Effect of Aging on 24-Hour Changes in Serotonin and Dopamine Turnover, and Somatostatin and Amino Acid Content, of the Rat Hypothalamus and Pituitary Gland

The effect of aging on neurotransmitter and peptide content in the hypothalamichypophysial unit has commonly been analyzed at single time points in the 24-h cycle. Since significant changes in circadian rhythmicity occur during aging, this study aimed to examine 24-h rhythmicity in hypothalamic and pituitary serotonin (5HT) and dopamine (DA) turnover and content, and somatostatin and amino acid content in 2 months-old and 18-20 months-old rats, killed at 6 different time intervals throughout the light-dark cycle. Aged rats showed suppressed or disrupted 24-h rhythms of 5HT and DA turnover and of somatostatin, glutamate, aspartate and taurine content (anterior hypothalamus), of 5HT and DA turnover and of somatostatin, glutamate, taurine and glycine content (medial hypothalamus) and of DA turnover and amino acid content (posterior hypothalamus). Twenty-four h variations in DA, somatostatin, aspartate, GABA and glycine content of the anterior hypophysis and in all parameters tested in the neurointermediate lobe became suppressed or disrupted in aged rats. Mean values generally decreased with age, except for DA content in the anterior pituitary lobe and aspartate content in the neurointermediate lobe. Conclusions: Examination of neurotransmitter and neuropeptide content at different times of the day is needed to analyze the effects of aging in the hypothalamic-hypophysial unit.     

Genetic variation associated with chronic water and nutrient stress in pinyon pine

We examined how genotypic variation at the glycerate dehydrogenase (GLY) locus in pinyon pine might be affected by environmental stress and herbivory. We compared GLY allelic and genotypic frequencies among mature and juvenile trees growing in stressful cinder soil and adjacent sandy-loam soil. While no association was found with herbivory, three lines of evidence support the hypothesis that GLY slow homozygotes (SS) are selected for under conditions of environmental stress. 1) We found no differences at the GLY locus between juvenile and mature trees growing in sandy-loam soil. 2) However, in the stressful cinder soil we found a lower frequency of SS homozygotes in juvenile trees than in mature trees, suggesting that selection has occurred in one generation. 3) Using biomass as a measure of fitness, SS homozygotes were superior to other GLY genotypes in cinder soil. Two lines of evidence were inconsistent with the hypothesis of selection for SS homozygotes in stressful environments. 1) SS homozygote frequency between habitats was not significantly different, suggesting that too few generations have passed for differentiation to occur, and/or insufficient selection pressure. 2) The low frequency of SS homozygote juvenile trees growing in cinder soil suggests that counterbalancing selection may prevent SS homozygotes from increasing in the population.