Prenatal administration of lipopolysaccharide induces sex-dependent changes in glutamic acid decarboxylase and parvalbumin in the adult rat brain.

RATIONALE: Recent clinical studies suggest GABA-ergic system abnormalities as a neuropathological mechanism of schizophrenia. OBJECTIVES: In the present study, we examined the effect of chronic prenatal lipopolysaccharide (LPS) administration on immunohistochemical changes of glutamate decarboxylase (GAD67) and parvalbumin (PV)-expressing neurons in the medial prefrontal cortex and hippocampus of rats. RESULTS: These data demonstrated that prenatal LPS administration during the final 2 weeks of pregnancy induced schizophrenia-like behavioral symptoms, such as deficits in sensorimotor gating (prepulse inhibition) and impairments in social interactions and exploration, in adult offspring. Moreover, immunohistochemical analysis revealed that in our neurodevelopmental model of schizophrenia, decreases in the total number of PV- and GAD67-positive neurons in the medial prefrontal cortices of adult females prenatally exposed to LPS were observed, whereas these immunochemical changes were primarily detected in the hippocampus of males. Additionally, a decrease in PV-labeled axon terminals of GABA-ergic cells, likely reflecting the perisomatic inhibitory innervation of pyramidal neurons, was observed in the medial prefrontal cortices in both sexes. CONCLUSION: This study provided evidence of a key role for the GABA system in neurodevelopment associated with the etiopathogenesis of schizophrenia and showed that the observed changes are sex-dependent. Moreover, this study is the first to present a model of schizophrenia based on prenatal LPS administration, which not only produced behavioral abnormalities but also changed the cytoarchitecture of the GABA inhibitory system.

Prenatal lipopolysaccharide treatment enhances MK-801-induced psychotomimetic effects in rats.

The aim of this study was to evaluate the effect of prenatal lipopolysaccharide (LPS) treatment, which is an animal developmental model of schizophrenia, on MK-801-induced psychotomimetic behavioral changes and brain aminergic system activity in adult offspring. Repeated LPS (1 mg/kg) injection in rats, that had started from 7th day of pregnancy and was continued every second day till delivery, resulted in a long-lasting disruption of prepulse inhibition (PPI) and elevation of locomotor activity in their offspring. The prenatally LPS-treated rats showed hypersensitivity to MK-801 (0.1 and 0.4 mg/kg) as evidenced by the enhancement of acoustic startle amplitude, reduced PPI, and enhanced locomotor activity. These behavioral changes were accompanied by a decrease in the dopamine and its metabolite, DOPAC concentration in the frontal cortex, enhanced dopaminergic system activity in the striatum and no changes in noradrenaline (NA) level. Furthermore, the significant augmentation of 5-HT and 5-HIAA content in the frontal cortex of females only was detected. No changes in the cortical NA tissue level were found. Summing up, the present study demonstrated that the activation of the immune system in prenatal period led to persistent behavioral hypersensitivity to psychotomimetic action of a non-competitive NMDA receptor antagonist, and attention/information processing deficits. The foregoing data indicate that prenatal administration of LPS model some of the clinical aspects of schizophrenia and these behavioral effects are connected with neurochemical changes.

Impact of postnatal blockade of N-methyl-D-aspartate receptors on rat behavior: a search for a new developmental model of schizophrenia.

The malfunction of glutamatergic neurotransmission in the neonatal or postnatal periods may be a risk factor for the appearance of neuroanatomical, neurochemical or functional changes that are characteristic of schizophrenia. Thus, the present study was undertaken to investigate whether blockade of N-methyl-d-aspartate (NMDA) receptors in the postnatal period influences rat behavior in tests characterizing schizophrenia-like deficits such as psychomotor agitation, impairments of sensorimotor gating, working memory, and intensity of social interactions. (E)-2-amino-4-methyl-5-phosphono-3-pentenoic acid (CGP 40116), a competitive antagonist of NMDA receptors, was given postnatally (1.25 mg/kg on days 1, 3, 6, 9; 2.5 mg/kg on days 12, 15, 18; and finally 5 mg/kg on day 21, all injections s.c.), and rats were tested at 60 days old. We found that blockade of NMDA receptors in the postnatal period led to an enhancement of exploration, mimicking psychomotor agitation, impairments in sensorimotor gating as measured by a prepulse-evoked inhibition of acoustic startle response, and an impaired working memory, as measured by an increase in the latency to achieve accurate rate of response in the delayed alternation task. Decreases in non-aggressive social interactions and increases in aggressive interactions were also observed. In addition to cognitive deficits typical of schizophrenia, rats treated postnatally with NMDA receptor antagonists also showed higher level of fear exhibited in the elevated plus maze. Thus, the blockade of NMDA receptors in the postnatal period may model deficits that are characteristic of schizophrenia.

