Cannabinoid CB1 receptors in rat medial prefrontal cortex are colocalized with calbindin- but not parvalbumin- and calretinin-positive GABA-ergic neurons

In the present study, we investigate putative localization of cannabinoid receptors 1 (CB1) protein on a population of cortical gamma-aminobutyric acid (GABA) - positive interneurons characterized by expression of calcium-binding proteins in rat medial prefrontal cortex (MPC). Parvalbumin (PARV)/calretinin (CALR)- and calbindin (CALB)-positive neurons form two distinct populations of GABA-ergic interneurons that comprise the axo-somatic/axo-axonic and axo-dendritic inhibitory systems of pyramidal cells. It has been found that CB1 receptor-positive cells are randomly distributed across the rat MPC. All spotted neurons that were positive for CB1 receptors were positive for GABA; however, the number of GABA-positive cells drastically exceeded the number of CB1 receptor-positive neurons. Subsequent experiments with double-labelling of CB1 receptors with PARV and CALR revealed no colocalization. CALB-positive neurons (e.g., double bouquet and bipolar cells) display colocalization: the degree of colocalization among CB1 receptor-positive cells reached 18%. The appearance of CB1 receptors in double bouquet and bipolar neurons indicates that CB1 receptors may control the activity of pyramidal neurons from presynaptic sites in axo-dendritic synapses formed on apical and basilar dendrites of pyramidal neurons, as is characteristic for CALB-positive cortical interneurons. The phenotype of GABA- and CB1 receptor-positive but CALB-negative neurons may represent a population of inhibitory neurons that allow axo-somatic control of information flow, governed by principal neurons of the MPC.

5-HT1A receptors mediate detrimental effects of cocaine on long-term potentiation and expression of polysialylated neural cell adhesion molecule protein in rat dentate gyrus

The present study investigated the involvement of 5-HT(1A) receptors in the inhibitory effect of single administration of cocaine (COC, 15 mg/kg i.p.) on the induction of long-term potentiation (LTP) in slices of rat dentate gyrus (DG), prepared 30 min and 2 days after COC administration. These effects of COC were blocked by an antagonist of 5-HT(1A) receptors, WAY 100635 (0.4 mg/kg i.p.), which had been administered 20 min before COC. The detrimental effect of COC on LTP in slices prepared 30 min after COC administration could be prevented by blocking glucocorticoid receptors (GRs) using mifepristone (RU 38486, 10 mg/kg s.c. given 1 h before COC), similar as in slices obtained 2 days after COC as reported previously [Maćkowiak et al. (2008) Eur J Neurosci 27:2928-2937]. After a single administration of an agonist of 5-HT(1A) receptors, 8-OH-DPAT, (0.5 mg/kg i.p.), the level of LTP in slices prepared 2 days later was significantly decreased resembling the effect of COC. This effect of 8-OH-DPAT was antagonized by WAY 100635 (0.4 mg/kg i.p.), administered 20 min before 8-OH-DPAT and by RU 38486, given 1 h before 8-OH-DPAT. COC-induced inhibition of LTP could be blocked by the inhibitor of mitogen-activated protein kinase kinase 1/2 (MEK1/2), SL 327 (50 mg/kg i.p.), administered 1 h before COC, but not by the inhibitor of phosphatidylinositol 3-kinase (PI3-kinase), LY 294002 (80 mg/kg i.p.). COC-induced reduction in the number of polysialylated neural cell adhesion molecule (PSA-NCAM)-positive neurons in rat dentate gyrus could also be prevented by WAY 100635, given 20 min before COC. These data indicate that the indirect 5-HT(1A) receptor activation by a single COC administration and subsequent stimulation of extracellular signal-regulated kinases (ERK 1/2) signaling pathway result in a decrease of the potential for long-term increase in synaptic efficacy in rat DG lasting at least two but less than 7 days, most likely via activation of the hypothalamic-pituitary-adrenal (HPA) axis.

Repeated risperidone treatment increases the expression of NCAM and PSA-NCAM protein in the rat medial prefrontal cortex

The present study investigates whether the anti-schizophrenic drug risperidone may evoke changes in the expression of NCAM/PSA-NCAM proteins, an indispensable element in the remodeling of synaptic arrangements, in the medial prefrontal cortex (mPFC). Rats were treated with risperidone (0.2 mg/kg, i.p.) either once or repeatedly (once a day, for 21 days). The expression of NCAM and PSA-NCAM proteins was analyzed via western blot and immunohistochemistry at intervals of 3 h and 3, 6, and 9 days after the single or the last risperidone dose. Repeated (but not acute) administration of risperidone was found to increase the expression of NCAM-180, NCAM-140 and PSA-NCAM proteins at 3 or 6 days after treatment. PSA-NCAM immunoreactivity was found in cell bodies, perisomatic-like sites, and in the neuropil of the mPFC. Neither single nor repeated risperidone administration changed the number of PSA-NCAM neurons in the mPFC. In contrast, the repeated risperidone treatment increased the number of PSA-NCAM perisomatic-like sites and the length density of PSA-NCAM positive neuropil at 3 days after the last injection. The data obtained indicate that risperidone, given repeatedly, may promote the remodeling of the structure of presumably GABA-ergic interneurons and that it may evoke the rearrangement of the synaptic contact in the mPFC.

