Microdialysates of amines and metabolites from core nucleus accumbens of freely moving rats are altered by dizocilpine

In vivo microdialysis combined with high performance liquid chromatography (HPLC) with electrochemical detection, was used to study the effect of MK-801 (0.1 mg/kg i.p.) on extracellular concentrations of dopamine (DA) 3,4-dihydroxyphenylacetic acid (DOPAC), serotonin (5-HT), norepinephrine (NE) and DOPAC/DA ratio in intact, 6-hydroxydopamine (6-OHDA)-lesioned, DSP4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzyl-amine hydrochloride)-lesioned and reserpine-treated rats. The results revealed high basal DA (0.735+/-0.05 fmol/microl), DOPAC (195.93+/-20.18 fmol/microl) and NE (0.585+/-0.01 fmol/microl), low 5-HT (0.334+/-0.032 fmol/microl) and high DOPAC/DA ratio (265.11+/-20.73) in intact cACC. 6-OHDA alone (8 microg/2 microl) depleted DA (-66%), DOPAC (-65%), and NE (-62%). On the other hand, in desipramine (DMI)-pretreated rats, 6-OHDA induced a large depletion of DA (-94%), DOPAC (-97%) and reduced DOPAC/DA ratio (-73%), but increased NE to 142% of intact and 369% of 6-OHDA-lesioned rats. DSP4 (50 mg/kg) decreased NE (-97%), DOPAC (-75%) and DOPAC/DA ratio (-69%). Reserpine (5 mg/kg s.c.) significantly decreased DOPAC (-84%), DOPAC/DA ratio (-81%), 5-HT (-69%) and NE (-86%), but nonsignificantly increased DA. In the intact rats, MK-801 did not change DA, but increased DOPAC and DOPAC/DA ratio. In 6-OHDA-lesioned rats, MK-801 increased DA, whereas in 6-OHDA+DMI rats MK-801 additionally increased DOPAC and DOPAC/DA ratio. DSP4 and reserpine reduced the ability of MK-801 to increase DOPAC and DOPAC/DA ratio. MK-801 did not change NE concentration in dialysates collected from intact rats, but increased that from 6-OHDA+DMI-lesioned rats. In DSP4-lesioned and reserpine-treated rats, MK-801 increased NE but to a level lower than that observed in the intact rats. These results suggest that systemic administration of a low dose of MK-801, which induces profound locomotor stimulation without stereotypy, increases DOPAC and DOPAC/DA ratio in the cACC of intact rats, whereas it additionally increases the depleted DA and NE concentrations especially in 6-OHDA-lesioned rats pretreated with DMI.     

Central noradrenergic involvement in yohimbine excitation of acoustic startle: Effects of DSP4 and 6-OHDA

It was previously shown that i.p. administration of the alpha 2-adrenergic antagonist yohimbine increased the magnitude of the acoustic startle response in rats. The purpose of the present study was to determine possible central noradrenergic involvement in yohimbine's effect on startle. Pretreatment with N-(2-chloroethyl)-N-ethyl-2-bromo-benzylamine (DSP4; 50 mg/kg, i.p.; 1-2 days before testing) completely blocked the excitatory effect of yohimbine on startle. DSP4 reduced forebrain and spinal cord NE levels by 47% and 56%, respectively, without affecting forebrain or spinal serotonin (5-HT), or forebrain dopamine (DA). Pretreatment with the NE reuptake blocker desmethylimipramine (DMI; 20 mg/kg, i.p.; 30 min before DSP4) prevented the ability of DSP4 to block the yohimbine effect. DMI partially reversed the NE-depleting effects of DSP4. Neither bilateral adrenalectomy nor intravenously administered 6-hydroxydopamine (6-OHDA; 20 mg/kg; 1-2 days before testing) altered the excitatory effect of yohimbine, indicating that peripheral NE is not involved. 6-OHDA (2 X 200 micrograms) injected into the lateral ventricles blocked yohimbine's effect, and depleted NE by 95% (spinal cord) and 86% (forebrain), without affecting 5-HT in either region. 6-OHDA also depleted forebrain DA levels by 49%. Finally, intrathecal administration of 6-OHDA (20 micrograms; 14 days before testing) into the subarachnoid space of the lumbar spinal cord blocked the excitatory effect of yohimbine, and produced an extensive (94%) depletion of spinal cord NE. Intrathecal 6-OHDA did not alter spinal levels of 5-HT or forebrain levels of NE, 5-HT or DA. In summary, these data indicate that central descending NE neurons are necessary for yohimbine's excitatory effect on startle.     

