Scheduled Daily Mating Induces Circadian Anticipatory Activity Rhythms in the Male Rat

Daily schedules of limited access to food, palatable high calorie snacks, water and salt can induce circadian rhythms of anticipatory locomotor activity in rats and mice. All of these stimuli are rewarding, but whether anticipation can be induced by neural correlates of reward independent of metabolic perturbations associated with manipulations of food and hydration is unclear. Three experiments were conducted to determine whether mating, a non-ingestive behavior that is potently rewarding, can induce circadian anticipatory activity rhythms in male rats provided scheduled daily access to steroid-primed estrous female rats. In Experiment 1, rats anticipated access to estrous females in the mid-light period, but also exhibited post-coital eating and running. In Experiment 2, post-coital eating and running were prevented and only a minority of rats exhibited anticipation. Rats allowed to see and smell estrous females showed no anticipation. In both experiments, all rats exhibited sustained behavioral arousal and multiple mounts and intromissions during every session, but ejaculated only every 2–3 days. In Experiment 3, the rats were given more time with individual females, late at night for 28 days, and then in the midday for 28 days. Ejaculation rates increased and anticipation was robust to night sessions and significant although weaker to day sessions. The anticipation rhythm persisted during 3 days of constant dark without mating. During anticipation of nocturnal mating, the rats exhibited a significant preference for a tube to the mating cage over a tube to a locked cage with mating cage litter. This apparent place preference was absent during anticipation of midday mating, which may reflect a daily rhythm of sexual reward. The results establish mating as a reward stimulus capable of inducing circadian rhythms of anticipatory behavior in the male rat, and reveal a critical role for ejaculation, a modulatory role for time of day, and a potential confound role for uncontrolled food intake

Evaluation of the involvement of the androgen receptor in motivated behaviour using male rats carrying the testicular feminization mutation

Androgen insensitive male rats carrying the Testicular Feminization mutation (TFM), a genetic mutation in the androgen receptor, have observed to display sexual performance abnormalities. The nature of this deficit has not been fully described, but androgens and estrogens are important in mediating sexual behaviour in normal (wild type; WT) males. This dissertation examined pre-copulatory behaviours (appetitive) and re-examined sexual performance (consumatory), as well as anxiety levels, in order to determine the contribution of this mutation to these behaviours. A re-examination of sexual behaviour in the TFMs confirmed previous studies showing that these mutants display decreased intromissions and few ejaculations; regions within the brain important for mating displayed male like activation patterns. The accessory olfactory bulbs, important for pheromone mediated sexual behaviour, revealed the TFMs did not display morphological abnormalities, but the activation of this region was different than the WT males. An analysis of partner preference and the latency to achieve mounts did not reveal any abnormalities in sexual motivation. However, an examination of 50 kHz ultrasonic vocalizations (USVs), a precopulatory behaviour important for enhancement of feminine receptivity, revealed the TFMs displayed far fewer USVs than WT males. The expression of Foxp2, a protein linked to USV production in mice, did not differ between TFMs and WT males, however, a sex difference was found in that both groups contained higher optical densities (suggesting higher protein content) than females. Estrogen receptor alpha levels were feminized in certain regions of the TFM brain important for sexual behaviour. In terms of anxiety levels, TFMs displayed masculine levels, but displayed abnormal motor activity. Overall, the data support the conclusion that some appetitive and consumatory sexual behaviours are affected by the androgen receptor (TFM) mutation, and these abnormalities may directly or indirectly contribute to the inability of the TFMs to display sexual behaviour

Effects of chronic estradiol, progesterone and medroxyprogesterone acetate on hippocampal neurogenesis and adrenal mass in adult female rats

Both natural estrogens and progesterone influence synaptic plasticity and neurogenesis within the female hippocampus. However, less is known of the impact of synthetic hormones on hippocampus structure and function. There is some evidence that administration of the synthetic progestin, medroxyprogesterone acetate (MPA) is not as beneficial as natural progesterone and can attenuate estrogen-induced neuroprotection. Although estradiol’s effects have been well studied, little is known about the effects of natural and synthetic progestins alone and in combination with estradiol on adult neurogenesis in the female. In the present study, we investigated the effects of chronic estradiol, progesterone, MPA, and a co-administration of each progestin with estradiol on neurogenesis within the dentate gyrus of adult ovariectomized female rats. Twenty-four hours following a bromodeoxyuridine (BrdU; 200mg/kg) injection, female rats were repeatedly administered with either progesterone (1 or 4 mg), MPA (1 or 4 mg), estradiol benzoate (EB), progesterone or MPA in combination with EB (10<g), or vehicle for 21 days. Rats were perfused on day 22 and brain tissue was analyzed for number of BrdU-labeled and Ki67 (an endogenous marker of cell proliferation)-expressing cells. EB alone and MPA+EB significantly decreased neurogenesis and surviving BrdU-labeled cells in the dorsal region of the dentate gyrus, independent of any effects on cell proliferation. Furthermore, MPA (1mg and 4mg) and MPA+EB treated animals had significantly lower adrenal/body weight ratios, and reduced serum corticosterone (CORT) levels. In contrast, P+EB treated animals had significantly higher adrenal/body weight ratios and 1mg P, P+EB, and EB significantly increased CORT levels. The results of the current study demonstrate that different progestins alone and in combination with estradiol can differentially affect neurogenesis (via cell survival) and regulation of the HPA axis. These findings have implications for women using hormone replacement therapies with MPA for both neuroprotection and stress-related disorders.Arts, Faculty ofOther UBCPsychology, Department ofReviewedFacult

Sex, hormones, and neurogenesis in the hippocampus : Hormonal modulation of neurogenesis and potential functional implications

