An assessment of factors contributing to instrumental performance for sexual reward in the rat

I love you with all my brain: laying aside the intellectually dull sword of biological determinism

Background

By organizing and activating our passions with both hormones and experiences, the heart and mind of sexual behavior, sexual motivation, and sexual preference is the brain, the organ of learning. Despite decades of progress, this incontrovertible truth is somehow lost in the far-too-often biologically deterministic interpretation of genetic, hormonal, and anatomical scientific research into the biological origins of sexual motivation. Simplistic and polarized arguments are used in the media by both sides of the seemingly endless debate over sexual orientation, equality, and human rights with such catch phrases as ‘born gay’ contrasted against attempts of “reparative therapy” or “pray the gay away”. Though long abandoned in practically every other area of psychology, this remnant of the nature-nurture controversy remains despite its generally acknowledged insufficiency in explaining any adult aspect of the human condition within the scientific community.

Methods

This theoretical review article identifies three factors: 1) good intentions with regard to the argument from immutability; 2) false dichotomies limiting intellectual progress by oversimplification of theory and thus hypothesis, and most dangerously, interpretation and; 3) Tradition: a historical separation of the disciplines of biology and psychology, which, to this day, interferes with the effective translation of well-conducted science into good public understanding and policy.

Results

Studies clearly demonstrate that progress toward sexual-orientation equality is being made, if slowly, despite the apparent irrelevance of the “born gay” argument from immutability. Evidence is further provided supporting the inadequacy of polarized, dichotic theories of sexual development, particularly those pitting “blank slate learning” against a fated, deterministic biological perspective. Results of this review suggest that an emerging interactionist perspective will promote both better scientific progress and better public understanding, hopefully contributing to progress toward nondiscriminatory public policy.

Conclusion

Accepting that the brain is a highly plastic, modularly dimorphic, developmentally biased organ of learning, one which is organized and activated by both hormones and experiences across the lifespan, is essential for doing “good science” well. Interactionist theories of psychosexual development provide an empirically sound, strong, yet modifiable foundation for testable hypotheses exploring biologically biased sexual learning.

Gonadal hormones modulate the potency of the disruptive effects of donepezil in male rats responding under a nonspatial operant learning and performance task

In contrast to estrogen in female rats, testosterone in male rats may decrease cholinergic activity in the brain, thereby attenuating behaviors mediated by the cholinergic system. To investigate this possibility, the interactive effects of the gonadal hormones and donepezil, an acetylcholinesterase (AChE) inhibitor, on the responding of male rats were examined under a multiple schedule of repeated acquisition and performance of response sequences and on AChE activity in specific brain regions. Donepezil dose-effect curves (0.56-10 mg/kg) were determined in males that were gonadally intact, gonadectomized (GX), GX with testosterone replacement (GX+T) or GX with estradiol replacement (GX+E). In all four groups, donepezil produced dose-dependent rate-decreasing and error-increasing effects in the acquisition and performance components. However, disruptions of response rate and accuracy in both components occurred at lower doses in GX and GX+E males than in intact males. The GX+E males also had the highest percentage of errors under control (saline) conditions in the acquisition components. In terms of AChE activity, GX males had higher levels in the prefrontal cortex, striatum and hippocampus, but lower levels in the midbrain, compared with intact males; hypothalamic and cortical levels were comparable for the GX and intact groups. Together, these results in male rats indicate that the potency of donepezil's disruptive effects on the responding under a complex operant procedure requiring learning and performance of response sequences depends upon the gonadal hormone status, and that the effects of testosterone on cholinergic activity vary among brain regions.

Human and rodent homologies in action control: corticostriatal determinants of goal-directed and habitual action

Recent behavioral studies in both humans and rodents have found evidence that performance in decision-making tasks depends on two different learning processes; one encoding the relationship between actions and their consequences and a second involving the formation of stimulus-response associations. These learning processes are thought to govern goal-directed and habitual actions, respectively, and have been found to depend on homologous corticostriatal networks in these species. Thus, recent research using comparable behavioral tasks in both humans and rats has implicated homologous regions of cortex (medial prefrontal cortex/medial orbital cortex in humans and prelimbic cortex in rats) and of dorsal striatum (anterior caudate in humans and dorsomedial striatum in rats) in goal-directed action and in the control of habitual actions (posterior lateral putamen in humans and dorsolateral striatum in rats). These learning processes have been argued to be antagonistic or competing because their control over performance appears to be all or none. Nevertheless, evidence has started to accumulate suggesting that they may at times compete and at others cooperate in the selection and subsequent evaluation of actions necessary for normal choice performance. It appears likely that cooperation or competition between these sources of action control depends not only on local interactions in dorsal striatum but also on the cortico-basal ganglia network within which the striatum is embedded and that mediates the integration of learning with basic motivational and emotional processes. The neural basis of the integration of learning and motivation in choice and decision-making is still controversial and we review some recent hypotheses relating to this issue.

