Robert B. Chiasson

Endocrine effects of diencephalic lesions in the White Leghorn hen

Abstract Electrolytic coagulation of areas on the diencephalon of the adult White Leghorn hen has been made with the assistance of a Stellar stereotaxic instrument and an X-ray machine. Comb and wattle factors, egg-laying cycles, acidophil counts, adrenal corticoid concentration, and histological studies of the oviducts, adrenals, and thyroid glands have been recorded. Cessation of egg-laying was brought about by lesions in the nucleus paraventricularis, median eminence, and pars tuberalis. These lesions also reduced the size of the comb and wattles. Some of the lesioned birds exhibited an increase in acidophils, possibly due to the destruction of an area controlling “normal acidophil levels”. There did not appear to be any correlation between lesioned areas and corticoid titer of any of the birds 2 weeks following the operations. Hens with lesions in the nucleus supraopticus, preoptic division, showed a thyroid histological picture that indicated a reduction in activity of the gland.

The Dentition of the Alaskan Fur Seal

The dentitional characteristics of mammals have long been considered to be of the greatest phylogenetic significance. Not only have dental patterns been important in differentiating between species and genera but also in determining the relationships of orders. Perhaps even more important in this last regard has been the mode of development and growth of the teeth. The fact that mammalian teeth are heterodont is used as an important criterion in defining the class; and even the origin of this great systematic group has been determined primarily by the fact that mammals, like synapsid reptiles, have a thecodont dentition. It is evident, then, that drastic differences in dental patterns between one member and another of the same order of mammals must be explained if the ordinal designations involved are to survive close scrutiny. Certainly the dentition of fissipeds differs drastically from that of the pinnipeds. Any attempt to establish the relationships of these two groups must take these differences into account, and any attempt to include both categories within the limits of a single order must explain the inordinate degree of variability in a normally stable character. The following description and discussion of the dentition in the fur seal, Callorhinus ursinus , attempts to clarify the position of the Pinnipedia as well as the dentitional characteristics which they possess. Fur seal specimens for this study consisted of three subadults and two pups, embalmed or preserved in formalin. Forty female and nine male skulls were used which, in both sexes, ranged in age from newborn to 18-year-old adults. For comparative purposes, skulls of three Zalophus , one Otaria , and two Eumetopias were borrowed from the Chicago Natural History Museum. The right upper canine teeth of fifteen additional animals of known sex and age were available for sectioning. Sections were cut on …

Alterations in type I and type II protein kinases in the thyroid and adenohypophysis in response to a dietary goitrogen.

Abstract The goitrogen, propylthiouracil (PTU), when administered in the diet of white leghorn chickens resulted in a marked increase in weight of the thyroid gland within 7 days which was maximal (160% of control) within 14 days. This system was used to determine the alterations in cyclic AMP-dependent protein kinase activity ratios and to assess the amounts of type I and type II cyclic AMP-dependent protein kinases present in the thyroid as well as any changes related to hypertrophy and hyperplasia of the thyroid. There was a marked elevation in the cyclic AMP-dependent protein kinase activity ratio ( −cAMP +cAMP ) 7 days after initiation of treatment as well as an increase in the total amount of supernatant cyclic AMP-dependent protein kinase activity (+cAMP) which doubled within 14 days of dietary PTU. Both type I and type II cyclic AMP-dependent protein kinase activities were detectable in the thyroid and adenohypophysis. Type I comprised 10% and type II 90% of the total cyclic AMP-dependent protein kinase activity in both tissues. The total amount of type I protein kinase activity increased significantly by 7 days. By 14 days, both type I and II protein kinases were increased twofold. The amount of type I returned to a control value by 21 days whereas type II remained elevated. Adenohypophysial type II protein kinase activity decreased to 70% of control by 14 days. Cyclic AMP is known to exert its effect on trophic responses through the activation of cyclic AMP-dependent protein kinase. These data implicate both activation of the enzymes as well as increased amounts of types I and II protein kinase activity in the thyroid in response to goitrogen-induced hypertrophy and hyperplasia.

Effects of thyroid state on ornithine decarboxylase activity of the adenohypophysis of the rat and chicken

Abstract In White Leghorn chickens, 0.5 ng/kg of thyrotropin-releasing hormone (TRH) increased ornithine decarboxylase activity in the rostral lobe of the adenohypophysis without any alteration of enzyme activity in the caudal lobe. In rats, administration of TRH (250 ng/100 g body weight) increased thyroid-stimulating hormone (TSH) release but did not increase ornithine decarboxylase activity in the adenohypophysis. However, surgical thyroidectomy performed on rats resulted in declining levels of T3 and T4 in the plasma, an increase in the plasma level of TSH, and a twofold increase in ornithine decarboxylase activity in the adenohypophysis. In the chicken, administration of both methimazole and thyroxine caused elevated ornithine decarboxylase activity in the rostral and caudal lobes of the adenohypophysis. The hormone stimulation of ornithine decarboxylase activity, an early indicator of new biosynthesis, is suggested as a marker to study control mechanisms in the adenohypophysis.

In vitro regulation of chicken thyrotropes.