The hippocampus is an area of the brain that undergoes dramatic plasticity in response to experience and hormone exposure. The hippocampus retains the ability to produce new neurons in most mammalian species and is a structure that is targeted in a number of neurodegenerative and neuropsychiatric diseases, many of which are influenced by both sex and sex hormone exposure. Intriguingly, gonadal and adrenal hormones affect the structure and function of the hippocampus differently in males and females. Sex differences in the effects of steroid hormones to modulate hippocampal plasticity should not be completely surprising as the physiology of males and females is different, with the most notable difference that the females gestate and nurse the offspring. Furthermore, reproductive experience (pregnancy and mothering) results in permanent changes to the maternal brain, including the hippocampus in females. Adult neurogenesis in the hippocampus is regulated by both gonadal and adrenal hormones in a sex and experience-dependent way. This review outlines the ability of gonadal and stress hormones to modulate multiple aspects of neurogenesis (cell proliferation and cell survival) in both male and female rodents. The function of adult neurogenesis in the hippocampus is linked to spatial memory and depression and this review provides early evidence of the functional links between hormonal modulation of neurogenesis to regulate cognition and stress.Arts, Faculty ofOther UBCPsychology, Department ofReviewedFacultyPostdoctora

Androgens Increase Survival of Adult-Born Neurons in the Dentate Gyrus by an Androgen Receptor-Dependent Mechanism in Male Rats

Gonadal steroids are potent regulators of adult neurogenesis. We previously reported that androgens, such as testosterone (T) and dihydrotestosterone (DHT), but not estradiol, increased survival of new neurons in the dentate gyrus of the male rat. These results suggest androgens regulate hippocampal neurogenesis via the androgen receptor (AR). To test this supposition, we examined the role of ARs in hippocampal neurogenesis using two different approaches. In Experiment 1, we examined neurogenesis in male rats insensitive to androgens due to a naturally occurring mutation in the gene encoding the AR (termed TFMs) compared to wild type males. In Experiment 2, we injected the AR antagonist, flutamide, into castrated male rats and compared neurogenesis levels in the dentate gyrus of DHT and oil-treated controls. In Experiment 1, chronic T increased hippocampal neurogenesis in wild type males but not in androgen-insensitive TFM males. In Experiment 2, DHT increased hippocampal neurogenesis via cell survival, an effect that was blocked by concurrent treatment with flutamide. DHT, however, did not affect cell proliferation. Interestingly, cells expressing doublecortin, a marker of newborn immature neurons, did not colabel with ARs in the DG, but ARs were robustly expressed in other regions of the hippocampus. Together, these studies provide complementary evidence that androgens regulate adult neurogenesis in the hippocampus via the AR but at a site other than the dentate gyrus. Understanding where in the brain androgens act to increase the survival of new neurons in the adult brain may have implications for neurodegenerative disorders.Arts, Faculty ofOther UBCNon UBCPsychology, Department ofReviewedFacult

Experiment 3: Group mean (±sem} waveforms illustrating anticipatory activity in response to scheduled mating.

<p>A. Baseline week, no scheduled mating. B. Week 4, late night mating (ZT21}. C. Week 4, daytime mating (ZT6}. D. Day 2 of constant dark without scheduled mating, after the daytime mating schedule. The black curve represents activity detected by the overhead motion sensor. The purple curve (with error bars below} represents activity in the tube to the locked cage. The red curve (with error bars above} represents activity in the tube to the mating cage. Scheduled mealtime is denoted by the opaque vertical bars with dashed red borders. The time of food availability is indicated by the heavy blue line at the top of each figure.</p

Experiment 1: Rats anticipate scheduled daytime mating with food and a running wheel continuously available.

<p>Panels A–B. Actograms of home cage motion (A} and wheel running (B} of a representative rat. Each line represents one day of recording, plotted in 10 minute bins from left to right, with consecutive days aligned vertically. Bins in which activity counts were registered are represented by heavy bars (in quartile weights}. Daily scheduled mating time is indicated by the vertical opaque bar outlined in red. Lights-off is indicated by grey shading. The triangles in panel B denote the 48 h during which the rats were confined to their mating cage to gain sexual experience. The home cage motion sensors could detect activity in some parts of the mating cage. Panels C–D. Group mean waveforms of home cage motion (C} and wheel running (D}, averaged over 5 baseline days (shaded curve, from days indicated by the upper bracket to the left of panels A and B} and 10 scheduled mating days (heavy blue curve, from days indicated by the lower bracket to left of panels A and B}. Zeitgeber time refers to the hour of the LD cycle (lights-off from ZT12-24}. Mate access time (ZT6-7} is denoted by the vertical bar (red dotted bars}.</p

Experiment 3: Group mean (±sem} mating anticipation ratios.

<p>The ratios were calculated by dividing activity during the 3 h prior to the mating hour by total daily activity, excluding the mating hour and the 2 h immediately following. Stars denote significantly different from baseline for that activity measure (p<.05}. Ratios for activity in the tube to the mating cage were significantly different from ratios for activity in the tube to the locked cage in the ZT21 mating condition (red dashed line}, but not in the ZT6 mating condition.</p

Experiment 2: One rat (Group 1, rat#3} eventually shows anticipatory activity to scheduled mating, with post-coital eating and wheel running blocked.

<p>Panels A–C. Actograms of home cage motion (A}, mating tube entry (B} and wheel running (C} in rat #3. Panels D–F. Average waveforms of activity in home cage motion (D}, mating tube entry (E} and wheel running (F} in rat#3. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0040895#pone-0040895-g002" target="_blank">Figure 2</a> for other plotting conventions.</p