Testosterone potentiates scopolamine-induced disruptions of nonspatial learning in gonadectomized male rats

Whereas research into the effects of the gonadal hormones on learning and memory has primarily focused on estrogen in females, recent evidence suggests that testosterone can also modulate learning in males through an interaction with the cholinergic system. In the present study, the interactive effects of testosterone and scopolamine (0.1- 0.32 mg/kg), a muscarinic receptor antagonist, on complex behavioral processes were investigated in male rats trained to respond under a multiple schedule of repeated acquisition and performance. In the acquisition component, subjects acquired a different 3-response sequence each session, whereas in the performance component, they responded on the same 3-response sequence each session. Although gonadectomy did not disrupt responding in either component, gonadectomized rats were less sensitive to the disruptive effects of scopolamine on both response rate and accuracy. In contrast, after receiving exogenous testosterone replacement, these gonadectomized males were more sensitive to the behavioral disruptions produced by scopolamine (i.e., the effects of scopolamine were similar to those obtained in gonadally intact males). These results suggest that testosterone replacement can enhance scopolamine-induced behavioral effects in gonadectomized male rats responding under a multiple schedule of repeated acquisition and performance, a finding that is in contrast to those previously found for certain spatial tasks. Furthermore, the present findings suggest that testosterone may decrease the activity of the cholinergic system during nonspatial tasks and thereby work in concert with the antagonism produced by scopolamine.

Emotion-induced amnesia in rats: working memory-specific impairment, corticosterone-memory correlation, and fear versus arousal effects on memory

We have shown previously that psychological stress (predator exposure) impairs spatial memory in rats. We have extended that finding here to show that predator stress selectively impaired recently acquired (hippocampal-dependent) spatial working memory without affecting long-term (hippocampal-independent) spatial reference memory. We also investigated why predator exposure impairs memory. Was spatial memory impaired because of the fear-provoking aspects of predator exposure or only because the cat was a novel and arousing stimulus? If the latter possibility was correct, then any novel and arousing stimulus, independent of its emotional valence (i.e., aversive or appetitive), would impair memory. We found that spatial working memory was not impaired when the male rats were exposed to a sexually receptive female rat, a stimulus that was novel and arousing to them, but not aversive. We also found that there was an equivalent increase in serum corticosterone levels in male rats exposed to either a cat or a female rat, but only the cat-exposed rats exhibited a significant correlation between corticosterone levels and impaired memory. Overall, this series of experiments demonstrates that (1). predator stress selectively impaired working (hippocampal-dependent), but not reference (hippocampal-independent), memory; (2). a fear-provoking stimulus, and not merely novelty and increased arousal, impaired spatial memory; and (3). increased corticosterone levels correlated with impaired spatial working memory only under predator exposure, that is, fear-provoking conditions.

Sexual experience interacts with steroid exposure to shape the partner preferences of rats

A three-phase experiment manipulated sexual experience and hormone exposure (perinatally and in adulthood) in female rats housed individually from weaning so as to limit peripubertal social and sexual experience. Noncontact partner preference for a male or estrous female rat was measured both before and after sexual experience, first while rats were under the influence of circulating testosterone propionate (TP) and later after priming them with ovarian hormones (estradiol benzoate and progesterone; EB & P). When implanted with TP capsules and tested while sexually naive, all groups of female rats preferred females to males without differing statistically. However, following three sexual experience sessions with estrous females, differences emerged between the masculinized and control groups in the magnitude of their female-directed preference, with masculinized females demonstrating a significantly greater preference for estrous females. Sexual experience with male rats under EB & P did not result in a significant shift in preference in any group. Histological assessment indicated that the volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) was increased by exposure to TP postnatally, and SDN-POA volume correlated positively with partner preference scores but only when rats were both sexually experienced and exposed to circulating TP in adulthood. These results suggest that sexual experience interacts with steroid exposure to shape partner preference.