Brian K. Follett

Annual Gonadal Cycles and Pituitary Gonadotropins in Zonotrichia leucophrys gambelii

The essential role of the anterior pituitary gland in the development and the function of the avian gonad has been recognized for more than three decades. However, little is known concerning annual variation of gonadotropic function in species with marked gonadal cycles. The only extensive information available appears to be that of Greeley and Meyer (1953) who investigated the gonadotropic activity of the anterior pituitary in relationship to the annual testicular cycle in Ring-necked Pheasants (Phasianus colchicus) held in captivity under semi-natural conditions. In order to extend our understanding of the regulation of the hypothalamo-hypophysio-gonadal axis in birds under natural conditions, we have investigated the annual cycle of pituitary gonadotropic potency in relation to gonadal cycles in free populations of the White-crowned Sparrow, Zonotrichia leucophrys gambelii Nuttall. Such data are also indispensable in the interpretation of the results of experiments conducted under controlled conditions. The annual testicular cycle of Whitecrowned Sparrows has been investigated by Blanchard and Erickson (1949), by Oakeson (1954), and by Oakeson and Lilley (1960). Our data extend these investigations, and describe also the annual ovarian cycle.

Copulation activates Fos-like immunoreactivity in the male quail forebrain

It has been demonstrated using Fos immunocytochemistry that copulation activates specific cell populations in the mammalian brain. Prior to this study, no similar work has been carried out in birds. In mammals, Fos has identified brain circuits activated by genital (penile)/somatosensory and by olfactory/vomeronasal stimuli. Such inputs, of course, should play little or no role in birds (no penis, little or no role for olfaction) and a differential responsiveness could therefore be expected. Male Japanese quail (Coturnix japonica) were allowed to interact freely with adult females and the presence of active sexual behavior, including cloacal contact movements, was confirmed in each case. Control subjects were exposed to a domestic chick (same size as an adult quail) and no sexual behavior was observed. Copulation induced the appearance of Fos-like immunoreactive (FLI) cells in the preoptic area, the hyperstriatum ventrale, parts of the archistriatum, and the nucleus intercollicularis. Induction of FLI cells was observed throughout the rostral to caudal extent of the preoptic region of males from the level of the tractus septomesencephalicus to the level of the anterior commissure, and in the rostral part of the hypothalamus to the level of the supraoptic decussation. The FLI cells did not lie directly adjacent to the third ventricle, but were located 500-1000 microns from the ventricle wall at the level of the lateral edge of the medial preoptic nucleus or, in more caudal sections, in a position ventrolateral to the bed nucleus striae terminalis. It is unlikely that the Fos induction in males resulted from copulation-induced endocrine changes because copulation did not affect plasma levels of luteinizing hormone or testosterone. It is concluded that the responses were due to copulation-associated somatosensory inputs and/or to stimuli originating from the female.

A QUANTITATIVE EXAMINATION OF OVARIAN GROWTH IN THE WHITE-CROWNED SPARROW

1. Ovarian development in Zonotrichia leucophrys gambelii subjected to long daily photoperiods is a logarithmic function of time until a weight of approximately 50 mg. is attained. Although there is a slight non-photoperiodic ovarian growth especially in first-year birds, it is clear that long daily photoperiods are essential for normal ovarian growth and constitute the basic environmental information used in the control of the ovarian cycle.2. The photoperiodic control mechanism in the female differs from that of the male in that the logarithmic growth phase brings the ovary to only approximately one-tenth of its maximum weight, whereas the logarithmic growth phase of the testes in photostimulated males brings them to about one half of maximum (See TABLE II in Source Pdf) weight. In addition, the female differs from the male in that complete gonadal development can be induced only rarely in captivity with either artificial or natural photoperiodic stimulation, whereas sufficiently long daily photoperiods...

