Adrenergic control of hypothalamic function during osmotic stress in the mallard duck (Anas platyrhynchos)

Endocrinological and behavioral changes associated with the onset of incubation in the duck

Plasma levels of prolactin were measured during the onset of incubation in ducks. A rapid rise in prolactin levels from a mean of 5.7 to 33.1 ng/ml occurred during the formation of the final 20% of the clutch; during which the females increased their nest-box occupancy from 9.9 to 22.2 hours per day. A pronounced decrease in plasma progesterone levels, but not estradiol, occurred in females in the days immediately preceding the onset of incubation and termination of egg laying. A similar decrease in plasma LH occurred. Plasma corticosterone levels also decreased during the transition from egg laying to incubation. In male ducks, who play no role in incubation, LH remained constant until well into incubation when it decreased. Changes in plasma levels of prolactin are discussed in relation to tactile stimulation from the clutch and nutritional stress.

Catecholamine hormones and the control of avian salt glands

Hypertonic saline loading (0.5 M NaCl, 15 ml.kg-1 i.v.) increased cardiac frequency and elicited nasal salt gland secretion in control ducks. Partial depletion of catecholamines by prior treatment with reserpine decreased body weight, lowered arterial pressure and abolished the tachycardiac responses to saline loading. Reserpine also increased plasma concentrations of Na, K and total osmolytes, yet altered neither the composition nor the flow rate of nasal fluid secretion. The preservation of the normal secretory responses to hypertonic stress in hypotensive, reserpine-treated ducks indicates that the nasal salt glands can function independently of changes in circulating catecholamine hormones.

Efferent projections of the medial preoptic nucleus and medial hypothalamus in the pigeon

The efferent projections of the medial preoptic nucleus (POM), anterior-medial hypothalamic area (AM), and the posteromedial hypothalamic nucleus (PMH) in the pigeon were traced by the autoradiographic technique. Similar and differential connections were noted from these regions. Projections from POM and AM-PMH were traced to nucleus septalis lateralis, nucleus dorsomedialis thalami, nucleus dorsolateralis anterior thalami (pars ventralis), posterior hypothalamic and medial mammillary areas, area ventralis tegmenti (Tsai), central gray of midbrain and nucleus intercollicularis and substantia grisea periventricularis of the midbrain. The density of silver grains in these regions differed with POM and AM-PMH injections. Other projections were observed exclusively from only one or two of the nuclear regions injected. Connections from POM and the rostral part of AM were seen to the median eminence, neurohypophysis, and the nucleus of anterior pallial commissure. Only cells of the anterior part of AM project fibers to nucleus septalis medialis. In the hypothalamus, projections from POM are concentrated in the periventricular region and in the preoptic-hypophyseal tract in the extreme lateral hypothalamus, while AM-PMH projections are heaviest in the medial hypothalamus and lateral preoptic area. A major difference in the connections of PMH from POM is the more substantial PMH projection to the midbrain. A prominent projection courses dorsolaterally and posteriorly from PMH toward nucleus ovoidalis and splits into two pathways: a lateral pathway which heavily innervates n. intercollicularis and the periventricular gray and a ventrolateral projection to the midbrain tegmentum. The projections described above provide anatomical substrates for neuroendocrine, autonomic, and behavioral functions.