Effect of chronic nicotine administration on monoamine and monoamine metabolite concentrations in rat brain

The effects on rat brain tissue monoamine and monoamine metabolite concentrations of chronic nicotine administration at two doses (3 and 12 mg/kg/day) using constant infusion were studied. After 21 days of treatment, tissue concentrations of dopamine (DA), norepinephrine (NE), 5-hydroxytryptamine (5-HT), and several metabolites in striatum, hypothalamus, and frontal cortex were determined by high performance liquid chromatography with electrochemical detection. Compared with a control group, nicotine treatment significantly decreased NE in frontal cortex but not in other regions. The concentration of 5HT also was decreased in frontal cortex but increased in the hypothalamus at the higher dose of nicotine. The 5HT metabolite 5-hydroxyindoleacetic acid (5-HIAA) was not significantly altered in any region. The 5HT index (5-HIAA/5-HT) was significantly decreased in the hypothalamus and increased in frontal cortex at the higher dose. Concentrations of DA and the metabolite homovanillic acid (HVA) were not significantly altered by nicotine. Nevertheless, significant decreases in the DA metabolite dihydroxyphenyl-acetic acid (DOPAC) were observed in both striatum and hypothalamus. Moreover, the DA index [(DOPAC + HVA)/DA] was significantly decreased in all three brain regions. In contrast to other studies using acute dose and in vitro perfusion paradigms that have reported increased CNS catecholamine release stimulated by nicotine, chronic administration appears to be associated with decreased catecholamine turnover in some brain regions.     

Effects of neonatal rat Borna disease virus (BDV) infection on the postnatal development of the brain monoaminergic systems

Effects of neonatal Borna disease virus infection (BDV) on the postnatal development of brain monoaminergic systems in rats were studied. Tissue content of norepinephrine (NE), dopamine (DA) and its metabolite, 3,4-dihydroxyphenol acetic acid (DOPAC), and serotonin (5-HT) and its metabolite, 5-hydroxyindole-3-acetic acid (5-HIAA) were assayed by means of HPLC-EC in frontal cortex, cerebellum, hippocampus, hypothalamus and striatum of neonatally BDV-infected and sham-inoculated male Lewis rats of 8, 14, 21, 60 and 90 days of age. Both NE and 5-HT concentrations were significantly affected by neonatal BDV infection. The cortical and cerebellar levels of NE and 5-HT were significantly greater in BDV-infected rats than control animals at postnatal days (PND) 60 and 90. Tissue content of NE in hippocampus was unaffected. In hippocampus, neonatally BDV-infected rats had lower 5-HT levels at PND 8 and significantly elevated levels at PND 21 and onwards. Neither striatal levels of 5-HT nor hypothalamic levels of 5-HT and NE were affected by neonatal BDV infection, suggesting that the monoamine systems in the prenatally maturing brain regions are less sensitive to effects of neonatal viral infection. 5-HIAA/5-HT ratio was not altered in BDV-infected rats indicating no changes in the 5-HT turnover in the brain regions damaged by the virus. Neither DA nor DOPAC/DA ratio was affected by neonatal BDV infection in any of the brain regions examined. The present data demonstrate significant and specific alterations in monoaminergic systems in neonatally BDV-infected rats. This pattern of changes is consistent with the previously reported behavioral abnormalities resulting from neonatal BDV infection.     

Neurochemical evidence that 5-hydroxytryptaminergic neurons tonically inhibit noradrenergic neurons terminating in the hypothalamus

The medial zona incerta (MZI) and dorsomedial nucleus of the hypothalamus (DMN), which contain cell bodies and terminals of incertohypothalamic dopaminergic (DA) neurons, are densely innervated by both noradrenergic (NE) and 5-hydroxytryptaminergic (5-HT) neurons. In view of emerging anatomical and pharmacological evidence suggesting possible interactions between 5-HT and catecholaminergic neurons, the effects of experimental procedures that inhibit or disrupt 5-HT neurons on the activities of catecholaminergic neurons terminating in these regions were examined in the present study. Catecholaminergic neuronal activity was estimated by measuring catecholamine synthesis (accumulation of 3,4-dihydroxyphenylalanine [DOPA] after administration of a decar☐ylase inhibitor) and metabolism (concentrations of the dopamine metabolite 3,4-dihydroxyphenylacetic acid (DOPAC) and the norepinephrine metabolite 3-methoxy-4-hydroxyphenyleneglycol (MHPG) in the MZI and DMN of both male and female rats. Inhibition of 5-HT neurons following administration of the 5-HT_1A autoreceptor agonist8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) increasedthe accumulation of DOPA in the DMN and the concentrations of DOPAC in the MZI and DMN, indicating an activation of catecholaminergic neurons in these regions. Concentrations of MHPG were increased in the MZI and DMN by 8-OH-DPAT or 5,7-dihydroxytryptamine-induced lesions of 5-HT neurons, revealing that NE neurons terminating in these regions were activated following procedures that decrease 5-HT neuronal function. Following destruction of NE neurons projecting to the MZI and DMN, 8-OH-DPAT no longer increased DOPAC concentrations in these brain regions. Taken together, these results reveal that 5-HT neurons tonically inhibit the activity of NE neurons terminating in the MZI and DMN, but do not influence the activity of incertohypothalamic DA neurons.     

