Effects of chronic exposure to ammonia concentrations on brain monoamines and ATPases of Nile tilapia (Oreochromis niloticus)

The effects of chronic exposure to total ammonia nitrogen (TAN) concentrations on the brain monoamines and ATPases of Nile tilapia, Oreochromis niloticus fingerlings, were studied. The period of exposure was 70 consecutive days, and the initial weight of the fingerlings was 18 ± 2.1 g. In addition to the control, three treatment groups exposed to 2.5 (low), 5 (medium), and 10 (high) mg TAN L^?1 concentrations were tested. The unionized ammonia nitrogen (NH₃) levels calculated in mg L^?1 were 0.059, 0.185, and 0.575 in aquaria at 26 °C. The brain monoamines were serotonin (5-HT), dopamine (DA), and norepinephrine (NE), as well as their derivatives, 5-hydroxyindoleacetic acid (5-HIAA) and dihydroxyphenylacetic acid (DOPAC). Compared with the controls, the levels of brain monoamines and Na⁺/K⁺- and Ca²⁺-ATPase activities were not significantly altered in fish exposed to low TAN concentration. However, there was a significant decrease in 5-HT, DA, and NE levels, and a significant increase in both serotonergic (5-HIAA/5-HT) and dopaminergic (DOPAC/DA) activities of fish exposed to medium TAN and high TAN concentrations. The activities of brain Na⁺/K⁺- and Ca²⁺-ATPases of fish exposed to medium TAN and high TAN concentrations significantly increased, while Mg²⁺-ATPase did not significantly change compared with that of the controls. The quantity of the detected alterations increased in fish exposed to high TAN concentration.     

Altered central monoamine response tod-amphetamine in rats chronically exposed to inorganic lead

Investigations of the mechanisms involved in the neurotoxicity resulting from chronic inorganic lead (Pb) exposure have centered on CNS biogenic amine function on the basis of behavioral and neurochemical findings. The following study examined the time course of the response of dopamine (DA) and 5-hydroxytryptamine (5-HT) neurons to d-amphetamine (AMPH) in rats chronically exposed to Pb from birth in order to further examine neurochemical mechanisms implicated by previous work. Offspring were exposed to 0.2% Pb acetate via the lactating dam and then weaned to the same drinking solution. At 120–140 days animals were injected with 1.0 mg/kg s.c. of the drug or with saline and sacrificed after various intervals. DA content in nucleus accumbens and corpus striatum in Pb-exposed animals was significantly higher than corresponding levels in controls at 20 minutes post-drug and remained significantly higher than baseline values at 80 minutes after the drug when DA concentrations in controls had returned to normal. These data suggest enhanced AMPH-induced DA synthesis in exposed rats. 5-Hydroxyindoleacetic acid (5-HIAA) content was significantly increased in three brain regions in exposed rats given AMPH compared to values in saline-injected exposed animals, indicating a compensation in these areas for the decreases in 5-HIAA values produced by Pb exposure alone. The results of this study reinforce the hypothesis that DA and 5-HT neurons are sensitive to relatively low levels of Pb exposure.     

Effects ofp-chlorophenylalanine on the metabolism of serotonin from 5-hydroxytryptophan