Blockade of NMDA receptors in postnatal period decreased density of tyrosine hydroxylase immunoreactive axonal arbors in the medial prefrontal cortex of adult rats.

Malfunction of glutamatergic neurotransmission in postnatal period is considered to be a risk factor for development of schizophrenia. Thus, the present study investigates the impact of NMDA receptor blockade in the postnatal period on the density of tyrosine hydroxylase immunoreactive axonal arbors in the rat medial prefrontal cortex. Behavioral experiments revealed that adult rats (60 days old) treated in the postnatal period with a competitive antagonist of NMDA receptors, CGP 40116 (1.25 mg/kg on days 1, 3, 6, 9; 2.5 mg/kg on days 12, 15, 18; and finally 5 mg/kg on day 21, all injections s.c.), showed enhancement of the locomotor activity stimulated by quinpirole (0.3 mg/kg s.c.) and amphetamine (0.5 mg/kg s.c.), which suggests development of functional supersensitivity of dopaminergic systems. It has been found that CGP 40116, given in postnatal period decreased the density of tyrosine hydroxylase immunoreactive axonal arbors in the medial prefrontal cortex of adult animals. The decrease was observed in superficial (II/III) and deep (V/VI) layers of the medial prefrontal cortex, while the average length of tyrosine hydroxylase immunoreactive axonal arbors was increased in both superficial and deep cortical layers. Changes in the density of tyrosine hydroxylase immunoreactive axonal arbors have not been followed by a significant decrease in the content of tyrosine hydroxylase protein measured by Western blot. Thus, NMDA receptor blockade in the early period of life evokes changes in architecture of tyrosine hydroxylase immunoreactive axonal arbors and that malfunction of glutamatergic neurotransmission, in early period of life may produce anatomical changes which resemble those observed in the brains of schizophrenics.

DOI, an agonist of 5-HT2A/2C serotonin receptor, alters the expression of cyclooxygenase-2 in the rat parietal cortex.

The hallucinogenic effect of DOI, serotonin 5-HT2A/2C receptor agonist, is known to be associated with the activation of cortical 5-HT2 receptors. However, the effect of DOI on excitability of cortical neurons and their subsequent function is still not quite understood. Previous immunohistochemical studies using Fos proteins expression as a marker of neuronal activity showed the involvement of arachidonic acid cascade, particularly cyclooxygenase metabolic pathway, in DOI-induced Fos proteins expression in the rat parietal cortex. DOI increases arachidonic acid release which is transformed itself via acceleration of cyclooxygenase metabolic pathway to biologically active metabolites, such as prostaglandins and thromboxanes. Since cyclooxygenase-2 (COX-2) expression correlates with neuronal activity, it was of interest to investigate whether DOI is capable of influencing the level of COX-2 protein and mRNA expression in the rat parietal cortex. It was observed that neurons which were positive for 5-HT2A receptors showed constitutive COX-2 immunoreactivity. It was found further, that COX-2 protein level was increased at 1 h, and returned to the control level at 3 and 6 h after DOI (5 mg/kg) administration. In contrast, DOI decreased the COX-2 mRNA expression at all tested time points (1 h, 3h and 6h after DOI treatment). The obtained results further support the suggestion that COX-2 activation and possibly arachidonic acid metabolites generated by COX-2 may be considered as important mediators of functional responses generated by activation of cortical 5-HT2A/2C receptors.

Immunohistochemical evidence for localization of NMDAR1 receptor subunit on dopaminergic neurons of the rat substantia nigra, pars compacta.

