Prolactin and its receptors in the chronic mild stress rat model of depression.

Prolactin (PRL) exhibits many physiological functions with wide effects on the central nervous system including stress responses. Our study aimed to investigate the effect of chronic unpredictable mild stress (CMS) - which is a good animal model of depression - on PRL receptor (PRLR) expression in the rat brain. Rats were exposed to CMS for two weeks and subsequently to CMS in combination with imipramine (IMI) treatment for five consecutive weeks. Behavioral deficit measured in anhedonic animals is a reduced intake of sucrose solution. Two weeks of CMS procedure allowed the selection of animals reactive to stress and displaying anhedonia, and the group which is considered as stress-non-reactive as far as behavioral measures are concerned. In this group the elevated level of PRL in plasma was observed, decrease in dopamine release in the hypothalamus, increase in [(125)I]PRL binding to PRLR in the choroid plexus, increase of mRNA encoding the long form of PRLR in the arcuate nucleus and the decrease of mRNA encoding its short form, and decrease in the mRNA encoding dopamine D2 receptor. All these alterations indicate these parameters as involved in the phenomenon of stress-resilience. The prolongation of the CMS procedure for additional five weeks shows the form of habituation to the stressful conditions. The most interesting result, however, was the up-regulation of PRLR in the choroid plexus of rats subjected to full CMS procedure combined with treatment with IMI, which may speak in favor of the role of this receptor in the mechanisms of antidepressant action.

The effect of an endogenous compound 1-methyl-1,2,3,4,-tetrahydroisoquinoline on morphine-induced analgesia, dependence and neurochemical changes in dopamine metabolism in rat brain structures.

1,2,3,4-Tetrahydroisoquinolines, among them the most interesting neuroprotective substance, an inhibitor of MAO, 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), are endogenous compounds present in the central nervous system of mammals and humans. In this study, we investigated the effect of 1MeTIQ on morphine-induced analgesia, tolerance and abstinence syndrome as well as its effect on morphine-induced changes in dopamine metabolism in rat brain structures (nucleus accumbens, striatum, substantia nigra) using HPLC methodology. The experiments were carried out on male Wistar rats. Morphine analgesia was measured in the "hot-plate" test. To induce tolerance, morphine was given chronically (20 mg/kg i.p.) alone or following 1MeTIQ (50 mg/kg i.p.) injection. The development of dependence was assessed in the naloxone (2 mg/kg i.p.) precipitation test, after 10 days of morphine administration. The behavioral studies have shown that an endogenous compound, 1MeTIQ produced strong potentiation of morphine analgesia, prevented the development of morphine tolerance and inhibited expression of morphine abstinence syndrome in morphine-dependent rats. In neurochemical studies, we have demonstrated that 1MeTIQ antagonized morphine-induced changes in dopamine metabolism observed in rat brain structures. The main finding of this study was demonstration for the first time of an anti-abuse effect of an endogenous compound, 1MeTIQ, and its efficiency in counteracting morphine-induced addiction in the way useful from clinical point of view. The obtained results suggested a possibility of clinical application of 1MeTIQ in morphine addiction.

An endogenous neuroprotectant substance, 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ), prevents the behavioral and neurochemical effects of cocaine reinstatement in drug-dependent rats.

Drug abuse disorder is induced by a variety of substances and results from their interaction with the brain reward system. It is characterized by a high frequency of relapse, usually associated with to craving. In this study we investigated the effects of 1-methyl-1,2,3,4-tetrahydroisoquinoline, an endogenous compound with antidopaminergic and neuroprotective activity, on cocaine-induced reinstatement in cocaine-dependent, self-administering rats. 1-methyl-1,2,3,4-tetrahydroisoquinoline (50 mg/kg i.p.) completely inhibited the expression of reinstatement of cocaine self-administration and accompanying neurochemical changes induced by a single priming cocaine dose (10 mg/kg i.p.). The priming cocaine dose inhibited dopamine metabolism in the structures containing nerve endings (frontal cortex, nucleus accumbens, and striatum) but not in the substantia nigra and ventral tegmental area. A behaviorally active dose of 1-methyl-1,2,3,4-tetrahydroisoquinoline administered 30 min before a priming dose of cocaine significantly increased the dopamine concentration in the limbic structures, and strongly inhibited dopamine metabolism in the substantia nigra and ventral tegmental area. Cocaine also inhibited noradrenaline and serotonin metabolism, and 1-methyl-1,2,3,4-tetrahydroisoquinoline abolished the inhibition in noradrenaline metabolism, while it intensified the inhibition of serotonin metabolism. Our results strongly support the view that 1-methyl-1,2,3,4-tetrahydroisoquinoline, an endogenous compound, has considerable potential as a drug for combating substance abuse disease through the attenuation of craving.

