordinate behaviors by intruders. These studies demonstrate that high levels of intraspecific aggression are exhibited during lactation in the rat and that the aggression is dependent upon stimuli from the litter for its expression.

Functional Analysis of Masculine Copulatory Behavior in the Rat

Publisher Summary This chapter describes the analysis the masculine copulatory behavior of the rat, and focuses over the behavioral elements, the temporal patterning of the elements, and the functional relations among the elements. Many measures of copulatory behavior, initiation latencies, copulatory rate, or number of intromissions, are found to vary rather independently of each other, and this evidence is taken as support for the view that sexual arousal is not unitary. The chapter explains how this functional analysis speaks to some of the models that have been developed. The data presented in the chapter explains that some or all of the arousal systems have inhibitory counterparts. This is particularly clear with respect to the absolute and relative post-ejaculatory refractory periods, but probably it is also true of systems controlling behavior prior to ejaculation. The evidence that the number of intromissions needed for ejaculation is substantially independent of the speed of this copulatory clock is also addressed. The chapter relates the behavioral analysis to a number of theoretical models of copulatory behavior. The primary concern in this chapter is to describe how the elements of copulatory behavior are wired together, rather than how the nervous system controlling that behavior is wired together. Nevertheless, behavioral and physiological analysis must proceed in parallel, and the consideration of the physiological evidence reminds us forcefully how little is known about the physiological mechanisms underlying sexual behavior.

Sexual behavior: stimulation by painful electrical shock to skin in male rats.

A mildly painful electric shock lasting 0.5 second was delivered every 30 seconds to the skin of male rats while they were with a receptive female rat. Sexual behavior occurred, with brief latency, after shocks; thus, successive shocks resulted in a pacing of sexual behavior. This effect is attributed to periodic augmentation of sexual arousal by a periodic, nonspecific arousing stimulus (that is, shock).

Induction of estrous behavior in ovariectomized rats by sequential replacement of estrogen and progesterone to the ventromedial hypothalamus.

The present experiment was designed to determine whether sequential replacement of estrogen and progesterone to the ventromedial hypothalamus (VMH) would be sufficient to induce estrous behavior in ovariectomized rats. Bilateral cannulae containing 17 beta-estradiol (E2) diluted with cholesterol (1:250) were lowered into the VMH, preoptic area or midbrain and left in place for 4 days. On day 5, the E2 inserts were removed and P-filled cannulae were lowered into half of the subjects. The remaining females received systemic progesterone (500 micrograms). This steroid regimen was repeated 2 weeks later with the mode of progesterone administration reversed. All subjects were tested for estrous behavior twice after progesterone treatment. In a second experiment, 3H-P:P-filled cannulae were lowered into the VMH of estrogen-primed females in order to estimate the extent of hormone spread from full-strength P-filled cannulae. Results indicated that estrogen and progesterone stimulation of the VMH is sufficient to activate estrous behavior in spayed female rats, however, precise localization of the hormone implants within the VMH is essential. 9 of the 11 females with both cannulae located within or at the border of the ventromedial nucleus (VMN) exhibited estrous behavior whereas only half of the females with only one implant resting in the VMN exhibited estrous responsiveness. Subjects with neither cannula located within or at the border of the VMN did not exhibit the behavior. The facilitative effects of P appeared to result from hormonal stimulation of the VMH and not from leakage of the steroid into other brain regions or into the systemic circulation. Following placement of tritiated progesterone implants into the VMH, high levels of radioactivity were recovered only from the mediobasal hypothalamus. The low levels of radioactivity measured in other brain regions, pituitary, uterus and blood indicate that relatively little if any hormone reached these tissues.

Dose-response and time-response relationships between progesterone and the display of patterns of receptive and proceptive behavior in the female rat

Abstract The relationship between administration of progesterone and the display of patterns of receptive (response to the male) and preceptive (female initiated) sexual behavior was examined in ovariectomized, estrogen-primed female rats in a “restrained male” test situation. It was found that the degree of receptivity and proceptivity displayed was directly proportional to progesterone dose and time from progesterone injection (up to 4.5 hr). Higher progesterone doses and longer period of time from progesterone injection (up to 4.5 hr) were both associated with shorter latencies to return to the male following intromission and ejaculation. Receptivity could be induced with estrogen alone but progesterone was required for the display of proceptivity and higher doses of progesterone were needed to effect increases in proceptivity relative to receptivity. Proceptive behavior also occurred in a narrower time range than did receptive behavior. Receptivity alone is characterized as the lowest degree, and receptivity plus proceptivity as the highest degree, of expression of the total behavior pattern of the estrous female rat. Receptivity and proceptivity together constitute a continuum of estrous responsiveness. Increasing the progesterone dose from 0 to 200 μg, and increasing the latency from progesterone injection from 0 to 4.5 hr, were associated with increasing degree of expression of the total behavioral continuum.