The effects ofD,L--chlorophenylalanine methyl ester (PCPA-methyl ester) and two of its metabolites, 2-(-chlorophenyl)-ethylamine (PCPEA) and -chlorophenylacetic acid (PCPAA), on the metabolism of serotonin (5-HT) fromD,L-5-hydroxytryptophan (5-HTP) ware studied in vitro and in vivo using the telencephalon and brainstem of the rat. For in vivo studies and some in vitro experiments, rats were injected with either 100 mg/kg PCPA-methyl ester or saline alone on days 1, 2, and 3, and were killed on day 15. When the in vivo metabolism of 5-HT was to be studied, the saline group and the PCPA group of animals were injected with 75 g/kg [³H]D,L-5-HTP 20 min before sacrificing. With respect to the values found for the saline-injected animals, the specific activity (S.A.; dpm/nmol) of 5-HIAA was significantly greater in the telencephanol and brainstem of the animals injected with PCPA-methyl ester. The S.A. of 5-HTP was the same in both groups; the S.A. of 5-HT was lower in the telencephalon of the PCPA group than in the saline group; in the brainstem, there was no difference. In both the saline- and PCPA-injected animals, the S.A. of 5-HIAA was greater than the S.A. of 5-HT. There was no difference between the saline- and PCPA-injected animals with regard to: (1)L-5-HTP decarboxylase activity; (2)L-5-HTP-induced release of [³H]5-HT in vitro from crude nerve ending fractions (P₂); or (3) in vitro uptake of [³H]D,L-5-HTP and its conversion to [³H]5-HT using the P₂ fraction. In vitro studies demonstrated that the PCPEA could directly cause a large increase in the release of [³H]5-HT from the P₂ fraction, whereas PCPA and PCPAA had little or no apparent effect. The data were interpreted to suggest that in the telencephalon of the animals treated with PCPA-methyl ester, there was a higher turnover of 5-HT than was found in the saline-treated group.     

Previous stress increases in vivo biogenic amine response to swim stress

In vivo microdialysis was used to determine biogenic amines in medial prefrontal cortex of rats exposed to eight minutes of swim stress on two consecutive days. On the first day of stress, norepinephrine (NE) efflux increased by 183% over baseline after stress, while dopamine (DA) and serotonin (5-HT) remained stable throughout. On the second day of stress, a robust increase was observed in all 3 neurotransmitters measured, with (NE), (DA), and (5-HT) increasing by 310%, 441% and 496% respectively, and remaining elevated for an hour or more after stress. This suggests that the first exposure to swim stress, while not causing dramatic changes in biogenic amine release, may sensitize biogenic amines in medial prefrontal cortex to subsequent swim stress. Our results also serve as preliminary data concerning the neurochemical changes which might underlie the forced swimming model of behavioral despair.     

Developmental Changes in Biogenic Amine Levels in the Central Nervous System and the Haemolymph of the Eastern Death's Head Hawk Moth,Acherontia styx (Lepidoptera: Sphingidae)

In an effort to understand the role of biogenic amines in insect development, changes in the levels of octopamine (OA), dopamine (DA), epinephrine (E), norepinephrine (NE), and serotonin (5-HT) in the brain, the optic lobes and the haemolymph of different developmental stages of Acherontia styx were analyzed using HPLC with electrochemical detector. In the brain, OA was the most abundant monoamine. DA, OA, and E levels in larvae peaked around the wandering stage (W). A dramatic increase in DA, 5-HT, and E levels was observed in the brain of the adult as compared to the pupal stage. NE, however, was not detected in the brain of most stages of the insect, except in the brain of 20-day-old pupae and adults. A 3-fold increase in OA levels was observed in the optic lobes of the adult as compared to late pupal stage. No changes were observed for E, DA, and 5-HT. NE was not detected in the optic lobes. In the haemolymph of 5^th instar larvae, OA was also the most abundant amine. Both DA and OA peaked prior to the onset of the W stage. In contrast, E and NE concentrations decreased with development of the 5^th instar larvae. 5-HT was not detected in the haemolymph. Finally, different profiles for amine levels were observed for the two forms of the 5^th instar larvae (green vs brown). These results are interpreted in the light of the role of biogenic amines and their relation to development in the nervous system of lepidopteran insects.     

Regulation of nucleus accumbens dopamine release by the dorsal raphe nucleus in the rat

