The role of aromatization in testosterone supplementation: effects on cognition in older men.

OBJECTIVE: To determine the contribution of conversion of testosterone (T) to estradiol on cognitive processing in a population of healthy older men who received T supplementation. METHODS: Sixty healthy, community-dwelling volunteers aged 50 to 90 years completed a randomized, double-blind, placebo-controlled study. Participants were randomized to receive weekly IM injections of 100 mg T enanthate plus daily oral placebo pill (T group, n = 20), 100 mg testosterone enanthate plus 1 mg daily of anastrozole, an aromatase inhibitor (oral pill), to block the conversion of T to estradiol (AT group, n = 19), or saline injection and placebo pill (placebo group, n = 21) for 6 weeks. Cognitive evaluations using a battery of neuropsychological tests were conducted at baseline, week 3 and week 6 of treatment, and after 6 weeks of washout. RESULTS: Circulating total T was increased from baseline an average of 238% in the T and AT treatment groups. Estradiol increased an average of 81% in the T group and decreased 50% in the AT group during treatment. Significant improvements in spatial memory were evident in the AT and T treatment groups. However, only the group with elevated estradiol levels (T group) demonstrated significant verbal memory improvement. CONCLUSION: In healthy older men, improvement in verbal memory induced by testosterone administration depends on aromatization of testosterone to estradiol, whereas improvement in spatial memory occurs in the absence of increases in estradiol.

Galanin receptors in the hippocampus and entorhinal cortex of aged Fischer 344 male rats.

Galanin (GAL) has been proposed to be an inhibitory modulator of cholinergic memory pathways because it acts within the hippocampus to inhibit the release and antagonize the postsynaptic actions of acetylcholine. Here we have used: 1) slice binding and quantitative autoradiography to assess the density and occupancy of GAL receptors; and 2) in situ hybridization histochemistry to assess expression of the GALR1 receptor subtype in the ventral hippocampus of 3-month-old and 21-month-old Fischer 344 male rats. We detected a small but significant (p < or = 0.0003) age-related reduction in 125I-GAL binding-site density in the ventral hippocampus and entorhinal cortex under standard binding conditions. Post-hoc analysis indicated that this reduction with age persisted in the CA1 radiatum and entorhinal cortex following GTP-induced desaturation to unmask pre-existent GAL receptors occupied by endogenous ligand. It was not associated with a significant change in peak GALR1 gene expression in the hippocampus. Because a portion of GAL receptors in this region have been postulated to function as presynaptic auto-receptors on cholinergic fiber terminals, the reduction in GAL binding sites with age may be a consequence of age-related alterations in GAL receptor expression by basal forebrain cholinergic neurons which project to the ventral hippocampus.

Nerve growth factor induces galanin gene expression in the rat basal forebrain: implications for the treatment of cholinergic dysfunction.

Nerve growth factor (NGF) is a potential treatment for cholinergic dysfunction associated with Alzheimer's disease (AD). In rats, NGF activates gene expression of the acetylcholine synthetic enzyme choline acetyltransferase (ChAT) and prevents age- and lesion-induced degeneration of basal forebrain (BF) cholinergic neurons. Cholinergic neurons in the BF coexpress galanin (GAL), a neuropeptide that has been shown to impair performance on memory tasks possibly through the inhibition of cholinergic memory pathways. NGF up-regulates both ChAT and GAL gene expression in cultured pheochromocytoma cells; however, the effect of chronic in vivo NGF administration on GAL gene expression within the BF has not been studied. We used in situ hybridization and quantitative autoradiography to assess GAL and ChAT gene expression within the BF of adult male rats following chronic intracerebroventricular infusion of NGF or cytochrome c. We now report that, in addition to stimulating ChAT gene expression, NGF strongly up-regulated the GAL gene in the rat cholinergic BF. NGF had no effect on GAL gene expression in other noncholinergic forebrain regions. NGF induction of GAL gene expression in the BF was specific, because gene expression for another neuropeptide, neurotensin, present within noncholinergic BF neurons was unchanged. Our data provide the first evidence that in vivo NGF administration up-regulates GAL gene expression in the cholinergic BF. These results suggest that the concurrent induction of GAL in the BF could limit the ameliorating actions of NGF on cholinergic dysfunction.

Decreased hypothalamic-pituitary-adrenal axis sensitivity to cortisol feedback inhibition in human aging.

Aging-related reduction in the sensitivity of the hypothalamic-pituitary-adrenal (HPA) axis to glucocorticoid feedback inhibition has been demonstrated in rodents, but aging effects on glucocorticoid feedback inhibition in humans are unclear. This study assessed the influence of aging on the sensitivity of the human HPA axis to feedback inhibition induced by cortisol. Endogenous cortisol feedback inhibition was removed by treatment with metyrapone, which reduces cortisol synthesis by inhibiting 11 beta-hydroxylase. Feedback inhibition was then reintroduced by infusing exogenous cortisol. Sixteen young (26 +/- 1 years old) and 16 older (70 +/- 2 years old) subjects underwent three study conditions in random order. In the two cortisol infusion conditions, oral metyrapone treatment was followed by intravenous infusion of 0.03 mg/kg/h (83 nmol/kg/h) or 0.06 mg/kg/h (166 nmol/kg/h) cortisol for 150 min. Feedback sensitivity was estimated by the latency to and extent of decline of plasma ACTH concentration during and following the cortisol infusion. In a placebo condition, placebo tablets were substituted for metyrapone and normal saline infusion was substituted for cortisol. Blood samples were drawn twice prior to and at 15-min intervals for 4 h following the onset of the infusions, and plasma was assayed for 11-deoxycortisol, cortisol and ACTH. Plasma cortisol suppression and ACTH and 11-deoxycortisol elevations did not differ between age groups after metyrapone. Older subjects exhibited delayed and blunted ACTH responses to infused cortisol. Within older subjects, the ACTH response to the higher dose cortisol infusion was blunted in older women compared to older men. These data provide direct evidence for reduced responsiveness to glucocorticoid feedback inhibition in human aging.