Analysis of ultrasonic vocalizations emitted by intruders during aggressive encounters among rats ( Rattus norvegicus ).

This investigation was concerned with the identification of the ultrasonic vocalizations produced by intruders during aggressive interactions and the role of these signals in agonistic behavior of rats. In the first experiment, experienced resident males were paired with both devocalized and intact vocalizing naive intruder males. Devocalization of the intruder males resulted in a drastic decrease in 50-kHz vocalizations and the elimination of all 22-kHz vocalizations. This almost total absence of ultrasonic vocalizations was not accompanied by any change in resident aggressive behavior or intruder defensive and submissive behavior. In a second experiment, naive intruders were tested with either deafened or intact resident males. Similarly, preventing residents from hearing intruder ultrasounds had no detectable effect on any aggressive behavior. These experiments are not consistent with the correlative evidence that intruder-produced 22-kHz vocalizations inhibit the aggressive behavior of the resident. The results also show that most of the ultrasonic vocalizations emitted during aggressive encounters are probably produced by the intruder.

Gonadal influence on agonistic behavior in the male domestic rat

Abstract The influence of androgen on agonistic behavior of the laboratory rat was investigated. Castrate males were tested with intact partners at 2-week intervals in neutral observation cages. The castrates were untreated in the first test, testosterone propionate treated in the second, and untreated again in the third test. Testosterone propionate treatment markedly increased the level of interaction between the pairs. Untreated castrate rats not only lacked the tendency to initiate conflict, but also failed to evoke aggressive responses from intact males. Castrate rats fought successfully if such conflict was precipitated, but this was rare. A second experiment tested the interaction between a home cage testing situation and the dependence of agonistic behavior on androgens. Male rats kept for 2 weeks in observation cages, were tested for agonistic behavior after the introduction of intruders; the frequency of occurrence of 15 behavioral acts was recorded. Residents were then castrated, allowed 2 weeks for recovery and retested. After the second test a 10-mg pellet of testosterone propionate was implanted subcutaneously; two additional weeks were allowed and a third test was performed. A third experiment identical to the second, except that testosterone propionate was not administered, was also performed. The expression of agonistic behavior was potentiated by androgen; aggressiveness and dominance were also greatly influenced by residence in the home cage.

Effects of morphine, β-endorphin and naloxone on catecholamine levels and sexual behavior in the male rat

Intraperitoneal administration of the opiate antagonist naloxone hydrochloride (30 mg/kg) to sexually experienced male rats caused a significant reduction in mount and intromission latencies, number of mounts preceding ejaculation and ejaculation latencies. Intraperitoneal adminstration of naloxone (30 mg/kg) also stimulated persistant non-copulators to begin mating and to ejaculate within a twenty minute test period. Conversely, intraperitoneal administration of morphine sulphate (6 mg/kg) as well as intraventricular injection of the endogenous opiate beta-endorphin (6 micrograms) produced a complete loss of copulatory behavior in male rats. The deficit in sexual behavior induced by beta-endorphin was correlated with a significant increase in hypothalamic norepinephrine levels. It is suggested that the endogenous opiates may be involved in the mediation of sexual behavior via an interaction with central catecholaminergic systems.

Brain monoaminergic control of male reproductive behavior. I. Serotonin and the post-ejaculatory refractory period

The present experiment was performed to examine the role of serotonergic mechanisms in the control of copulation and the post-ejaculatory refractory period in the male rat. Disruption of central serotonergic systems in two separate groups of animals was achieved by: (1) selective electrolytic lesions of the midbrain raphe nuclei, or (2) localized intraventricular or intracerebral injection of a specific serotonergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT). A third group of animals was tested for sexual behavior following intraperitoneal injection of p-chlorophenylalanine (PCPA), an inhibitor of serotonin synthesis. Both electrolytic and neurochemical lesions localized in the dorsal raphe nucleus produced a highly significant shortening of the ejaculatory latency, and the post-ejaculatory refractory period. Disruption of serotonergic mechanisms following intraventricular injection of 5,7-DHT or systemic administration of PCPA also caused a significant reduction in the length of the refractory period. These results support the hypothesis that central serotonergic systems are normally inhibitory to certain facets of male copulatory behavior and suggest the existence of a serotonergic control system which normally exerts an inhibitory influence over the resumption of mating following ejaculation.

Correlation of dopamine release in the nucleus accumbens with masculine sexual behavior in rats

Extracellular dopamine (DA) and 3,4-dihydroxyphenylacetic acid (DOPAC) in the nucleus accumbens (N. Acc.) were measured by in vivo microdialysis during male sexual activity. DA and DOPAC were significantly increased during copulation, but not during mild tail pinch. These results are consistent with studies showing increases in N. Acc. DA associated with positively reinforcing environmental stimuli.