Photoperiodic activation of Fos-like immunoreactive protein in neurones within the tuberal hypothalamus of Japanese quail

Photoperiodic stimulation of quail (Coturnix coturnix japonica) resulted in the appearance of a nuclear fos-like protein within neurones of the basal tuberal hypothalamus. On transfer to long days the number of neurones containing this fos-like immunoreactivity increased from about 150 to 700, the neurones being scattered throughout the length of the tubero-infundibular complex. This activation had occurred by early in the second long day and was maintained for at least three long days. Over this period circulating levels of LH increased seven-fold, indicating that photoperiodic induction had taken place in the birds. A similar time-course of fos-like induction occurred in castrated quail exposed to a single long day and then returned to short days. Activation mirrored the long-term changes in LH secretion found in this paradigm and fos-like immunoreactivity showed the same “carry-over” characteristics of photoperiodic induction, being maximal two days after the quail had been exposed to the single long day (and were again on short days) and when LH secretion was at its maximum. Activation of fos-like immunoreactive cells did not take place when long-day quail were transferred to short photoperiods. The evidence supports the view that the neurones being activated are involved in a specific fashion in the avian photoperiodic response.

Thyroidectomy abolishes seasonal testicular cycles of Soay rams.

The hypothesis that thyroid hormones are required for the expression of normal cycles of reproductive activity was tested in Soay rams, a widely used subject for studies on seasonality. Six rams were thyroidectomized and six sham-operated in October, just before the expected peak of reproductive activity. All were then placed in long days (18 h light and 6 h dark, 18L:6D) for 12 weeks and then transferred to short days (8L:16D). All animals exhibited an initial short-term increase in testicular size and serum concentrations of follicle-stimulating hormone and luteinizing hormone then, as expected, these parameters decreased in sham -operated animals for the remainder of the time they were maintained on long days. Four weeks after transfer back to short days, gonadotrophin concentrations in the control animals were significantly raised above the lowest level, and scrotal size increased after eight weeks. By contrast, in thyroidectomized rams all parameters remained high throughout the experiment. Thyroidectomy therefore abolished seasonal changes in reproductive activity, indicating a requirement for thyroid hormones for the normal expression of such patterns. It is unlikely that this was related to any generalized metabolic disturbances caused by thyroidectomy, as body masses were similar in both groups of animals throughout the experiment.

Vertebrate ancient opsin photopigment spectra and the avian photoperiodic response

In mammals, photoreception is restricted to cones, rods and a subset of retinal ganglion cells. By contrast, non-mammalian vertebrates possess many extraocular photoreceptors but in many cases the role of these photoreceptors and their underlying photopigments is unknown. In birds, deep brain photoreceptors have been shown to sense photic changes in daylength (photoperiod) and mediate seasonal reproduction. Nonetheless, the specific identity of the opsin photopigment ‘sensor’ involved has remained elusive. Previously, we showed that vertebrate ancient (VA) opsin is expressed in avian hypothalamic neurons and forms a photosensitive molecule. However, a direct functional link between VA opsin and the regulation of seasonal biology was absent. Here, we report the in vivo and in vitro absorption spectra (λmax = ∼490 nm) for chicken VA photopigments. Furthermore, the spectral sensitivity of these photopigments match the peak absorbance of the avian photoperiodic response (λmax = 492 nm) and permits maximum photon capture within the restricted light environment of the hypothalamus. Such a correspondence argues strongly that VA opsin plays a key role in regulating seasonal reproduction in birds.

Effect of day length on plasma FSH and LH in castrated and intact white-crowned sparrows

Follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were measured in the plasma of male white-crowned sparrows (Zonotrichia leucophrys gambelii) using heterologous radioimmunoassay systems. Levels were determined in intact birds during a photo-periodically induced (20L:4D) gonadal cycle and compared with those in castrates on the same photoregime. In the intact birds testicular weight increased rapidly between Days 10 and 55 while plasma LH reached a maximum level by Day 6 and remained high until Day 50. Between Days 50 and 75 there was a decline in circulating LH to basal levels, coincident with the onset of photorefractoriness and spontaneous gonadal regression. Control birds on short days (8L:16D) showed no changes in plasma levels of LH. In contrast, levels of FSH increased gradually on 20L:4D to reach a maximum by Day 36 when the testes and almost attained maximum size. Thereafter, they steadily declined to basal levels by Day 75. Control birds on 8L:16D had plasma FSH levels below the detectable limits of the assay. During photostimulation (20L:4D) of castrated sparrows, plasma levels of FSH and LH reached levels up to tenfold those in intact birds. The temporal patterns in both gonadotropins were similar with maxima at Day 16, and declining to basal levels by Day 75. Short-day castrates sampled over the same time period showed a slight increase in plasma LH levels, whereas plasma FSH remained undectable.