Sex difference in coexpression by galanin neurons accounts for sexual dimorphism of vasopressin in the bed nucleus of the stria terminalis.

Vasopressin (VP) neurons in the bed nucleus of the stria terminalis (BNST) are steroid sensitive and sexually dimorphic. The number of VP messenger RNA (mRNA)-expressing neurons is larger in male than in female rats. This initial observation suggested that sexual dimorphism resulted from enhanced proliferation and/or survival of VP neurons after gonadal hormone exposure during the critical perinatal period. However, galanin (GAL) and VP mRNAs were recently reported to be coexpressed in the BNST of adult male rats, and GAL gene expression, unlike VP gene expression, is not sexually dimorphic. These findings are consistent with the hypothesis that the sex difference in VP cell number in the BNST results from a sex difference in the number of GAL neurons dedicated to express the VP gene. To test this hypothesis, double in situ hybridization histochemistry was performed for GAL and VP mRNAs in the BNST of adult male and female rats. For quantification, the posterior BNST was divided into its two anatomical regions: medial (BSTM) and lateral (BSTL) divisions. Extending previous results for the whole BNST, the number of GAL-expressing cells in either the BSTM or the BSTL was not sexually dimorphic. A significant sex difference was found in the number of GAL cells coexpressing VP in the BSTM (mean +/- SE, male, 124 +/- 8; female, 56 +/- 6; P < or = 0.0001), but not in the BSTL (male, 80 +/- 9; female, 83 +/- 15). Accordingly, the number of cells expressing GAL mRNA only was significantly lower (P < or = 0.002) in the BSTM of male (43 +/- 5) than in female (85 +/- 9) rats. Evidence is provided that the reduced incidence of coexpression of VP by GAL neurons in the BSTM of female rats may account for the reported sex difference in VP cell number in the entire BNST. The results suggest that gonadal hormones in the perinatal period may not influence the proliferation and/or survival of VP neurons in the BNST per se but influence, instead, the capacity of GAL neurons to synthesize VP.

Extra-hypothalamic vasopressin neurons coexpress galanin messenger RNA as shown by double in situ hybridization histochemistry.

Vasopressin (VP) neurons in the bed nucleus of the stria terminalis (BNST) and medial amygdala (AMe) exhibit sexual dimorphism and steroid dependency. VP neurons in the supraoptic nucleus and paraventricular nucleus have been shown to coexpress other transmitters including galanin (GAL). However, little is known about what other neurotransmitters may be colocalized with VP in the BNST and AMe. Here, we have used radio-labeled and digoxigenin-labeled cRNA probes to perform double in situ hybridization histochemistry for VP and GAL in the BNST and AMe of intact, adult male rats. We provide evidence that in the basal state, the majority of VP-synthesizing cells in the BNST and AMe of the adult male rat also express galanin mRNA. Likewise, the majority of GAL-expressing neurons in these regions also contain VP mRNA. These findings give further evidence for the similarity of the BNST and AMe and provide a rationale for studies investigating the role of GAL in functions involving extrahypothalamic VP pathways.

Testosterone reverses a senescent decline in extrahypothalamic vasopressin mRNA.

The biosynthetic activity of extra-hypothalamic vasopressin (VP) neurons in the bed nucleus of the stria terminalis (BNST) is regulated by gonadal steroids. These neurons have also been implicated in a number of behaviors that are impaired in aging. We previously reported that VP mRNA labelling in the BNST is decreased in senescent rats. We hypothesized that the age-related decrease in VP mRNA labelling is due to the decline in circulating testosterone (T) levels in aged animals. T or saline was administered peripherally for 1 month in physiologic or superphysiologic doses to 3 month old or 24 month old Fischer 344 male rats. In situ hybridization and quantitative autoradiography for VP mRNA in the BNST were performed using a 48-base 35S-labelled oligonucleotide probe. Administration of T completely reversed the decline in VP mRNA labelling in the aged animals. Superphysiologic T further increased VP gene expression in both age groups. These data are consistent with a previous report of T-induced increase in VP immunoreactive fiber density in other extrahypothalamic regions of the brain in aged rats. This study offers further evidence that alterations in the hormonal milieu may play an important role in modulating neuronal biosynthetic activity in senescence.

Acute psychosis, increased water ingestion, and inappropriate antidiuretic hormone secretion.

The authors describe three postmenopausal women with agitated psychotic depression, increased water ingestion, and electrolyte values consistent with the syndrome of inappropriate antidiuretic hormone (ADH) secretion. They hypothesize that this clinical triad represents a syndrome reflecting underlying dysfunction of the hypothalamus and limbic system of the brain. The diagnosis of inappropriate ADH in one of the patients was directly confirmed by a recently developed serum radioimmunoassay.