Modification of dopamine and norepinephrine metabolism in the rat brain by monoamine oxidase inhibitors

Summary The treatment of Sprague-Dawley rats with monoamine oxidase (MAO) inhibitors (pargyline, tranylcypromine) profoundly affects dopamine (DA) and norepinephrine (NE) metabolism in the brain. In these rats injection of L-dopa led to large increases in norepinephrine (NE), normetanephrine (NMN) and 3-methoxytyramine (3-MT) in brain tissues. The response of MAO-inhibited rats to L-dopa contrasted sharply with those not treated with the MAO inhibitor; the latter showed no change in NE, NMN and 3-MT after similar administration of L-dopa. The increase of NE in pargyline-treated rats correlated closely with that of DA in the hypothalamus and in the brain stem. This response was greatly diminished in rats previously treated with the neurotoxin 6-hydroxydopamine, but was restored when the treatment with 6-hydroxydopamine was accompanied by desimipramine. This suggests that noradrenergic neurons were the origin of the NE response. The NMN and 3-MT increases occurring only in the rats treated with a MAO inhibitor were highly correlated. The results suggested that MAO inhibitor may affect entry of DA into catecholaminergic storage where NE synthesis takes place and from where DA is released.     

Oligodendrocyte progenitor proliferation and maturation is differentially regulated by male and female sex steroid hormones

Using primary cultures of oligodendrocyte progenitors isolated from male and female neonatal rodent brains, we observed more oligodendrocytes in female-derived compared to male-derived cultures. To determine whether the observed differences were due to a differential effect of sex hormones on proliferation, we treated cultures with increasing doses of 17beta-estradiol, testosterone or progesterone and labeled cells with bromodeoxyuridine to identify cells in S phase. Treatment with 17beta-estradiol, but not progesterone or testosterone, delayed the exit of oligodendrocyte progenitor cells from the cell cycle. In addition, 17beta-estradiol treatment enhanced membrane sheet formation, while progesterone increased cellular branching. Interestingly, the estrogen modulator tamoxifen mimicked the effect of 17beta-estradiol on cell cycle exit, but not on membrane formation. Immunocytochemical localization of estrogen receptors (ERs) showed ERbeta mainly localized to the cytoplasm of oligodendrocytes, suggesting that the effect of 17beta-estradiol on membrane formation could be mediated by interaction with this receptor. We conclude that sex steroids differentially regulate oligodendrocyte progenitor number and myelin formation, possibly contributing to gender-specific differences in repair.     

The effects of early life adversity on growth,maturation, and steroid hormones in male and female rats

Early life adversity is a risk factor for psychiatric disorders, yet the mechanisms by which adversity increases this risk are still being delineated. Here, we used a limited bedding and nesting (LBN) manipulation in rats that models a low resource environment to examine effects on growth, developmental milestones, and endocrine endpoints. In LBN, dams and pups, from pups’ postnatal days 2–9, are exposed to an environment where dams lack proper materials to build a nest. This manipulation is compared to control housing conditions, where rat dams have access to ample nesting materials and enrichment throughout pups’ development. We found that the LBN condition altered maternal care, increasing pup‐directed behaviors while reducing self‐care. This, perhaps compensatory, increase in nursing and attention to pups did not mitigate against changes in metabolism, as LBN reduced weight gain in both sexes and this effect persisted into adulthood. Although adult stress hormone levels in both sexes and vaginal opening and estrous cycle length in females were not disrupted, there was other evidence of endocrine dysregulation. Compared to controls, LBN rats of both sexes had shortened anogenital distances, indicating reduced androgen exposure. LBN males also had higher plasma estradiol levels in adulthood. This combination of results suggests that LBN causes a demasculinizing effect in males that could contribute to lasting changes in the brain and behavior. Importantly, alterations in metabolic and endocrine systems due to early life adversity could be one mechanism by which stress early in life increases risk for later disease.     