Effects of Newcastle disease virus administration to mice on the metabolism of cerebral biogenic amines, plasma corticosterone, and lymphocyte proliferation

Newcastle disease virus (NDV) administration to mice increased concentrations of plasma corticosterone, with a maximal effect at 8 h. This elevation of plasma corticosterone concentrations was not observed in hypophysectomized animals in which the completeness of the hypophysectomy was verified by functional tests. NDV administration consistently increased concentrations of free tryptophan in all brain regions examined (prefrontal cortex, hypothalamus, and brain stem). It also caused an activation of cerebral catecholamine and indoleamine metabolism as determined by measurement of the amines and their catabolites. 3-Methoxy,4-hydroxyphenylethyleneglycol (MHPG), the major catabolite of norepinephrine (NE), homovanillic acid (HVA), a major catabolite of dopamine (DA), and 5-hydroxyindoleacetic acid (5-HIAA), the major catabolite of serotonin (5-HT), were all increased in both hypothalamus and brain stem. Ratios of catabolites to the parent amine, considered to be an index of utilization of the neurotransmitters, were increased for NE, DA, and 5-HT in the hypothalamus and for DA and 5-HT in the brain stem. This pattern of changes resembles that observed following stressors such as footshock or restraint. There were also significant increases of tryptophan, HVA, dihydroxyphenylacetic acid (DOPAC), and 5-HIAA in hypophysectomized relative to sham-operated mice. The NDV treatment also increased thymus weights and markedly decreased the proliferative responses of isolated spleen cells to phytohemagglutinin, concanavalin A, pokeweed mitogen, and Escherichia coli lipopolysaccharide. These changes were not caused by increased circulating corticosterone because they were present at equal magnitude in hypophysectomized mice. Thymosin alpha 1 concentrations in the plasma were not altered by NDV or hypophysectomy. These results indicate that administration of NDV to mice can initiate neurochemical and endocrine responses like those observed during stress and can also cause immunosuppression. They are thus consistent with the hypothesis that a virus can be a stressor.     

Variability among brain regions in the specificity of 6-hydroxydopamine (6-OHDA)-induced lesions

Summary 6-Hydroxydopamine (6-OHDA; 200 g, 150 g or 110 g) or vehicle was infused stereotaxically into the lateral ventricles of rats, usually following pretreatment with desmethylimipramine (DMI). Various brain regions were then assayed for dopamine (DA), serotonin (5-HT) and norepinephrine (NE). As expected, 6-OHDA depleted DA in all brain regions examined. Unexpectedly, however, the two highest doses of 6-OHDA significantly decreased 5-HT levels in the hippocampus and increased 5-HT levels in the striatum. In addition, despite pretreatment with doses of DMI commonly considered adequate to block 6-OHDA-induced depletion of NE, all doses of 6-OHDA tested significantly reduced NE levels in the hippocampus, hypothalamus and septum.We interpret our data as suggesting that some brain regions are susceptible to nonspecific toxic effects of 6-OHDA at doses commonly employed. Furthermore, these nonspecific effects may or may not occur, depending on seemingly minor variations in experimental technique.     

Catecholamines and serotonin in the rat central nervous system after 6-OHDA, 5-7-DHT and p-CPA

Summary The norepinephrine (NE), epinephrine (EPI), dopamine (DA) and serotonin (5-HT) contents were measured radioenzymatically in seven anatomically defined regions (frontal cerebral cortex, hippocampus, hypothalamus, midbrain, pons-medulla oblongata, cerebellum and spinal cord) in adult normal animals, after treatment with the tryptophan hydroxylase inhibitor p-chlorophenylalanine (p-CPA), and after the intraventricular administration of either 6-hydroxydopamine (6-OHDA) or 5, 7-dihydroxytryptamine (5, 7-DHT). The effects of p-CPA seemed not restricted to 5-HT, since reductions in catecholamine (CA) content were detected in several regions. After 5, 7-DHT given under desimipramine (DMI) protection, comparable reductions in 5-HT levels were obtained but the changes in CA were less severe than after p-CPA. The neurotoxin 6-OHDA decreased the CA in all regions but also 5-HT content in hippocampus, hypothalamus and ponsmedulla. The significance and the interpretation of these changes are discussed in relation to the specificity of the drugs employed, together with an assessment of the local monoamine turnover and the possible functional effects of monoamine interactions in the CNS.Abreviations CA catecholamines - NE norepinephrine - EPI epinephrine - DA dopamine - 5-HT serotonin - p-CPA para-chlorophenylalanine - 6-OHDA 6-hydroxydopamine - 5, 7-DHT 5, 7-dihydroxytryptamine     