Increased striatal neuropeptide Y immunoreactivity and its modulation by deprenyl, clonidine and L-dopa in MPTP-treated mice.

The aim of this study was to evaluate the effect of MPTP (2 x 45 mg/kg s.c., 20 h apart) on striatal neuropeptide Y-like immunoreactivity (NPY-LI) in C57BL/6 mice. NPY-LI markedly increased 2 weeks after MPTP but it remained unchanged after 24 h, 1 or 6 weeks. The increase in NPY-LI was accompanied by depletion of dopamine (-80%), DOPAC (-70%), 3-MT (-44%) and HVA (-52%). L-Deprenyl completely prevented the MPTP-induced NPY-LI increase, neurodegeneration of the striatal dopamine system and motor dysfunction. Clonidine attenuated the neurotoxin effect on NPY-LI and dopaminergic neurons. L-dopa/carbidopa protected NPY neurons against MPTP but slightly enhanced MPTP-induced decrease in the levels of dopamine and its metabolites. The relationship between changes in NPY-LI and dopamine and serotonin metabolism determined by HPLC was discussed. The results further extend the range of MPTP-elicited modifications in striatum and demonstrate that drugs with antiparkinsonian activity can protect NPY neurons against MPTP toxicity.

Different action on dopamine catabolic pathways of two endogenous 1,2,3,4-tetrahydroisoquinolines with similar antidopaminergic properties.

The effect of single and multiple 1-methyl-1,2,3,4-tetrahydroisoquinoline (1MeTIQ) and 1-benzyl-1,2,3,4-tetrahydroisoquinoline (1BnTIQ) administration on concentrations of dopamine and its metabolites: homovanillic acid (HVA) and 3,4-dihydroxyphenylacetic acid (DOPAC) and 3-methoxytyramine (3MT) in three brain areas was studied HPLC with electrochemical detection in Wistar rats. The rate of dopamine catabolism in the striatum along the N-oxidative and O-methylation pathways was assessed by calculation of the ratio of appropriate metabolites to dopamine concentration. In addition, the spontaneous and apomorphine-stimulated locomotor activity, and muscle rigidity was studied after acute administration of 1MeTIQ and 1BnTIQ. We have found that 1MeTIQ did not change the level of dopamine and HVA in all investigated structures both after a single and chronic administration. However, the levels of intermediary dopamine metabolites, DOPAC and 3MT, were distinctly affected. The level of DOPAC was strongly depressed (by 60-70%) while the level of extraneuronal matabolite 3MT was significantly elevated (by 170-200%). In contrast to 1MeTIQ, 1BnTIQ depressed the level of dopamine (by approximately 60%) and increased the level of total metabolite, HVA, (by 40%) especially in the striatum, but the levels of DOPAC and 3MT remained unchanged. The paper has shown that 1MeTIQ and 1BnTIQ produced different effects on dopamine catabolism. Potential neuroprotective compound 1MeTIQ did not change the rate of total dopamine catabolism, it strongly inhibited the monoamine oxidase (MAO)-dependent catabolic pathway and significantly activated the catechol-O-methyltransferase (COMT)-dependent O-methylation. In contrast 1BnTIQ, a compound with potential neurotoxic activity, produced the significant increase of the rate of dopamine metabolism with strong activation of the oxidative MAO-dependent catabolic pathway. Interestingly, both compounds produced similar antidopaminergic functional effects: antagonism of apomorphine hyperactivity and induction of muscle rigidity. The results may explain the biochemical basis of the neuroprotective and of the neurotoxic properties endogenous brain tetrahydroisoquinoline derivatives.