Abstract The results of morphological studies of the avian pituitary [ Mikami (1958) , J. Fac. Agr. Iwate Univ. , 3 , 473–545; Tixier-Vidal et al. (1967) , C. R. Acad. Sci. , 264 , 1739–1742, (1968) Z. Zellforsch. , 92 , 610–635] and of the avian pituitary portal system [ Vitums et al. (1964) , Z. Zellforsch. , 64 , 541–569; Sharp and Follett (1968) , J. Anat. , 104 , 227–232] suggest that releasing hormones from the rostral hypothalamus may be transported to the rostral pars distalis and those from the caudal hypothalamus to the caudal pars distalis . Physiological studies of the avian hypothalamus [ Egge and Chiasson (1963) , Gen. Comp. Endocrinol. , 3 , 346–361; Gehrmann (1967) PhD dissertation, The University of Arizona; Egge et al. (1975) , Poultry Sci. , 54 , 1628–1630] and of the avian pituitary [ Radke and Chiasson, (1974) , J. Endocrinol. , 60 , 187–188] suggest that TRH is produced in the rostral hypothalamus (and is therefore transported only to the rostral pars distalis ) but that TSH is produced in both lobes of the pars distalis . The present in vitro study was initiated to resolve this apparent conflict between these various studies and to determine the mechanisms controlling the hypothalamic-pituitary-thyroid axis of the chicken. Control incubated portions had a considerably higher content of TSH than did in vivo glands. This was interpreted to be due to the lack of thyroid hormone inhibition. Gland portions incubated with T 4 had a reduced amount of TSH in both portions. Glands incubated with TRH usually had a higher mean level of TSH in the rostral lobe but the caudal lobe was unchanged. It was concluded that thyrotropes responding to circulating levels of thyroid hormone were distributed throughout both lobes of the gland but thyrotropes responding to hypothalamic TRH were only in the rostral lobe.

Age-related changes in pituitary/thyroid function in chickens.

Pituitary cyclic AMP-dependent protein kinase (cAMP-PK) activity ratios are not increased in response to thyrotropin-releasing hormone (TRH) in old chickens (retired White Leghorn breeders). This reduced responsiveness may be due to reduced hypothalamic function, reduced thyrotrope function, or to a reduction in TRH membrane receptors. The thyroid cAMP-PK activity ratio of old males does not respond to TRH treatment but the thyroid of old females does have an increased activity ratio ater TRH injection. Both males and females have a much higher basal cAMP-PK activity ratio than young birds. This higher basal level is thought to be due to an increased thyroid-stimulating hormone (TSH) stimulation, and the failure of old males to increase activity after TRH injections may be due to a loss of the thyroids ability to respond to direct TRH stimulation.

The effect of propylthiouracil and temperature on avian thyroid activity

Abstract High ambient temperatures cause a reduction in thyroid gland size of chickens but propylthiouracil (PTU) treatment produces an increase in gland size regardless of temperature. This increase in size after PTU treatment during high temperature is evident after 7 days of PTU treatment but not after 14 days of treatment. Cyclic AMP-dependent protein kinase is activated in the thyroid gland with PTU treatment during high temperatures with no alteration in activity in the pituitary. These results suggest that the pituitary is not activated by TRH during periods of high ambient temperature and the thyrotrophs may release TSH in direct response to lowered serum thyroid levels produced by PTU treatment.

Thyroid stimulating hormone distribution in the pars distalis of the Japanese quail

Abstract Delta Cells have been proposed as the TSH secreting cells of the quail pars distalis ( Tixier-Vidal et al. , 1968 ; Mikami, 1958 ) and these cells are equally distributed throughout the gland. The present study is an assay of the TSH content of the rostral and caudal lobes of the quail pars distalis. The rostral lobe contains the predominant amount of TSH and assays of the caudal lobe were erratic in revealing a very minor amount or no TSH in this portion.

The effects of castration and/or methimazole feeding on the pituitary response to temperature extremes by cockerels ☆

The pituitary of goitrogen-treated White Leghorn cockerels is smaller in size than control birds and the pituitaries of castrated cockerels is nearly twice the size of control birds. The pituitary cells generated by these treatments may not be functional thyrotrophs or gonadotrophs and may not be able to respond to their usual stimuli. Low ambient temperature is a well-known stimulus to the thyroid gland acting through pituitary TSH. Cyclic-AMP-dependent protein kinase activity levels are used here as an index of cellular activity in the pituitary and thyroid glands. Castrated cockerels with or without methimazole treatment do not have an increased pituitary cAMP-dependent protein kinase activity in cold. Methimazole-treated birds have an exaggerated pituitary protein kinase response to cold stress when compared with controls. Pituitary cAMP-dependent protein kinase activity is paralleled by a similar activity increase in the thyroid gland of methimazole-treated cockerels and no increase in the thyroid of castrated birds. Castrated birds at all temperatures have an elevated thyroid cAMP-dependent protein kinase activity ratio which is interpreted as the result of removal of testosterone inhibition.

CYCLIC AMP-DEPENDENT PROTEIN KINASE ACTIVITY IN THE AVIAN PITUITARY AND THYROID GLANDS FOLLOWING GOITROGEN TREATMENTS

Publisher Summary This chapter discusses the cyclic AMP (cAMP)-dependent protein kinase activity in the avian pituitary and thyroid glands following goitrogen treatments. Thyroid gland functions are initiated by the pituitary glycoprotein hormone, thyrotropin that binds to specific receptor sites on the thyroid follicular cell surface. The effects of cyclic AMP in turn are thought to be mediated by the activation of a cyclic AMP-dependent protein kinase and a subsequent specific protein phosphorylation. Cyclic AMP-dependent protein kinase activation has been implicated in the mediation of the action of TSH on thyroid function. The acute exposure of bovine thyroid slices to TSH results in the rapid activation of cyclic AMP-dependent protein kinase which is correlated with an elevation in cyclic AMP. An increase in cAMP-dependent protein kinase activity in the thyroid of a rat following goitrogen treatment is reported. The decrease in pituitary type II protein kinase in the chicken may reflect atrophy of some cells as has been reported for the rat following thyroidectomy. It is demonstrated that the specific activity of both types I and II protein kinase decrease to 60% of controls in the rat thyroid 2 weeks after hypophysectomy.