[Ultrastructure of the median eminence and posterior lobe of the hypophysis in newborn Diocrostonyx torquatus lemmings during a decline in the population count].

Electron microscopically using morphometric analysis, the median eminence and hypophysis posterior lobe have been studied in newborn lemmings (Dicrostonyx torquatus Pallas) at the stage of decreasing population. A comparative characteristics of capillaries in the primary plexus of the portal system and capillaries of the hypophysis posterior lobe is presented. Overtaking developmental rate is demonstrated in the posterior hypophyseal lobe in comparison to that of the median eminence. In the lemmings investigated level of differentiation of the neurohemal areas of the hypothalamus is lower than development of these areas in laboratory mice and rats, according to the literature data. Possible results of weak development of the hypothalamo-hypophyseal connections in newborn lemmings at the stage of decreasing population are discussed.