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.

Rapid Facilitation of Ultrasound Production and Lordosis in Female Hamsters by Horizontal Cuts Between the Septum and Preoptic Area

Horizontal cuts between the septum and preoptic area (anterior roof deafferentation, or ARD) dramatically affect sexual behavior, and in ways that could explain a variety of differences across behavioral categories (precopulatory, copulatory), species, and the sexes. Yet little is known about how these effects develop. Such information would be useful generally and could be pivotal in clarifying the mechanism for ultrasonic vocalization in female hamsters. Ultrasounds serve these animals as precopulatory signals that can attract males and help initiate mating. Their rates can be increased by either ARD or lesions of the ventromedial hypothalamus (VMN). If these effects are independent, they would require a mechanism that includes multiple structures and pathways within the forebrain and hypothalamus. However, it currently is not clear if they are independent: VMN lesions could affect vocalization by causing incidental damage to the same fibers targeted by ARD. Fortunately, past studies of VMN lesions have described a response with a very distinctive time course. This raises the possibility of assessing the independence of the two lesion effects by describing just the development of the response to ARD. To accomplish this, female hamsters were observed for levels of ultrasound production and lordosis before and after control surgery or ARD. As expected, both behaviors were facilitated by these cuts. Further, these effects began to appear by two days after surgery and were fully developed by six days. These results extend previous descriptions of the ARD effect by describing its development and time course. In turn, the rapid responses to ARD suggest that these cuts trigger disinhibitory changes in pathways that differ from those affected by VMN lesions. 2013

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.

Responses to Central Oxotremorine and Scopolamine Support the Cholinergic Control of Male Mating Behavior in Hamsters

The responses of hamsters to intracranial injections of the cholinergic agonist oxotremorine (OXO) implicate cholinergic mechanisms in the medial preoptic area (MPOA) in the control of male mating behavior. To extend these observations, we ran three studies of responses to cholinergic drugs delivered singly or in combination to the vicinity of the MPOA. The first tested responses to OXO, confirming its ability to reduce the postejaculatory interval. The second complemented the first by examining responses to MPOA microinjections of the cholinergic antagonist scopolamine (SCO). These caused several changes revolving around intromission. These included increases in intromission frequency and ejaculation latency. They also included a change in the patterning of intromissions, marked by continuous strings without the usual separation by dismounts. The final study resembled the others in examining the effects of MPOA injections of OXO and SCO but focused on the ability of each drug to antagonize responses to the other. Most of the responses to OXO and SCO individually replicated earlier findings, though the measures examined here also permitted the description of effects on some noncopulatory sexual behaviors, specifically the male's inspection of the female. However, the most interesting results may be those suggesting asymmetry in the responses to the addition of the second drug: Whereas responses to OXO tended to be antagonized by SCO, OXO was less effective at counteracting responses to SCO. Though the explanation of this asymmetry is not completely clear, it is consistent with previous suggestions of differences in the affinities of these drugs for subtypes of muscarinic receptors. Therefore, it suggests that the cholinergic synapses and circuits controlling distinct elements of male behavior could differ in their dependence on these receptors. Copyright 2013 Elsevier Inc. All rights reserved.

The Effects of Apomorphine on Sexual Behavior and Aggression in Male Golden Hamsters

The general dopamine agonist apomorphine has been shown to have mostly facilitative effects on sexual behavior in rodents (Domingues & Hull, 2005; Bitran & Hull, 1987). A study looking at the effectsof apomorphine on sexual behavior in male golden hamsters observed that after systemic injections of apomorphine the males became aggressive towards the estrous females (Floody, unpublished). Studies on aggressive behavior have shown that apomorphine has facilitative effects on aggression in rodents (Nelson & Trainor, 2007; van Erp & Miczek, 2000; Ferrari, van Erp, Tornatzky, & Miczek, 2003). The studies presented here attempt to unravel the effects that apomorphine has on sexual and aggressive behavior in male golden hamsters. Studies 1, 2, 3, and 4 focused on the effects of apomorphine on aggression and Study 5 focused on the effects of apomorphine on sexual behavior. It was important for the purposes ofthis study to have separate, specific measures of aggression and sexual behavior that did not involve a social context that would involve multiple behaviors and motivations. The measure used to assessaggression was flank marking behavior. The measure used to assess sexual behavior was the number of vocalizations in response to sexual stimuli. The results from Studies 1, 2, and 3 suggested thatapomorphine increased aggressive motivation in a dose-dependent manner. In Studies 1 and 2 there was a high occurrence of stereotyped cheek pouching that interfered with the flank marking behavior. In Study 3 the procedure was modified to prevent cheek pouching and flank marking was observed uninhibited. Study 5 suggested a decrease in vocalizations after apomorphine treatment. However, this decrease may have been a result of the increase in stereotyped licking behavior. Results suggested that systemic apomorphine treatments increase aggressive motivation in hamsters. The increase in aggressive motivation may confuse the perception of the sensory signals that the males receive from the estrous females. They may haveperceived the estrous female as a nonestrous female which they would normally associate with an aggressive interaction (Lehman, Powers, & Winans, 1983).

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.