Activation of CB1 cannabinoid receptors impairs memory consolidation and hippocampal polysialylated neural cell adhesion molecule expression in contextual fear conditioning

We investigated the role of CB1 receptors in hippocampal-dependent memory consolidation mediated by polysialylated neural cell adhesion molecule (PSA-NCAM) during contextual fear conditioning (CFC). The CB1 receptor agonist 3-(1,1-dimethylheptyl)-(-)-11-hydroxy-Delta(8)-tetrahydrocannabinol (HU-210) (0.1 mg/kg) was given immediately after training during the memory consolidation phase, and freezing behavior was measured 24 h after conditioning. Administration of HU-210 attenuated freezing behavior measured in CFC. Western blot analysis showed that CFC induced a decrease in the expression of NCAM-180, but did not change the level of NCAM-140 and increased PSA-NCAM expression measured 24 h after training in the rat hippocampus. HU-210 (0.1 mg/kg) injection did not affect the reduction in NCAM-180 levels induced by CFC, but it blocked the increase in PSA-NCAM expression. Since the dentate gyrus (DG) of the hippocampus is known to be involved in memory consolidation and expresses a high level of PSA-NCAM protein, we measured the effects of CFC and HU-210 administration on PSA-NCAM-immunoreactive (IR) cells in the DG. CFC caused an increase in the number of PSA-NCAM-IR cells in the DG, but not K(i)-67- or doublecortin (DCX)-IR cells. This increase in PSA-NCAM-IR cells was abolished by HU-210 injection. Administration of the CB1 receptor antagonist N-(piperidin-1-yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide (AM-251) (3 mg/kg immediately before HU-210) inhibited the effects of HU-210 on freezing behavior and PSA-NCAM expression in the DG. These results indicate that activation of CB1 receptors disturbs consolidation of fear memory in CFC, likely by affecting PSA-NCAM expression in the DG, which plays an important role in synaptic rearrangement during the formation of memory traces.

Detrimental effect of postnatal blockade of N-methyl-D-aspartate receptors on sensorimotor gating is reversed by neuroleptic drugs

Postnatal hypofunction of N-methyl-D-aspartate (NMDA) receptors leads to several behavioral deficits in adult rats resembling deficits typical of schizophrenia-like deficits of sensorimotor gating. Thus far, it is not known whether the above disruptions are sensitive to neuroleptic drugs. In order to verify the above model in pharmacological terms, we investigated whether deficits in the sensorimotor gating evoked by administration of NMDA receptor antagonists in the postnatal period is sensitive to neuroleptic drugs. We also investigated whether such treatment evoked alterations in the expression of dopamine D(1), D(2) and D(3) receptors in the nucleus accumbens, a key structure for dopamine-dependent alterations in sensorimotor gating. CGP 40116, a competitive antagonist of NMDA receptors was given in doses of 1.25 mg/kg on days 1, 3, 6 and 9; 2.5 mg/kg on days 12, 15 and 18; and 5 mg/kg on day 21 (all injections were sc). The efficacy of sensorimotor gating was tested on rats at the age of 60 days using a prepulse-induced inhibition of the startle reflex. In order to measure the expression of dopamine D(1), D(2) and D(3) receptors, we used quantitative autoradiography and tritiated ligands i.e. [(3)H]-SCH 23390, [(3)H]-Spiperone and [(3)H]-7-OH-DPAT, respectively. Haloperidol (0.1 mg/kg, sc), risperidone (1.0 mg/kg, sc) and clozapine (2.5 mg/kg, sc) reversed deficits of sensorimotor gating observed in adult rats evoked by the postnatal administration of CGP 40116. We also observed enhanced density of dopamine D(3), but not D(1) and D(2) receptors in the nucleus accumbens of CGP40116 treated rats. It is concluded that models of cognitive dysfunction, typical for schizophrenia based on postnatal administration of NMDA receptor antagonists, are sensitive to neuroleptic drugs and possibly not dependent on alteration in the density of dopaminergic receptors.