Non-fluorescent, double-labeling techniques were used in order to investigate whether NMDAR1 receptor subunits are localized on dopaminergic (i.e. tyrosine hydroxylase-positive) neurons of the rat substantia nigra, pars compacta. It has been found that NMDAR1 receptor subunits are highly abundant in the pars compacta neurons and their dendritic processes. It was also found that vast majority, if not all, of pars compacta neurons which are positive for the presence of NMDAR1 receptor subunits are dopaminergic ones. It is concluded that if NMDAR1 receptor subunits, an indispensable element of functional NMDA receptor ion channel complex, is co-assembled with other subunits of NMDA receptor ion channel complex, NMDA receptors might directly control the activity of dopaminergic neurons.

Metyrapone, an inhibitor of corticosterone synthesis, blocks the kainic acid-induced expression of HSP 70.

It is shown in the present study that metyrapone (100 mg/kg), an inhibitor of corticosterone synthesis, given twice, 30 min before and 6 h after kainic acid (10 mg/kg) administration, blocks the kainic acid-evoked induction of heat shock proteins 72 kDa (HSP 70). Specifically, it was observed that metyrapone completely prevented kainic acid-induced appearance of HSP 70 in the rat amygdala, habenula, parietal cortex, and significantly decreased the number of HSP 70-positive neurons in the CA1, CA3, and CA4 subregions of hippocampus. The reduction in HSP 70 induction was paralleled by a complete prevention of the kainic acid-induced rise in the circulating corticosterone level by metyrapone; however, in applied doses metyrapone evoked slight enhancement of blood corticosterone. Despite the fact that metyrapone blocked/attenuated the kainic acid-evoked induction of HSP 70, its administration did not affect the behavioral effects of kainic acid, regarded as "limbic status epilepticus." It is concluded that the blockade of corticosterone synthesis might have neuroprotective effects in the pathological states associated with the overstimulation of glutamatergic receptors.

WAY 100135, an antagonist of 5-HT1A serotonin receptors, attenuates psychotomimetic effects of MK-801.

In the present study, we investigated whether the antagonist of 5-HT1A receptors, WAY 100135, was capable of modifying the psychostimulant and psychotomimetic effects of MK-801, a non-competitive antagonist of NMDA receptors. It was found that: 1) WAY 100135 (10 and 20 mg/kg, but not 1.25, 2.5, and 5 mg/kg) transiently, in a dose dependent manner, attenuated the locomotor stimulant effects of MK-801 (0.4 mg/kg). Given alone, WAY 100135 had no effect on the locomotor activity of rats; 2) WAY 100135 (1.25 and 2.5 mg/kg, but not 10 or 20 mg/kg), attenuated or abolished the disruptive effects of MK-801 on the sensorimotor gating measured in a prepulse-induced inhibition of the acoustic startle response paradigm. WAY 100135 in all tested doses had no effect on the sensorimotor gating or amplitude of the acoustic startle response; 3) WAY 100135 (1.25, 2.5 mg/kg, but not 5 mg/kg) attenuated the detrimental effects of MK-801 on working memory and selective attention, measured in a delayed alternation task. Again, given alone, WAY 100135 did not influence the behavior of rats in that experimental paradigm; and 4) MK-801 (0.4 mg/kg) had no effect on the 5-HT1A receptor mRNA level in rat hippocampus, measured 2 and 24 hours after MK-801 administration. These data indicate that 5-HT1A receptors might be involved in the psychotomimetic effects of non-competitive NMDA receptor antagonists. In addition, 5-HT1A serotonin receptor antagonists and partial agonists may have potential antipsychotic properties.

Cortical localization of dopamine D4 receptors in the rat brain--immunocytochemical study.

