Monoamine levels after pilocarpine-induced status epilepticus in hippocampus and frontal cortex of Wistar rats

Pilocarpine-induced status epilepticus (SE) is an useful model to study the involvement of neurotransmitter systems as epileptogenesis modulators. Some researches have shown that pharmacological manipulations in dopaminergic, serotonergic, and noradrenergic systems alter the occurrence of pilocarpine-induced SE. The control group was treated with 0.9% saline (control group, s.c.). Another group of rats received pilocarpine (400 mg/kg, s.c.) and both groups were sacrificed 24 h after the treatment. This work was performed to determine the alterations in monoamine levels (dopamine (DA), serotonin (5-HT) and norepinephrine (NE)) and their metabolites (3,4-hydroxyphenylacetic acid (DOPAC), homovanilic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA)) after pilocarpine-induced SE in hippocampus and frontal cortex of adult rats. The monoamines and their metabolites were determined by reverse-phase high-performance liquid chromatography with electrochemical detection. DA and 5-HIAA concentrations were not altered in the hippocampus of the pilocarpine group, but in the same group the 5-HT (160%), DOPAC (316%) and HVA (21%) levels increased, whereas, the NE (47%) content declined. For the frontal cortex determinations, there was an increase of 20 and 72% in DA and DOPAC levels, respectively, and a decrease in NE (32%), 5-HT (33%) and 5-HIAA (19%) concentrations, but HVA content remained unaltered. These results indicate that pilocarpine-induced SE can alter monoamine levels in different ways depending on the brain area studied, suggesting that different mechanisms are involved.     

Behavioral and neurochemical alterations evoked by p-Chlorophenylalanine application in rats examined in the light-dark crossing test

The aim of the present study is to examine the effects of serotonin synthesis inhibition with p-Chlorophenylalanine (p-CPA) in rats on (1) anxiety behavior examined in the light-dark crossing test and, (2) regional brain concentration of monoamines (NA, DA and 5-HT) and their metabolites (MHPG, DOPAC, HVA and 5-HIAA) as well as GABA in the hypothalamus, amygdala, hippocampus, midbrain central gray matter and the frontal cortex. Treatment of animals with p-CPA produced a significant increase in time out from the illuminated part of the chamber and in time of locomotor activity in the illuminated part of the chamber. HPLC analysis showed a significant reduction of 5-HT and 5-HIAA concentration in all examined brain regions with the exception of the frontal cortex. Additionally, a significant decrease in DA and its metabolites, DOPAC and HVA occurred in the hypothalamus and amygdala. Moreover, we observed a significant decrease in frontal cortex NA concentration after p-CPA administration. The results of our study suggest that administration of p-CPA is effective in reduction of anxiety through depletion of 5-HT accompanied by diminution of catecholamines, especially DA and its metabolites in the main emotional brain regions.     

Evidence for involvement of N-methyl-D-aspartate receptor in tonic inhibitory control of dopaminergic transmission in rat medial frontal cortex

Bilateral infusion of DL-2-amino-5-phosphonovalerate (DL-APV) (which is a competitive antagonist for N-methyl-D-aspartate (NMDA) receptor) into the medial frontal cortex of conscious rats increased the amount of 3,4-dihydroxyphenylacetic acid (DOPAC) and the DOPAC/dopamine (DA) ratio in the cortical area. Moreover, intra-prefrontal injection of DL-APV, D-APV, DL-2-amino-7-phosphonoheptanoate and 3-[(+/-])-2-carboxypiperazin-4-yl]-propyl-1-phosphonate (which are selective NMDA receptor antagonists), but not the L-isomer of APV and gamma-glutamyl-aminomethyl sulphonate (a relative antagonist for non-NMDA receptors), facilitated prefrontal DA utilization in a NMDA-reversible manner. These findings suggest that NMDA-type excitatory amino acid receptors may be involved in a tonic inhibitory regulation of dopaminergic transmission in the medial frontal cortex in vivo.     