The effects of microinfusingl-glutamate, serotonin (5-HT), (±)-8-hydroxy-2-(di-N-propylamino) tetralin (8-OH DPAT; a 5-HT_1A agonist), and muscimol (a GABA_A agonist) into the dorsal raphe nucleus on the extracellular levels of 5-HT, dopamine (DA) and their metabolites in the nucleus accumbens were studied in unanesthetized, freely moving, adult male Wistar rats, using the technique of microdialysis coupled with small-bore HPLC. Administration of 0.75 gl-glutamate produced a 25–50% increase (P<0.05) in the extracellular levels of both 5-HT and DA. On the other hand, infusion of 8-OH DPAT and, to a lesser extent, 5-HT produced a significant (P<0.05) decrease in the extracellular levels of both 5-HT and DA. Muscimol (0.25 or 0.50 g) had little effect on the extracellular concentrations of 5-HT or DA following its administration. In general, the extracellular levels of the major metabolites of 5-HT and DA in the nucleus accumbens were not altered by microinfusion of any of the agents. The data indicate that (a) the 5-HT neurons projecting to the nucleus accumbens from the dorsal raphe nucleus can be activated by excitatory amino acid receptors and inhibited by stimulation of 5-HT_1A autoreceptors, and (b) the dorsal raphe nucleus 5-HT neuronal system may regulate the ventral tegmental area DA projection to the nucleus accumbens.Special issue dedicated to Dr. Morris H. Aprison     

Time-dependent changes in brain biogenic amine dynamics following castration in male rats

—Alterations in whole-brain and hypothalamic levels of serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), norepinephrine (NE), dopamine (DA) as well as the turnover rates of NE and DA of adult male rats were analysed fluorometrically at either 3 weeks or 6 weeks following castration. Significant increases were observed in whole-brain (minus hypothalamus) 5-HIAA levels and hypothalamic DA levels, fractional rate constants and utilization rates at the 3 but not the 6 week intervals. Elevated levels of 5-HT were observed at both time intervals while an increase in whole-brain DA was seen only at the 6 week interval. Whole brain NE turnover rates of castrated animals did not differ significantly from those of sham-castrate control animals at either test interval. However, a tendency toward increased hypothalamic NE turnover rates was seen in the castrated animals. These biochemical changes resulted in decreased NE/5-HT and DA/5-HT ratios for the castrate rats as compared to controls. The results are discussed in relation to emotional and aggressive behavior and are interpreted as being consistent with the hypothesis purporting an inhibitory role for 5-HT and excitatory role for NE and DA in sex-specific behavior patterns including aggression.     

Peculiarities of L-DOPA treatment of Parkinson’s disease

Summary. L-Dihydroxyphenylalanine (L-DOPA), the anti-parkinsonian drug affording the greatest symptomatic relief of parkinsonian symptoms, is still misunderstood in terms of its neurotoxic potential and the mechanism by which generated dopamine (DA) is able to exert an effect despite the absence of DA innervation of target sites in basal ganglia. This review summaries important aspects and new developments on these themes. On the basis of L-DOPA therapy in animal models of Parkinsons disease, it appears that L-DOPA is actually neuroprotective, not neurotoxic, as indicated by L-DOPAs reducing striatal tissue content of the reactive oxygen species, hydroxyl radical (HO), and by leaving unaltered the extraneuronal in vivo microdialysate level of HO. In addition, the potential beneficial anti-parkinsonian effect of L-DOPA is actually increased because of the fact that the basal ganglia are largely DA-denervated. That is, from in vivo microdialysis studies it can be clearly demonstrated that extraneuronal in vivo microdialysate DA levels are actually higher in the DA-denervated vs. the intact striatum of rats – owing to the absence of DA transporter (i.e., uptake sites) on the absent DA nerve terminal fibers in parkinsonian brain. In essence, there are fewer pumps removing DA from the extraneuronal pool. Finally, the undesired motor dyskinesias that commonly accompany long-term L-DOPA therapy, can be viewed as an outcome of L-DOPAs sensitizing DA receptors (D₁–D₅), an effect easily replicated by repeated DA agonist treatments (especially agonist of the D₂ class) in animals, even if the brain is not DA-denervated. The newest findings demonstrate that L-DOPA induces BDNF release from corticostriatal fibers, which in-turn enhances the expression of D₃ receptors; and that this effect is associated with motor dyskinesias (and it is blocked by D₃ antagonists). The recent evidence on mechanisms and effects of L-DOPA increases our understanding of this benefical anti-parkinsonian drug, and can lead to improvements in L-DOPA effects while providing avenues for reducing or eliminating L-DOPAs deleterious effects.     

