Rat brain: effects of environmental enrichment on wet and dry weights.

Wet weight of rat cerebral cortex was increased by exposure to an enriched environment, as compared with standard colony or impoverished conditions. Dry weights and wet weights were compared and both yielded identical percentage differences between brains of animals experiencing enrichment and those experiencing impoverishment.

Environmental influences on serotonin and cyclic nucleotides in rat cerebral cortex.

The response to different environmental conditions and negative air ions was investigated on cerebral cortical serotonin and cyclic nucleotides. The results indicated that negative air ions alter the weight of the cerebral cortex and that concentrations of serotonin and cyclic nucleotides can be altered both by different environments and by negative air ions. The data stress the importance of the role of the environment when studying the structure and chemistry of the cerebral cortex.

Effects of methyltestosterone on insulin secretion and sensitivity in women.

The frequent coexistence of hyperandrogenism and insulin resistance is well established; however, whether a cause and effect relationship exists remains to be established. In this study we tested the hypothesis that short-term androgen administered to women would induce insulin resistance. To test this hypothesis, regularly menstruating, nonobese women were studied before and during methyltestosterone administration (5 mg tid for 10-12 days) by the hyperglycemic (n=8) and euglycemic, hyperinsulinemic (n=7) clamp techniques. Short-term methyltestosterone administration had no significant effects on the fasting levels of glucose, insulin, c-peptide, glucagon, or glucose turnover. During the hyperglycemic clamp studies, the mean glucose level during the final hour was 203+/-2 and 201+/-1 mg/dL in the methyltestosterone and control studies, respectively. The insulin response to this hyperglycemic challenge was slightly but not significantly greater during methyltestosterone treatment (first phase 59+/-8 vs. 50+/-8 microU/mL in controls; second phase 74+/-9 vs. 67+/-9 microU/mL in controls; total insulin response 133+/-16 vs. 117+/-15 microU/mL in controls). In spite of this, glucose uptake was reduced from the control study value of 10.96+/-1.11 to 7.3+/-0.70 mg/kg/min by methyltestosterone (P < 0.05). The ratio of glucose uptake per unit of insulin was also significantly reduced from a control study value of 14.3+/-1.4 to 9.4+/-1.3 mg/kg/min per microU/mL x 100 during methyltestosterone administration. In the euglycemic hyperinsulinemic clamp studies, insulin was infused at rates of 0.25 and 1.0 mU/kg/min to achieve insulin levels of approximately 25 and 68 microU/mL, respectively. During low-dose insulin infusion, rates of endogenous hepatic glucose production were equivalently suppressed from basal values of 2.37+/-0.29 and 2.40+/-0.27 mg/kg/min to 0.88+/-0.25 and 0.77+/-0.26 mg/kg/min in the methyltestesterone and control studies respectively. Whole body glucose uptake during low-dose insulin infusion was minimally affected. During the high-dose insulin infusion, endogenous hepatic glucose production was nearly totally suppressed in both groups. However, whole body glucose uptake was reduced from the control value of 6.11+/-0.49 mg/kg/min to 4.93+/-0.44 mg/kg/min during methyltestosterone administration (P < 0.05). Our data demonstrate that androgen excess leads to the development of insulin resistance during both hyperglycemic and euglycemic hyperinsulinemia. These findings provide direct evidence for a relationship between hyperandrogenemia and insulin resistance, and its associated risk factors for cardiovascular disease.

A comparison of dendritic spine number and type on pyramidal neurons of the visual cortex of old adult rats from social or isolated environments.

The present study determined the effect of the housing condition experienced by old adult male rats on the appearance and number of dendritic spines. Specifically, 20-month-old rats were killed following 6 months of living in either a social environment (three to a cage) or living alone. The total number of dendritic spines per unit length was examined along segments of oblique, basal, and apical dendritic branches of pyramidal cells from layers II, III, Va, and Vb of the visual cortex. In addition to determining the total spine number, the spines were differentiated into two topographical categories: those with a lollipop configuration (type L) and those with a nubbin configuration (type N). Our results show that neither the total spine density nor the type L spine density were generally influenced by the two housing conditions. However, the density of type N spines was almost always greater on neurons from rats which had been living alone irrespective of the cortical layer or the dendritic segment counted. Some differences in total spine density and type L spine density were noted when neurons from the same environment but different cortical layers were compared, and these findings are discussed. However, the major focus of this paper was to extend our previous report of a selective increase in type N spines with age. We now show that in addition to increasing with age, type N spine density is also selectively increased by the condition of social deprivation.

Hormonal effects on the development or cerebral lateralization.

The morphology of cerebral cortical laterality patterns differs between the sexes. In the male Long-Evans rat, the thickness of the cerebral cortex is, in general, greater on the right side than on the left, with many areas showing statistically significant differences. In the female Long-Evans rat, the left side is thicker more often than the right, but the differences, in general, are not statistically significant. These laterality patterns are maintained throughout the lifetime of the animal with few variations. Some of the male and female laterality patterns reverse with old age. The numbers of neurons and glial cells in the area sampled, area 39, support the direction of cortical thickness measurements in male and female rats. Removal of the testes or ovaries at birth alters the usual cortical laterality patterns, illustrating that the sex steroid hormones play some role in determining laterality. In the neonates of both sexes, estrogen receptors are found in the cerebral cortex, but the concentration is greater in the left male cortex than in the right, the opposite being true for the female. Factors other than the sex steroid hormones, such as stress, can alter cortical laterality. Many studies indicate that plasticity of laterality is a factor to be considered when dealing with cortical morphology and, in turn, behavior.