Brain microsomal metabolism of phencyclidine in male and female rats

These studies examined the microsomal brain metabolism of phencyclidine (PCP) in male and female Sprague–Dawley rats. Several monohydroxylated metabolites of PCP were detected including cis- and trans-1-(1-phenyl-4-hydroxycyclohexyl)piperidine (c-PPC and t-PPC) and 1-(1-phenylcyclohexyl)-4-hydroxypiperidine (PCHP). The in vitro formation of these metabolites required NADPH and was inhibited by carbon monoxide. c-PPC was formed in the male and female brain microsomes at rates of 7.1±1.3 and 5.7±1.1 fmol/min per mg, respectively, while t-PPC was formed at rates of 16.2±3.3 and 16.5±4.2 fmol/min per mg. PCHP had the highest formation rate at 50.7±8.9 and 48.2±8.8 fmol/min per mg, respectively. Although previous studies with rat liver microsomes find higher levels of PCP metabolism in male rats and the formation of an irreversibly bound metabolite in male rats, the present study of brain metabolism found no sex differences in brain metabolism. The formation of PCP metabolites in male rat livers is at least partially mediated by the male-specific isozyme CYP2C11, and possibly CYP2D1. Nevertheless, the formation of the major brain metabolite, PCHP, was not inhibited by an anti-CYP2C11 or an anti-CYP2D6 antibody. However, PCHP formation was inhibited by drug inhibitors of CYP2D1-mediated metabolism, suggesting the involvement of a CYP2D isoform. These data indicate brain metabolism of PCP is significant, but unlike the liver it is not sexually dimorphic.     

Influence of cholecystokinin octapeptide sulfate ester on brain monoamine metabolism in rats

Summary The effects of intracerebroventricular administration of an 80 pmole dose of cholecystokinin octapeptide sulfate ester (CCK-8-SE) were tested on the dopamine (DA), norepinephrine (NE) and serotonin (5-HT) turnovers of the hypothalamus, mesencephalon, amygdala, septum, striatum and cerebral cortex in rats.CCK-8-SE in an 80 pmole dose decreased the DA turnovers of the hypothalamus, mesencephalon, amygdala and septum, while it increased that of the striatum. The NE turnovers were increased in the hypothalamus and amygdala, but decreased in the striatum. The 5-HT turnover decreased only in the hypothalamus.     

Chronic ingestion of uranyl nitrate perturbs acetylcholinesterase activity and monoamine metabolism in male rat brain

Recent animal studies have shown that uranium can reach the brain after chronic exposure. However, little information is available on the neurological effects of chronic long-term exposure to uranium. In the present study, the effects during 1.5, 6 and 9-month periods of chronic ingestion of uranyl nitrate (UN) in drinking water (40 mg of uranium per litre) on cholinergic acetylcholinesterase (AChE) activity and on dopaminergic and serotoninergic metabolisms were investigated in several areas of male Srague Dawley rat brains. Uranium brain accumulation and distribution was also investigated after 1.5 and 9 months. Both after 1.5, 6 and 9 months of exposure, AChE activity was unaffected in the striatum, hippocampus and frontal cortex. Nevertheless, AChE activity was transitionally perturbed in the cerebellum after 6 months of exposure. After 1.5 months of exposure, DA level increased in hypothalamus. After 6 months of exposure, a tiny but significant modification of the DAergic turnover ratio was detected in the frontal cortex. And after 9 months, UN produced a significant decrease in the 5HIAA level and the 5HTergic turn-over ratio in the frontal cortex and also a decrease in the DOPAC level and DAergic turn-over ratio in the striatum. Uranium brain accumulation was statistically significant in striatum after 1.5 months and in striatum, hippocampus and frontal cortex after 9 months of exposure. Although neurochemical changes did not always correlated with increased accumulation of uranium in specific areas, these results suggest that chronic ingestion of UN can cause chronic and progressive perturbations of physiological level of neurotransmitter systems. Considering previous reports on behavioural uranium-induced effects and the involvement of neurotransmitters in various behavioural processes, it would be crucial to determine whether these neurochemical disorders were accompanied by neurobehavioral deficits even at 40 mg of uranium per litre exposure.     

