The gonadotropin-producing and other cell types in the distal lobe of the pituitary of the common frog, Rana temporaria

Pituitaries of male Rana temporaria were fixed in Bouin-sublimate, sagittally sectioned at 4 μ, and stained with different trichrome methods, with PAS-orange G, Gabe's AF or Herlant's Alcian blue-PAS-orange G. Four chromophilic cell types have been described in the distal lobe of the pituitary, i.e. α-cells or acidophils, β-cells or amphiphils type I, γ-cells or amphiphils type II, and δ-cells or cyanophils. The same cell types were observed in sagittal sections of the pars distalis of Bufo bufo and Xenopus laevis. β-Cells were absent from the pituitaries of juvenile Rana temporaria. One and three years after castration hyperactivity was observed in the β-cells. Secretory activity of these cells was reduced after the administration of testosterone, and was stimulated in frogs which were kept at high temperatures during the hibernation period. Moreover, in two out of four frogs the γ-cells had increased in number three years after gonadectomy, and a correlation was found between the atrophy of the secondary sex characters and the regression of the γ-cells in frogs which were kept at high temperatures. It is inferred that the β-cells produce a gonadotropic hormone, probably FSH, and that the γ-cells may secrete ICSH

Nomenclature of the hormone-producing cells in the adenohypophysis : A report of the international committee for nomenclature of the adenohypophysis

The International Committee for Nomenclature of the Adenohypophysis calls attention to the necessity for improving the present chaotic situation in the nomenclature of the hormone-producing cells in the adenohypophysis. A full description of the cell types must be based upon both morphological and functional criteria, but there will be cases in which a morphological description is the only practical one. The Committee recommends a standard system of functional names for the cell types but is unable to recommend a standard system of morphological nomenclature. However, the Committee draws attention, to certain criteria that must be satisfied if morphological descriptions are to be satisfactorily reproducible

The pituitary of the African lungfish Protopterus sp.

In general structure, the distal lobe closely resembles that of an amphibian, whereas the elaborate intermingling of nervous and intermediate lobes recalls the typical fish condition. In cell types, the majority of the intermediate-lobe cells have the same reactions as in amphibians but there is in addition another cell type which appears to be unique. In the distal lobe there are three types of basophils and two of acidophils, in many respects resembling the same five cell types found in amphibians. Developmental stages help to explain the structure of the neural-intermediate complex

The African catfish, Clarias gariepinus, a model for the study of reproductive endocrinology in teleosts

In their natural habitat African catfish, Clarias gariepinus, show a discontinuous reproductive cycle. This cycle follows changes in the gonadotropic activity of the pituitary. Gonadotropin release has been shown to be under dual hypothalamic control, i.e. a gonadotropin-releasing hormone (GnRH) and a gonadotropin release-inhibiting factro (GRIF), which turned out to be dopamine. Gonadal sex hormones influence gonadotropin release by a negative feedback, and a model has been developed to explain their mode of action. Steroid formation has been studied in testes, seminal vesicles and ovaries and correlated with the annual reproductive cycle. Steroid glucuronides, originating from the seminal vesicle, act as male sex pheromones; ovulation seems to be synchronized by female pheromones. Techniques for the induction of ovulation were developed. Only broodfish, reared from eggs to maturity under favourable conditions, show a continuous reproductive cycle and can be induced to produce viable eggs throughout the year

