M.L. Leret

Neurochemical changes in newborn rat’s brain after gestational cadmium and lead exposure

Gestational administration of cadmium (10 mg/l) and lead (300 mg/l) produced a strong decrease in proteins at birth (-17%) and on day 5 (-31%) as well as in brain lipid amount on both days (-11 and -23%, respectively). At day 5 postnatal the exposure also produced a marked decrease in DNA and RNA concentrations with respect to the control group. On the other hand, we found a significant increase of indoleamine content in all brain areas studied in the cadmium-lead group and so the dopamine and its metabolite in mesencephalon, whereas dopamine levels in metencephalon decreased significantly. This data suggests that gestational and early lactational exposure to low dose of cadmium and lead could produce alterations in monoaminergic metabolism that can place the exposed animal to a significant risk in adulthood.

The effect of perinatal exposure to estrogens on the sexually dimorphic response to novelty

In this study we investigated the sexually dimorphic anxiety response to a novel environment in the absence of estrogens neonatally or in adulthood. There was a sexual dimorphism in the plus-maze test after the open-field test, females being more active and less anxious. In the absence of estrogens neonatally but not in the adulthood, the activity levels were similar to those shown by females, while the anxiety level was similar to males. These results suggest the need of a normal estrogen environment during the critical period of development for the normal differentiation of female anxiety responses to a novel environment.

Distribution of indoleamines and [3H]paroxetine binding in rat brain regions following acute or perinatal Δ9-tetrahydrocannabinol treatments

The effects of Δ9-tetrahydrocannabinol (Δ9-tetrahydrocannabinol-THC) administration on the central serotoninergic system were evaluated by biochemical assays of tissue levels of indoleamines; a measure of the serotonin (5-HT) innervation was obtained by using [3H]paroxetine as a maker of 5-HT uptake sites. Two different Δ9-THC treatments were chosen, i.e: acute and chronic perinatal maternal exposure. Following acute treatment (5mg/kg), the 5-HT content increased in dorsal hippocampus (+35%), Substantia nigra (+61%) and neostriatum (+62%) but remained unchanged in cingulate cortex, Raphe nuclei, Locus coeruleus and anterior hypothalamus. Endogenous 5-hydroxyindole-3-acetic acid (5-HIAA) decreased in anterior hypothalamus (−23%) and Raphe nuclei (−21%). Following maternal exposure to Δ9-THC (5 mg/kg per day; from gestational day 13 to postnatal day 7), levels of 5-HT were increased in the neostriatum (+22%) but decreased in anterior hypothalamus (−25%), Raphe nuclei (−29%) and Locus coeruleus (−20%) of the litters. Tissue 5-HIAA was increased in anterior hypothalamus (+23%) and Substantia nigra (+48%). There were no changes in 5-HT uptake site density, determined by [3H]paroxetine binding, except for an increase (+50%) in the cingulate cortex of perinatal-treated rats when compared to acutely-treated animals. The present results show that acute and maternal exposure to Δ9-THC produced different effects on the central 5-HT system of the offspring, with a clear regional especifity, but with no changes in the densities of 5-HT uptake sites.

Effect of Δ9-tetrahydrocannabinol on short-term memory in the rat

Abstract We have reported that marihuana and its principal psycoactive compound, Δ 9 -tetrahydrocannabinol ( Δ 9 -THC) produce alterations in several cerebral areas after acute treatment. Based on the involvement of 5-hydroxytryptamine (5-HT) on memory and learning and the reported effects of Δ 9 -THC on short-term memory, we designed an experiment to evaluate the memory performance and its possible relationship with serotonergic alterations after Δ 9 -THC administration. Male Wistar rats received an acute oral dose of THC (5 mg/kg). Short-Term memory was tested on a radial 8-arm maze with a 5 s delay, after 35 days of trainning. The animals were food deprived and adjusted for growth. 5-HT and its metabolite, 5-HIAA, levels were measured in cerebral cortex, dorsal hippocampus, ventral hippocampus, rostral neoestriatum and amygdala basal nucleus, by HPLC-ED. The experiment indicates an impairment of short-term memory in the radial maze test after Δ 9 -THC administration. The control group performed the test without errors, while the treated group made a significant number of errors (Z = 0.019, Mann-Whitney test). This behavioral effect did not seem to be related to serotonergic alterations, as the 5-HT turnover rate was not different between treated and control animals.

Gestational administration of cadmium alters the neurotransmitter levels in newborn rat brains.

The effects of gestational and early lactational intoxication by cadmium (Cd) were studied in the brain of young Wistar rats. Pregnant rats were exposed to 10 mg of cadmium acetate per litre of drinking water, from initiation of pregnancy to parturition or until postnatal day 5. At birth or on postnatal day (PND) 5 the pups were weighed, sacrificed and brains were removed and frozen for later study. Protein, lipid and nucleic acid contents were measured and the brain Cd concentration was determined. Levels of dopamine (DA), 5‐hydroxytryptamine (5‐HT) and their respective metabolites 3,4‐dihydroxyphenylacetic acid (DOPAC) and 5‐hydroxyindoleacetic acid (5‐HIAA) were measured in neonatal pup brain by higher performance liquid chromatography with electrochemical detection. The results from this experiment showed that Cd increased the 5‐HT and 5‐HIAA contents in all areas of the brain and the DA and DOPAC levels in mesencephalon, but decreased the DA and DOPAC levels in the metencephalon. On the other hand, Cd intoxication did not modify the other biochemical parameters measured, with the exception of a decrease in nucleic acids on PND 5.