Dose related effects of 6-OHDA on rabbit retinal dopamine concentrations and ERG B-wave amplitudes

The purpose of this study was to examine the dose related effects of 6-hydroxydopamine (6-OHDA) on the electroretinographic (ERG) B-wave amplitude and on retinal concentrations of dopamine (DA) and its main metabolites homovanillic acid (HVA) and dihydroxyphenylacetic acid (DOPAC). Doses of 6-OHDA (60, 300 or 1200 micrograms) were dissolved in a 0.9 percent NaCl and ascorbic acid solution and administered intravitreally in 300 microliter volume in one eye of adult pigmented rabbits. The fellow eye received a similar volume of the drug vehicle. With the smallest dose of 6-OHDA (60 micrograms) no changes in ERG B-wave amplitude or retinal concentrations of DA, DOPAC or HVA were found. With the largest dose of 6-OHDA (1200 micrograms) complete extinction of the ERG and almost total disappearance of DA, DOPAC and HVA were observed. With the intermediate dose of 300 micrograms 6-OHDA significant increases in B-wave amplitudes and decreases in retinal DA, DOPAC and HVA concentrations were obtained. This latter dose did not affect retinal concentrations of serotonin (5-HT), 5-hydroxyindole acetic acid (5-HIAA) and norepinephrine (NE). These results demonstrate that selective reductions of retinal dopamine and its metabolites can be obtained with a single intravitreal injection of 300 micrograms 6-OHDA in rabbits. The observed concomitant increase in B-wave amplitudes lends support to the hypothesis that DA acts as a mediator of lateral inhibition in the retina.     

Regional changes in monoamine content and uptake of the rat brain during postnatal development.

Regional norepinephrine (NE), dopamine (DA) and serotonin (5-hydroxytryptamine, 5-HT) contents in the developing rat brain were estimated. The rate of increase in NE content was the highest in diencephalon, followed by the lower brain stem, limbic-striatum, neocortex and cerebellum. With postnatal aging, DA concentration increased markedly in limbic-striatum, slightly in the neocortex and negligibly in other regions. In each region except cerebellum, 5-HT content increased gradually but the rate of increase in diencephalon was relatively high. Comparison of the kinetics of high affinity uptake of L-[3H]NE and [3H]5-HT between the neonatal and the adult brain indicated that Km values of L-[3H]NE and [3H]5-HT uptake were 2.9 X 10(-7) M and 1.7 X 10(-7) M respectively in neocortex, diencephalon and lower brain stem and 4.3 X 10(-7) M and 2.3 X 10(-7) M in limbic-striatum in the neonate as well as in the adult. Vmax values of both amines uptake differed regionally and the values in the neonate were lower than those in the adult in all regions. Limbic-striatum showed a higher Vmax value than other regions in uptake of both amines. These results suggested that innervation of monoaminergic neurons in the brain progressed with increasing age, that projections of both NE and 5-HT neurons were relatively high into hypothalamus and limbic-striatum and that DA neuron projections concentrated at striatum. Although the brain, except for limbic-striatum, showed neither regional nor developmental differences in affinity of L-[3H]NE and [3H]5-HT to synaptosomes, the density of nerve terminal of both monoaminergic neurons increased in all regions of the brain during postnatal development. In limbic-striatum, higher Km and Vmax values of both amines, uptake suggest the existence of both amines' uptake into DA terminal to some extent.     

Effects of intraventricular injection of 6-hydroxydopamine in the developing kitten. II. On the central monoaminergic innervation