Plasma luteinizing hormone in male ring doves during the breeding cycle

Plasma levels of LH were analyzed in male ring doves throughout a breeding cycle. LH levels were low in visually isolated animals [(8.0 ± 1.6 ng/ml) (X ± SE)], peaked the day after pairing with a female (14.3 ± 2.52 ng/ml), and declined to baseline levels during incubation and brooding. If eggs or squab were removed during the period of parental care, LH levels rose. The increase in LH following removal of eggs was more prolonged in late incubation than in early incubation. We conclude that the female enhances while the young (eggs or squab) suppress LH in male ring doves.

Photoperiodic control of the termination of reproduction in Japanese quail (coturnix coturnix japonica)

Typically, birds come into breeding in the spring as a response to long days, and end reproduction some weeks later by becoming refractory to those long days. The refractory state is subsequently dissipated by the short days of autumn and winter, so producing once again a bird that can respond to long days. Bird species differ in the extent to which refractoriness is developed; the present experiments took advantage of the relative, rather than the absolute, refractoriness in quail to measure quantitatively the dissipation process. Quail were made refractory by exposure to long days, then transferred to short days and at various times thereafter photostimulated with longer daylengths, the degree of photoresponsiveness being assessed by measuring changes in luteinizing hormone (LH) secretion or cloacal gland size or both. The most clearcut results came from using 13L:11D as the test stimulus to measure photoresponsiveness, and this indicated, in both intact and castrated quail, no response to 13L:11D after one week of short days, a minor response after two weeks, a strong response after three weeks and a full response after five weeks. Thus refractoriness appears to be dissipated gradually under short days, and not in an all-or-none fashion. Confirmation of this conclusion came from experiments in which refractory quail were moved to short days and after one or two weeks transferred to a range of long daylengths. After one week of short days no responses were obtained to 13L:11D or 14L:10D and moderate responses only to 16L:8D, but after two weeks of short days the magnitudes of all the responses were increased. Other experiments showed that the depth of refractoriness (as assessed by transferring to short days and then to 13L:11D) was dependent upon the previous duration of exposure to long days and to the length of that long day. Finally, the development of refractoriness over a three month period on long days was also investigated.

The endocrine control by luteinizing hormone of testosterone secretion from the testis of the Japanese quail

Injections of chicken or ovine luteinizing hormone (LH) into sexually mature male Japanese quail greatly increased plasma levels of testosterone. Maximal responses were obtained within 15 min of an iv injection and between 1 and 2 hr following sc or im injections. Saline treatment had no effect on plasma testosterone. In chronically castrated quail LH was not effective in altering androgen levels. The responses to LH were dose related, significant increases being obtained following sc injections of 5 μg of chicken LH (fraction AE1) or 10 μg of ovine LH (NIH-LH-S19). Chicken LH (AE1) was appropriately 1.8 times as potent as NIH-LH-S19. Ovine FSH (NIH-FSH-S10) stimulated testosterone release in very large doses (1 mg) but was at least 100 times less active than LH-S19. An iv injection of an antiserum raised against chicken LH into mature male quail caused a rapid decrease in plasma testosterone levels. Treatment with FSH-S-10 for up to 1 week failed to facilitate the subsequent response to an injection of LH. The responsiveness of the testis to exogenous LH was tested at various times during a photoinduced gonadal growth cycle. Sexually immature quail showed only a marginal response to an sc injection of 20 μg of NIH-LH-S19. A marked increase in responsiveness occurred after 6 long days. This coincides with the time when plasma testosterone levels increase naturally after transfer to long daylengths and with the period when Leydig cell maturation becomes complete. These in vivo results add further weight to the belief that, in birds, or at least in the quail, peripheral androgens are controlled by pituitary LH and that FSH plays no significant role in the acute release of testosterone from the mature testis.