Dopamine D1-like receptors agonist SKF 38393 increases cFOS expression in the paraventricular nucleus of the hypothalamus--impact of acute and chronic cocaine

The present study indicates that activation of dopamine D1-like receptors by administration of SKF 38393 leads to dose-dependent (doses: 5, 10 and 20 mg/kg) increases in the expression of cFos proteins in the rat paraventricular nucleus of the hypothalamus (PVN). This effect was abolished by administration of SCH 23390, a dopamine D1-like receptor antagonist (0.5 and 1 mg/kg, given 30 min before SKF 38393--10 mg/kg), suggesting that the apparent effect is specific for activation of dopamine D1-like receptors. Expression of cFos after SKF 38393 (10 mg/kg) was observed in some, but not all, CRF-immunoreactive neurons, as well as in small portion of oxytocin- but not vasopressin-immunoreactive neurons (double-immunofluorescence experiments). There were also certain populations of nuclei that showed expression of cFos but did not co-localize with the above markers. We also found that both acute and repeated (once daily for 5 consecutive days) exposure to cocaine (25 mg/kg) attenuated the induction of cFos expression triggered by SKF 38393 when administered 24 hours after single or the last dose of cocaine (25 mg/kg). Attenuation was observed at the same level after single and chronic exposure to cocaine, indicating a rapid functional down-regulation of dopamine D1-like receptors that are resistant to subsequent doses of cocaine. These data provide evidence for the functional role of dopamine D1-like receptors in the PVN and indicate a functional adaptation of dopamine D1-like receptors following a single dose of cocaine without further progression of adaptation or resistance of D1-like receptor-mediated genomic function in the course of repeated cocaine intake.

A search for colocalization of serotonin 5-HT2A and 5-HT1A receptors in the rat medial prefrontal and entorhinal cortices--immunohistochemical studies

Recently developed antipsychotic drugs ameliorating the negative symptoms of schizophrenia act not only on dopamine D2 receptors but also on serotonin 2A (5-HT2A) and 1A (5-HT1A) receptors in specific regions of the cerebral cortex. Since it is not yet known whether serotonin 5-HT1A and 5-HT2A receptors coexist in the same population of neurons in the cortex, the present study investigated their colocalization in the rat medial prefrontal (MPC) and entorhinal (EC) cortices. Using antibodies that recognize epitopes specific to the serotonin 5-HT2A or 5-HT1A receptors, studies employing confocal microscopy have shown that in the MPC 5-HT2A receptors are preferentially, if not exclusively, present on the pyramidal neurons and that 5-HT1A-immunopositive material is present in the axonal hillocks and, to lower extend, in cytoplasm of presumably pyramidal cell bodies. With the regard of labeling of active receptors (i.e. present in shafts and axonal hillocks) we found that about 38% of neurons positive for the presence of serotonin 5-HT2A receptors, are also positive for serotonin 5-HT1A receptors in the MPC. In the EC, only 22% of serotonin 5-HT2A-positive neurons were positive for serotonin 5-HT1A receptor-immunoreactivity. In the respect of cytoplasmatic serotonin 5-HT1A receptor-immunoreactivity (possibly inactive receptors), 65% and 73% of serotonin 5-HT2A receptor-positive neurons were colocalized with serotonin 5-HT1A receptors in the MPC and EC, respectively. Data obtained on serotonin 5-HT2A and 5-HT1A receptor localization provide anatomical grounds for at least three distinct populations of pyramidal neurons, one governed only by 5-HT2A, one only by 5-HT1A and one by both types of serotonin receptors.

Glutamatergic neurons of rat medial prefrontal cortex innervating the ventral tegmental area are positive for serotonin 5-HT1A receptor protein

The present study was designed to investigate whether serotonin 5-HT1A receptor protein (5-HT1A receptor-immunoreactivity), is present on cortical pyramidal neurons of the rat medial prefrontal cortex (MPC) innervating the ventral tegmental area (VTA). Recent data stress the role of serotonin 5-HT1A receptors in the pathology of schizophrenia, and in the mechanism of action of novel antipsychotic drugs. It was found that approximately 52% of cells in layers II/III of the MPC whose axons initial segments were immunoreactive for serotonin 5HT1A receptor were also labeled with Fluoro-Gold (FG), a retrograde tracer injected into the VTA, indicating that certain portion of neurons forming glutamatergic innervations of the VTA may be controlled by serotonin 5-HT1A receptors. In deep cortical layers (V/VI) retrogradely labeled neurons never colocalized with serotonin 5-HT1A receptormmunoreactivity. These anatomical data indicate that serotonin 5-HT1A receptors might potentially control the excitability and propagation of information transmitted by the pyramidal cells to the VTA. Moreover, our results indicate that the drugs operating via serotonin 5-HT1A receptors in the MPC, might control from this level the release of glutamate in the VTA and restore function of glutamate neurotransmission, whose dysfunction is observed for example in schizophrenia.