From a standpoint of psychiatry: effects of conditioned fear stress on monoaminergic systems in the rat brain]

The effects of electric footshock stress(EFS) and conditioned fear stress(CFS) on dopamine(DA) and serotonin(5-HT) metabolism in seven various brain regions of the rat were studied by measuring dihydroxyphenylacetic acid(DOPAC), homovanillic acid(HVA) and 5-hydroxyindoleacetic acid(5-HIAA). EFS for 30 min increased DOPAC and HVA levels in all seven brain regions and increased 5-HIAA levels in the medial prefrontal cortex(mPFC), nucleus accumbens and amygdala. CFS(exposure to an environment paired previously with footshock) increased plasma corticosterone levels and defecation, and induced freezing behavior. It also increased DOPAC levels in the mPFC, paraventricular nucleus of the hypothalamus and lateral hypothalamus, increased HVA levels in the mPFC and amygdala, and increased the 5-HIAA level in the mPFC. In contrast to EFS, which increased DA and 5-HT metabolism in several other brain regions, increased metabolism of both DA and 5-HT was especially marked in the mPFC after CFS. In this model, two classes of anxiolytics were examined for effects on freezing behavior. The benzodiazepine diazepam, a classical anxiolytic, reduced the freezing response. The new anxiolytic ipsapirone, a selective 5-HT1A agonist, also reduced the freezing response. These findings suggest the usefulness of this model for detecting the anxiolytic potential of drugs and examining the relation between 5-HT and anxiety.     

Dopamine release in the nucleus accumbens of freely moving rats determined by on-line dialysis: effects of apomorphine and the neuroleptic-like peptide desenkephalin-gamma-endorphin

This study examined the effects of apomorphine, sulpiride, desenkephalin-gamma-endorphin (DE gamma E) and a combination of DE gamma E with apomorphine on the release of dopamine (DA) and its main metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the nucleus accumbens of freely moving rats. A fully automated on-line brain dialysis system was used. A small dose of s.c. administered apomorphine induced a decrease in the output of DA and DOPAC. Sulpiride, infused into the nucleus accumbens, induced a 2-fold increase in the output of DA, DOPAC and HVA. DE gamma E hardly modified either the basal release of DA, DOPAC and HVA or the apomorphine-induced attenuation of the release of DA and DOPAC. These results indicate a dissociation between the behavioural effects of DE gamma E and its effect on the release of DA in vivo.     

Cold restraint alters dopamine metabolism in frontal cortex, nucleus accumbens and neostriatum

The concentrations of dopamine (DA) and dihydroxyphenylacetic acid (DOPAC) were assayed in the striatum, nucleus accumbens and frontal cortex of rats following 2 hours of cold restraint. The concentration of DA was significantly decreased in both the striatum (-16%) and nucleus accumbens (-41%) relative to unstressed controls. The content of DOPAC was significantly increased in both striatum (+56%) and frontal cortex (+76%), but not in nucleus accumbens. The DOPAC/DA ratio was increased in all three regions, that in frontal cortex approaching three-fold. These results extend earlier findings of an activation by acute stressors of frontal cortex DA metabolism, but suggest an involvement of other DA systems as well. The finding of the greatest response in frontal cortex, and the previous observations that this was the only region to show significant changes, may be ascribed to the suggested lack of presynaptic autoreceptors in this region.     

Active transport pumps of HVA and DOPAC in dopaminergic nerve terminals.

The effect of the membrane potential on the efflux of HVA and DOPAC from DA neurons was studied in anesthetized (1% halothane in gas mixture of 70% N2O and 30% O2) cats. Extracellular DA, HVA and DOPAC were measured continuously from the putamen, the hypothalamus, the thalamus, the raphe nuclei and the cortex using brain microdialysis technique combined with HPLC-ED monoamine measurements. HVA and DOPAC concentrations were highest in the putamen and lowest in the cerebral cortex. Extracellular HVA levels exceed those of the DOPAC. Increases in the extracellular potassium from 4 to 120 mM invariably produced decreases of the extracellular HVA and DOPAC in all the tested brain regions. These decreases were inversely proportional to the extracellular potassium concentration. Thus, it is concluded that the HVA and the DOPAC are extruded from inside the cell to the extracellular space by active mechanisms of transport similar to that reported for 5-HIAA in serotonergic neurons.     

Alcohol-preferring rats: genetic sensitivity to alcohol-induced stimulation of dopamine metabolism

The effect of ethanol on brain dopamine (DA) metabolism in the caudate nucleus (CN), olfactory tubercle (OT) and medial prefrontal cortex (MPFC) was compared in two selectively bred rat lines, one ethanol preferring and the other ethanol nonpreferring. Male rats from the 16th and 17th generations of both lines that never experienced ethanol beforehand were used. No differences in the basal concentrations of DA and its metabolites, DOPAC and HVA, in the above brain regions were found between the two lines. The oral administration of 2 g/kg of ethanol to ethanolnonpreferring rats increased DOPAC and HVA and reduced DA levels in the CN and OT but was ineffective in the MPFC. On the other hand, ethanol administration to ethanol-preferring rats decreased DA content and increased DOPAC and HVA levels, not only in the CN and OT, but also in the MPFC. Moreover, the changes induced by ethanol on DA metabolism in the latter group were significantly greater than in ethanol nonpreferring rats. These results indicate that ethanol preferring rats have a genetic high sensitivity to the ethanol effect on DA metabolism, and suggest that such a trait might play a role in ethanol preference.     

