Pars Intermedia of the Hypophysis of Rats after Early-Postnatal Lesions of the Basal Hypothalamus: Quantitative and Qualitative Observations

Abstract

Lesions were made by electrical coagulation in the base of the hypothalamus of rats, 20 to 24 h after birth. Subsequent growth of the hypophysis was examined volumetrically and histologically on the 40th and 60th days after the operation, paying special attention to the pars intermedia. Growth retardation of the hypophysis was noticeable after 60 days in rats with lesions of the hypophysial stalk (groups 1 and 2) and the posterior portion of the median eminence (group 4), especially in animals in which the stalk was completely (group 1) or almost completely (group 2) transected. Notwithstanding the growth retardation of the hypophysis, the ratios of the volume of the pars anterior to that of the whole hypophysis in groups 1 and 2 were not significantly different from those in group 3 (animals with a lesion of the anterior portion of the median eminence), groups 4 and 5 (animals with a lesion in the hypothalamus elsewhere than the stalk and median eminence), and normal controls of the same age (group 6). In contrast to this, the ratio of the volume of the pars nervosa to the total gland in group 3, and more especially in groups 1 and 2, had considerably diminished, and that of the pars intermedia in groups 1 and 2 had markedly increased, after 60 days in comparison with those in groups 3, 4, 5, and 6. These results indicate that the pars intermedia of animals in groups 1 and 2 was hypertrophic compared with the pars anterior and pars nervosa. These volumetric data seem to correspond with the finding that neurosecretory material was not present in the pars nervosa in groups 1 and 2, but was abundant in groups 3, 4, 5, and 6. After 60 days, the pars intermedia of group 1 consisted chiefly of well-developed cells, as in normal adult rats. On electron microscopic examination, however, they were found to differ from normal mature cells in the following three points: (1) most of the secretory granules were vesicular with little or no opacity; (2) the endoplasmic reticulum frequently showed cisternae; (3) nerve terminals were not encountered at the surface of the glandular cells. The former two points suggest that these cells are functionally active, an observation that agrees with the results of volumetric findings. It is concluded from these data that, in the absence of hypothalamic control, the pars intermedia of the hypophysis in rats grows actively after birth, while the anterior hypophysis seems to be inactive and atrophic [unpublished].

Modifications of pars intermedia cells of ovariectomized rats by oestrogen and progesterone

“…These vesicles are observed 32 and 56 h after EB injection and 24 and 48 h after administration, following MSH release. Similar vesicles have also been observed in rat PI cell culture (Back et al 1982) and in PI of rats with hypothalamic lesions (Ooki et al 1973), conditions where the -MSH release was stimulated. In con¬ trast, the 'empty vesicles' are rarely seen in normal PI and in chronically ovariectomized rats in which the -MSH release is inhibited.…”

Effects of Hypothalamic Lesions and Drugs Interfering with Dopaminergic Transmission on Pituitary MSH Content of Rats

“…In contrast to H amori [1960], we did not observe cytological changes in the pars intermedia of lesioned rats. In addition, electronmicroscopical studies [Ooki et al, 1973] showed a normal appearance of pars intermedia cells 40-60 days after lesioning the mediobasal hypothalamus of infant rats. Thus, although elevated melanotropic activity has been reported in rat blood after destruction of the hypothalamo-hypophysial connection [Carrillo et al, 1973;Celis et al, 1973], there is no convincing morphological evidence for an endocrine hyperactivity of the pars intermedia.…”

The Mammalian Pars Intermedia: A Review of Its Structure and Function

“…With the elec¬ tron microscope, both neurosecretory-type fibres and fibres apparently devoid of the characteristic neurosecretory granules have been described coursing within the pars intermedia of the cat, rat, ferret, guinea-pig and rabbit (Bargmann & Knoop, 1960;Kurosumi et al 1961 ;Ziegler, 1963;Kobayashi, 1964Kobayashi, , 1965Howe & Maxwell, 1966, 1968Bargmann, Lindner & Andres, 1967;Wittkowski, 1967;Vincent & Kumar, 1968Vincent, 1969 ;Cameron & Foster, 1971). Nerve terminals, with and with¬ out neurosecretory granules, make contact with Type 1 pars intermedia cells (Kuro¬ sumi et al 1961;Ziegler, 1963;Green, 1964;Howe & Maxwell, 1966, 1968Vincent & Kumar, 1968Vincent, 1969;Ooki, Kotsu, Kinutani & Daikoku, 1973).…”

“…The nerve fibres enter the pars intermedia by way of the pituitary stalk and neural lobe (Hillarp & Jacobsohn, 1943;Fuxe, 1964;Vincent, 1969); they disappear after stalk section (Vincent, 1969;Ooki et al 1973). Although their origins have not yet been defined precisely, it is clear that most are axons arising from perikarya situated in the hypothalamus (see Hillarp & Jacobsohn, 1943;Green & Harris, 1947;Holmes, 1961;Fuxe, 1964, for references), in particular the para ventricular and supraoptic nuclei (Olivecrona, 1957; Olmos, Orias & Tomatis, 1967;Howe & Thody, 19696, c) and the periventricular nucleus (Nobin, Björklund & Stenevi, 1972).…”