The intraventricular administration of 6-hydroxydopamine (6-OHDA) to kittens between 5 days and 4 months of age induced marked changes in the endogenous levels of DA, NE and 5-HT in various brain areas. In contrast to the well-known selective effect of 6-OHDA against catecholaminergic neurones in the rat, serotoninergic neurones were also markedly affected by 6-OHDA treatment in kittens; particularly in the hippocampus and the colliculi, 5-HT levels were markedly and permanently decreased after the intraventricular administration of 6-OHDA. A significant but less pronounced reduction in 5-HT levels was also noted in other areas such as the piriform cortex, the cerebral neocortex, the cerebellum and the septum. Only very discrete changes were detected in the caudate nucleus, the olfactory tubercle and the raphe area. The administration of chlorimipramine (10 mg/kg, i.p.) 1 h before 6-OHDA treatment completely prevented the effects of the neurotoxic agent on serotoninergic innervation. Marked regional differences were also noted concerning the effects of 6-OHDA treatment on dopaminergic neurones. Whereas DA levels in the raphe area and the hypothalamus were almost unaffected, they were permanently reduced by about 50% in the caudate nucleus and the olfactory tubercle after the intraventricular administration of 6-OHDA. In the caudate nucleus, the reduction was even much more pronounced (−90%) when 6-OHDA was administered during the first 3 postnatal weeks.

In most forebrain areas (hippocampus, piriform cortex and cerebral neocortex) and in the cerebellum, NE levels were permanently reduced to about 10% of those of control kittens as soon as the third day following the intraventricular injection of 6-OHDA. In contrast, after a transient drop, NE levels in the lateral brain stem (containing the locus coeruleus) of 6-OHDA-treated kittens returned and even surpassed (+100%) those found in age-paired controls. Analyses of the characteristics ofl-[³H]NE uptake in synaptosomes indicated that 6-OHDA treatment resulted in both a striking loss of specific uptake sites in forebrain areas and a significant increase in the V_max of the NE uptake process in synaptosomes from the lateral brain stem. However, in contrast to the rapid increase in NE levels, this change in V_max occurred much later, since it was first detected at more than one month after 6-OHDA treatment. This delay suggests that the doubling in NE levels occurring for the first month following the intraventricular administration of 6-OHDA simply resulted from an increased accumulation of the catecholamine in noradrenergic terminals in the lateral brain stem. Later on, the change in V_max might indicate a sprouting of new noradrenergic terminals in the vicinity of the locus coeruleus area. The intraventricular administration of 6-OHDA resulted in a significant increase in the maximal stimulatory effect ofl-isoproterenol on adenylate cyclase activity in homogenates of the cerebral cortex and the lateral brain stem. Therefore, not only the degeneration (in the cerebral cortex) but also the proliferation (in the lateral brain stem) of noradrenergic terminals were associated with an increase in the density of beta-adrenergic receptors. These results are discussed in relation to the possible function of the noradrenergic sprouts in the lateral brain stem.     

Noradrenergic lesions differentially alter the expression of two subtypes of low Km cAMP-sensitive phosphodiesterase type 4 (PDE4A and PDE4B) in rat brain

This study examined the effects of selective, central noradrenergic dennervation with 6-hydroxydopamine (6-OHDA) on the expression of type 4 phosphodiesterases (PDE4). Twenty-one days following i.c.v. injection of 6-OHDA (200 microg) hypothalamus, neostriatum, and cerebellum were dissected. Infusion of 6-OHDA reduced norepinephrine (NE) content in all the brain areas examined (to 17%, 76% and 16% of sham-operated controls in hypothalamus, striatum, and cerebellum, respectively). 6-OHDA injections also reduced dopamine levels in hypothalamus (53%) and neostriatum (68%). Administration of desipramine (20 mg/kg, i.p.) 30 min prior to 6-OHDA injection protected neostriatal and cerebellar noradrenergic neurons NE levels (110-122% of the control levels). Desipramine partially attenuated the 6-OHDA-mediated decrease in NE content of hypothalamus, but had little or no effect on either striatal or hypothalamic dopamine (DA) levels. Western blot analysis using a PDE4A-selective antibody revealed three major bands (109 kDa PDE4A5, 102 kDa PDE4AX and 76 kDa PDE4A1) in hypothalamus and striatum. Infusion of 6-OHDA decreased the expression of PDE4A5 and PDE4AX but not of PDE4A1 in hypothalamus, as determined by quantitative Western blotting. Pretreatment of rats with desipramine attenuated the 6-OHDA-induced down-regulation of PDE4A5 and PDE4AX bands in hypothalamus. The PDE4B selective antibody K118 labels 5 major bands in all the brain regions studied. One hundred kDa PDE4B3, 86 kDa PDE4B2 and a 78 kDa PDE4B band was identified using recombinant proteins. Treatment of rats with 6-OHDA resulted in a 52% decrease in the PDE4B3 and 58% decrease in 78 kDa PDE4B variant in hypothalamus; administration of desipramine attenuated the 6-OHDA-induced down-regulation of both PDE4B variants. Neither 6-OHDA nor desipramine altered striatal PDE4A or PDE4B isozymes. In contrast, cerebellar PDE4B3 variant is up-regulated by 6-OHDA treatment and were partially normalized to control values by desipramine pretreatment. These data demonstrate that PDE4 subtypes are differentially regulated by presynaptic noradrenergic activity and may play an important role in the maintaining homeostasis of noradrenergic signal transduction in rat brain.     