Age-related changes in dopaminergic and serotonergic indices in the rat forebrain

Age-related changes in the content of dopamine (DA), homovanillic acid (HVA), dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3-MT), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in anterior cerebral cortex, hippocampus and striatum of the rat have been investigated using HPLC with electrochemical detection. A significant decrease in HVA was observed in the striatum and hippocampus of the aged (27 months) animals, as compared to the controls (2.4 to 2.6 months). A significant decrease in DA levels was also observed in the hippocampus but not in the striatum. In contrast, the level of DA in the cerebral cortex was markedly increased in the aged animals. A concomitant increase in 3-MT level was observed. Finally the level of 5-HIAA was significantly increased in striatum and hippocampus.     

Use of dynamic weight bearing as a novel end-point for the assessment of Freund's Complete Adjuvant induced hypersensitivity in mice

The neurotoxins methamphetamine (METH) and MPTP are well-known for their effects on the nigrostriatal dopaminergic system and use in modeling neurodegenerative disorders such as Parkinson's disease. It is not well-known though, how METH or MPTP affects the visual system and specifically the retinal dopaminergic system. This study was designed to examine acute effects of multiple doses of METH and MPTP on the retinal dopaminergic system. Mice were exposed to either low- (LD) 10 mg/kg total dose or high-dose (HD) 30 mg/kg total dose, of METH or MPTP and the retinal catecholaminergic system was analyzed by HPLC. METH produced no significant changes in dopamine (DA), its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) or DA usage in the retina. LD-MPTP produced no change in DA level, but significantly decreased DOPAC and HVA. LD-MPTP also significantly decreased DA usage as measured by the DOPAC/DA and HVA/DA ratios. HD-MPTP significantly decreased DA, DOPAC and HVA, but did not affect DA usage. Taken together these results suggest that inhibition of the DA metabolizing enzymes monoamine oxidase A (MAO) or catechol-O-methyl transferase (COMT) may take place at lower doses of MPTP treatment; conversely, higher doses of MPTP may cause decreases in DA, DOPAC and HVA through another mechanism.     

Increased utilization of dopamine in the nucleus accumbens but not in the cerebral cortex after dorsal raphe lesion in the rat

Dihydroxyphenylacetic acid (DOPAC) and dopamine (DA) levels were estimated in the frontal cortex, the nucleus accumbens and the striatum of the rat after electrolytical lesion of the dorsal raphe nucleus. The efficiency of this lesion was tested by measuring the decline in serotonin (5-HT) levels in the striatum. 5-HT levels were reduced by 90% when compared to those of sham-operated rats 11 days after the lesion. As revealed both by the increase in DOPAC levels and in the DOPAC/DA ratio, the rate of DA utilization was markedly increased in the nucleus accumbens, slightly enhanced in the striatum and in contrast remained unaffected in the frontal cerebral cortex 4 days after the lesion. Changes in DOPAC levels in the nucleus accumbens were also seen 11 and 30 days after the lesion but they were less pronounced than those observed at 4 days. These results suggest that neurons originating from the dorsal raphe and projecting to the ventro-tegmental area are regulating the activity of the meso-nucleus accumbens dopaminergic neurons but not that of the meso-cortical dopaminergic neurons.     

Regional differences in the distribution of norepinephrine and epinephrine in human cerebral cortex: a neurochemical study using HPLC and electrochemical detection

We performed neurochemical quantitation of the catecholamines dopamine (DA), norepinephrine (NE) and epinephrine (E) and their major metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 3-methoxy-4-hydroxyphenylethylene glycol (MHPG) in 22 cortical regions of 6 postmortem human brains. Statistical analysis indicated a clear regional difference for NE and E while DA and all the metabolites under study are homogeneously distributed over the cortex. These consistent regional differences suggest the possible role of NE and E as neurotransmitters or neuromodulators in human cerebral cortex.     