Gonadal morphology and sex hormones in male and female Wistar rats after long-term lamotrigine treatment

Drug-induced disturbances in reproductive hormones and gonadal morphology have been observed both in patients with epilepsy and in non-epileptic animals. Less is known about the influence of newer antiepileptic drugs including lamotrigine on reproduction. Lamotrigine is now increasingly used both in epilepsy and psychiatric disorders. Sixty-five Wistar rats were fed by gastric tube either 5 mg kg(-1) lamotrigine solution (males=15, females=20) or 0 (vehicle control, males=15, females=15) twice daily for 90 days. In males, no significant differences were found in body or testicular weight. Testicular atrophy was observed in one control animal and in two of the rats receiving lamotrigine. No morphological changes were seen in the other organs investigated (liver, kidney, pancreas, brain, lymphatic tissue, heart). None of the animals showed over-expression of p53. No significant differences were observed between the control rats and the male rats receiving lamotrigine regarding testosterone, FSH and LH. In females, no changes in ovarian morphology or alterations in other tissues were observed. Serum testosterone, FSH, LH, insulin and progesterone remained unchanged in the lamotrigine treated animals, while serum estrogen was significantly reduced.     

Effects of gonadal hormones and persistent pain on non-spatial working memory in male and female rats

There are indications of a modulatory role carried out by gonadal hormones and pain in cognitive functions. We have examined this issue in male and female rats by assessing the impact of gonadectomy and persistent pain on the object recognition test. Intact and gonadectomized male and female rats were exposed to an open field (15 min) in which three objects were placed (Trial 1); the same test was repeated 2 h later (Trial 2), after the replacement of a "familiar" object with a novel one. Three days later (Day 2), the same procedure was repeated (Trial 3 and 4 with 2 h in between) but half of the animals were exposed to formalin-injection immediately before Trial 3. The latency, frequency and duration of approaching the three objects were recorded in each trial and compared by sex, gonadectomy and formalin treatment. The results showed that gonadectomized males and females had lower levels of approach to all objects and less locomotor/exploratory activity than intact animals in all experimental trials; their behaviour was not affected by repetition of the test or by pain. On Day 1, intact males showed a higher level of approach to the novel object than females. In intact males, the 2 h delay between the first and second trial failed to induce any significant modification of exploration of the novel object with respect to the familiar one, while in intact females the novel object was approached much less than the familiar one. Similarly on Day 2, the novel object was approached for a longer time by intact males than by all the other groups. In conclusion, our data show that physiological levels of circulating gonadal hormones significantly affected the performance of male but not female rats when exposed to the object recognition test.     

Effects of chronic lithium treatment on brain monoamine metabolism and amphetamine-induced locomotor stimulation in rats

Summary The aim of the present study was to investigate how chronic lithium treatment affects brain monoamine metabolism and amphetamine-induced locomotor stimulation in rats. Chronic lithium treatment was found to increase the synthesis of brain 5-hydroxytryptamine, an effect which may be mediatedvia increased brain levels of tryptophan. The synthesis and release of dopamine were, on the other hand, found to be decreased. Finally, chronic lithium treatment was found to suppress amphetamine-induced locomotor stimulation, probably due to counteraction by lithium on amphetamine-induced release of catecholamines.     

Brain monoamine metabolism and behavior in portacaval-shunted rats

Animals with a portacaval shunt exhibit several biochemical abnormalities in plasma and brain similar to patients with portal-systemic encephalopathy, i.e., hyperammonemia, amino acid imbalance, and neurotransmitter disturbances. We investigated behavior and brain monoamine metabolism in operated, sham-operated, and nonoperated rats 1 day and 2, 4, and 6 weeks after operation. In order to quantitate the turnover in the brain indoleamine and catecholamine systems, 5-hydroxytryptophan (5-HTP) and dihydroxyphenylalanine were measured after decarboxylase inhibition with NSD 1015. The brains were dissected into five regions. All rats with the shunt had high plasma ammonia concentrations. Behavioral tests revealed a reduction in spontaneous locomotion 2, 4, and 6 weeks after portacaval shunt and reduced exploratory behavior compared with control rats. These changes coincided with profound alterations of the indoleaminergic system. As early as 1 day after surgery, rats with the shunt showed a marked increase in the accumulation of 5-HTP in all brain regions, indicating an enhanced tryptophan hydroxylase activity. The changes in indoleamine synthesis were most profound in the cortex and the midbrain. Only minor alterations of the catecholaminergic system could be detected. The alterations in behavior and indoleamine neurotransmitter metabolism may be pathophysiologically interrelated and may serve as the basis for experimental studies of portal-systemic encephalopathy.     