Acute and repeated cocaine induces alterations in FosB/DeltaFosB expression in the paraventricular nucleus of the hypothalamus

Apart from activation of the brain reward system, cocaine administration influences the activity of the hypothalamo-pituitary-adrenal (HPA) axis by affecting CRH neurons in the paraventricular nucleus of the hypothalamus (PVN). In order to find a molecular mechanism of cocaine-evoked effects in the PVN, in the present study, we investigated the impact of cocaine on the expression of FosB/DeltaFosB transcription factors in the PVN. Using an immunohistochemical method, we found that acute cocaine treatment (25 mg/kg) induced a relatively long-lasting (at least 72 h) expression of FosB/DeltaFosB in the PVN, whereas repeated cocaine administration (25 mg/kg, once daily for 5 consecutive days) caused accumulation of FosB/DeltaFosB in the PVN. The latter observation was further confirmed by the Western blot technique which revealed that repeated exposure to cocaine specifically increased the expression of a stable isoform of DeltaFosB (35 kDa). Using a double-labeling immunofluorescent method, it was established that FosB/DeltaFosB proteins induced by repeated cocaine treatment were present in a small population of CRF-immunoreactive neurons of the PVN. Furthermore, it was found that pretreatment with the specific antagonist of dopamine D1-like receptors SCH 23390 (1 mg/kg) attenuated the expression and accumulation of FosB/DeltaFosB in the PVN, evoked by repeated cocaine administration. Although functional consequences of the above effects for the process of addiction remain to be established, the obtained results indicate that cocaine administration can produce relatively long-lasting changes in the expression of FosB/DeltaFosB transcription factors in PVN neurons (in some populations of CRF-immunoreactive neurons, among others) and that dopamine D1-like receptors are involved in the above effects. Finally, it is proposed that the long-lasting expression as well as the accumulation of DeltaFosB in the PVN may constitute a molecular basis underlying adaptive changes occurring in the HPA axis after relatively high doses of cocaine.

Purvalanol A, inhibitor of cyclin-dependent kinases attenuates proliferation of cells in the dentate gyrus of the adult rat hippocampus

Several recent findings indicate that intensity of neurogenesis in adult brain might be regulated by enzymes involved in the cell cycle. Therefore, in the present study, we investigated whether the inhibition of cyclin-dependent kinases (CDKs) evoked by intraventricular administration of purvalanol A may influence the proliferation of cells in the dentate gyrus (DG) of the rat hippocampus. Purvalanol A, a selective inhibitor of CDKs, was injected into the brain lateral ventricle at concentrations of 4 nmol/3 microl or 40 nmol/3 microl. The number of proliferating cells was determined by analysis of nuclear incorporation of BrdU (100 mg/kg, i.p.). BrdU was given at two times points (0.5 h and 2.5 h) after vehicle or purvalanol A injection. It was found that purvalanol A given 0.5 h before BrdU injection did not cause any significant changes in the number of BrdU-positive nuclei in the DG. However, a higher dose of purvalanol A i.e. 40 nmol/3 microl given 2.5 h before BrdU administration significantly decreased the number of BrdU-positive nuclei in the DG of the hippocampus (by approximately 35%). In contrast, a lower dose of the CDKs inhibitor (4 nmol/3 microl) given at the same time point did not affect the number of BrdU-positive cells in the DG. It appears that purvalanol A inhibits the hippocampal proliferation in concentration- and time-dependent manner. Moreover, the present data indicate that CDKs are involved in generation of new cells in the adult rat hippocampus.

The effect of ‘binge’ cocaine administration on the expression of cyclin-dependent kinase 5 and its activator p35 in various regions of rat brain

The present study was aimed at determining whether the administration of cocaine in 'binge' pattern regimen that evoked tolerance to the locomotor stimulant effects of cocaine also influenced the expression of cyclin-dependent kinase 5 (Cdk5) and its activator p35 in the amygdala, medial prefrontal cortex, nucleus accumbens septi and caudate-putamen. Western blot techniques revealed that acute and repeated 'binge' cocaine decreased expression of the Cdk5 protein in the amygdala. In the medial prefrontal cortex, only exposure to repeated 'binge' cocaine decreased the content of the Cdk5 protein. 'Binge' cocaine administration also altered the expression of Cdk5 activator p35 protein. In the amygdala, only repeated 'binge' cocaine decreased the expression of p35, while in the medial prefrontal cortex, a decrease was observed after acute and repeated 'binge' cocaine exposure. In neither the nucleus accumbens septi nor the caudate-putamen acute or repeated 'binge' cocaine modified the expression of Cdk5 and p35. The above data indicate that in contrast to sensitizing doses of cocaine, a single and repeated binge of cocaine, which evoked tolerance to its locomotor stimulant effects, decreases expression of Cdk5 and p35 and possibly decreases the efficacy of neurotransmission or induces brain plastic changes regulated by Cdk5 and its activator p35.

