Muscarinic M1, but not M4, receptor antagonism impairs divided attention in male rats.

Divided attention may be more important than ever to comprehend, given ubiquitous distractors in modern living. In humans, concern has been expressed about the negative impact of distraction in education, the home, and the workplace. While acetylcholine supports divided attention, in part via muscarinic receptors, little is known about the specific muscarinic subtypes that may contribute. We designed a novel, high-response rate test of auditory sustained attention, in which rats complete variable-ratio runs on one of two levers, rather than emitting a single response. By doing this, we can present a secondary visual distractor task during some trials, for which a correct nosepoke response is reinforced with a more palatable food pellet. The nonspecific muscarinic antagonist scopolamine impaired performance, and slowed and reduced lever press activity. We then explored antagonists that preferentially block the M1 and M4 subtypes, because these receptors are potential therapeutic targets for cognitive enhancers. Telenzepine, an M1-preferring antagonist, impaired divided attention performance, but not performance of the attention task without distraction. Telenzepine also had fewer nonspecific effects than scopolamine. In contrast, the M4-preferring antagonist tropicamide had no effects. Analysis of overall behavior also indicated that accuracy in the main attention task decreased as a function of engagement with the distractor task. These results implicate the M1 receptor in divided attention.

Effects of progesterone treatment during adulthood on consummatory and motivational aspects of sexual behavior in male rats.

In males of a variety of species, administration of progesterone during adulthood has been shown to decrease the expression of consummatory sexual behaviors and androgen receptors. However, it remains to be determined if the progesterone-induced decrease in androgen-receptor signaling and consummatory sexual behaviors correspond with less of a preference for a sexually receptive female relative to another male, a behavioral phenotype indicative of sexual motivation. Consistent with the effects of progesterone reported in males of other species, progesterone-treated rats, relative to vehicle-treated rats, exhibited fewer intromissions and ejaculations. Correspondingly, the weights of the androgen sensitive bulbourethral glands were lighter in progesterone-treated rats. In addition, unlike vehicle-treated rats, progesterone-treated rats did not exhibit a preference for a female rat during the early stages of testing. However, across the entire test, both treatment groups exhibited a preference for a female rat, and consequently, there were no differences between the conditions in overall sexual motivation. Progesterone treatment did not alter activity or anxiety-like behaviors. The results of the current study suggest that the lower levels of androgen-receptor signaling and consummatory sexual behaviors in males following progesterone treatment are associated with a transient deficit in the preference for a female sexual incentive.

Sexual motivation in male rats is modulated by tropomyosin receptor kinase B (TrkB).

The expression of brain derived neurotrophic factor (BDNF) and tropomyosin receptor kinase B (TrkB) are regulated by gonadal hormone signaling and are expressed in brain areas that are important for sexual behaviors. Accordingly, BDNF and TrkB signaling have been shown to be important for the expression of consummatory sexual behaviors. However, the role of TrkB in sexually motivated behaviors remains to be fully elucidated. To this end, male rats were administered either the TrkB antagonist, ANA-12, or a vehicle control prior to sexual motivation testing, which took place on a noncontact version of a partner preference task. Vehicle treated rats, but not rats treated with ANA-12, exhibited a preference for the sexually receptive stimulus female rat relative to the sexually active stimulus male rat, as indicated by the percentage of time and entries in the vicinity of the female throughout the entire 20-min test. In addition, when compared directly with vehicle treated rats, rats treated with ANA-12 exhibited a significant decrease in levels of sexual motivation as indicated by the magnitude of each group's preference for the female during the early stages of testing. Collectively, these results suggest that TrkB plays a role in the sexual preferences and corresponding initial levels of sexual motivation in male rats. (PsycINFO Database Record (c) 2019 APA, all rights reserved).