Using polyclonal antibody against dopamine D4 receptor we investigated cortical distribution of D4 receptors, with the special emphasis on regions of the prefrontal cortex. Prefrontal cortex is regarded as a target for neuroleptic drugs, and engaged in the regulation of the psychotic effects of various substances used in the experimental modeling of schizophrenia. Western blot analysis performed on samples from the rat cingulate, parietal, piriform cortices and also striatum revealed that antibody recognized one main band of approximately 40 kD, which corresponds to the predicted molecular weight of D4 receptor protein. In immunocytochemical studies we found D4 receptor-positive neurons in all regions of prefrontal cortex (cingulate, agranular/insular and orbital cortices) and all cortical regions adjacent to prefrontal cortex, such as frontal, parietal and piriform cortex. Substantial number of D4 receptor-positive neurons has also been observed within the striatum and nucleus accumbens. In general, a clear stratification of the D4 receptor-positive neurons was observed in the cortex with the highest density seen in layers II/III and V/VI. D4 immunopositive material was also found in the dendritic processes, particularly clearly visible in the layer II/III. At the cellular level D4 receptor immunoreactivity was seen predominantly on the periphery of the cell body, but a certain population of neurons with clear cytoplasmatic localization was also identified. In addition to cortical distribution of D4 receptor-positive neurons we tried also to define types of neurons expressing D4 receptor protein. In double-labeling experiments, D4 receptor protein was found in nonphosphorylated neurofilament H-positive, calbindin-D28k-positive, as well as parvalbumin-positive cells. Since, used proteins are markers of certain populations of pyramidal neurons and GABA-ergic interneurons, respectively, our data indicate that D4 receptors are located on cortical pyramidal output neurons and their dendritic processes as well as on interneurons. Above localization indicates that D4 receptors are not only directly influencing excitability of cortical inter- and output neurons but also might be engaged in dendritic spatial and temporal integration, required for the generation of axonal messages. Additionally, our data show that D4 receptors are widely distributed throughout the cortex of rat brain, and that their cortical localization exceeds the localization of dopaminergic terminals.

Distribution of dopamine D1 receptors in the nucleus paraventricularis of the hypothalamus in rats: an immunohistochemical study.

The present study investigated the distribution of dopamine D1 receptor protein in the nucleus paraventricularis of the hypothalamus. It was found that the nucleus paraventricularis of the hypothalamus contains a relatively large number of cells which are positive for presence of dopamine D1 receptor protein. The vast majority of dopamine D1 receptor-positive neurons was found in the magnocellular part, but they were also present in considerable quantity in the parvocellular part of this subregion of the hypothalamus. When measured by the Western blot technique, the quantity of D1 receptor protein found in the paraventricular nucleus of the hypothalamus was at the level found in the prefrontal cortex. It was also found that dopamine D1 receptor protein was present in neurons constitutively displaying phosphorylated CREB protein, i.e. neurons which are, as might be speculated, under the tonic influence of neurotransmitters whose receptors operate via cAMP and pCREB as second or third messengers. The presence of dopamine D1 receptors in the nucleus paraventricularis of the hypothalamus may suggest, at an anatomical level, that these receptors are involved in controlling the release of hormones, as well as their synthesis at the level of transcription, which is regulated by phosphorylation of CREB protein. Finally, the present immunocytochemical findings offer an anatomical substrate for the role of dopamine and its receptors of D1 subtype in the regulation of the activity of paraventricular neurons seen in the functional studies.

c-Fos proteins, induced by the serotonin receptor agonist DOI, are not expressed in 5-HT2A positive cortical neurons.

In the present study, we tried to find out whether the expression of c-Fos proteins induced by DOI, an agonist of 5-HT2A/2C receptor subtypes is colocalized with 5-HT2A receptor protein in cortical neurons. 5-HT2A receptor protein was found in two major neuronal elements: dendritic processes (seen in layers II/III-V) and less abundantly in cell bodies (layer V). In our experiment, DOI (8 mg/kg) induced a robust appearance of c-Fos proteins mainly in neuronal nuclei of the upper part of layer V/IV, and a moderate amount of sparsely distributed nuclei in deep cortical layers (V and VI). It was found that c-Fos proteins never occurred in cortical neurons, which were immunopositive for the presence of 5-HT2A receptor protein. It is concluded that the induction of c-Fos proteins expression by DOI though initiated by activation of 5-HT2A receptors, requires the involvement of intermediate neurotransmitter(s). Additionally, our study indicates that the appearance of DOI-induced c-Fos proteins cannot be used as a simple and direct marker of localization and site of activation of 5-HT2A receptors.

The corticosterone synthesis inhibitor metyrapone decreases dopamine D1 receptors in the rat brain.