Alterations in the dendritic morphology of prefrontal pyramidal neurons in adult rats after blockade of NMDA receptors in the postnatal period

The present study assessed whether the blockade of NMDA receptors in the postnatal period, used to model the symptoms of schizophrenia altered morphology of pyramidal neurons in the medial prefrontal cortex of rats. CGP 40116, an antagonist of NMDA receptors, was given postnatally (days 1-21 after birth). The analysis of the morphology of pyramidal neurons visualized by the Golgi-Cox technique revealed that the exposure to an antagonist of NMDA receptors in the postnatal period diminished the length of basilar dendrites, while that of apical dendrites remained unchanged. The number of dendritic branches and the spine density remained unchanged. It is concluded that the blockade of NMDA receptors in the postnatal period only partially models morphological changes in pyramidal neurons of the medial prefrontal cortex, which are observed in some cases of schizophrenia.

Acute and repeated administration of cocaine differentially regulates expression of PSA-NCAM-positive neurons in the rat hippocampus

Recent data indicating that addictive substances are able to alter brain plasticity and its morphology inclined us to determine whether acute and chronic cocaine administration could modify the expression of a polysialylated form of the neuronal cell adhesion molecule (PSA-NCAM) in the dentate gyrus of the rat hippocampus. Alterations in the PSA-NCAM expression are known to effect a variety of neuroanatomical rearrangements in the brain structure. Cocaine was administered acutely (15 mg/kg, i.p.) or repeatedly (15 mg/kg, i.p. once a day for five consecutive days). The number of PSA-NCAM immunopositive cells was determined at six time points after cocaine treatment: 6 h and 1, 2, 4, 6, and 10 days (both in acute and repeated treatment). It was found that a single injection of cocaine induced a time-dependent decrease in the number of PSA-NCAM cells in the dentate gyrus. The decrease was observed on day 1 after cocaine treatment and lasted for at least 6 days. In contrast, an increase in the number of PSA-NCAM-positive cells in the dentate gyrus was observed 2 and 4 days after the last dose of repeated cocaine. It is concluded that cocaine can evoke long-lasting changes in the PSA-NCAM protein expression in the dentate gyrus and that the direction of cocaine-induced PSA-NCAM changes depends on the regimen of cocaine administration. It is postulated that cocaine may have impact on hippocampal plasticity and subsequent processes that are controlled by plastic changes in the hippocampal structure.

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.

Regulation of alpha-synuclein expression in limbic and motor brain regions of morphine-treated mice

Chronic exposure to opiates produces dependence and addiction, which may result from neuroadaptations in the dopaminergic reward pathway and its target brain regions. The neuronal protein alpha-synuclein has been implicated in neuronal plasticity and proposed to serve as a negative regulator of dopamine neurotransmission. Thus, alpha-synuclein could mediate some effects of opiates in the brain. The present study investigated the influence of acute and chronic morphine administration on alpha-synuclein mRNA and protein expression in the brains of mice. Downregulation of alpha-synuclein mRNA was observed in the basolateral amygdala, dorsal striatum, nucleus accumbens, and ventral tegmental area of mice withdrawn from chronic morphine treatment. The changes were the most pronounced after longer periods of withdrawal (48 h). In contrast, levels of alpha-synuclein protein, as assessed by Western blotting, were significantly increased in the amygdala and striatum/accumbens (but not in the mesencephalon) of morphine-withdrawn mice. In both brain regions, levels of alpha-synuclein were elevated for as long as 2 weeks after treatment cessation. Because alpha-synuclein is a presynaptic protein, the detected opposite changes in its mRNA and protein levels are likely to take place in different populations of projection neurons whose somata are in different brain areas. Axonal localization of alpha-synuclein was confirmed by immunofluorescent labeling. An attempt to identify postsynaptic neurons innervated by alpha-synuclein-containing axon terminals revealed their selective apposition to calbindin D28K-negative projection neurons in the basolateral amygdala. The observed changes in alpha-synuclein levels are discussed in connection with their putative role in mediating suppression of dopaminergic neurotransmission during opiate withdrawal.

Behavioral pharmacology of sigma-ligands

Sigma (sigma) receptors, first defined as a subclass of opioid receptors, later confounded with the high affinity phencyclidine (PCP) binding sites, now are regarded as unique binding sites, distinct from opiate and PCP receptors, and related to higher brain function. The investigation of functional significance of sigma receptors in the brain has been hampered for many years by relative lack of specific tool drugs and by the unavailability of their coherent classification into postulated agonists and antagonists. However, a potential involvement of sigma receptors in psychotic disorders was first suggested soon after their discovery. The sigma receptors are classified into two subtypes, sigma (1) and sigma (2) receptors, of which the first was recently cloned from rodent and human tissues while the second has not yet been fully characterized. Although the precise mechanism of the functional response of these receptors is still uncertain, it is accepted that sigma receptors can modulate a number of central neurotransmitter systems, including noradrenergic, glutamatergic and dopaminergic ones. The sigma receptors have been postulated to be involved in numerous pharmacological and physiological functions, including motor disorders, psychotic disorders, neuroprotective mechanisms. In the last years, a number of compounds with a high affinity and selectivity for sigma binding sites have been discovered and investigated for their therapeutic potential. In this review, we try to summarize the behavioral effects of sigma receptor ligands that have been described, and their activity in animal models related to some brain disorders, especially schizophrenia and affective disorders.