Lithium increases gastrointestinal tract weight of male or female rats but it increases body weight only in females

Lithium treatment of patients and laboratory animals causes increased body weight but no single organ or system has been found responsible. In the present work, we showed that lithium increased the weight of the female rat's gastrointestinal (GI) tract including its contents. The weight gain of the female rat GI tract was the same order of magnitude as the weight gain of the whole body of the females. All three parts of the GI tract (stomach, small intestine, colon) participated in the weight gain. Lithium treatment of male rats also increased GI tract weight, but lithium did not increase their overall body weight because of loss of weight at other sites.     

Effects of 8-OH-DPAT and NAN-190 on anxiety behavior,monoamine metabolism,and the level of sex hormones in female rats during the estrus cycle

In this study, we performed a comparative analysis of the effects of chronic administration of an agonist of 5-HT_1A receptors, 8-OH-DPAT, (0.05 mg/kg, subcutaneously) and an antagonist of 5-HT_1A receptors, NAN-190, (0.1 mg/kg, intraperitoneally) for 14 days on the anxiety behavior, monoamine metabolism in the hippocampus and amygdala, and the level of sex hormones in the blood of adult female rats during the estrus cycle. Anxiety behavior was tested in an elevated X-maze. The level of monoamines and their metabolites was evaluated using HPLC with an electrochemical detector; the content of sex hormones in the blood was measured using an enzyme immunoassay. We found that chronic administration of 8-OH-DPAT has an anxiolytic effect in rats in estrus and proestrus. After treatment with NAN-190, we found clear modulation of anxiety behavior that depended on the phase of the estrus cycle, an anxiolytic effect at a high level of endogenous estrogens and an anxiogenic effect at a low level of estrogens. The anxiolytic effect of 8-OH-DPAT in female rats was accompanied by its suppressive influence on the pituitary-ovarian and noradrenergic systems and by its activating effect on the dopaminergic system of the brain. In contrast, the behavioral effects of NAN-190 in female rats during key phases of the estrus cycle corresponded to its stimulating effect of the pituitary-ovarian system and the absence of any effect on the monoaminergic systems of the brain. These data suggest that the mechanisms of anxiety include tight interaction between the ovarian hormonal system and the serotonergic brain system.     

Progesterone treatment attenuates brain edema following contusion injury in male and female rats

To assess the effectiveness of progesterone as a treatment for edema following traumatic brain injury, male and female rats were injected with progesterone or the oil vehicle over a 3-day period following a cortical contusion injury. Oil-treated rats showed significant localized edema as measured by the wet weight/dry weight tissue punch technique. Progesterone-treated rats, both male and female, showed marked attenuation, or in some cases, absence of this post-injury edema. We conclude that progesterone shows promise as a treatment for edema following traumatic brain injury.     

Subcellular analysis of the accumulation of estrogen by the brain of male and female rats.

