The accumulation of 3H-testosterone and its metabolites in the brain of neonatal and prepubertal rats was measured following injections of the hormone in vivo, or after incubation of minced brain tissue with 3H-testosterone in tissue culture medium. Radioactivity associated with purified nuclei and various cytoplasmic fractions of brain tissue was determined in 2-5-day, 10-12-day, and 25-32-day-old animals. Comparisons of radioactive steroids, accumulated 2 h after s.c. injections of 3H-testosterone or 3H-estradiol, showed that testosterone (T) is accumulated to a lesser extent than estradiol (E), but the age-related patterns of uptake are similar for both steroids. A continuous decrease in radioactivity was observed in nuclear and cytoplasmic fractions from the brains of 2-, 4-, and 12-day-old animals that were given injections of 3H-testosterone in vivo. This age-related pattern of decreasing uptake of radioactivity was not observed when excised brain tissue was incubated with 3H-testosterone in tissue culture medium. Thus, it appears that the age-related responsiveness of neonatal rats to T may be due more to the fact that decreasing amounts of the hormone reach the brain in older animals than that an inherent difference exists in tissue susceptibility during this period. Most of the radioactivity accumulated in the brain was associated with cytoplasmic fractions. Less than 1% of the homogenate radioactivity accumulated in purified nuclei. This restricted uptake and the kinetics of 3H-testosterone nuclear accumulation suggest that a nuclear site of action of T and/or its metabolites exists in the neonatal rat brain.

Animals↗

PubMed1976

Cytoplasmic and nuclear metabolism of testosterone in the brains of neonatal and prepubertal rats.

The metabolism of testosterone (T) in neonatal rat brains was measured following in vivo and in vitro incubations with 3H-testosterone.Steroids associated with nuclear and cytoplasmic fractions of brain tissue from 4, 12, and 32-day-old male and female rats were identified. Although there are quantitative differences under different methods of incubation, in all cases more than 95% of the radioactivity was recovered and identified as T, or the 5alpha-reduced metabolities, DHT and 3alpha-androstanediol. Most of the metabolism of T occurred in the cytoplasm but 5alpha-reduced metabolities were also associated with purified nuclei. Reaction kinetics indicate that the metabolic sequence is T leads to DHT leads to 3alpha DIOL. DHT levels were similar in the cytoplasmic fractions from the neonates (4 and 12-day-old animals) and prepubertal animals (32-day-old animals), but 3alpha-androstanediol was significantly reduced in these fractions from prepubertal animals compared to those from neonates. Sex differences in the metabolism of T in the various subcellular fractions were not detectable.

Age Factors↗

PubMed1975

Spectral analysis of olfactory responses of adult spawning chum salmon (Oncorhynchus keta) to stream waters.

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Adaptation, Physiological↗

PubMed1975

Ultrastructure of pars nervosa and pars intermedia of the Lamprey, Lampetra tridentata.

The pars intermedia of the adult lamprey is separated by perivascular spaces and a capillary plexus from the pars nervosa. No penetration of nerve fibers into the pars intermedia was found. The pars nervosa, which constitutes the posterior wall of the infundibulum, consists of an ependymal layer and a fuchsinophilic fiber layer; the latter contains at least four different types of axonal endings. The pars intermedia is avascular and is composed of a small proportion of non-secretory cells and a large proportion of secretory cells. The secretory granules in the cells of the pars intermedia seem to be discharged toward the capillaries that separate the pars intermedia from the pars nervosa. Although no direct nervous or vascular connections were found between the pars nervosa and pars intermedia, a mechanism of control of secretory activity in the pars intermedia cells by the central nervous system appears likely.

Animals↗

PubMed1975