Experiments were performed to examine the effect of metyrapone, an inhibitor of corticosterone synthesis, on the level of dopamine D1 receptors and their transcripts in the caudate-putamen, nucleus accumbens and olfactory tubercle of the rat brain. The binding to dopamine D1 receptors was measured by receptor autoradiography using the specific D1 receptor antagonist [3H]SCH 23390. The level of dopamine D1 receptor messenger RNA was determined by in situ hybridization histochemistry. The results obtained have shown that metyrapone (two injections of 150 and 50 mg/kg, i.p., given 20 and 3 h before killing, respectively) induced a decrease in the D1 receptor-specific binding in the studied areas of the rat brain. In the caudate putamen, the decrease in [3H]SCH 23390 binding was stronger in the medial (31-39%) than in the lateral part (24-27%). Decreases similar to those in the caudate-putamen were observed in the nucleus accumbens (21%) and olfactory tubercle (32%). Furthermore, metyrapone decreased the level of dopamine D1 receptor messenger RNA in the caudate putamen (17-28%), nucleus accumbens (20%) and olfactory tubercle (18%). In conclusion, our study indicates that glucocorticoids might be involved in the regulation of dopamine D1 receptor level in the rat brain. since metyrapone (which inhibits the synthesis of these hormones) decreases the messenger RNA encoding D1 receptor synthesis, as well as the specific binding to this receptor.

Single doses of MK-801, a non-competitive antagonist of NMDA receptors, increase the number of 5-HT1A serotonin receptors in the rat brain.

In the present study, we investigated the impact of MK-801, a non-competitive NMDA receptor antagonist, on the density of serotonergic receptors of the 5-HT1A subtype and on the metabolism of serotonin in various regions of the rat brain containing terminals and cell bodies of serotonergic neurons. The binding of [3H]8-OH-DPAT to 5-HT1A serotonin receptors was increased after MK-801 (0.4 mg/kg) as was shown by autoradiographic studies in the frontal, cingulate and part of enthorinal cortex, subregions of the hippocampus and raphe nuclei. The above receptor changes were observed at 2 h and, in some brain regions, at 24 h after MK-801. In saturation binding studies, an increase in the Bmax value in the rat hippocampus was found after MK-801 (0.4 mg/kg) while no changes being noted in the Kd value. MK-801 (0.4 mg/kg) increased the concentration of the serotonin metabolite 5-HIAA in the prefrontal cortex and hippocampus, respectively, at 2 and 3 or 3 h after administration, being without effect on the level of serotonin. In the dorsal raphe nucleus, MK-801 (0.4 mg/kg) decreased the level of serotonin without affecting the level 5-HIAA (0.5 h after administration) or increased the level of 5-HIAA without altering the concentration of serotonin (3 h after administration). It is concluded that single administration of MK-801 may alter the density of serotonergic 5-HT1A receptors and in consequence influence the function of the central nervous system associated with activation of 5-HT1A receptors.

Impact of metyrapone on MK-801-induced alterations in the rat dopamine D1 receptors.

Our earlier studies have shown that changes in serum corticosterone levels played an important role in the acquisition of sensitization to MK-801, a non-competitive NMDA receptor antagonist. Dopaminergic mechanisms are found to be particularly important in the development of sensitization; hence in the present study we assessed the binding of [3H]SCH 23390 at brain dopaminergic D1 receptors, after administration of MK-801 (0.4 mg/kg), in rats in which corticosterone synthesis was inhibited by metyrapone (150 + 50 mg/kg). Such metyrapone pretreatment prevented the increases in serum corticosterone level induced by MK-801. The binding studies, using receptor autoradiography, were performed in the following brain structures: the striatum, nucleus accumbens, olfactory tubercle and substantia nigra. Metyrapone per se did not change or slightly increased D1 receptor binding in the substantia nigra, while in other brain structures tested it decreased the number of these receptors by about 30%. MK-801 increased the level of D1 receptors in the nucleus accumbens core and olfactory tubercle, being without effect in the remaining brain structures tested. In rats which were pretreated with metyrapone, the effect of MK-801 on D1 receptors was inhibited in the nucleus accumbens core only. In substantia nigra, metyrapone provoked the MK-801-induced decrease in D1 receptors whereas in all other structures MK-801 reversed the effects of metyrapone on D1 receptors. Additionally, the effect of metyrapone and MK-801 on grooming behavior induced by D1 receptor agonist SKF 38393 (10 mg/kg) was tested. Metyrapone did not influence grooming induced by SKF 38393, but significantly potentiated the inhibitory effect of MK-801 on this behavior. Finally, we found that metyrapone did not influence the expression of the sensitization induced by MK-801. Our results seem not to support hypothesis that MK-801 evokes enhancement of dopaminergic neurotransmission (at the level of D1 receptors) via corticosterone liberation, since in most brain regions studied inhibition of increases in corticosterone level did not prevent MK-801-induced effects on D1 receptors. The present study may suggest that NMDA receptors are involved in the corticosterone-dependent regulation of the density of the D1 receptors.