Hypothalamo-hypophysial relations in amphibian larvae

The results of studies on the differentiation of the preoptic nucleus and of experiments regarding the effects of propylthiouracil and extirpation of the preoptic area demonstrate that in Xenopus laevis tadpoles a thyrotropin-releasing factor (TRF) is formed in peptidergic cells in the dorsal part of the preoptic nucleus. The differentiation of this nucleus depends on thyroid hormones, but at the same time these hormones inhibit the activity of the TRF cells. Young larvae of X. laevis acquire the ability to adapt themselves to a white background simultaneously with the appearance of aminergic neurosecretory centers in the caudal hypothalamus. During prometamorphosis these centers comprise a paraventricular organ (PVO), a nucleus infundibularis, fiber tracts to the telencephalon and to the pars intermedia of the adenohypophysis, and a nucleus in the caudalmost part of the dorsal tuber cinereum. The PVO consists of sensory nerve cells and cells secreting products into the cerebrospinal fluid; the infundibular nucleus contains numerous liquor-contacting neurons. The aminergic neurosecretory cells contain catecholamines such as dopamine. Depletion of these cells by reserpine leads to a dispersion of melanin granules in the skin melanophores. It is believed that among the functions of the aminergic neurosecretory centers is the production of a melanotropin-inhibiting factor. In the ventral tuber cinereum of X. laevis, neurosecretory cells are situated that are neither peptidergic nor aminergic. They are more active in adult animals than in tadpole

The regulation of gonadotropin release by neurohormones and gonadal steroids in the African catfish, Clarias gariepinus

The secretion of gonadotropic hormone (GTH) from the pituitary of teleosts is considered to be regulated by neuropeptides and neuroamines of cerebral origin and steroid hormones from the gonads. This paper reviews our studies concerning the control of GTH release in the African catfish, Clarias gariepinus. It was demonstrated that luteinizing hormone releasing hormone (LHRH) stimulates GTH release and that the gonadotropin release-inhibiting activity of dopamine is restricted to the LHRH-induced GTH release. With regard to the inhibitory action of steroid hormones on GTH release, a hypothesis was postulated which links together the inhibitory actions of dopamines and gonadal steroids. According to this hypothesis, only aromatizable androgens should feed back on the release of GTH and the effects of catecholestrogens and dopamine on GTH release should be comparable

Annual correlative changes in gonads and pituitary gonadotropes of feral African catfish, Clarias gariepinus

The reproductive cycle of male and female African catfish (Clarias gariepinus) can be divided into a breeding period (May–August), a resting period (September–February) and a period of full gametogenesis (March–April). The pituitary gonadotropin (GTH) content and the ultrastructure of the gonadotropes largely parallel the cyclical changes in the gonads. The main characteristics of the pituitary GTH cycle are a prespawning GTH surge and a postspawning regression of the gonadotropes. These phenomena are suppressed when African catfish are kept under favourable husbandry conditions. Under such circumstances the pituitary stores large amounts of GTH and shows a limited, continuous secretion of the hormone, sufficient for a sustained gametogenesis and gonadal steroid production, but not for spontaneous spawning. Under such adequate fish culture conditions, ovulation can be induced and healthy larvae obtained at any time of year

Estrogen-2-hydroxylase in the brain of the male African catfish, Clarias gariepinus

Estrogen-2-hydroxylase activity, involved in the biosynthesis of catecholestrogens, was localized in the brain of the male African catfish, Clarias gariepinus, by means of a radiometric assay using [2-3H]estradiol as substrate. Fore- and midbrain were divided in 18, 500-μm thick, transverse sections from which small defined areas were punched out and assayed. The estrogen-2-hydroxylase activity was calculated from the release of tritium during hydroxylation, and expressed in femtomole catecholestradiol · milligram−1 tissue · hour−1. The enzyme could be demonstrated throughout the brain. A high activity (>350 fmol) was observed in the telencephalon, in particularly the rostral part and the area ventralis pars dorsalis; in the diencephalon in the preoptic region, including the magnocellular part of the preoptic nucleus and the rostral part of the anterior periventricular nucleus; and in the area tuberalis, including the nucleus lateralis tuberis, the rostral part of the nucleus anterior tuberis, the caudal part of the nucleus posterior periventricularis, and in the nucleus recessus posterioris. Also a high activity was detected in the mesencephalic tectum opticum and the dorsolateral part of the torus semicircularis. The ventral mesencephalon showed a moderate (200–350 fmol) to low (<200 fmol) activity, whereas the lowest activity was found in the hindbrain (118 fmol). The significance of the biosynthesis of catecholestrogens in the brain is discussed in light of the negative feedback mechanism off gonadal steroids on gonadotropin release