Kenneth J. Renner

Age and sex-dependent decreases in ChAT in basal forebrain nuclei

Microdissection techniques were utilized to measure the activity of choline acetyltransferase (ChAT) (enzyme responsible for synthesis of acetylcholine) in individual basal forebrain nuclei of aged (24 month) and young (4 month) male and female rats. Small but consistent decreases in the activity of ChAT in aged rats were found, and the location of the changes was dependent on the sex of the rat. Aged female rats showed approximately 30% lower ChAT and 40% lower acetylcholinesterase (AChE) activity in the ventral globus pallidus (vGP). Aged males did not show decreased ChAT in the vGP but activity in the medial aspect of the horizontal diagonal band nucleus was 50% lower than in the young males. ChAT activity in four other closely aligned basal forebrain nuclei was not different between the young and aged rats. Analysis of cell number, density and area in the vGP by AChE histochemistry showed no significant differences between aged and young females. In addition, age and sex-dependent changes were measured in pituitary glucose-6-phosphate dehydrogenase activity. The relationship of the changes to age-dependent decrements in memory, the possible influence of gonadal hormones on aging, and the mechanisms responsible for age-related declines in ChAT activity are discussed.

Determination of monoamines in brain nuclei by high performance liquid chromatography with electrochemical detection : Young vs. middle aged rats

A previously described high performance liquid chromatographic method for simultaneously measuring norepinephrine, dopamine, serotonin and 5-hydroxyindole acetic acid has been modified to permit analysis of the monoamines in microdissected brain nuclei from a single rat. Results of measurements in 12 nuclei of young and middle aged male rats are presented.

Intrahypothalamic 5,7-dihydroxytryptamine: temporal analysis of effects on 5-hydroxytryptamine content in brain nuclei and on facilitated lordosis behavior.

The long-term relationship between serotonin (5-HT) levels in discrete hypothalamic nuclei and female rat sexual behavior, the lordosis response, was examined following intrahypothalamic injection of 5,7-dihydroxytryptamine (5,7-DHT). One week following 5,7-DHT injection, 5-HT levels in the ventromedial hypothalamic nucleus, dorsomedial nucleus, anterior hypothalamic nucleus and the medial preoptic nucleus were approximately 90% depleted as compared to sham animals. Other hypothalamic and preoptic areas including the arcuate-median eminence, vertical nucleus of diagonal band and lateral septal nucleus showed smaller reductions in 5-HT, from 40 to 70% of sham values. At this time estrogen-dependent lordosis behavior in the lesioned group was facilitated. Behavioral facilitation was greatest at 4 weeks post lesion when depletion of 5-HT in the VMN was maximal. 5-HT levels increased at 57 days after 5,7-DHT treatment in most areas, and by 71 days post lesion, no significant differences in 5-HT levels were found between sham and 5,7-DHT-treated groups. Concomitant with the increases in 5-HT, facilitated lordosis behavior gradually decreased. Loss of behavioral facilitation appeared to be most closely related to increases in content of 5-HT in the ventromedial nucleus. These results further support the hypothesis that 5-HT endings in the hypothalamus exert tonic inhibitory regulation over hormone-dependent lordosis in the female rat. They also indicate that regenerating 5-HT fibers in the hypothalamus can reinstate a normal pattern of hormone-dependent behavioral function.

Effect of progesterone on monoamine turnover in the brain of the estrogen-primed rat