Three experiments were preformed to provide additional information on the interaction of estrogen with subcellular components of the brain of male and female rats. In experiment 1 tritiated estradiol was administered to adult gonadectomized male and female rats which were then sacrificed 15,60 or 120 min later. Hypothalamic, cortical and pituitary samples were taken and were separated into nuclear and cytosol fractions. For the hypothalamic tissue from females nuclear concentration of radioactivity increased throughout the 2 h period while for males nuclear concentration rose during the first h and then declined. There was a significant sex difference in hypothalamic nuclear concentration of estrogen, male levels being lower. For both sexes cytosol levels progressively declined. For cortical tissue, nuclear radioactivity levels were low and relatively constant for both sexes, while cytosol levels fell during the 2 h period. Pituitary tissue showed a pattern in both nuclear and cytosol fractions which resembled the hypothalamic pattern although absolute levels were higher in the nuclear fraction. In experiment 2 male and female rats were administered labeled and unlabeled estradiol concurrently and were sacrificed 60 and 120 min later. Radioactivity levels were reduced in hypothalamic and pituitarynuclei, but not in cortical nuclei in comparison with animals not administered unlabeled hormone. In experiment 3 males and females were administered tritiated estradiol and were sacrificed 2 h later. The brain of each animal was split longitudinally. One half of each hypothalamic and cortical sample was subjected to nuclear separation while the other half was digested in tissue solubilizer before radioactivity counting. The former procedure showed a substantially greater nuclear concentration of radioactivity for hypothalamic tissue from females than from males. The whole tissue analysis showed only a slight sex difference for hypothalamic tissue. Sex differences were small by either procedure for cortical tissue. It was concluded that the hypothalamus of both male and female rats contains a limited capacit nuclear binding system for estrogen, but that the system is quantitatively less effective in binding estrogen in males.     

Effects of prenatal stress on neuroactive steroid responses to acute stress in adult male and female rats

Acute swim stress results in the robust production of several neuroactive steroids, which act as mediators of the stress response. These steroids include glucocorticoids, and positive GABA_A receptor modulatory steroids such as allopregnanolone and tetrahydrocorticosterone (THDOC), which potentiate inhibitory GABA signalling, thereby playing a role in the negative control of the hypothalamic‐pituitary‐adrenal (HPA) axis. Prenatally stressed (PNS) offspring exhibit increased vulnerability to stress‐related disorders and frequently display exaggerated HPA axis responses to stressors during adulthood, which may be a result of reduced neuroactive steroid production and consequently inhibitory signalling. Here, we investigated whether exposure of rats to prenatal social stress from gestational day 16‐20 altered neuroactive steroid production under non‐stress conditions and in response to an acute stressor (swim stress) in adulthood. Using liquid chromatography‐mass spectrometry, nine neuroactive steroids were quantified (corticosterone, deoxycorticosterone [DOC], dihydrodeoxycorticosterone, THDOC, progesterone, dihydroprogesterone, allopregnanolone, pregnenolone, testosterone) in plasma and in five brain regions (frontal cortex, hypothalamus, amygdala, hippocampus, brainstem) of male and female control and PNS rats. There was no difference in the neuroactive steroid profile between control and PNS rats under basal conditions. The increase in circulating corticosterone induced by acute swim stress was similar in control and PNS offspring. However, greater stress‐induced corticosterone and DOC concentrations were observed in the brainstem of male PNS offspring, whereas DOC concentrations were lower in the hippocampus of PNS females compared to controls, following acute stress. Although PNS rats did not show deficits in allopregnanolone responses to acute stress, there were modest deficits in the production of THDOC in the brainstem, amygdala, and frontal cortex of PNS males and in the frontal cortex of PNS females. The data suggest that neuroactive steroid modulation of GABAergic signalling following stress exposure may be affected in a sex‐ and region‐specific manner in PNS offspring.     

Behavioral differences between male and female rats: effects of gonadal hormones on learning and memory

The organizational, activational and reorganizational effects of gonadal hormones have been extensively investigated with respect to sexual, aggressive and maternal behavior. It has thus been established that manipulations of gonadal hormones during critical periods in development functionally affect reproductive behavior. The effects of gonadal hormones on nonreproductive behavior are not immediately obvious because of the fact that the behavioral effects of gonadal hormones on learning and memory have been investigated in a large number of unrelated experimental procedures. The present paper provides an organized overview of these different experimental procedures, summarizes the most important findings and discusses some of the variables which determine the effects of manipulations in gonadal hormones on learning and memory in male and female rats.     