The Effects of Ecstasy (MDMA) on Brain Serotonin Transporters Are Dependent on Age-of-First Exposure in Recreational Users and Animals

Rationale and Objective

Little is known on the effects of ecstasy (MDMA, a potent 5-HT-releaser and neurotoxin) exposure on brain development in teenagers. The objective of this study was to investigate whether in humans, like previous observations made in animals, the effects of MDMA on the 5-HT system are dependent on age-of-first exposure.

Methods

5-HT transporter (SERT) densities in the frontal cortex and midbrain were assessed with [¹²³I]β-CIT single photon emission computed tomography in 33 users of ecstasy. Subjects were stratified for early-exposed users (age-at-first exposure 14–18 years; developing brain), and late-exposed users (age-at-first exposure 18–36 years; mature brain). In parallel, we investigated the effects of age experimentally with MDMA in early-exposed (adolescent) rats and late-exposed (adult) rats using the same radioligand.

Results

On average, five years after first exposure, we found a strong inverse relationship, wherein age-at-first exposure predicted 79% of the midbrain SERT variability in early (developing brain) exposed ecstasy users, whereas this was only 0.3% in late (mature brain) exposed users (p = 0.007). No such effect was observed in the frontal cortex. In rats, a significant age-BY-treatment effect (p<0.01) was observed as well, however only in the frontal cortex.

Conclusions

These age-related effects most likely reflect differences in the maturational stage of the 5-HT projection fields at age-at-first exposure and enhanced outgrowth of the 5-HT system due to 5-HT’s neurotrophic effects. Ultimately, our findings stress the need for more knowledge on the effects of pharmacotherapies that alter brain 5-HT levels in the pediatric population.     

Brain glucose and insulin: effects on food intake and brain biogenic amines of rainbow trout

The effects of central (intracerebroventricular, 9 g fish^–1) and peripheral (intraperitoneal, 4 mg kg^–1) administration of bovine insulin, as well as the effect of hyperglycemia (oral administration of 1 g glucose fish^–1) and brain glucodeprivation (intracerebroventricular administration of 2-deoxy-D-glucose) on food intake and levels of brain (telencephalon, preoptic area, and hypothalamus) biogenic amines (serotonin, dopamine, noradrenaline and their metabolites 5-hydroxyindoleacetic acid, and dihydroxyphenylacetic acid) were assessed on rainbow trout (Oncorhynchus mykiss). Treatment with insulin inhibited food intake after 26 or 52 h of administration, central or peripheral, respectively. This effect was still apparent after 74 h of central treatment. When assessing changes in the levels of biogenic amines after 26 h of central insulin administration, there was a significant increase in the levels of 5-hydroxyindoleacetic acid, and in the ratio of dihydroxyphenylacetic acid/dopamine of insulin-treated fish, in telencephalon and hypothalamus, respectively. These results suggest that peripherally administered insulin is involved in a feedback regulatory loop with food intake and body weight. Moreover, at least part of the effects of insulin could be mediated by hypothalamic dopaminergic activity. The strong hyperglycemia induced by oral administration of glucose did not induce significant changes either on food intake (control versus treated), or in brain levels of biogenic amines. The intracerebroventricular administration of 2-deoxy-D-glucose induced an increase in food intake without altering plasma glucose levels, suggesting that fish brain possesses a control system for detecting hypoglycemia in plasma and therefore keep brain glucose levels high enough for brain function.Abbreviations 2-DG 2 Deoxy-D-glucose - 5-HIAA 5-Hydroxyindoleacetic acid - 5-HT 5-Hydroxytryptamine or serotonin - DA Dopamine - DOPAC Dihydroxyphenylacetic acid - EDTA Ethylenediaminetetraacetic acid - FI Food intake - HPLC High pressure liquid chromatography - icv Intracerebroventricular - i.p. Intraperitoneal - MS 222 3-Aminobenzoic acid ethyl esther methanesulfonate salt - NA Noradrenaline     