Antidopaminergic effects of 1,2,3,4-tetrahydroisoquinoline and salsolinol.

Immediate behavioral and biochemical effects of single doses of 1,2,3,4-tetrahydroisoquinoline (TIQ, 50 mg/kg) and salsolinol (100 mg/kg), suspected of involvement in etiology of Parkinson's disease, were investigated. Apomorphine (0.25 mg/kg) or haloperidol (1 mg/kg) were administered to TIQ or salsolinol pretreated Wistar rats. In additional experiment the displacement of [3H]apomorphine by TIQ, salsolinol and dopamine receptor agonists and antagonists was tested. Both tetrahydroisoquinolines only slightly affected behavior and dopamine metabolism in naive rats, but very effectively abolished the behavioral and biochemical effects of apomorphine (hyperactivity, depression of striatal HVA level). The behavioral and biochemical effects of haloperidol were unchanged by administration of TIQ nor salsolinol. The tetrahydroisoquinolines displaced [3H]apomorphine from its binding sites with effectiveness comparable to that of dopamine. The results support the hypothesis that endogenous tetrahydroisoquinolines may play an important role in regulation of dopaminergic activity in non-senescent organisms.

Neurochemical changes induced by acute and chronic administration of 1,2,3,4-tetrahydroisoquinoline and salsolinol in dopaminergic structures of rat brain.

The finding that endogenous tetrahydroisoquinolines may be involved in the etiology of Parkinson's disease suggests that their administration may cause changes resembling those observed in parkinsonian brain. We tested, using a high-performance liquid chromatography method, how single and chronic administration of 1,2, 3,4-tetrahydroisoquinoline and salsolinol affects dopamine and serotonin metabolism in the neurons of extrapyramidal and mesolimbic dopaminergic systems. We report that chronic administration of tetrahydroisoquinoline and salsolinol causes a decrease in a dopamine metabolism: the effect of tetrahydroisoquinoline was limited to the striatum, while salsolinol caused also a dramatic decline of dopamine level in the substantia nigra. The effect of both compounds on serotonin metabolism was small or absent. The tetrahydroisoquinolines produced no changes in the nucleus accumbens. The results indicate that tetrahydroisoquinoline and salsolinol specifically affect the nigrostriatal dopamine system, but only when administered chronically, and thus are compatible with the view that endogenous tetrahydroisoquinolines may participate in pathogenesis of Parkinson's disease.

Postmortem instability of dopamine and its metabolites in rat striatum and limbic forebrain.

The level of dopamine (DA) and its metabolites 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 3-methoxytyramine (3-MT) were determined in the brains of rats kept 24 h after death at two different temperatures, 4 degrees C and 22 degrees C. The estimations were carried out in the striatum and limbic forebrain containing: nucleus accumbens, septum, limbic cortex, amygdala, tuberculum olfactorium. Brain tissue of control rats was dissected immediately after decapitation, frozen over solid CO2 and stored at -70 degrees C until assayed. DA and its metabolites were measured, using high-performance liquid chromatography (HPLC) with electrochemical detection. The levels of DA, DOPAC and HVA in the striatum were significantly decreased (from 50% to 80%) when rats were kept 24 h after death. The changes were more pronounced at 22 degrees C than at 4 degrees C. As the decrease in DA concentration was stronger than that of its final metabolite HVA, the ratio of HVA/DA concentration measured as an index of the rate of DA metabolism was even increased (from 8 to 11). Different changes occurred in the limbic region, where the levels of DA and HVA did not change neither at 4 degrees C nor 22 degrees C. The level of intraneuronally formed DA metabolite-DOPAC was elevated (by about 60%). The level of 3-MT, extraneuronally formed DA metabolite, was significantly increased both in the striatum (200%) and limbic DA structures (500%). These data demonstrate regional postmortal differences in stability of DA and its metabolite levels, which are in the striatum temperature-, time-, and storage-dependent. That implicates a careful assessment of postmortem studies when measuring the neurotransmitter dynamics in human necropsy material.

Increase in salsolinol level in the cerebrospinal fluid of parkinsonian patients is related to dementia: advantage of a new high-performance liquid chromatography methodology.