Neurogenesis in the adult brain

Neurogenesis is a process that involves cell proliferation, migration and differentiation. Adult neurogenesis has been discovered by Altman in the mid 1960s. It is known now that neurogenesis occurs in two main neurogenic areas of the adult mammalian brain: the olfactory bulb and the hippocampal dentate gyrus, although other brain regions, such as cortex or substantia nigra cannot be excluded. The rate of neurogenesis can be regulated in a positive and negative manner by several factors like, age, growth factors, hormones, environmental or pharmacological stimuli. Functional significance of adult neurogenesis is still under investigation, however, several evidences suggest involvement of newly generated neurons in cognitive processes. There are also several findings indicating that the impairment of adult neurogenesis may be involved in the pathophysiology of some brain diseases, like depression, epilepsy, ischemia or neurodegenerative disorders. It appears that alterations in the rate of neurogenesis may have important functional and therapeutic implications.

Different pattern of brain c-Fos expression following re-exposure to ethanol or sucrose self-administration environment

Exposure of alcohol addicts to alcohol-related environmental cues may elicit alcohol-seeking behavior and lead to relapse to heavy drinking. The aim of the present study was to identify brain regions activated by alcohol (ethanol)-related stimuli in Wistar rats trained to lever press for 8% ethanol solution in operant self-administration cages. Ethanol self-administration was stabilized in a maintenance phase, which lasted for 30 days. c-Fos protein expression was used as a marker of neuronal activation.Re-exposure to ethanol self-administration environment after 30-day but not after 24-h abstinence increased the number of Fos-positive nuclei in the thalamic paraventricular nucleus, granular insular cortex and medial prefrontal cortex. In general, no differences were found in c-Fos protein expression between the rats allowed to self-administer alcohol and the subjects exposed only to alcohol-related stimuli. In contrast, no increase in c-Fos immunoreactivity was observed in rats trained to lever press for sucrose solution and exposed to sucrose-related environmental stimuli after 30-day abstinence. Taken together, these results suggest that at least some thalamo-cortical circuits become more responsive to ethanol-paired stimuli after prolonged abstinence and that ethanol- and sucrose-seeking behavior may be regulated by partially different neural mechanism(s).

Serotonin 5-HT1A receptors might control the output of cortical glutamatergic neurons in rat cingulate cortex

The present study was designed to investigate the distribution of serotonin 5-HT1A receptor protein (5-HT1A-immunoreactivity) and its localization within cortical pyramidal neurons of the rat cingulate cortex. This experimental direction was inspired by recent data showing the role of 5-HT1A receptors in the pathology of schizophrenia, and in the mechanism of action of novel antipsychotic drugs as well as by the importance of the cingulate cortex in regulation of cognitive functions. It was found that 5-HT1A-immunoreactivity was densely distributed in neuronal eyelash-like elements, and their size, shape and spatial orientation may suggest concentration of 5-HT1A-immunopositive material in the proximal fragments of axons of cortical neurons. Moreover, it was observed that these 5-HT1A-immunopositive fragments were present predominately on proximal fragments of axons of pyramidal neurons, which was evidenced by double labeling experiments using glutamate and non-phosphorylated neurofilament H as markers of the cortical pyramidal cells. The 5-HT1A receptor immunoreactivity was localized distally to the inhibitory GABAergic terminals of chandelier and basket cells surrounding the pyramidal cell bodies and occasionally surrounding short initial segment of axonal hillock of pyramidal neurons. These anatomical data indicate that 5-HT1A receptors might control the excitability and propagation of information transmitted by the pyramidal cells. Moreover, our results indicate that drugs operating via 5-HT1A receptors in the cingulate cortex might control from this level the release of glutamate in the subcortical structures. Finally, the 5-HT1A receptors present in the cingulate cortex, as demonstrated in the present study, may constitute an important target for drugs used to repair dysfunction of glutamate neurotransmission, which is observed for example in schizophrenia.

