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SUMMARY
Pinealectomy (10 animals) or superior cervical ganglionectomy (14 animals) prevented the acceleration of oestrus in ferrets by two different daily regimes of artificial light. Both sets of animals came into oestrus in the spring following operation at about the same time as normal ferrets kept in daylight. Neither procedure affected the duration of the oestrous period. The interval between onsets of successive postoperative annual oestrous periods in both control-operated and normal animals kept in daylight supplemented by 6 hr. artificial evening illumination was about 1 yr., but was much greater in pinealectomized or ganglionectomized ferrets. An attempt to section the nn. conarii failed to provide direct evidence for a functional link between the superior cervical ganglia and the pineal, but there was a relation between the volume of pineal remaining after this procedure and the activating effect of artificial light on oestrus.
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SUMMARY
Removal of the pineal gland from ferrets kept entirely in daylight prevented the appearance of the normal annual oestrous rhythm. Animals were operated upon in the autumn; that is, at the start of their anoestrum. Oestrus in pinealectomized ferrets began at the usual time the following spring, as in control-operated and normal animals. However, during the second year after operation, pinealectomized ferrets came into oestrus 20–30 weeks after controls. Mean intervals between onsets of successive oestrous periods were: pinealectomized, 73·8 weeks (4 animals); control-operated, 52·9 weeks (7 animals); and normal animals, 52·5 weeks (10 animals). The duration of the oestrous period was not altered by removing the pineal.
Three other pinealectomized ferrets kept in artificial photoperiods (14 h light: 10 h darkness) showed an oestrous rhythm indistinguishable from those pinealectomized and kept in daylight, whereas four controls that had also been put into artificial light showed greatly prolonged oestrous periods lasting more than a year.
These experiments indicate that the pineal is concerned with timing the annual breeding season of ferrets in natural daylight as well as in artificial illumination. The anterior pituitary gland of pinealectomized ferrets seems unresponsive to either natural or artificial light under the conditions used in these studies. The duration of oestrus may be self-limited, but can be prolonged if the pineal gland is stimulated by the artificial 'long day'.
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SUMMARY
Bilateral electrolytic lesions have been made in the thalamus, caudate nucleus or adjacent areas, in fourteen anoestrous ferrets; in another ten animals control operations were performed which were identical except that an electrolytic current was not passed.
Most of the experimental animals came into heat precociously. This effect was independent of the size, position, or even the presence of an electrolytic lesion, but depended only upon operative interference with the cerebrum.
It was concluded that these procedures acted as a non-specific stimulus for the production of gonadotrophic hormone and that more specific interpretations of the results of similar investigations involving central nervous lesions were, therefore, not necessarily valid.
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SUMMARY
The effect of dexamethasone, given either alone or together with testosterone propionate or androstenedione, was studied in nine female rhesus monkeys (paired with three males) by making quantitative observations on behaviour in the laboratory.
Dexamethasone (0·5 mg/kg/day) given to oestrogen-treated ovariectomized female monkeys made them sexually unreceptive, and there was an associated decline in the level of the male's mounting activity. Testosterone propionate (100 or 200 μg/day) reversed completely the effects of dexamethasone on sexual behaviour. Androstenedione (100, 200 or 400 μg/day) had similar, but less marked, effects whereas cortisol (10 mg/day) or progesterone (100, 200 or 500 μg/day) were ineffective. Treating a female with testosterone prevented dexamethasone from reducing sexual receptivity. Parallel determinations of urinary free cortisol showed that the dexamethasone had suppressed the secretory activity of the adrenal cortex. There were no consistent changes, under any treatment, in the females' vaginal epithelia, sexual skins or clitorides, or in their water or electrolyte metabolism.
These findings indicate that adrenal androgens regulate sexual receptivity in these female primates, probably by an action on the central nervous system.
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SUMMARY
The effect on sexual behaviour of testosterone propionate (1, 5 or 25 mg./day) or oestradiol monobenzoate (50 μg./day) administered to ovariectomized female rhesus monkeys was studied in the laboratory in six females and three males. One milligram testosterone increased the frequency with which the females 'presented' to the males—that is, invited them to mount. But the proportion of these presentations effective in stimulating the male, and the males' sexual activity, remained low. Oestradiol had a similar, but lesser, effect on the females' behaviour but resulted in marked stimulation of the males' mounting activity, and increased the sexual response of the males to the females' sexual presentations. Larger doses of testosterone had a decreasing effect upon the females' presentations, but increased their aggression towards the males; some females became progressively less receptive to the males' attempts to mount. The effects of these hormones on behaviour and on the females' vaginal smears, sexual skins and clitorides were compared. These studies did not finally establish the site of action of administered hormone, but suggested that testosterone may have stimulated the females' receptivity by an action mainly on their central nervous systems, whereas oestrogen increased their sexual attractiveness to the male principally by an action on their genitalia.