Effect of chronic naltrexone administration and its withdrawal on the regional activity of neurons that contain norepinephrine, dopamine and serotonin

A method is described that permits the simultaneous quantitation of norepinephrine (NE), dopamine (DA) serotonin (5-HT) and their respective major metabolites, 3-methoxy-4-hydroxy phenylglycol (MHPG), 3-methoxytyramine (3-MT), dihydroxyphenyl acetic acid (DOPAC) and 5-hydroxyindole acetic acid (5-HIAA) in discrete brain regions. The ratio of MHPG/NE, DOPAC/DA and 5-HIAA/5-HT was used to assess the effects of the chronic administration of the narcotic antagonist, naltrexone, and its withdrawal on the regional activity of neurons that contain NE, DA and 5-HT respectively. Chronic administration of naltrexone (8 days) is associated with a significant increase in the ratio of 5-HIAA/5-HT and DOPAC/DA in the frontal cortex and dorsal hippocampus respectively. Under this condition the thalamic concentration of 3-MT in 4 of 8 animals is also significantly elevated. In contrast, the mesolimbic forebrain exhibited a decrease in the MHPG/NE ratio (4 out of 8 animals). One day following naltrexone pellet removal the above ratios, as well as the mean content of 3-MT in the thalamus, returned to control values. At this time the content of 3-MT in the thalamus (5 of 5 animals) and frontal cortex (3 of 9 rats) was appreciably elevated, while its content in the dorsal hippocampus was significantly reduced (6 of 9 rats). These data suggest that the activity of several central monoaminergic neuronal systems are regulated by an opioid input that is tonically active.     

Effects of ketamine on dopamine metabolism during anesthesia in discrete brain regions in mice: comparison with the effects during the recovery and subanesthetic phases

The effects of ketamine on the levels of dopamine (DA), norepinephrine (NE), 5-hydroxytryptamine (5-HT, serotonin) and their metabolites were examined in discrete brain regions in mice. A high dose of ketamine (150 mg/kg, i.p.) did not change DA metabolism in the frontal cortex, nucleus accumbens, striatum and hippocampus, but did decrease it in the brainstem during anesthesia. In contrast, during recovery from the ketamine anesthesia, the high dose increased the level of homovanillic acid (HVA) in all brain regions. A low subanesthetic dose of ketamine (30 mg/kg, i.p.) increased the concentrations of both 3,4-dihydroxyphenylacetic acid (DOPAC) and HVA only in the nucleus accumbens. The DA level was not affected by any ketamine treatment. During ketamine anesthesia, the content of 3-methoxy-4-hydroxy-phenylglycol (MHPG) was decreased in the brainstem, whereas during recovery from anesthesia, the MHPG level was increased in the frontal cortex, nucleus accumbens and brainstem. The NE content was not altered in any region by ketamine treatment. The concentration of 5-hydroxyindoleacetic acid (5-HIAA) was reduced in the frontal cortex, striatum, hippocampus and brainstem during ketamine anesthesia. The 5-HT level was unaltered in all regions except the brainstem where it was reduced. In contrast, after anesthesia, the concentrations of both 5-HT and 5-HIAA were increased in the striatum. During the subanesthetic phase, however, the levels of NE, 5-HT and their metabolites were unchanged. These neurochemical results are consistent with the electrophysiological findings that a high dose of ketamine does not change the basal firing rates of nigrostriatal DA neurons during anesthesia, while low subanesthetic doses significantly increase those of ventral tegmental DA neurons.     

Modification of gonadectomy-induced increases in brain monoamine metabolism by steroid hormones in male and female rats

Concentrations of monoamines (dopamine, DA; serotonin, 5-HT) and their major metabolites (homovanillic acid — HVA; dihydroxyphenylacetic acid — DOPAC; 5-hydroxyindolacetic acid — 5-HIAA) were measured in selected brain areas of chronically gonadectomized, steroid- or oil-treated male and female rats. Concentrations of DOPAC and HVA were markedly increased in the hypothalamus (male, female), striatum (male, female) and brainstem (male) following gonadectomy, whereas the levels of DA remained unaltered in most of the brain areas examined. Most of the changes were reversed or attenuated by chronic estradiol (EB) substitution. In contrast, chronic treatment with physiological concentrations of testosterone (TP) reduced indexes of DA turnover only in the striatum of ovariectomized (OVX) and brainstem of orchidectomized (ORDX) rats. ORDX-related increases in striatal levels of DOPAC and HVA were not reversed by either EB or TP. ORDX increased the levels of 5-HIAA (hypothalamus, striatum) and decreased those of 5-HT (hypothalamus, hippocampus). These changes were reversed by chronic treatment with either TP or EB. Brain metabolism of 5-HT remained unaltered following OVX.