Effect of aging on monoamines and their metabolites in the rat brain

Concentrations of dopamine (DA), norepinephrine (NE), serotonin (5-HT) and their acid merabolites were assayed in specific brain areas of Wistar rats of various ages. DA and its metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) were significantly lower in striatum and mesolimbic areas of old (24 mos) rats than young adult (3 mos), but not mature (12 mos) rats. The decrease of homovanillic acid (HVA) was significant in mesolimbic areas but not in striatum. Neither cortical NE nor its metabolite methoxydroxyphenylglycol sulphate (MHPG-SO₄) were significantly changed by aging. 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in the brainstem showed a tendency to a decrease and increase respectively in aged animals compared with young adults, but the differences were not statistically significant. However, the ratio of 5-HIAA to 5-HT concentrations was significantly higher in aged animals. The conclusion can be drawn that, in these brain areas, DA is more vulnerable to aging than NE and 5-HT, the metabolism of the latter being even enhanced.     

In vitro release of endogenous monoamines and amino acids from several CNS regions of the rat

The in vitro release of endogenous norepinephrine (NE), dopamine (DA), serotonin (5-HT), GABA, glutamate (GLU), aspartate (ASP), glycine (GLY), taurine (TAU) and alanine (ALA) from superfused slices of cerebral cortex (CTX), striatum (STR), hippocampus (HIP), hypothalamus (HYPO), midbrain (MB), thalamus (THAL), nucleus accumbens (ACC), pons-medulla (PM) and spinal cord (SC) was studied. Under resting conditions or with 60 mM K⁺ in the absence of Ca²⁺, there was little or no release of NE, DA, 5-HT, GABA, GLU or ASP from any region. In most regions, there was a measurable resting release of ALA, GLY and TAU; of these three amino acids, only GLY in the PM and SC showed an increased release in the 60 mM K⁺ plus 2.5 mM Ca²⁺ medium. In 8 of the regions studied, the release of both GABA and GLU were stimulated by 60 mM K⁺ in the presence of 2.5 mM Ca²⁺. For the amino acids, no reliable data were obtained for release from the ACC because of its small size. The highest amount of K⁺-stimulated, Ca²⁺-dependent release of GABA was found with slices from the HYPO, THAL and MB while the highest amount of GLU was released from slices of STR, HIP and CTX. In those regions where reliable levels of K⁺-stimulated, Ca²⁺-dependent release of ASP were observed (STR, CTX, THAL), the amount of ASP was at least 5-fold lower than the values for GLU. A K⁺-stimulated, Ca²⁺-dependent release of NE, DA and 5-HT was observed for all 9 CNS regions studied. The highest release of (a) DA occurred from slices of CTX, STR and ACC; (b) NE was found in the HYPO and ACC; and (c) 5-HT occurred in the HYPO. The data (a) do not support a transmitter role for ALA and TAU in the CNS; (b) support a major transmitter function for GLY only in the PM and SC; and (c) support a transmitter role for GABA, GLU, NE, DA and 5-HT in the CNS regions examined (with the exception of GABA and GLU in the ACC where no data were obtained).     

Effect of administration of 5-hydroxytryptophan and an inhibitor ofl-aromatic amino acid decarboxylase on glucose metabolism in rat brain

The effect of 5-hydroxytryptophan (5-HTP)—the precursor of serotonin (5-hydroxytryptamine, 5-HT)—and of an inhibitor,N-(dl-seryl)-N-(2,3,4-trihydroxybenzyl)hydrazine (Ro4-4602), ofl-aromatic amino acid decarboxylase on the metabolism of glucose to amino acids in brain tissue was investigated. Labeled glucose (20 Ci, 0.24 mg in 0.2 ml 0.9% saline) was injected intravenously into fed rats pretreated with Ro4-4602 (50 mg/kg intraperitoneally) either alone or in combination with 5-HTP (30 mg/kg intravenously) or with the appropriate vehicle. After the injection of Ro4-4602 plus 5-HTP, the concentrations of 5-HT and 5-HTP in brain were increased, but the increase of 5-HTP that Ro4-4602 slightly inhibits the reaction of decarboxylation in the brain, although at the dose used the drug is usually considered to act only peripherally. After administration of Ro4-4602 alone or combined with 5-HTP, the concentration of glucose in plasma was not significantly increased. However, the concentration of glucose in brain was markedly increased with such treatments. The administration of Ro4-4602 alone or combined with 5-HTP reduced the flux of¹⁴C from labeled glucose to amino acids in brain. The concentrations of amino acids in brain were little changed by these treatments.     