8-OHDPAT-induced disruption of prepulse inhibition in rats is attenuated by prolonged corticosterone treatment

The present study investigated the impact of acute and repeated administrations of corticosterone (10 mg/kg, twice daily, for 7 days) on serotonin (5-HT)(1A) receptor function, density and expression. The effect on 5-HT(1A) receptor function was assayed in rats by assessing the corticosterone-induced modulation of disruption of prepulse inhibition (PPI) of acoustic startle response induced by 8-OHDPAT, a 5-HT(1A) receptor agonist. Our experiments revealed that repeated but not acute treatment with corticosterone attenuated the 8-OHDPAT-evoked disruption of PPI without having any effect on PPI or startle amplitude alone. Chronic corticosterone treatment modulated also the neuronal activity of serotonergic pathways in the brain decreasing the level of 5-HIAA in the raphe nuclei and increasing both 5-HT and 5-HIAA levels in the hippocampus. Nevertheless, the effects of 8-OHDPAT on 5-HT metabolism were not changed by corticosterone. However, 5-HT(1A) receptor binding in the ventral hippocampus and entorhinal cortex but not in the raphe nuclei was decreased after chronic corticosterone treatment. It is concluded that chronically elevated corticosterone level is capable of inducing functional desensitization of 5-HT(1A) receptors which is paralleled by decreases in the 5-HT(1A) receptor binding in the ventral hippocampus and entorhinal cortex, the brain structures shown to be engaged in the regulation of PPI. Alterations in 5-HT(1A) receptors may be one of important mechanisms by which glucocorticoids/stress influence various psychiatric conditions.

Endomorphin-2, deltorphin II and their analogs suppress formalin-induced nociception and c-Fos expression in the rat spinal cord

In this study, we evaluated the effects of intrathecally administered agonists of mu- and delta-opioid receptor and their analogs on the pain-induced behavior and expression of c-Fos immunoreactivity in the spinal cord, elicited by intraplantar injection of 12% formalin to the hindpaw of the rat. Previous report from our laboratory and other author's study indicated that intrathecal administration of mu agonists morphine and endomorphin-2 and delta-opioid agonist deltorphin II produced a dose-dependent antinociceptive effects in acute and inflammatory pain. In this study, intrathecal injection of morphine (10 microg), endomorphin-2 (5 microg) and its analog Dmt-endomorphin-2 (10 microg) significantly decreased the formalin-induced pain behavior, and lowered a number of c-Fos positive neurons in the laminae I, II and III of the spinal cord by about 40%, 30% and 40%, respectively. Significant reduction of formalin-induced behavioral responses was also observed after i.th. administration of deltorphin II (15 microg) and its analog ile-deltorphin II (15 microg). Agonists of delta-opioid receptor significantly reduced a number of c-Fos positive neurons by about 28% and 40%, respectively. Analog of endomorphin-2 and analog of deltorphin II suppressed more potently expression of c-Fos in the dorsal horn of the spinal cord than the parent peptides. Our study indicates that new analogs of mu- and delta-opioid receptor exhibit strong antinociceptive potency similar or even higher than the parent peptides, and that their effect is positively correlated with the inhibition of c-Fos expression.

A search for colocalization of mglula receptors with CRF or NPY in the rat brain amygdala

Excitatory neurotransmitter glutamate, as well as corticoliberin (CRF) and neuropeptide Y (NPY) play an important role in fear and anxiety. Among the brain structures engaged in these effects the important one is amygdala. In the present study, a single and double immunohistochemical staining techniques were used in order to visualize CRF, NPY and metabotropic glutamate receptors (mGluR1a) in rat amygdala. MGluR1a belongs to class of postsynaptic excitatory receptors and has a preferable somatic localization. CRF and NPY were localized using rabbit polyclonal antibodies, and mGluR1a using a mouse monoclonal one. Then, ABC-peroxidase and DAB or benzidine were used. Upon single immunostaining, NPY and CRF were found in some nerve cell bodies and fibres in the amygdala. The immunoreactivity of mGluR1 a was observed in some nerve cells, processes and fibres, especially on the border between the central and the basolateral nuclei and ventrally to that region. Double staining revealed mGluR1 a-IR on some CRF- and NPY-immunoreactive nerve cell bodies and processes. The obtained results indicate that mGlu1a receptors may control at least some NPY and CRF neurons in the amygdala.

Prolonged corticosterone treatment alters the responsiveness of 5-HT1A receptors to 8-OH-DPAT in rat CA1 hippocampal neurons

Hippocampal 5-HT(1A) receptors have been shown to be suppressed by glucocorticoids in a variety of animal studies, however the molecular mechanism and the functional meaning of this effect are still not well understood. The present study was designed to investigate the impact of repeated administration of corticosterone (10 mg/kg s.c. twice daily for 7 days) on the functional consequences of 5-HT(1A) receptor stimulation measured electrophysiologically in hippocampal slices. Additionally, the effects of corticosterone on 5-HT(1A) receptor binding and on receptor mRNA levels in the hippocampus were studied. Prolonged, but not acute treatment with corticosterone attenuated (+/-)-8-hydroxy-2-di- N-propylamino)tetralin hydrobromide (8-OH-DPAT)-induced inhibition of population spikes, and 8-OH-DPAT-induced hyperpolarization in rat CA1 hippocampal neurons. Chronic, but not acute treatment with corticosterone also decreased 5-HT(1A) receptor binding in the CA1 region (in the ventral part only) and the dentate gyrus. A single dose of corticosterone increased [(3)H]8-OHDPAT binding in the dentate gyrus and in the CA3 and CA4 hippocampal regions. Only acute, but not prolonged treatment with corticosterone decreased the level of 5-HT(1A) receptor mRNA in the CA1 region and dentate gyrus of the hippocampus. 5-HT turnover in the hippocampus was not influenced by chronic corticosterone. It is concluded that a chronically elevated level of corticosterone can induce functional desensitization of 5-HT(1A) receptors in the CA1 area of the hippocampus, although this effect is not always followed consequently by decreases in 5-HT(1A) receptor synthesis in this or other areas of the hippocampus.