Gonadectomy and chronic steroid replacement therapy appear to alter brain monoamine metabolism in a brain region and sex-dependent manner. Our data demonstrate that gonadectomy-related increases in the activity of brain monoaminergic neurons in both male and female rats was attenuated more effectively with physiological concentrations of estradiol than with testosterone. Insensitivity of monoaminergic neurons in a number of brain areas (e.g., hypothalamus, striatum) to the action of testosterone was evident in both sexes.     

Levels of biogenic amines and their metabolites in rat whole brain after rapid tissue fixation with microwave irradiation (author's transl)]

Levels of norepinephrine (NE), dopamine (DA), serotonin (5-HT), 3, 4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxy-indoleacetic acid were measured fluorometrically in the whole brain of rats killed either by decapitation or by 5kW microwave irradiation for 1.6 sec. which inactivates the relevant brain enzymes rapidly and irreversibly. There were statistically no differences in the levels of NE, DA, 5-HT and 5-HIAA between the two methods of sacrifice, while the level of DA increased slightly in irradiated brains. On the other hand, the level of DOPAC, an oxidative deaminated metabolite of DA, increased significantly and the level of HVA, a final metabolite of DA, reduced markedly in the irradiated brains compared to that in the decapitated brains, respectively. These findings suggest that the turnover rates for metabolism of DA at synaptic nerve terminals and synaptic clefts may be relatively rapid. Therefore, it may be concluded that rapid inactivation of the brain enzymes involved in metabolism of DA is necessary prior to analysis of DA and its metabolites and microwave irradiation is the most suitable method available at the present time.     

Amphetamine and mCPP Effects on Dopamine and Serotonin Striatalin vivo Microdialysates in an Animal Model of Hyperactivity

In the neonatally 6-hydroxydopamine (6-OHDA)-lesioned rat hyperlocomotor activity, first described in the 1970s, was subsequently found to be increased by an additional lesion with 5,7-dihydroxytryptamine (5,7-DHT) (i.c.v.) in adulthood. The latter animal model (i.e., 134 microg 6-OHDA at 3 d postbirth plus 71 microg 5,7-DHT at 10 weeks; desipramine pretreatments) was used in this study, in an attempt to attribute hyperlocomotor attenuation by D,L-amphetamine sulfate (AMPH) and m-chlorophenylpiperazine di HCl (mCPP), to specific changes in extraneuronal (i.e., in vivo microdialysate) levels of dopamine (DA) and/or serotonin (5-HT). Despite the 98-99% reduction in striatal tissue content of DA, the baseline striatal microdialysate level of DA was reduced by 50% or less at 14 weeks, versus the intact control group. When challenged with AMPH (0.5 mg/kg), the microdialysate level of DA went either unchanged or was slightly reduced over the next 180 min (i.e., 20 min sampling), while in the vehicle group and 5,7-DHT (alone) lesioned group, the microdialysate level was maximally elevated by approximately 225% and approximately 450%, respectively--and over a span of nearly 2 h. Acute challenge with mCPP (1 mg/kg salt form) had little effect on microdialysate levels of DA, DOPAC and 5-HT. Moreover, there was no consistent change in the microdialysate levels of DA, DOPAC, and 5-HT between intact, 5-HT-lesioned rats, and DA-lesioned rats which might reasonably account for an attenuation of hyperlocomotor activity. These findings indicate that there are other important neurochemical changes produced by AMPH- and mCPP-attenuated hyperlocomotor activity, or perhaps a different brain region or multiple brain regional effects are involved in AMPH and mCPP behavioral actions.     

