c-fos expression in the forebrain and brainstem of White Leghorn hens following osmotic and cardiovascular challenges.

In chickens, hyperosmolality and hemorrhage increase hypothalamic vasotocin (AVT) gene expression and stimulate the secretion of AVT from the posterior pituitary gland. In this study, c-fos expression was used to identify areas in the forebrain and brainstem of the domestic chicken that are activated following acute osmotic stress and hemorrhage-induced hypotension. Conscious hens were osmotically stimulated by administering a single intraperitoneal injection of 3 M NaCl (5 ml/kg). Urethane-anesthetized hens were bled to a mean systemic arterial pressure of 80-90 mm Hg and maintained at this blood pressure for 1 h with additional bleedings as required. In both studies, the expression of c-fos was determined in control and experimental birds by using Northern blot analysis and in situ hybridization analysis. Osmotic stress and hemorrhage-induced hypotension increased c-fos expression in the same brain regions. Prominent structures in the forebrain that expressed c-fos mRNA following acute osmotic stress and hemorrhage-induced hypotension included the supraoptic nucleus and paraventricular nucleus and nuclei within the hypothalamus that are anterior and ventral to the third ventricle. In the chicken, this region includes the organum subseptale, the o. vasculosum laminae terminalis, and the nucleus septalis medialis. In the brainstem, following either injection of 3 M NaCl or hemorrhage-induced hypotension, increased c-fos expression was observed in the nucleus of the solitary tract, parabrachial nucleus, area postrema, and locus ceruleus. Thus, the chicken central nervous system appears to use shared neuronal circuitry to stimulate hypothalamic AVT release in response to disturbances in body fluid composition and decreases in either systemic blood pressure or volume.

Arginine vasotocin gene expression and secretion during osmotic stimulation and hemorrhagic hypotension in hens.

In chickens, hyperosmolality stimulates the secretion of vasotocin (AVT) and up-regulates hypothalamic AVT gene expression. Hemorrhage, on the other hand, has not been considered an effective stimulus for AVT release in this species. The effects of acute osmotic stress and prolonged hemorrhagic hypotension on AVT gene expression and secretion were studied in White Leghorn hens. Conscious hens were osmotically stimulated by administering a single ip injection of 3 M NaCl (5 ml/kg). Urethane-anesthetized hens were bled to a mean arterial pressure of 80-90 mm Hg and the pressure was maintained within this range by additional bleeding. A total of about 30% of the estimated blood volume was removed. Both experiments were terminated after 1 hr of stimulation. Plasma AVT levels in the hyperosmotic and hypovolemic hens were 4- and 2-fold higher, respectively, compared to controls. Hypothalamic AVT mRNA levels, detected by Northern blot analysis, were 2.5- and 2-fold higher in the osmotically stimulated and hypotensive groups, respectively, compared to control groups. As determined by in situ hybridization, both osmotic stimulation and hypovolemia resulted in an increase in the number of AVT mRNA-containing neurons in the supra-optic and paraventricular nuclei. Our results indicate that, under the conditions used, hypotension and hyperosmolality are equally effective in stimulating AVT gene expression and secretion of AVT.

Hypothalamic obese, functionally castrated hens are hypersensitive to estrogenic modulation of lipid metabolism.

Estradiol benzoate (E2) increases plasma lipids in hypothalamic obese, functionally castrated (OFC), obese laying (OL), and control laying hens (CONT). However, E2 reduces fattiness in OFC but not in OL or CONT hens. Antiestrogen, such as tamoxifen (TAM), reduces plasma lipids in OL and CONT, but not in OFC, hens and has no effect on fattiness in any of them. Apolipoprotein VLDL-II (apo-VLDL-II), lipoprotein lipase (LPL), and rate of lipolysis may mediate these estrogenic effects. In the present study, effects of E2 and TAM on fattiness, plasma apo-VLDL-II, in vitro lipolysis, and LPL activity in postheparin plasma and abdominal adipose tissue (AAT) were determined in OFC, OL, and CONT hens. Basomedial hypothalamic lesions were performed in 3-month-old White Leghorn hens. At the static phase, 10 months later, OFC OL, and CONT hens were divided into three subgroups and injected IM on alternate days, with either 2 mg E2/kg b.wt., 10 mg TAM/kg, or vehicle corn oil, for 5 weeks. In OL and OFC hens, body and AAT weights were higher than in CONT poullets. Food intake and ovarian weight were similar in OL and CONT, higher than in OFC hens. Plasma LPL activity was higher, whereas plasma apo-VLDL-II and stimulated lipolysis were lower in OFC than in OL and CONT hens. In OFC hens LPL activity per unit of AAT was half than in OL and CONT. Total LPL activity in AAT was similar in OFC and CONT and higher in OL hens. Levels of basal lipolysis were similar in all experimental hens. TAM did not affect any of the measured parameters in OFC hens. In OL and CONT hens, TAM depressed apo-VLDL-II, increased plasma LPL activity, but had no effects on AAT LPL activity, on stimulated lipolysis, or fattiness. E2 increased apo-VLDL-II to similar levels in all groups and reduced LPL activity in plasma and AAT of obese hens. Only in OFC hens did E2 enhance basal and stimulate lipolysis and reduce FI and fattiness. We conclude that in adult laying hens, unlike in cockerels and juvenile hens, estrogen reduces lipid incorporation in fat depots by enhancing apo-VLDL-II production that reduces plasma and AAT LPL activity. This may increase lipoprotein available for incorporation into developing yolks. The lack of estrogen in OFC hens reduces circulating apo-VLDL-II and thus increases LPL activity and amount of fat depots.

