Processes Regulating the Initiation and Postejaculatory Resumption of Copulatory Behavior in Male Hamsters

Studies using factor analysis have helped describe the organization of copulatory behavior in male rodents. However, the focus of these studies on a few traditional measures may have limited their results. To test this possibility, 74 sexually-experienced male hamsters were observed as they copulated with stimulus females. The measures collected exceeded the conventional ones in number, variety and independence. The factor analysis of these data revealed a structure with seven factors collectively accounting for 80% of the variance. Most resembled the factors in previous reports, reinforcing the contributions that the processes suggested by these factors make to the organization,of male behavior. But several other factors were more novel, possibly reflecting the use of measures that were novel or revised for greater independence. The most interesting of these were two factors focusing on early steps in the progression leading to ejaculation. Importantly, both incorporated measures from each of the three copulatory series that were observed. Past work suggests that independent processes control the times required to initiate copulation and later resume it after an ejaculation. In contrast, these results suggest the existence of two processes, each of which contributes to both the initiation and reinitiation of copulation. (C) 2014 Elsevier B.V. All rights reserved.

Effects of apomorphine on mating behavior, flank marking and aggression in male hamsters

In male rats, the dopamine agonist apomorphine (APO) generally facilitates copulatory behavior. However, disruptive effects of high APO doses have been reported. These have been interpreted in diverse ways, as products of a dopaminergic system that inhibits sexual behavior or as consequences of APO's stimulation of competing responses. To test the generality of these effects, we observed APO's impact on copulatory behavior in male hamsters. Several effects were observed, all attributable to a relatively high dose and involving the disruption of male behavior. More unexpectedly, APO treatment caused males to attack estrous stimulus females in the course of these tests. To clarify these effects, we observed the effects of APO on flank marking, a type of scent marking closely allied to aggression and dominance in hamsters. Treatment reliably decreased the latency of marking. It also increased the rate of marking when appropriate measures were taken to prevent this effect from being obscured by drug-induced cheek pouching. Together, these results confirm and extend APO's well-known ability to increase aggression. Further, they suggest that APO-induced aggression can intrude into other contexts so as to disrupt, or possibly facilitate, other forms of social behavior.

Role of Acetylcholine in Control of Sexual Behavior of Male and Female Mammals

The results of studies using systemic or central applications of cholinergic drugs suggest that acetylcholine makes important contributions to the neurochemical control of male- and female-typical reproductive behaviors. In males, cholinergic control seems largely specific to some elements or aspects of copulatory behavior that can vary significantly across species. Synapses in or near the medial preoptic area represent part of this mechanism, but the entire system appears to extend more widely, perhaps especially to one or more structures flanking some part of the lateral ventricle. In females, the lordosis response that essentially defines sexual receptivity is clearly responsive to cholinergic drugs. The same seems likely to be true of other elements of female sexual behavior, but additional studies will be needed to confirm this. Changes in cholinergic activity may help to mediate estrogenic effects on female sexual behavior. However, estrogen exposure can increase or decrease cholinergic effects, suggesting a relationship that is complex and requires further analysis. Also presently unclear is the localization of the cholinergic effects on female sexual responses. Though periventricular sites again have been implicated, their identity is presently unknown. This review discusses these and other aspects of the central cholinergic systems affecting male and female sexual behaviors. Copyright 2014 Elsevier Inc. All rights reserved.

Oxotremorine Delays and Scopolamine Accelerates Sexual Exhaustion When Applied to the Preoptic Area in Male Hamsters

Acetylcholine (ACh) has not been tested for a role in the development of sexual exhaustion in males. However, male hamsters receiving infusions into the medial preoptic area (MPOA) of the muscarinic agonist oxotremorine (OXO) or antagonist scopolamine (SCO) show changes in the postejaculatory interval, one of the measures that changes most consistently as exhaustion approaches. In addition, central SCO treatments cause changes in the patterning of intromissions that resemble those signaling exhaustion. To extend these observations and more thoroughly test the dependence of sexual exhaustion on ACh, male hamsters received MPOA treatments of OXO, SCO or the combination of the two before mating to exhaustion. Relative to placebo, OXO infusions caused small but consistent increases in ejaculation frequency and long intromission latency, delaying the appearance of exhaustion. Scopolamine treatments did the reverse, dramatically accelerating the development of exhaustion. Consistent with and possibly responsible for these changes were effects on the quality of performance prior to exhaustion. These included differences in overall copulatory efficiency (e.g., ejaculations/intromission), which was increased by OXO and decreased by SCO. They also extended to several standard measures of copulatory behavior, including intromission frequency, ejaculation latency and the postejaculatory interval: Most of these were increased by SCO and decreased by OXO. Finally, whereas most or all effects of OXO were counteracted by SCO, most or all of the responses to SCO resisted change by added OXO. This asymmetry in the responses to combined treatment raises the possibility that the effects of these drugs on sexual exhaustion and other elements of male behavior are mediated by distinct muscarinic receptors. Copyright 2013 Elsevier Inc. All rights reserved.