Mental stimulation increases circulating CD4-positive T lymphocytes: a preliminary study.

To stimulate the dorsolateral frontal cortex, 12 healthy, adult, human females played contract bridge for 1.5 h between initial and final blood sample collections. Flow cytometric analyses of samples, performed in triplicate, showed a significant increase in CD4-positive T lymphocytes. The dorsolateral frontal cortical thickness is significantly and bilaterally reduced in immune-incompetent female, nude mice. Thymic transplants reverse the deficient cortical thickness and CD4-positive cell numbers.

Gender influences counterregulatory hormone responses to hypoglycemia.

It has been generally assumed that counterregulatory hormone responses to hypoglycemia are not influenced by gender. To test this assumption, we analyzed three separate hypoglycemic insulin clamp studies in age-matched, healthy, non-obese females (n = 33) and males (n = 37). In one study (12 females, 17 males), plasma glucose level was rapidly decreased to about 57 mg/dL for 100 minutes with a 0.65-mU/kg/min insulin infusion. Despite an identical decrease in glucose level, the increase in epinephrine (361 +/- 64 v 188 +/- 38 pg/mL, P < .05), norepinephrine (132 +/- 28 v 47 +/- 19 pg/mL, P < .01), and growth hormone ([GH] 16.0 +/- 3.8 v 4.9 +/- 1.9 ng/mL, P < .05) levels, but not glucagon or cortisol levels, were significantly greater in males than in females, respectively. In the second study (10 females, eight males), a 5.0-mU/kg/min insulin infusion was used to decrease glucose levels to 55 mg/dL for 180 minutes. Epinephrine (P < .05) and GH (P < .01) responses were greater in males than in females. In a third study (11 females, 12 males), plasma glucose level was gradually decreased to about 50 mg/dL over 240 minutes. Again epinephrine (P < .01), norepinephrine (P < .01), GH (P < .05), and cortisol (P < .01) responses were nearly twofold greater in males (P < .01). Multivariate analysis of all 70 subjects identified gender as the most significant factor contributing to the epinephrine (P < .001) and norepinephrine (P < .005) responses, and also as a significant contributor to the GH response (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Sex differences in the rat forebrain.

In the first postnatal month, the thickness of the cerebral cortex has different patterns of development in the male and female Long-Evans rat. All areas of the male cortex appear to develop at similar rates, very rapidly for the first 10 days, then more gradually reaching a peak somewhere between 30 and 40 days of age before beginning to decrease in thickness. The same is not true for the female; for example, at birth her medial frontal cortex is further developed than her lateral posterior parietal cortex and the rate of growth in the first weeks varies immensely. The male right cortex is thicker than the left from birth to 904 days of age, but the differences become less significant with age. The female cortex is thicker on the left side in the majority of the cases, from 7 to 400 days of age, but the differences are not in general statistically significant. Estrogen receptors are found in both male and female rat cerebral cortices at birth and apparently disappear after one month. In the male the greatest concentration of receptors is in the left cortex, and in the female, in the right. The number of neurons and glia per unit area is greater in the right cortex (area 39) in the male; and in the female, in the left cortex. Ninety days after ovariectomy at birth, the female right cortex is thicker than her left, establishing a pattern similar to that of the male. In the male gonadectomized at birth, the left cortex is thicker 90 days later in the frontal and somatosensory regions but not in the occipital or posterior region.(ABSTRACT TRUNCATED AT 250 WORDS)

Thymus graft reverses morphological deficits in dorsolateral frontal cortex of congenitally athymic nude mice.

The present investigation offers a basis for demonstrating that the cerebral cortex can be directly accessed through the immune system. This project was undertaken to provide a necessary step in confirming that the localized, deficient area of the cerebral cortex in the congenitally athymic nude mouse is related to the thymus, a gland necessary for the development of T-cells and the regulation of the neuro-endocrine system. We report that thymus engraftment, confirmed by reconstitution of CD4 and CD8 T-cells, in 30-day-old congenitally athymic female mice reverses deficiencies in the frontal cortex by day 60. A concomitant increase in serum prolactin was observed in thymic-grafted nude mice, suggesting a role by which prolactin may produce the morphological changes observed in the cerebral cortex.

A quantitative Golgi study in the occipital cortex of the pyramidal dendritic topology of old adult rats from social or isolated environments.

It has been previously established that the housing condition influences the appearance of the dendritic tree in young animals. The purpose of this investigation was to determine the extent of the influence that the housing condition exerts on morphometric studies involving old animals. Specifically, we found superficial pyramidal cells from the visual cortex of socially aged 20-month-old rats had more extensive oblique dendritic trees than neurons from isolated rats of the same age. The basal dendritic tree of neurons from socially reared rats was denser nearest layer IV while the basal dendritic tree of neurons from isolated rats appeared to shift away from layer IV. Our results indicate that the external environment is an independent variable and cortical dendritic morphology is a dependent variable in studies on old adult rats. Thus, the external environment should be considered in reporting results of aging studies on dendritic topology.