Effects of estradiol and tamoxifen on feeding, fattiness, and some endocrine criteria in hypothalamic obese hens.

In White Leghorn hens, basomedial hypothalamic (BMH) lesions result in two syndromes: a) obese, functionally castrated (OFC) hens, in which both the ventromedial hypothalamic nucleus (VMH) and the mammillary nuclei are damaged and plasma estrogen is very low; and b) obese laying (OL) hens, which have normal levels of plasma estrogen and are less obese than the former, and whose lesion is limited to the VMH. In the present study, the involvement of estrogen in regulation of fattiness and energy metabolism was assayed in OFC, OL, and control (CONT) hens. BMH lesions were made at 13 weeks of age. When the typical syndromes reached the static phase, 20 weeks later, CONT, OFC, and OL hens were divided into three subgroups and were injected for 10 weeks on each alternate day, with either 10 mg tamoxifen (TAM)/kg, 2 mg estradiol benzoate (E2)/kg, or the vehicle, corn oil (0.5 ml). E2 raised plasma total lipids and reduced plasma glucose, insulin, and hematocrit in all treated hens, and increased liver weight in OL and OFC, but not in CONT hens. In OFC hens only, E2 reduced food intake (FI) and fattiness. In OL and CONT hens, E2 increased plasma T3, but raised the resting metabolic rate (RMR) only in CONT ones. In OFC hens, E2 reduce plasma T3 and T4 without affecting RMR. E2 reduced comb weight and egg production in CONT and more severely in OL hens. In the latter, E2 diminished ovarian and oviduct weights, whereas in OFC hens it increased the size of the atrophied oviduct. TAM had no visible effect on OFC hens.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of bilateral basomedial hypothalamic lesions on feeding, fattiness, and reproductive functions in the White Leghorn hen.

During the last three decades, syndromes caused by bilateral destruction of the basomedial hypothalamus (BMH) were extensively studied in cockerels but not in hens. In the present study bilateral electrolytic lesions in the BMH of White Leghorn (WL) hens produced two main sets of symptoms: (a) Obese, functionally castrated hen (OFC); and (b) Obese, laying hen (OL). Following the placement of the hypothalamic lesion, the OFC hens developed transient hyperphagia, that was followed by hypophagia. Weight gain was accelerated in both periods, and marked obesity developed. These hens had high hematocrit values, and atrophied ovary, oviduct, comb, and adenohypophysis. Plasma estrogen, and total lipids and liver weight were reduced in the OFC hens. In these hens, the lesioned area included the ventromedial hypothalamic nucleus (VMH), the mammillary nuclei, and in some birds also the arcuate nuclei, and the tuberal nucleus. The OL hens manifested transient hyperphagia that subsided into normophagia with the development of obesity. These hens were less obese than the OFC ones and showed normal reproductive traits. The lesioned area in the OL hens was limited to the VMH. Unlike functionally castrated cockerels, where the induced fattiness is accompanied with higher rate of lipogenesis, the OFC hen manifested a unique syndrome: increased fattiness with arrest in estrogen-dependent lipogenesis.

Tamoxifen advances puberty in the White Leghorn hen.

1. Tamoxifen (TAM) administration advances puberty in cockerels. In the present study the effect of TAM administration on the sexual development of White Leghorn hens was studied. 2. Two-week-old White Leghorn females were injected intramuscularly with TAM on alternate days at doses of 0.1 mg (0.1 TM), 1 mg (1TM), 5 mg (5TM) and 10 mg/kg body weight (10TM) respectively, while the controls were injected with maize oil (vehicle). The experiment was terminated at 23 weeks of age, when all the control hens laid eggs. Sample autopsies were made on chicks of 6, 14 and 23 weeks of age. 3. Body growth was not affected by any of the treatments. 4. Comb growth was accelerated by all doses of TAM, while hematocrit increased in the 1TM, 5TM and 10TM hens. 5. Egg laying advanced in the 0.1TM and 1TM birds, was delayed in 5TM hens and did not occur at all in the 10TM females. 6. TAM caused a precocious increase in plasma oestrogen and androgen, suppressed adiposity in a dose-related manner and, at low doses, advanced the development of the gonadal system. 7. At 23 weeks of age, when the gonadal system of the controls was fully active, TAM caused a dose-related depression in abdominal fat, liver, ovary, and oviduct weights, plasma total lipids and calcium concentrations and a dose-related increase in plasma oestrogen and androgen titres, and comb weight. 8. It seems that TAM increased gonadotropic activity and its androgen stimulating action, but suppressed peripheral signs of the elevated plasma oestrogen titres. Low doses of TAM enhanced gonadotropic activity and egg laying but the antioestrogenic effect depressed development of the gonadal system, suppressing egg production when high doses were administered. It therefore seems that oestrogens are necessary for normal ovarian development in hens.