Brain serotonin and catecholamine responses to repeated stress in rats

This study was designed to compare the effects of single and repeated administration of a discrete 2-min restraint stress on serotonin (5-HT) and catecholamine neuron activity in various regions of rat brain. A single 2-min restraint stress significantly increased the 5-hydroxyindoleacetic acid (5-HIAA) and 5-HT responses in hypothalamus and cerebral cortex and the 5-HIAA response in brainstem. A second 2-min restraint stress applied 90 min after the initial stress did not appreciably alter the steady-state concentrations of 5-HIAA and 5-HT nor did it produce any further changes in the 5-HIAA and 5-HT responses compared to those seen following a single stress in these 3 brain regions. In addition, the synthesis rate of 5-HT in anterior hypothalamus, posterior hypothalamus, hippocampus and brainstem was not altered by a second stress applied 90 min after the initial stress. In contrast, a second 2-min restraint stress applied 30 or 60 min after the initial stress significantly increased the 5-HIAA concentration in hypothalamus, cerebral cortex and brainstem. Also, the synthesis rate of 5-HT was greater following application of a second stress at 30 min than following either a single stress or a second stress applied at 90 min. Following application of a single 2-min restraint stress the hypothalamic concentration of norepinephrine (NE) was significantly decreased at 5 min after onset of the stress and returned to prestress levels by 15 min; the hypothalamic dopamine (DA) concentration was significantly increased at 30 min after the onset of the stress, while the hypothalamic epinephrine (EPI) concentration remained unchanged. A second 2-min restraint stress applied at 30 min markedly lowered NE concentrations in whole and mediobasal hypothalamus but not in laterobasal hypothalamus, and the NE concentrations remained decreased for a period lasting at least 60 min; there was a significant decrease in the hypothalamic EPI concentration 60 min after application of the second stress at 30 min. In addition, the synthesis rate of catecholamines was significantly greater in anterior but not in posterior hypothalamus after application of a second stress 30 min after the initial stress than following either a single stress or a second stress applied at 90 min. Negative correlations were demonstrated between increased synthesis rates of both hypothalamic 5-HT and anterior hypothalamic catecholamines and decreased corticosterone response to single and repeated stress.(ABSTRACT TRUNCATED AT 400 WORDS)     

Hypothalamic monoamines and their catabolites in relation to the estradiol-induced luteinizing hormone surge

Monoamines and non-conjugated catabolites (serotonin (5-HT), 5-hydroxyindole acetic acid (5-HIAA), 3,4-dihydroxyphenyl-acetic acid (DOPAC), homovanillic acid (HVA), 4-hydroxy-3-methoxyphenylethyleneglycol (MHPG), norepinephrine (NE), and dopamine (DA] were measured in the medial basal hypothalamus (MBH) and preoptic area (POA) of ovariectomized (OVX) and OVX estradiol (E2)-treated rats using high-performance liquid chromatography with electrochemical detection. These E2 treatments were sufficient to induce an LH surge. The use of MHPG/NE ratios as estimates of NE release was validated in the rat hypothalamus by the major decreases of MHPG after injection of the alpha 2-adrenergic agonist, clonidine, and by MHPG increases after the alpha 2-antagonist, yohimbine. The ratio, MHPG/NE, decreased between morning and afternoon in the MBH but not in the POA; there were no differences between OVX and E2-treated rats. Previous studies using a variety of methods indicate that NE turnover increases during LH surges. The present data suggest that unconjugated MHPG is not a sensitive measure of NE release in the rat hypothalamus, but can detect the large changes produced by stimulating or inhibiting the alpha 2-adrenergic autoreceptor. The ratios of DOPAC/DA and 5-HIAA/5-HT in the MBH decreased consistently between morning and afternoon in OVX rats, with or without E2 treatment. This suggests that the release of DA and 5-HT decreases during the day regardless of steroidal milieu.     

Effects of neurotensin on regional brain concentrations of dopamine, serotonin and their main metabolites.

The effects of neurotensin, 7.5 or 30 micrograms, on concentrations of DA, DOPAC, (HVA), serotonin 5-HT and 5-HIAA were measured in 8 regions of the rat brain either 5 or 30 min following intracerebroventricular administration. Regions examined include the frontal cortex, striatum, nucleus accumbens, amygdala, septum, hypothalamus, ventral tegmentum and substantia nigra. Results indicate that both doses of neurotensin significantly elevated concentrations of dopamine in the striatum and amygdala 5 min following injection. The effects of the peptide on DOPAC and HVA were more pervasive and enduring, with significant increases in metabolite levels occurring in both mesolimbic and nigrostriatal terminal regions. In order to assess effects on turnover of dopamine, the ratios of each metabolic to dopamine concentrations were examined. Results indicate that, while the DOPAC/DA ratio was elevated in many regions, the HVA/DA ratio was increased in all regions examined. The effects of neurotensin on serotoninergic parameters were less pervasive and more variable, with both increases and decreases in 5-HT and 5-HIAA concentrations being observed. The effects of the peptide on 5-HIAA/5-HT were limited to the nucleus accumbens, where this ratio was increased, and the ventral tegmentum, where 5-HIAA/5-HT was decreased. These findings reveal that the effects of the neurotensin on dopaminergic transmission are more widespread than previously reported in that all major dopamine pathways are affected by the peptide. Also, the observed changes in the ratios of both DOPAC and HVA to DA suggest that neurotensin enhances the turnover of this transmitter.