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Ovulatory failure associated with hyperprolactinaemia has been attributed to the inability of oestrogen to evoke a preovulatory discharge of gonadotrophins. This hypothesis was tested in ovariectomized rhesus monkeys rendered hyperprolactinaemic by treatment with two dopamine antagonists, domperidone, a compound reported not to cross the blood–brain barrier in rats, and sulpiride, a drug with known actions on both pituitary and central dopaminergic receptors. An artificial surge of oestrogen similar to that observed at mid-cycle in intact monkeys was obtained with subcutaneous capsules filled with oestradiol-17β. Treatment with either drug increased prolactin concentrations to 1·0 i.u./l or more compared with control values of 0·1–0·3 i.u./l. In the presence of these greatly increased prolactin levels, a normal discharge of LH, indistinguishable from that observed in control animals, was provoked by oestrogens in all but one drug-treated monkey. Furthermore, neither the basal (pre-oestrogen) level of LH nor the negative feedback action of oestrogen was consistently altered in hyperprolactinaemic monkeys. Administration of progesterone or 17α-hydroxyprogesterone to simulate more closely the conditions observed in intact animals during the periovulatory period did not alter the LH discharge induced by oestrogen in animals treated with domperidone.
The present results suggest that the high levels of prolactin brought about by dopaminergic blockade do not affect the positive feedback action of oestrogen. Furthermore, low levels of progestins do not sensitize the hypothalamic-pituitary axis towards an inhibitory action of prolactin on oestrogen-induced LH release. The rhesus monkey thus differs from other species, including man, in which artificially induced hyperprolactinaemia may impair or abolish the positive feedback action of oestrogen.
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SUMMARY
Oestrous ferrets became anoestrous on exposure to short photoperiods (8 h light: 16 h darkness, 8L:16D) at the summer solstice, and this effect was prevented by pinealectomy. Removal of the pineal alone did not alter the duration of oestrus in animals kept in natural daylight. Melatonin (1 mg, thrice weekly) given to oestrous ferrets kept in daylight also terminated oestrus prematurely. Animals made photorefractory by prolonged exposure to long photoperiods (14L:10D) became photosensitive again if either given melatonin or transferred to short photoperiods (8L:16D) for 7 weeks. These findings show that the pineal gland of the oestrous ferret is involved in the termination of oestrus when the animal is exposed to experimental short photoperiods. This is in addition to its role in inducing oestrus when anoestrous animals are exposed to long days, an effect shown previously. Thus, neither phase of the annual breeding cycle is altered by experimental lighting regimes in pinealectomized animals. Furthermore, some of the effects of short days (but not of long days), including that on photosensitivity, can be replicated by melatonin in the ferret.
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SUMMARY
Grooming behaviour was studied quantitatively by observing pairs of oppositely sexed, adult rhesus monkeys during regular hourly test sessions over 2 yr.; at all other times the animals were caged singly. Rhythmic fluctuations in both male and female grooming occurred in relation to the menstrual cycle; the grooming times of males reached a maximum near mid-cycle, at which time the females' grooming was at a minimum. In some pairs, there were additional changes in the grooming times immediately before menstruation in the same direction as those near mid-cycle. Bilateral ovariectomy of the female of the pair abolished all rhythmic variations and reduced the grooming of the males. Subcutaneous injections of oestradiol into the ovariectomized female restored the grooming of males to the levels seen near mid-cycle. The subsequent addition of progesterone partially, but always consistently, antagonized the effects of oestradiol. Analysis of the hormone-induced alterations in grooming behaviour indicates a primary influence on the effectiveness of the grooming invitations of females, the proportion accepted by males increasing with oestradiol administration. These findings indicate that endocrine factors play a role in regulating grooming activity which constitutes an important aspect of the social behaviour of primates.
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SUMMARY
Male sexual behaviour was studied quantitatively by observing pairs of oppositely sexed, adult rhesus monkeys during regular hourly test sessions over 2 yr.; at all other times the animals were housed singly. Rhythmic fluctuations in the mounting behaviour of males occurred in relation to the menstrual cycles of female partners. Two patterns were seen: those with high and low levels of mounting, respectively, in follicular and luteal phases, and those with more isolated maxima near mid-cycle. Ejaculation times were shortest and mounting rates highest near ovulation. Bilateral ovariectomy of females abolished all rhythmic variations in the behaviour of the males, which also stopped ejaculating. Subcutaneous injections of oestradiol into ovariectomized females restored the sexual performance of males, an effect which was partly antagonized by the subsequent addition of progesterone. These findings indicate that sexual behaviour in a male primate is influenced, in some way, by the secretory activity of the female's ovaries.
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ABSTRACT
This study investigated the relationship of two overt circadian rhythms, locomotor activity and melatonin synthesis in the pineal gland, by comparing their responses to asymmetrical reductions in photoperiod. Transfer of male Syrian hamsters from long to short daylengths led to an increase in the duration of both locomotor activity and the period of melatonin synthesis. Over the course of re-entrainment, the two rhythms were held in a stable phase relationship, and the direction of the switch did not influence the rate of decompression or the final phase relationships established after 8 weeks in short daylengths. Decompression of the activity rhythm was not influenced by pinealectomy. Exposure to short photoperiods caused gonadal regression and a consequent decline in serum testosterone levels from 10 to <1 nmol/l. The direction of the photoperiodic switch did not affect the time-course of gonadal regression. These data demonstrate the important influence of photoperiod upon the duration of the nocturnal peak of melatonin production by the pineal and also demonstrate that this effect is one example of a more widespread response of the circadian system. A qualitatively similar signal controls both locomotor activity and melatonin synthesis, although the neural basis of this common mechanism is unclear.
J. Endocr. (1987) 114, 221–229