Neurochemical correlates of conditioned circling within localized regions of the striatum

Summary Two experiments were conducted to determine the effects of conditioned circling on the concentrations of dopamine (DA), 3,4-dihydroxy-phenylacetic acid (DOPAC) and homovanillic acid (HVA) within discrete regions of the striatum (STR). The first study assessed the inherent regional distributions of these compounds with respect to the three primary axes: anterior-posterior, dorsal-ventral and medial-lateral. Concentrations of DA, DOPAC and HVA and the ratios of each metabolite to DA were found to vary across each dimension. However, the topographical distribution of each compound was unique. The results of the first experiment confirm that the STR is not a homogeneous structure. It is possible that the regional variations in dopamine metabolism underly the diverse functions which the STR is thought to modulate. The second experiment determined whether specific regions of the STR were differentially involved in the mediation of conditioned circling. DA metabolism, as estimated by metabolite concentrations and metabolite to DA ratios, was bilaterally increased within the anterior dorsomedial and dorsolateral STR, relative to noncircling, water-deprived controls. DOPAC and the corresponding ratio were enhanced selectively within the dorsomedial region, whereas HVA and its ratio to DA were increased preferentially within the dorsolateral STR. The ratio of DOPAC to DA was also enhanced within the anterior ventromedial STR. No other significant neurochemical effects were detected. These results support the hypothesis that the dorsal STR critically subserves circling. Moreover, it is possible that the medial and lateral regions of the dorsal STR are differentially involved in circling. These results also confirm previous reports of bilateral augmentation of striatal DA metabolism in association with high rates of conditioned circling.     

Striatal 3-methoxytyramine as an index of dopamine release effects of electrical stimulation

Electrical stimulation of the substantia nigra elicited frequency-dependent increases in striatal 3-methoxytyramine (3-MT). Subsequently, successive increases in dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) were measured. Inhibition of nigrostriatal cell firing with HA-966 resulted in decreased striatal 3-MT, but in this case elevated DOPAC and HVA were also observed. These data indicate that 3-MT is a reliable index of dopamine (DA) release but that concurrent measurements of DOPAC, HVA and DA provide the most reliable interpretation of drug effects on dopaminergic function.     

Neurotransmitter levels in two populations of larval Fundulus heteroclitus after methylmercury exposure

The effects of methylmercury (MeHg) exposure on neurotransmitter (NT) levels in larval mummichogs (Fundulus heteroclitus) obtained from a mercury-polluted site (Piles Creek (PC), NJ) and a reference site (Tuckerton (TK), NJ) were examined. Population differences between PC and TK larvae in neurochemical composition and in neurochemical changes in response to MeHg intoxication were found. Heads of untreated PC larvae (7 days posthatch (dph)) contained considerably higher levels of dopamine (DA) and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) than TK. However, they had comparable levels of serotonin (5-hydroxytryptamine (5-HT)) and 5-hyroxy-3-indoleacetic acid (5-HIAA)/5-HT ratios. Changes in NTs with age were noticed, especially in PC larvae. Exposure of larvae to 10 microg/l MeHg induced neurochemical alterations. A significant increase in DA and 5-HT, as well as depressed dopaminergic and serotonergic activity (i.e. decreased DOPAC/DA, HVA/DA and 5-HIAA/5-HT ratios) were seen in TK larvae. Exposure of PC larvae to 10 microg/l MeHg reduced 5-HT at 14 dph, increased serotonergic activity at 7 dph, and altered dopaminergic activity (i.e. increased DOPAC/DA ratios, but decreased HVA/DA ratios). Changes in DA levels were inconsistent over time. The DA level, which was considerably higher than the control at 7 dph, was significantly lower than the control at 14 dph. For the two populations, the level of 5-HT and serotonergic activity, as well as DOPAC and HVA levels, were correlated with previously noted spontaneous activity. The changes in NT levels after exposure to MeHg are an indication of neurological dysfunction in larvae.     