The effect of progesterone (P) on monoamine levels and turnover was evaluated in 8 brain nuclei in estrogen-primed rats. Animals were subcutaneously (SC) injected with P or vehicle 21 hours after SC treatment with 5 micrograms of estradiol benzoate (EB). EB-primed animals treated with P showed high levels of lordosis behavior and an LH surge three hours later. Initial concentrations of norepinephrine (NE), dopamine (DA), serotonin (5HT) and 5-hydroxyindole acetic acid were determined in EB-saline treated controls 3 hours after P or vehicle. NE and DA turnover was estimated from the exponential decline of these amines 2 hours after IP injection of alpha-methyl-p-tyrosine (5 hours after P or vehicle). The accumulation of 5HT 20 min following IP injection of pargyline was used as an index of 5HT turnover. P did not affect the initial NE, 5HT or 5HIAA concentrations in any of the brain nuclei studied, but decreased DA content in the arcuate-median eminence region (Ar-ME). The DA rate constant was elevated in the nucleus of the diagonal band of Broca and the DA turnover rate was decreased in the Ar-ME. In the periventricular region (PVE, anterior hypothalamic level) the NE turnover rate (K, pg/microgram protein/hr) and rate constant (k, hr-1) decreased following P treatment. Progesterone treatment decreased the accumulation of 5HT in the ventromedial hypothalamus (VMN, pars lateralis) and the dorsal midbrain central grey (MCG). Progesterone effects on monoamine turnover were not found in the lateral septal, medial preoptic, anterior hypothalamic or dorsal raphe nuclei.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of temporal and dose-dependent effects of estrogen on monoamines in brain nuclei.

Levels of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) were measured in hypothalamic and limbic nuclei of ovariectomized rats after various doses of estradiol and at various intervals after estradiol administration. Of 13 areas examined, time- and dose-dependent effects of estrogen on monoamine content were restricted to only a few, discrete areas which concentrate estradiol. Subcutaneous administration of 1-50 micrograms of estradiol benzoate (EB) and measurement of monoamines 24 h later was associated with dose-dependent increases of NE in the medial preoptic nucleus, diagonal band nucleus and periventricular area of the anterior hypothalamus, and increased levels of DA in the periventricular area of the preoptic area. No changes were found in 5-HT levels, but dose-dependent increases in the level of the 5-HT metabolite, 5-hydroxyindole acetic acid (5-HIAA), were measured in the lateral portion of the ventromedial nucleus. Effects of 5 micrograms of EB were evaluated at 1.5, 6, 12 and 45 h after administration. No changes were noted at 1.5 h, but 5-HIAA in the ventromedial nucleus was elevated at 6 and 12 h. NE levels were elevated at 12 and 45 h in the diagonal band and preoptic nuclei and at 45 h in the lateral septum and periventricular area of the hypothalamus. DA levels decreased in the arcuate-median eminence area 45 h after estrogen. Intravenous administration of 10 micrograms of estrogen and measurement of monoamines 1 h later was not associated with altered levels of any monoamine suggesting that the estrogen-dependent changes are consistent with the genomic model for steroid hormone action.(ABSTRACT TRUNCATED AT 250 WORDS)

Monoamine levels and turnover in brain: relationship to priming actions of estrogen

Norepinephrine (NE), dopamine (DA) and serotonin (5HT) levels and turnover rates were studied in 8 discrete brain nuclei of ovariectomized rats 24 hours after the administration of 5 microgram of estradiol benzoate (EB) or sesame oil vehicle. This estrogen paradigm, by itself, did not induce sexual behavior or alter LH levels at the time these parameters were evaluated. However, combined with progesterone, the estrogen treatment was sufficient to generate an LH surge and induce sexual receptivity. Steady state concentrations of NE were significantly higher in the diagonal band of Broca (NDB) and the periventricular nucleus (PVE2; anterior hypothalamic level) following EB treatment. In addition, 5-hydroxyindole acetic acid (5HIAA) concentrations were elevated in the dorsal raphe of EB treated animals. Estrogen did not affect steady state concentrations of DA or 5HT in any of the brain nuclei studied. Turnover rates (K, pg/microgram protein/hr) and rate constants (k, hr-1) for NE were increased in the lateral septum (K, 140%; k, 120%), NDB (K, 160%; k, 130%) and the PVE2 (K, 140%; k, 70%) in EB treated animals. Estrogen decreased the rate constant for NE by 30% in the medial preoptic area. In contrast, DA and 5HT turnover rates were not significantly affected by estrogen. These results localize sites where estrogen induces changes in noradrenergic activity and suggest that these changes may be involved in the priming action of the steroid in inducing sexual behavior and/or gonadotropin secretion.