The study was carried out on the lumbar cerebrospinal fluid (CSF) samples taken from nonparkinsonian, early parkinsonian, and advanced parkinsonian patients. Some patients showed dementia, and some were treated with L-dopa. In the samples, salsolinol (1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline) was assayed with a newly developed sensitive high-performance liquid chromatography (HPLC) method; 3-O-methyldopa (3-O-MD) and homovanillic acid (HVA) were also assayed by HPLC. CSF salsolinol concentrations were significantly enhanced in patients with signs of dementia, regardless of the degree of parkinsonism, and were not affected by L-dopa treatment; HVA and, particularly, 3-O-MD levels were elevated in patients receiving L-dopa. The strong association of CSF salsolinol level with dementia, but not with L-dopa treatment suggests that salsolinol does not originate from L-dopa metabolism, and that its elevation is an indicator of neurodegenerative processes resulting in damage to brain areas mediating cognitive functions. We found no correlation between the advancement of parkinsonism and the concentrations of 3-O-MD and HVA.

Ca2+ channel blockade prevents lysergic acid diethylamide-induced changes in dopamine and serotonin metabolism.

To investigate the effect of a single and multiple administration of lysergic acid diethylamide (LSD) on cerebral metabolism of dopamine and serotonin, male Wistar rats were treated with low and high doses (0.1 and 2.0 mg/kg i.p.) of LSD and the levels of dopamine, 3,4-dihydroxyphenylacetic acid, homovanillic acid, 3-methoxytyramine, serotonin and 5-hydroxyindoleacetic acid were assayed by HPLC in the nucleus accumbens, striatum and frontal cortex. Some rats received nifedipine, 5 mg/kg i.p., before each injection of LSD to assess the effect of a Ca2+ channel blockade. High-dose LSD treatment (8 x 2 mg/kg per day) caused a strong stimulation of dopamine metabolism in the nucleus accumbens and striatum, and serotonin metabolism in the nucleus accumbens: the changes were observed 24 (but not 1 h) after the last dose. The changes induced by the low-dose treatment (8 x 0.1 mg/kg per day) had a different pattern, suggesting the release of dopamine from vesicles to cytoplasm. Co-administration of nifedipine completely prevented the LSD-induced biochemical changes. The results suggest that Ca2+ channel blocking agents may prevent development of some behavioral consequences of chronically used LSD.

[Salsolinol, 3-O-methyl-dopa and homovanillic acid in the cerebrospinal fluid of Parkinson patients]. / Salsolinol oraz 3-0-metyldopa i kwas homowanilinowy w plynie mózgowo-rdzeniowym u osób z choroba parkinsona.

Salsolinol is one of the dopamine-derived tetrahydroisoquinolines, supposed to be a potent dopaminergic neurotoxin, similar to MPTP. Its systemic administration induced parkinsonism in monkeys. The aim of the study was to compare the concentration of salsolinol and the metabolite of L-dopa, 3-O-MD, and the metabolite of dopamine, HVA, in the cerebrospinal fluid of patients with different degrees of parkinsonism, treated or nontreated with l-dopa. Lumbar CSF was obtained from 26 patients with Parkinson's disease (15 early and 11 advanced parkinsonism) and from six healthy controls. The presence of salsolinol, HVA and 3-O-MD was assayed with a sensitive HPLC method employing C18 (Hypersil BDS) column. The analysis of the results demonstrated that the concentration of salsolinol was related to the degree of parkinsonism but not affected by l-dopa treatment. In contrast, HVA and 3-O-MD were significantly elevated in patients receiving l-dopa but did not correlate with the severity of parkinsonism. The results suggest that salsolinol in the cerebrospinal fluid does not originate from exogenous l-dopa and its elevation in cerebrospinal fluid may be an indicator of the advancement of parkinsonism.

Differences in effects of Ca2+ channel antagonists on dopamine metabolism in the limbic and extrapyramidal dopaminergic structures.