Evidence that conditioned stress enhances outflow of dopamine in rat prefrontal cortex: a search for the influence of diazepam and 5-HT1A agonists.

We evaluated the impact of conditioned stress on outflow of dopamine in the rat prefrontal cortex. Exposure of rats to an environment associated with aversive stimuli-foot shock enhanced outflow of dopamine in a similar way as seen during the conditioning session when foot shocks were applied. Diazepam (2.5 and 10 mg/kg) dose-dependently decreased outflow of dopamine and, when given in a dose of 10 mg/kg, but not 2.5 mg/kg, decreased enhanced dopamine outflow evoked by conditioned stress. On the other hand, ipsapirone (10 mg/kg, but not 2.5 mg/kg) and buspirone (2.5 mg/kg) enhanced basal outflow of dopamine. When ipsapirone (10 mg/kg) and buspirone (2.5 mg/kg) were given to rats exposed to conditioned stress, the stress-evoked elevation in dopamine outflow was abolished. Ipsapirone in a dose of 2.5 mg/kg was ineffective in the stress paradigm tested. It is concluded that conditioned stress in vivo enhances dopaminergic neurotransmission in the rat prefrontal cortex, this effect being attenuated by diazepam, a classic anxiolytic drug, and by such novel anxiolytics as ipsapirone and buspirone, which operate via serotonergic 5-HT1A receptors. Although ipsapirone and buspirone blocked stress-induced enhancement of dopamine outflow, this effect seems to result from their influence on the basal outflow of dopamine. Differential effects of diazepam and 5-HT1A agonists on basal and stress-induced alterations in dopamine outflow are discussed in terms of their possible effectiveness in various types of general anxiety disorders.

Ipsapirone enhances the dopamine outflow via 5-HT1A receptors in the rat prefrontal cortex.

In the present study, we investigated both the effect of ipsapirone on the dopamine outflow and its selectivity towards 5-HT1A receptors in the rat prefrontal cortex. Using a brain microdialysis method in freely moving animals, it was found that ipsapirone, 5 and 10 mg/kg dose-dependently enhanced the outflow of dopamine, while 2.5 mg/kg was ineffective. The above effects of ipsapirone were mimicked by buspirone (2.5 and 5 mg/kg), another 5-HT1A receptor agonist, but not 1-PP (1-pyrimidinylpiperazine, 5 mg/kg)-a centrally active metabolite of ipsapirone. The effect of ipsapirone (10 mg/kg) on the dopamine outflow in the rat prefrontal cortex was antagonized by 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine (NAN-190, 1 mg/kg) and (N-tert-butyl-3-(4-(2-methoxyphenylpiperazin-1-yl)-2- phenylpropionamide (WAY 100135, 10 mg/k.g.), i.e. substances with agonistic/antagonistic and antagonistic properties in relation to 5-HT1A receptors, respectively. NAN-190 (1 mg/kg) enhanced the outflow of dopamine, while WAY 100135 (10 mg/kg) failed to alter it. It is concluded that 5-HT1A receptor agonists may be involved in the regulation of dopaminergic neurotransmission in the rat prefrontal cortex and may have therapeutic potential in the treatment of disorders associated with dysfunction of the mesocortical dopaminergic system.

The impact of a competitive and a non-competitive NMDA receptor antagonist on dopaminergic neurotransmission in the rat ventral tegmental area and substantia nigra.

