Summary. Seasonal cycles in testicular activity in rams were monitored in groups of wild (mouflon), feral (Soay) and domesticated breeds of sheep (Shetland, Blackface, Herdwick, Norfolk, Wiltshire, Portland and Merino) living outdoors near Edinburgh (56\s=deg\N). The changes in the blood plasma concentrations of FSH, inhibin and testosterone, and the diameter of the testis were measured every half calendar month from 1 to 3 years of age. There were significant differences between breeds in the magnitude and timing of the seasonal reproductive cycle. In the mouflon rams, the seasonal changes were very pronounced with a 6\p=n-\15-fold increase in the plasma concentrations of FSH, inhibin and testosterone from summer to autumn, and a late peak in testicular diameter in October. In the Soay rams and most of the domesticated breeds, the seasonal increase in the reproductive hormones occurred 1\p=n-\2months earlier with the peak in testicular size in September or October. In the two southern breeds (Portland and Merino), the early onset of testicular activity was more extreme with the seasonal maximum in August. In cross-bred rams, produced by mating Soay ewes (highly seasonal breed) with Portland or Merino rams (less seasonal breeds), there was a seasonal reproductive cycle that was intermediate compared to that of the parents. A comparison between all 11 breeds showed a significant correlation between the timing of the seasonal cycle in plasma FSH concentration and testicular diameter (time of peak FSH vs testis, r = 0\m=.\95).The overall results in the rams are consistent with a primary role of FSH in dictating the seasonal cycle in testicular size and the secretion of inhibin. The earlier seasonal onset in the testicular cycle in the southern breeds of domesticated sheep, and the differences from the wild type, are taken to represent the effects of genetic selection for a longer mating season.

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Ovariectomized rats with bilateral cannulae near the ventromedial nucleus of the hypothalamus were hormonally primed with 10μg estradiol benzoate and 500μg progesterone. Sexually receptive females were infused bilaterally with 200 ng of the 5-HT 1A receptor agonist, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT), or with a combination of 200 ng 8-OH-DPAT and 2000 ng of the 5-HT 2 receptor agonist, (±)-2,5-dimethoxy-4-iodophenyl-2-aminopropane HCl (DOI). 8-OH-DPAT inhibited lordosis behavior and DOI reduced this inhibition. However, if females were preinfused with the PKC inhibitor, bisindolymaleimide I hydrochloride (BIM), DOI's effect was eliminated. BIM's attenuation of the effects of DOI was time-dependent. When BIM was infused 90 min, but not 30 min, before the 5-HT receptor agonists, BIM eliminated DOI's protection against the lordosisinhibiting effects of 8-OH-DPAT. A concentration of BIM as low as 10 −5 nmol in a 0.5μl infusion volume was effective and there was little evidence of dose responsivity between 10 −5 and 10 −1 nmol of BIM. In contrast, prior infusion with vehicle or with 10 −7 nmol BIM had no impact on the female's response to the 5-HT receptor agonists. These findings allow the suggestion that DOI's ability to increase PKC may be responsible for attenuation of the effects of 8-OH-DPAT on lordosis behavior. KeywordsPKC inhibitor; 5-HT 1A receptors; 5-HT 2 receptors; ovariectomized; sexual behavior IntroductionWithin the ventromedial nucleus of the hypothalamus (VMN), serotonin (5-HT) modulates female rat sexual behavior by acting on multiple 5-HT receptors [39]. Lordosis behavior, a supraspinal estrogen-dependent reflex of sexually receptive females [29], is inhibited by 5-HT 1A receptor agonists and facilitated by 5-HT 2 receptor agonists and their coactivation attenuates the lordosis-inhibitory effects of 5-HT 1A receptor agonists [39]. We have proposed that this 5-HT 1A /5-HT 2 receptor interaction enables the female to fine-tune her behavior so that it is most adaptive to environmental conditions [42]. However, the mechanisms for this interaction are not known.