The effect of single and multiple administration of Ca2+ channel antagonists, nifedipine and verapamil, on concentrations of dopamine and its metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), was investigated in the mesolimbic (cortex, nucleus accumbens) and extrapyramidal (striatum) structures in Wistar rats. A single dose of nifedipine (10 mg/kg IP) produced some activation of the dopaminergic system in both cortex (increase in DOPAC) and n. accumbens (increase in HVA); verapamil (20 mg/kg IP) produced an increase in HVA in the cortex only. Chronic treatment with either Ca2+ channel antagonist produced more marked activation of dopamine metabolism in the cortex and nucleus accumbens. Those changes were most expressed 1 h after the last treatment, but lasted for at least 24 h. No changes in dopamine metabolism were observed in the striatum. The present data suggest that Ca2+ channel antagonists after chronic treatment specifically activate the dopaminergic system in limbic structures.

Immediate and "day-after" effects of morphine on dopamine and serotonin metabolism in various structures of the rat brain.

The effects of a single dose of 20 mg/kg ip of morphine on dopaminergic and serotonergic systems in the limbic (cortex, nucleus accumbens) and extrapyramidal (striatum) structures were investigated in rats. The action of morphine was assessed by measuring the regional concentrations of dopamine, serotonin and their metabolites (homovanillic acid- HVA,3,4-dihydroxyphenylacetic acid - DOPAC, 5-hydroxyindoleacetic acid - 5-HIAA) by means of HPLC. We have demonstrated that a single large dose of morphine produces a biphasic change in limbic dopaminergic and serotonergic structures, with an initial activation followed by significant inhibition 24 h later. In contrast, the striatum depression of dopamine level was observed during the initial phase with normalization on the next day.

Differential involvement of voltage-dependent calcium channels in apomorphine-induced hypermotility and stereotypy.

The involvement of the voltage-dependent calcium channel in behavioral effects of apomorphine was tested in naive rats and in animals which were morphine-abstinent or were subjected to chronic electroconvulsive treatment (ECS). In naive rats a calcium channel blocker, nifedipine, which by itself does not affect locomotor activity, inhibited the locomotor stimulation induced by apomorphine, while it facilitated stereotyped behavior. Morphine-abstinent and ECS-treated rats displayed elevated responsiveness to apomorphine, reflected by hypermotility and stereotyped behavior after a dose of 1 mg/kg IP that does not produce overt behavioral effects in naive animals. Nifedipine, 5 mg/kg IP, significantly reduced hypermotility produced by apomorphine in morphine abstinent or ECS-treated rats. The calcium channel blocker did not, however, antagonize enhanced stereotyped behavior. The results indicate that apomorphine hypermotility is controlled by dihydropyridine calcium channels and that enhancement of calcium channel density produced by morphine abstinence and by chronic ECS potentiates the hypermotility response. Calcium channels seem to be differently involved in control of apomorphine-induced hypermotility and stereotypy.

The effect of calcium channel blockade during electroconvulsive treatment on cerebral cortical adrenoceptor subpopulations in the rat.

Chronic administration of nifedipine (5 mg/kg/day for 10 days) induced some biochemical effects consistent with those of antidepressants: a significant depression in cortical alpha 2-adrenoceptor density and reduction of beta-adrenoceptor affinity; nifedipine co-administration with electroconvulsive treatment potentiated the beta-downregulatory effect of the latter.

Reduction of morphine dependence and potentiation of analgesia by chronic co-administration of nifedipine.

Nifedipine, 5 mg/kg IP, potentiated the morphine-induced analgesia measured in the hot-plate, but not in the tail-flick test. Further experiments were carried out using the hot-plate test only. Pretreatment with nifedipine partially restores the analgesic action of morphine in morphine-tolerant rats. Co-administration of nifedipine with morphine in a chronic experiment did not prevent the loss of morphine efficiency (an increase in latency of 44% was not significant) and did not prevent the debilitating effect of chronic morphine administration reflected by an inhibition of the body weight gain, but prevented naloxone-induced withdrawal syndrome (quantified by counting head shakes) in the test carried out 24 h after the injection of nifedipine, when the drug did not affect morphine analgesia. Chronic treatment with either morphine or nifedipine did not produce a significant increase in the density of [3H] naloxone or [3H]prazosin binding sites in the cortex and in the rest of the brain (measured 24 h after the last dose), but the combined treatment resulted in a significant increase in the cortical [3H]prazosin binding site density. The present results suggest that opiate tolerance and physical dependence may be separated by co-administration of nifedipine and suggest that the combined chronic treatment with morphine and nifedipine may increase the efficacy of morphine during chronic treatment and prevent development of abstinence.