Nicotine treatment produces persistent increases in amphetamine-stimulated locomotor activity in periadolescent male but not female or adult male rats

Nicotine is a popular addictive drug used among the adolescent population, and it has long been questioned whether nicotine use in adolescence may lead to the use of other psychostimulant drugs. It is not fully understood, however, how nicotine alters behavior and brain neurochemistry in the adolescent age cohort and how this may affect subsequent illicit drug use. In the current study, periadolescent and adult male and female rats were treated with nicotine for 7 days. One day or 30 days after this treatment, the effects of amphetamine on locomotor activity were studied. Sensitization to nicotine occurred in periadolescent female and adult male and female rats, but not in periadolescent male rats over the course of the 7-day treatment period. On day 8 (1 day after treatment with nicotine ended) and on day 37 (30 days after treatment with nicotine ended), nicotine-pretreated periadolescent male rats were sensitized to the locomotor-activating effects of amphetamine. The response to amphetamine of periadolescent female and adult male and female rats was unchanged at either time point after nicotine pretreatment. Thus, adolescent males are more sensitive than adults or females to the stimulant effects of amphetamine after exposure to nicotine, and this effect is long-lasting. These data suggest that nicotine use during adolescence may carry a greater risk than during adulthood and that male adolescent smokers may be particularly vulnerable to the risk of stimulant abuse.     

Changes in monoamine neurotransmitter metabolism in brain ischemia measured by in vivo voltammetry

A preliminary work with in vivo voltammetry (IVV) in the ischemic brain had been performed by the authors in rats after cardiac arrest, which showed that the IVV system is useful to investigate ischemic brain. In the present report, IVV was applied to ischemic brain by 4-vessel occlusion in rat and changes in dopamine and serotonin metabolism were investigated by measuring peak 2 (3,4-dihydroxyphenylacetic acid, DOPAC) and peak 3 (5-hydroxyindoleacetic acid, 5-HIAA) in the striatum. The change of cerebral blood flow (CBF) were also assessed by a temperature-controlled thermoelectrical method in the striatum of the same model. The heights of peaks 2 and 3 were significantly increased to 600-900% and 200-300% respectively in the striatum during 30 minutes of 4-vessel occlusion. The increase of each peak was maximum at 10 minutes after occlusion. These changes may reflect that release of monoamine neurotransmitters is increased by the ischemia and outward transport of their metabolites are disturbed. On the other hand, after reperfusion by release of carotid occlusion, the heights of peaks 2 and 3 rapidly decreased below the control values, thereafter, peaks 2 and 3 gradually increased to over control values at 180-210 minutes after reperfusion. rCBF in the striatum decreased to almost 0 ml/100 g/min during 4-vessel occlusion ischemia and increased to over control values transiently for 30 minutes after reperfusion, followed by gradual decrease for about 240 minutes. Since monoamine neurotransmitters are known to have various effects on cerebral metabolism and CBF, their disorders may contribute to the change of CBF and the development of postischemic brain damage.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prolactin release induced by histamine in maturing male and female rats

Summary It has been previously shown that histamine (HA) increases PRL release in adult rats. The purpose of the present work was to determine the ontogeny of the HA-induced PRL response in male and female rats. Animals from day 1 to day 40 after birth were injected, under ether anesthesia, into the lateral brain ventricles with 9.0g HA (free base) per rat. Fifteen minutes later a sample of blood was taken from the jugular vein and plasma PRL levels were determined by RIA. Results obtained indicate that HA is able to induce increased PRL release in developing rats. Sex differences were observed. In male rats, the earliest PRL response was observed at day 10 whereas female rats showed clearcut responses at day 1. During development, males showed a quite regular pattern of responses but in female rats there were highly irregular; positive responses did present a 5-day periodicity. In general terms, the magnitude of the PRL responses in developing rats was lower than observed in adult rats. However, in 20-day old male and female rats and 40-day old female rats, a marked increase of PRL took place after the HA injection.A short communication of this study was presented at the V. Congress of the Sociedad Argentina de Endocrinología, Bariloche, Argentina.