Influence of hypo- and hyperthyroidism on the turnover rate of noradrenaline, dopamine and serotonin in various rat cerebral structures]

The effect of chronic treatment with tyroxine (T4) or propylthiouracile (PTU) on the turnover of norepinephrine (NE), dopamine (DA) and 5-hydroxytryptamine (5-HT) has been studied in various areas of the rat brain (brain stem, hypothalamus, striatum and "rest of the brain"). The turnover of NE and DA was determined by the decay in endogenous levels after inhibition of tyrosine hydroxylase by alpha-methylparatyrosine and the turnover of 5-HT was evaluated by the initial accumulation of endogenous 5-HT after inhibition of monoamine oxydase by pargyline. T4 treatment accelerated the release of DA from the striatum but had no significant effects on NA release in the various cerebral areas : nevertheless the NE endogenous level was significantly reduced in the brain stem. PTU treatment delayed the release of DA and NA only from the "rest of the brain". Concerning 5-HT, the only significant variation was observed in the hypothalamus of PTU-treated rats and implied increased turnover. The possible relations between the changes in cerebral monoamines turnover and the behavioural alterations which are observed in thyroid disfunction are discussed.     

β2 Mediated inhibition of [3H]dopamine release from nucleus accumbens slices and monoamine levels in a rat model for attention-deficit hyperactivity disorder

The spontaneously hypertensive rat (SHR) has been proposed as an animal model for attentiondeficit disorder (ADHD). The behavioural problems have been suggested to be secondary to altered reinforcement mechanisms in which nucleus accumbens dopaminergic activity plays an important role. Interaction between the noradrenergic and dopaminergic system in the nucleus accumbens has been implicated in the locomotor hyperactivity and impaire discriminative performance of SHR. The present study therefore investigated whether there was any change in the ₂-adrenoceptor mediated inhibition of dopamine release from nucleus accumbens slices of SHR in comparison with their normotensive Wistar-Kyoto (WKY) controls. The electrically stimulated release of [³H]dopamine (DA) from nucleus accumbens slices was decreased to a similar extent by UK14,304, an ₂-adrenoceptor agonist, in SHR and WKY. Basal norepinephrine (NE) levels were increased in locus coeruleus (LC) and A₂ noradrenergic nuclei, but not in the A₁ nucleus of SHR, while basal serotonin (5-HT) levels were increased in all these pons-medulla nuclei. These results suggest that a primarily dysfunctional LC and A₂ nucleus does not have a secondary effect on dopaminergic transmission in the nucleus accumbens via ₂-adrenoceptor mediated inhibition of DA release. Basal monoamine levels in several brain areas of SHR were significantly different from that of WKY. DA, and 5-HT turnover were decreased in SHR versus WKY suggesting hypofunctional dopaminergic and serotonergic systems in some brain areas of SHR.     

