In several species, including man and the rat, hyperprolactinaemia is associated with suppression of gonadotrophin release and male sexual behaviour. However, in the hyperprolactinaemic male mouse, plasma LH and FSH levels and copulatory behaviour are increased rather than suppressed. In an attempt to identify mechanism(s) which may be responsible for these effects of hyperprolactinaemia in the mouse, we have examined the effects of two ectopic pituitary isografts on several indices of hypothalamic and pituitary function in adult DBA/2J males. Animals with pituitary grafts had markedly increased plasma concentrations of prolactin, LH and FSH and enlarged seminal vesicles, whereas testicular and pituitary weights were not affected. Content of LHRH receptors and activity of aromatase in the pituitary, as well as dopamine-beta-hydroxylase activity in the hypothalamus were nearly identical in pituitary-grafted and sham-operated males. Biosynthesis of dopamine and turnover of noradrenaline in the median eminence were significantly increased in grafted males. We suggest that the increase in the activity of hypothalamic noradrenergic neurones may mediate stimulatory action of hyperprolactinaemia on LH and FSH release in the mouse. Comparison of these results with those obtained previously in the rat suggests that species differences in the effects of prolactin on gonadotrophin release may be related to its divergent effects on noradrenaline turnover.

In contrast to mammals in which the pineal gland is a discrete structure situated dorsally in the brain, the "pineal gland" in teleost fishes is composed of a number of separate but connected constituent parts, collectively described as the "pineal complex." In this paper, we have described the pineal complex in a common Indian carp, Catla catla, which exhibits an annual reproductive cycle. Attempts have been made to (a) provide an in-depth description of the structure of the pineal complex; and (b) identify the photoreceptor cells of the pineal, by exposing the animals to constant light (LL) and constant darkness (DD). Furthermore, we examined any possible influence of the reproductive status of the fish on the responsiveness of the pineal photoreceptor cells in C. catla following exposure to LL and DD. To this end, a total of four experiments were carried out during the four different phases of the annual reproductive cycle that is characteristic of this species. Each of these four experiments was carried out for a period of 30 days after which the fishes were sacrificed, different parts of the pineal complex were dissected out, and processed for histological and karyometric studies. Our results showed that the pineal complex in this species is composed of three separate but connected parts, (a) an end vesicle (EV); (b) a dorsal sac (DS); and (c) a long and thin pineal stalk (PS) that attaches the EV to the DS. Detailed karyometric and histo-morphologic studies following exposure of the animals to DD and LL showed that constant darkness led to a stimulatory effect on the pineal photoreceptor cells of the EV as evident from a significant increase in the nuclear diameter. In contrast, the nuclear diameter of the photoreceptor cells in animals subjected to constant light showed a significant reduction. Furthermore, the observed cellular changes in the EV of fish exposed either to LL or DD were independent of the stage of the gonadal cycle. The apparent lack of any cellular responses either in the PS, or in the DS, following exposure to LL and DD, suggests that in C. catla the photoreceptor cells are located only within the epithelial lining of the EV and that these cells respond in a manner similar to mammalian pinealocytes when subjected to comparable photoperiod-induced experimental conditions.

Nerve endings on adrenaline cells in male rat adrenal medullas were investigated by quantitative electron microscopy, with sampling at 8 times during a standard light:dark (12:12) photoperiod. Number (N) per unit area of 2 vesicle types (small clear vesicle, SCV; large granular vesicle, LGV) and % of LGV per total vesicle N were determined. Normal (non-operated) animals showed a circadian rhythm (p < 0.005) in mean SCVN and one with nearly opposite phase relations in %LGVN. Doubly sham-operated animals had a similar rhythm in %LGVN but diminished circadian change in SCVN. Pinealectomized animals had a circadian pattern in SCVN, but this differed from that of normals in having a 2nd peak, a delay or phase shift of the primary peak, and an increased amplitude of the rhythmic changes.

In this report, we have examined the effects of aging on adrenomedullary catecholaminergic activity by evaluating the levels of activity of adrenal dopamine-beta-hydroxylase (DBH) in three species of laboratory rodents. Groups of male Fischer 344 rats (3-, 18-, and 28-month-old), Chinese hamsters (4- and 30-month-old), and Mongolian gerbils (3- and 26-month-old) were killed, and their adrenal DBH activities were measured by a sensitive radioenzymatic method. The results indicated that adrenomedullary DBH activities showed a progressive age-related increase in all three species investigated. Specifically, (a) adrenal DBH activity in the 18-month-old rats was significantly (p less than .001) higher than that of 3-month-old rats, and the enzyme activity in the 28-month-old rats was significantly (p less than .001) higher than that of the 18-month-old rats; (b) adrenal DBH activity in the 30-month-old hamsters showed a significant (p less than .001) increase over that found in the 4-month-old hamsters; and (c) DBH activity in the 26-month-old gerbils was significantly (p less than .05) higher than that noted in 3-month-old gerbils. These results suggest that an age-related increase in adrenal DBH activity may, at least in part, contribute to increased levels of circulating catecholamines.

The structure of the pineal complex and the annual reproductive cycle in a major Indian carp, Catla catla, were investigated in the present study. Additionally, given the well-known inhibitory effects of the pineal on reproductive function in mammals, attempts were made to investigate whether or not the pineal exerts an inhibitory influence on reproductive function in this piscine species as well. Sexually adult animals were utilized in all experiments. The cytomorphology of the pineal complex and a number of parameters for testicular function--such as testicular cytology, serum testosterone levels, and testicular activities of two steroidogenic enzymes, 17beta-hydroxysteroid dehydrogenase (17beta-HSD) and delta5-3beta-hydroxysteroid dehydrogenase (delta5-3beta-HSD) were examined over a period of two years. Our studies showed that the pineal complex in this species consists of three separate but distinctly connected components: (a) an end vesicle (EV); (b) a long pineal stalk (PS); and (c) a dorsal sac (DS). Of these, the epithelial lining of the EV consists of cells that have rounded vesicular nuclei and long apical cytoplasmic processes that reach the lumen, features suggestive of photoreceptor cells. The cells of the PS have some similarity with those of the EV, while DS cells appear columnar and ciliated. With regard to gonadal activity, germ cell profiles revealed that this species has four distinct phases during the annual reproductive cycle: (a) preparatory (January-April); (b) pre-spawning (May-June); (c) spawning (July); and (d) post-spawning (August-December). During the spawning phase (July), seminiferous tubular diameter, percentage of late spermatids within seminiferous tubules, and serum testosterone levels showed the highest values compared to those obtained in most of the other phases of the reproductive cycle. Also in July, along with peak serum testosterone levels, the activities of 17beta-HSD and delta5-3beta-HSD were at their highest levels. In a correlation between the pineal cytology and testicular functional status, it was noted that both the nuclear diameter and the apical cytoplasmic projections of the EV photoreceptor cells showed a significant reduction, thus suggesting a reduced synthetic activity, during the month of July, the spawning phase of the reproductive cycle. In contrast, the same features of the EV cells during the other phases of the reproductive cycle showed an increased cellular and metabolic activity--a time when the gonads were less active and in a quiescent stage. These data suggest an inhibitory role of the pineal on gonadal function and thus provide additional credence to the concept that, as in higher mammals, there exists an inverse relationship between the pineal activity and gonadal function in teleost fishes as well.