Naltrexone facilitation of sexual receptivity in the rat

Naltrexone hydrochloride (3mg/kg) facilitated sexual receptivity in ovariectomized female rats given estradiol benzoate 44 hr previously. The latency of naltrexone facilitation is 3 hr, which is similar to that by progesterone. Other doses of naltrexone (1 and 5 mg/kg) were ineffective. Unlike the effect of progesterone, the facilitation of behavior by naltrexone is not blocked by the protein synthesis inhibitor anisomycin. Naltrexone facilitation was blocked by pargyline, a monoamine oxidase inhibitor.

Corticosterone-dependent alterations in utilization of catecholamines in discrete areas of rat brain

This study investigated the impact of chronic adrenalectomy (ADX), and subsequent corticosterone (CORT) replacement to ADX rats, on brain levels of norepinephrine (NE) and dopamine (DA) and their extent of depletion after alpha-methyl-p-tyrosine (alpha-MpT) administration. Seven discrete hypothalamic areas, namely, the paraventricular nucleus (PVN), medial preoptic nucleus (POM), dorsomedial nucleus (DMN), ventromedial hypothalamus (VMH), perifornical lateral hypothalamus (PLH), supraoptic nucleus (SON), and arcuate nucleus/median eminence (ARC-ME), were examined. The steady-state content of NE and DA in all areas remained essentially unaltered 7 days after ablation of the adrenal glands, as well as after subsequent CORT replacement therapy in ADX rats. However, ADX, which reduced circulating CORT levels to 0.3 microgram % as compared to greater than 3.0 micrograms % in sham rats, caused a significant increase in the depletion of NE following alpha-MpT treatment, in 4 out of the 7 brain sites examined (PVN, PLH, DMN and ARC-ME). In these brain sites, the NE turnover rate (K, pg/microgram protein/h) and rate constant (K, h-1) increased following ADX. The chronic subcutaneous CORT implant (200 mg), which raised circulating CORT levels of ADX rats to 11 micrograms %, prevented this enhancement of NE turnover in the PVN, PLH and ARC-ME, but not the DMN. Unlike NE, DA utilization in the 7 discrete hypothalamic areas of alpha-MpT-treated rats remained unaltered after ablation of the adrenal glands, as well as after the CORT replacement therapy in ADX rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Pargyline-induced increase in serotonin levels : correlation with inhibition of lordosis in rats

The effect of intrahypothalamic infusion of the monoamine oxidase inhibitor pargyline on lordosis behavior and monamine levels in the preoptic area and hypothalamus was examined. Progesterone-facilitated lordosis was blocked by pargyline in half the treated rats. The inhibition of lordosis was correlated with increases in serotonin and dopamine levels in the ventromedial nucleus of the hypothalamus and serotonin levels in the arcuate nucleus-median eminence when compared to controls or pargyline-treated rats with high levels of lordosis responding. Changes in norepinephrine levels were not correlated with changes in behavior. The results provide further evidence for an inhibitory role of basomedial hypothalamic serotonin in the control of female sexual behavior.

Serotonin and 5-hydroxyindoleacetic acid levels in discrete hypothalamic areas of the rat brain: relation to circulating corticosterone

We examined the influence of adrenalectomy (ADX), and chronic corticosterone (CORT) replacement, on serotonin (5-HT) and 5-hydroxyindolacetic acid (5-HIAA) levels in discrete hypothalamic areas of the rat brain. A significant decrease in 5-HT (-25%) and 5-HIAA (-28%) content was observed in the paraventricular nucleus (PVN) 7 days following ADX. A similar decrease in 5-HT levels (-27%) was observed in the preoptic area (POM) following ADX. In contrast, 5-HT and 5-HIAA levels in the supraoptic nucleus (SON) were significantly elevated by 82% and 54%, respectively. Replacement therapy with subcutaneous CORT implants (200 mg) was effective in preventing these effects of ADX in some cases. These findings suggest that the pituitary-adrenal endocrine system may influence various physiological and behavioral functions via its action on serotonergic neurons within specific hypothalamic sites.