The study compares effects of the competitive and non-competitive NMDA receptor antagonists, CGP 40116 and MK-801 respectively, on the metabolism of dopamine and on the density of D-1 and D-2 dopaminergic receptors in the rat ventral tegmental area and substantia nigra. The effects of CGP 40116 were tested in a range of doses which either were devoid of or had locomotor- or stereotypy-stimulating effects. It was found that (1) CGP 40116 given in a dose of 5 mg/kg enhanced the locomotor activity of rats and evoked a stereotypy-like activity; doses of 1.25 and 2.5 mg/kg were devoid of such effects; (2) CGP 40116 (5 mg/kg) enhanced the concentrations of dopamine, DOPAC and HVA in the ventral tegmental area, whereas the lowest dose, 1.25 mg/kg was without effect; a dose of 2.5 mg/kg increased the concentration of dopamine only; the only effect of CGP 40116 (5 mg/kg) observed in substantia nigra, was an increase in dopamine concentration; its doses of 1.25 and 2.5 mg/kg were ineffective. (3) MK-801 (0.2 and 0.4 mg/kg) enhanced the concentrations of dopamine, DOPAC and HVA in both structures. A dose of 0.1 mg/kg increased the dopamine concentration only. The effects of MK-801 in substantia nigra were quantitatively weaker than those observed in ventral tegmental area. (4) Both CGP 40116 (5 mg/kg) and MK-801 (0.4 mg/kg) evoked alterations in the density of dopaminergic receptors. D-2 receptors, were up-regulated by MK-801 in ventral tegmental area and subregions of substantia nigra, i.e. pars compacta and pars reticulata, whereas CGP 40116 evoked similar effects in ventral tegmental area only. D-1 receptors in pars compacta and pars reticulata of substantia nigra were down-regulated after administration of either drug. It is concluded that competitive NMDA receptor antagonists in doses which evoke hyperlocomotion and stereotypy-like activity, may have a substantial impact on the dopaminergic neurotransmission in the rat ventral tegmental area and substantia nigra, similar to that described for MK-801, a non-competitive NMDA receptor antagonist. The obtained results may suggest that CGP 40116 and, possibly, other competitive NMDA antagonists may have dopaminomimetic properties, and that their clinical potentials may be limited by the risk of evoking dopamine-dependent psychotomimetic and abusing effects, similar to those described for MK-801.

MP-3022, a new putative antagonist at pre- and postsynaptic 5-HT1A receptors.

The receptor binding and pharmacological profile of the new, putative 5-HT1A receptor antagonist MP-3022 (4-[3-(benzotriazol-1-yl)propyl]-1-(2-methoxyphenyl)piperazine) were studied. Another 5-HT1A receptor antagonist, (S)-WAY 100135 ((S)-N-tert-butyl-3-[4-(2-methoxyphenyl)piperazine-1-yl]-2- phenylpropanamide), was used as a reference drug in functional models. MP-3022 showed a high affinity (Ki) of 25 nM and 69 nM, respectively, at 5-HT1A binding sites and alpha 1-adrenoceptors in vitro. The Ki values of MP-3022 in relation to other binding sites examined (5-HT2A, alpha 2- or beta-adrenoceptors, dopamine D1 and D2) were 20-100-fold lower. In functional studies, MP-3022 significantly attenuated the 8-OH-DPAT (8-hydroxy-2-(di-n-propylamino)tetralin)-induced decrease in the population spike evoked in the CA1 cell layer of the hippocampal slice preparation, without producing its own effects. The 8-OH-DPAT-evoked increase in the corticosterone concentration in the serum as well as the 8-OH-DPAT-mediated decrease in the 5-HT turnover in the hippocampus were attenuated by MP-3022. MP-3022 increased the serum corticosterone concentration only at the highest dose used, but it did not change the 5-HT turnover in the hippocampus. Like MP-3022, (S)-WAY 100135 antagonized the 8-OH-DPAT-induced effects. It has also been demonstrated that (S)-WAY 100135 is devoid of an intrinsic activity at 5-HT1A receptors. The data obtained demonstrate that, like (S)-WAY 100135, MP-3022 behaves like a functional antagonist at pre- and postsynaptic 5-HT1A receptors.