Role of calcium channels in effects of antidepressant drugs on responsiveness to pain.

The effect of acute and chronic treatment with three antidepressant drugs on the cortical L-type calcium channel (measured as [3H]nitrendipine binding sites) and on the responsiveness to pain (assessed in the hot-plate test) was tested on the Wistar rat. Acute administration of antidepressants did not affect the characteristics of calcium channels and did not significantly prolong the hot-plate latency. However, a combination of antidepressants with nifedipine brought about analgesia. Chronic administration of imipramine did not significantly affect the characteristics of calcium channels but produced a moderate analgesic effect. In contrast, chronic administration of citalopram and chlorprothixene increased the density of [3H]nitrendipine binding sites and induced hyperalgesia, which was nullified by acute administration of nifedipine. The results confirm that calcium channels may be involved in analgesia and hyperalgesia and indicate that chronic treatment with some antidepressant may induce an increase in the density of cortical calcium channels.

Cortical dihydropyridine binding sites and a behavioral syndrome in morphine-abstinent rats.

The density of cortical [3H]nitrendipine binding sites was elevated by over 40% in rats rendered morphine-abstinent by administration of naloxone after chronic treatment with morphine. The morphine-abstinent rats had significantly shortened response latencies in the hot-plate test. Nifedipine treatment abolished the signs of abstinence and normalized the hot-plate latencies in morphine-dependent, naloxone-treated rats. The results indicate that the symptoms of abstinence are related to a functional state of cortical dihydropyridine-sensitive calcium channels.

Effect of repetitive electroconvulsive treatment on sensitivity to pain and on [3H]nitrendipine binding sites in cortical and hippocampal membranes.

The effect of electroconvulsive shock (ECS) on the responsiveness to pain (measured by the hot-plate test) and on the characteristics of L-type calcium channels (measured as [3H]nitrendipine binding sites) in the cortex and hippocampus was tested on the Wistar rat. In animals receiving a single ECS, the calcium channel density and affinity 24 h after treatment did not differ from the controls; the response to pain was also at the control level. Repeated ECS (eight once-daily shocks) resulted in an increased responsiveness to pain (shortening of response latency) and in an increase in the density of cortical, but not hippocampal, calcium channels. The KD value for [3H]nitrendipine binding sites in either brain region remained unaltered by ECS. The calcium channel antagonist nifedipine, which by itself did not significantly alter the response to pain, prevented the enhancement of pain sensitivity brought about by ECS. The results suggest activation of calcium-dependent mechanisms by repeated ECS and confirm the involvement of calcium channels in pain mechanisms.

Behavioral and biochemical effects of intraventricular kainic acid.

Wistar rats received intraventricularly solutions of kainic acid (KA) and behavioral symptoms and changes in the brain concentrations of biogenic amines and 5-hydroxy-indole-acetic acid (5-HIAA) following the injection were observed. KA produced a characteristic behavioral syndrome dominated by episodes of "wet dog shakes" (WDS), which were most frequent after doses of 0.25-1.5 nmole, 10-25 min after the injection. Multiple injections of KA produced only negligible inhibition of the response in initial experiments, and the effect was significantly below the control level on the 6th consecutive treatment. WDS were more frequent in rats which had undergone central chemosympathectomy with 6-hydroxydopamine. Serotoninolytics did not inhibit WDS; the shakes were strongly inhibited by pretreatment with compounds inhibiting the transmission in the noradrenergic neurons, clonidine and aceperone, by a neuroleptic, spiperone, and by opiates stimulating the opiate receptor; morphine, azidomorphine and N-cyclopropylmethylnorazido-morphine, but not by an opiate receptor antagonist, naloxone. KA depressed the cerebral level of norarenaline 35 min after the administration, byt 6 days after a single injection the brain levels of noradernaline and 5-HIAA were elevated. It i suggested that the catecholaminergic systems and opiate receptors play an important role in the syndrome observed, and that the syndrome resembles the syndrome of morphine abstinence.