The influence of testosterone in the brain of the male rat on levels of serotonin (5-HT) and hydroxyindole-acetic acid (5-HIAA)

There were two groups of rats: one was injected with testosterone propionate (10 mg/kg) every 7 days starting from weaning (23 days old); the other group had gonadectomy on the same day. The levels of 5-HT and 5-HIAA were measured by spectrofluorometry. The concentrations of 5-HT in the diencephalon of the testosterone propionate injected rats decreased significantly at 45 days, tending to become reestablished at 60 days; the rest of the brain followed the same pattern, but was less pronounced. The concentrations of 5-HIAA in the diencephalon and the rest of the brain decrease throughout postnatal development, although the differences are not significant. The castrated rats showed a marked increase at 45 days and later decreased at 60 days without recovering their initial values, in both brain areas. 5-HIAA concentrations were similar to those found in the injected animals. These facts can have various interpretations: early modifications in the brain, feed-back regulation mechanisms at the level of the hypothalamus, decrease in the release of the amine or reduction of its catabolism.

Study of the neurochemical alterations produced in discrete brain areas by perinatal low-level lead exposure

Although the neurotoxic effects of Pb are well documented, the subcellular mechanisms of this action in the central nervous system are not fully understood. The present work examines some neurochemical parameters in discrete brain areas of pups whose mothers were intoxicated via drinking water with lead (300 mg/L), from day 1 of pregnancy until postnatal day 12. Lead intoxication produced a significant reduction in the activity of the enzymes alkaline phosphatase and ATP-ase in the brain. Furthermore, the levels of adenine nucleotides were significantly altered by treatment, the striatum being the area more affected, whereas lead did not vary the levels of ATP, ADP and AMP in the hypothalamus. On the other hand, there was a general decrease in neurotransmitter levels in all areas, specially in the hippocampus. These data suggest that gestational and lactational exposure to low dose of lead could produce neurochemical changes in discrete brain areas which can be responsible for the neurophysiological and behavioral changes described in lead-intoxicated animals.

Role of monoamines in the male differentiation of the brain induced by androgen aromatization

Cerebral androgen aromatization has been described as a mechanism responsible for masculinization of the brain, and monoamines seem to be involved in sexual differentiation of the brain. The aim of this study was to investigate the possible implication of monoamines in the masculinization of the brain induced by cerebral androgen aromatization not only in the classic hypothalamic areas but also in some extrahypothalamic ones. For this purpose, 1-day-old male Wistar rats were injected intraventricularly with 5 mg/kg of a suspension of an aromatase inhibitor, LY43578. Saline was administered to male and female control groups. At adulthood, open-field, heterotypical, and homotypical sexual behavior tests were performed and cerebral amines were determined by HPLC-ED. Behavioral tests revealed feminine-like exploratory activity and defecation rate in the treated group, as well as an 89% lordotic response and decreased number of mounts plus intromissions. Testosterone levels were not affected by the treatment. Striatal and limbic serotonergic metabolism showed a sexual dimorphism, higher in males than females, that disappeared in the treated group. From these results, we suggest a possible role of extrahypothalamic serotonin in the mediation of the estrogen-induced mechanisms of behavioral sexual differentiation.

Deprenyl protects from MPTP-induced Parkinson-like syndrome and glutathione oxidation in rat striatum

An intrastriatal injection with 18.8 nmoles of the neurotoxic agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced in rats a progressive parkinsonism characterized by a major loss of striatum dopamine (DA) levels and an increased turnover of this neurotransmitter 96 h after the administration. In addition, the intrastriatal administration of MPTP produced an alteration in various behavioral markers of motor activity. Loss of DA was accompanied by a significant decrease of reduced glutathione (GSH) and an increase in GSH oxidation in the striatum. When deprenyl (10 mg/kg) was i.p. administered 2 h before the intrastriatal injection of MPTP, DA, GSH, glutathione redox status and the indexes of motor activity were not altered. These results show that MPTP increases striatum oxidative stress leading to cellular and in vivo degenerative changes which are prevented by pretreatment with deprenyl.

Influence of sexual differentiation on striatal and limbic catecholamines

The influence of sexual differentiation of the brain on catecholamine content in the corpus striatum and limbic system was studied. Our results suggest that circulating ovary hormones during the critical period play an important role in the sexual differentiation of dopaminergic neurons in the corpus striatum and limbic system. Absence of androgenic steroids in the critical period leads to permanent alterations in the DA content of the limbic system in the male rat. Gonadectomy does not significantly alter NA levels in either of the two studied brain areas.