Feeding and hypothalamic stimulation increase dopamine turnover in the accumbens

The hypothesis that the dopaminergic system plays a role in feeding behavior was tested in three experiments. First, microdialysis was performed in the nucleus accumbens (NAC) at 20 min intervals during free feeding in rats at 80% of normal body weight. Extracellular concentration of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) increased significantly during eating indicating an increase in DA turnover. Second, microdialysis samples were collected from the NAC during bar pressing with a) a signal light on and food available, b) the light on but no food available, c) neither light nor food. Only when food was available did extracellular DA, DOPAC and HVA increase significantly. This increase in DA turnover occurred in the accumbens but not in the ventral striatum. Third, electrical stimulation of the perifornical lateral hypothalamus (LH) that was capable of inducing feeding increased extracellular DA, DOPAC and HVA in the NAC. This occurred whether the animal had food to eat or not. The effect of LH stimulation on DA turnover resembled the effects of free feeding and operant feeding in Experiments 1 and 2. Perifornical LH stimulation did not increase dopamine turnover in the ventral striatum. The results show that perifornical LH stimulation activates the mesolimbic dopamine system and that dopamine release in the accumbens is involved in feeding. The increase in dopamine turnover outlasted the consummatory act. This suggests that accumbens dopamine may be related to sensory input, feeding reflexes, food reward or memory processes and not just to the consummatory act itself.     

The long-term effects of neurotoxic doses of methamphetamine on the extracellular concentration of dopamine measured with microdialysis in striatum.

The extracellular concentrations of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) in the striatum were measured by in vivo microdialysis in freely moving rats one week after the animals were treated with neurotoxic doses of methamphetamine. Methamphetamine produced a marked depletion of striatal DA measured in postmortem tissue, and in the extracellular concentrations of DOPAC, HVA and 5-HIAA. In contrast, the resting extracellular concentration of DA in striatum was the same as in saline-pretreated controls. Furthermore, methamphetamine-pretreated rats were able to increase their concentration of extracellular DA to the same extent as controls in response to a (+)-amphetamine challenge. It is suggested that this adaptive response is probably responsible, at least in part, for the absence of obvious behavioral deficits in animals exposed to neurotoxic doses of methamphetamine.     

Comparison of the effects of intracerebrally administered MPP+ (1-methyl-4-phenylpyridinium) in three species: microdialysis of dopamine and metabolites in mouse, rat and monkey striatum

Intracerebral microdialysis in 3 awake species allowed the measurement of the basal output of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindole-acetic acid (5-HIAA) from rat and mouse striatum and monkey caudate in vivo. The DOPAC/HVA ratios in dialysates from mouse and rat striatum were about 1 and 2 respectively, but only 0.09 in monkey caudate dialysates. The extracellular levels of the metabolites correlated well with reported tissue levels, while extracellular DA levels were 3 orders of magnitude lower than tissue concentrations. The effects of the intracerebrally administered dopaminergic neurotoxin 1-methyl-4-phenylpyridinium (MPP+) were essentially similar in the 3 species. In all cases an immediate, massive release of DA was accompanied by a pronounced decrease in the output of the metabolites. Basal DA release was no longer detectable 5-12 h after MPP+ administration and a second MPP+ perfusion failed to increase the release of DA.     

Agonist action of the agonist/antagonist analgesic butorphanol on dopamine metabolism in the nucleus accumbens of the rat

The action of butorphanol, an opiate agonist/antagonist, was studied on dopamine (DA) metabolism in several mesocortical and mesolimbic areas and compared with its effects on the nigrostriatal DA pathway. While butorphanol had a bell-shaped dose-response relationship for elevation of DA metabolites in the striatum, it had no action on DA metabolites in the entorhinal, prefrontal, pyriform and cingulate cortices and in the olfactory tubercle. In all of these areas morphine stimulated dopamine metabolism (except for the entorhinal cortex). In contrast, in the nucleus accumbens, butorphanol increased the levels of dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 3-methoxytyramine (3-MT) with no increase in DA steady state levels. This effect was reversible by both opiate antagonists, naloxone and WIN 44441-3 and appears to be mu-opioid receptor-mediated.     

In vivo release of dopamine and its metabolites following a direct infusion of L-dopa into the caudate nucleus of awake, freely behaving rats using a push-pull cannula

In vivo release of dopamine (DA) and its metabolites were determined following a direct infusion of 3,4-dihydroxyphenylalanine (L-DOPA) through a push-pull cannula in the caudate nucleus of unanesthetized, freely behaving rats. L-DOPA infusions increased the release of DA and dihydroxyphenylacetic acid (DOPAC) beginning with 10(-5) M L-DOPA, while homovanillic acid (HVA) was released consistently only following 10(-3) M L-DOPA. Maximal release of DA preceded that of DOPAC which preceded that of HVA. No salient changes in 5-hydroxyindoleacetic acid or behavior were observed following any L-DOPA dose.