Brain tissue transplanted to the anterior chamber of the eye

Summary Small pieces of fetal rat brain selected to contain a high number of noradrenaline (NA), dopamine (DA), or 5-hydroxytryptamine (5-HT) neuroblasts were transplanted to the anterior chamber of the eye of adult rats. The sympathetic ground plexus of the host iris was removed by superior cervical ganglionectomy so that transmitter mechanisms of the different central monoamine fibers innervating the iris could be selectively studied after intraocular maturation. Such irides, containing NA, DA, or 5-HT nerve terminals were incubated with radiolabelled transmitters and then stimulated by an electrical field while superfused, to investigate the spontaneous and stimulation-induced release of amine, both in drug-free buffer and buffer containing drugs acting on monoamine receptors.The central monoamine neurons of all three types were able to take up exogenous amines and release them upon stimulation by an electrical field, in much the same way as corresponding nerves in situ in slices of cerebral cortex (NA, 5-HT) or olfactory tubercle (DA).The -adrenergic receptor blocking agent phentolamine increased the stimulation-induced release of ³H-NA from central NA fibers on the iris significantly. The dopamine receptor stimulating agent apomorphine decreased the stimulation-induced release of ³H-DA from central DA fibers on the iris. Pimozide, a DA receptor blocking drug tended to increase the ³H-DA release. The 5-HT receptor stimulating agent ergocornine tended to reduce the stimulation-induced release of ³H-5-HT from central 5-HT fibers on the iris. It was concluded that all three types of central monoamine nerve fibers develop essentially normal transmitter storage and release mechanisms also in an environment completely devoid of normal postsynaptic receptors. The drug experiments add strong support to the view that there are presynaptic monoamine receptors (autoreceptors) able to modulate transmitter release present on the monoamine nerve terminals.Supported by the Swedish Medical Research Council (04X-3185 and 04X-2330) and by grants from Magnus Bergvalls Stiftelse and Karolinska Institutets Fonder, we thank Miss Ingrid Strömberg and Miss Ulla Enberg for skilful technical assistance.     

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

The effects of ⁹-tetrahydrocannabinol (⁹-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 ⁹-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 ⁹-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 ⁹-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.Abbreviations Hypo anterior hypothalamus - Cin cingulate cortex - dHipp dorsal hippocampus - 5-HIAA 5-hydroxyindole-3-acetic acid - HPLC high-performance liquid chromatography - 5-HT serotonin - 5-HTP 5 hydroxy-1-tryptophan - LC Locus coeruleus - rNS rostral neostriatum - MRN midbrain Raphe nuclei region - SN Substantia nigra - ⁹-THC ⁹-Tetrahydrocannabinol     

Effects of the Serotonin1A Agonist, 8-Hydroxy-2-(Di-n-Propylamino)tetralin on Neurochemical Responses to Stress

Abstract: The effects of intracerebroventricular administration of the 5-hydroxytryptamine (5-HT)_1A agonist, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 0.1 pmol) on adrenocortical and neurochemical responses to stress were examined in conscious male rats. The following stress paradigms were used: acoustic stimulation (105 dB for 2 min); footshock (0.2 mA, five shocks over 5 min); conditioned fear (animals placed in a footshock chamber for 5 min, 24 h after footshock); restraint (5 min); intraperitoneal (i.p.) injection of recombinant human interleukin-1α (rHu-IL-1α, 20 µg/kg); and injection of cocaine hydrochloride (20 mg/kg, i.p.). As previously shown, 8-OH-DPAT was able to attenuate the adrenocortical response to acoustic stress, conditioned fear, rHu-IL-1α, and cocaine administration. Cocaine decreased 5-hydroxyindoleacetic acid (5-HIAA)/5-HT and dihydroxyphenylacetic acid/dopamine (DOPAC/DA) ratios and norepinephrine (NE) concentration in the prefrontal cortex, hypothalamus, and brainstem in all experiments, and 8-OH-DPAT reversed the changes in DOPAC/DA ratio without affecting 5-HIAA/5-HT ratios or NE content. 8-OH-DPAT alone had no effect on these parameters, although it decreased NE content in the prefrontal cortex in several experiments, and in the brainstem in one experiment. Significant decreases in NE content were observed in some brain regions following some of the stressors, but these changes were not generally affected by 8-OH-DPAT. Increases in the 5-HIAA/5-HT and DOPAC/DA ratios were also observed in some brain sites following some stressors, but these changes were not affected by 8-OH-DPAT except in the case of the increased 5-HIAA/5-HT ratio in the prefrontal cortex following the conditioned fear response. These results indicate that although 8-OH-DPAT is able to decrease plasma corticosterone responses following acoustic stress, conditioned fear, rHu-IL-1α, and cocaine administration, these effects do not appear to be related to an action of the 5-HT_1A agonist on biogenic amine metabolism. This observation indicates that the predominant effect of 8-OH-DPAT on adrenocortical responses is mediated at postsynaptic sites not involved in the regulation of cerebral biogenic amine metabolism.