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.

Inhibition of arachidonic acid cascade attenuates the induction of c-Fos proteins by DOI, 5-HT2A/2C receptor agonist, in the rat cortex

Previous immunohistochemical studies have shown that c-Fos proteins induced by DOI, a 5-HT2A/2C agonist, are present in the population of cortical neurons, which are devoid of 5-HT2A receptors. A mechanism of the induction of c-Fos proteins expression by DOI is still unclear. However, the involvement of the 5-HT2A and AMPA, but not 5-HT2C receptors in this process has been reported. In the present study, we investigated whether arachidonic acid, a retrograde messenger, is involved in the above mechanism of c-Fos induction. Phospholipase A2 pathway, which leads to the subsequent generation of arachidonic acid and its metabolites, is known to be coupled to 5-HT2A receptor activation. The inhibition of arachidonic acid cascade both at the level of phospholipase A2 (by dexamethasone, 1.5 mg/kg) or at the level of cyclooxygenases that catalyze arachidonic acid biotransformation (by indomethacin, 3 mg/kg), decreased the number of c-Fos immunopositive cells after induction by DOI (8 mg/kg). Our results suggest that arachidonic acid cascade may be involved in the induction of c-Fos proteins by DOI in the rat parietal cortex.

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.

Effects of imidazoline antihypertensive drugs on sympathetic tone and noradrenaline release in the prefrontal cortex

1. The aim of the present study was to compare the effects of the centrally acting antihypertensive drugs rilmenidine, moxonidine, clonidine and guanabenz on sympathetic tone with their effects on noradrenaline release in the cerebral cortex. In particular, the hypothesis was tested that rilmenidine and moxonidine, due to their high affinity for sympatho-inhibitory imidazoline I(1) receptors and low affinity for alpha(2)-adrenoceptors, lower sympathetic tone without causing an alpha(2)-adrenoceptor-mediated inhibition of cerebrocortical noradrenaline release. 2. In rats anaesthetized with urethane, blood pressure and heart rate were measured and the concentration of noradrenaline in arterial blood plasma was determined. The release of noradrenaline in the medial prefrontal cortex was estimated by microdialysis. Intravenous administration of rilmenidine (30, 100, 300 and 1000 microg kg(-1)), moxonidine (10, 30, 100 and 300 microg kg(-1)), clonidine (1, 3, 10 and 30 microg kg(-1)) and guanabenz (1, 3, 10 and 30 microg kg(-1)) led to dose-dependent hypotension and bradycardia; the plasma noradrenaline concentration also decreased. After the two highest doses, all four drugs lowered noradrenaline release in the prefrontal cortex. At doses eliciting equal hypotensive and sympatho-inhibitory responses, rilmenidine and moxonidine inhibited cerebral cortical noradrenaline release at least as much as clonidine and guanabenz. 3. The results show that rilmenidine and moxonidine lower cerebrocortical noradrenaline release at doses similar to those which cause sympatho-inhibition. This effect was probably due to an alpha(2)-adrenoceptor-mediated inhibition of the firing of locus coeruleus neurons and, in addition, to presynaptic inhibition of noradrenaline release at the level of the axon terminals in the cortex. The results argue against the hypothesis that rilmenidine and moxonidine, due to their selectivity for sympatho-inhibitory I(1) imidazoline receptors, do not suppress noradrenergic neurons in the central nervous system.

[Distribution of dopamine D1 receptors in the paraventricular nucleus of the rat hypothalamus and their colocalization with phosphorylated forms of CREB protein]

The aim of the present immunohistochemical study was to investigate distribution of dopamine D1 receptors in the paraventricular nucleus of hypothalamus and to estimate whether D1 receptors colocalize with pCREB protein, a functional marker of stimulation generated via receptors positively linked to cAMP/PKA system. D1 receptors were found in numerous neurones of the paraventricular nucleus of hypothalamus, especially in its magnocellular part. In double-staining experiment, 74% of all stained neurones showed colocalization of D1 receptors and pCREB protein, 23% of neurones was pCREB-positive only and 3%--D1 receptor-positive only. The presence of D1 receptors in the paraventricular nucleus of hypothalamus indicates that these receptors may be possibly engaged in regulation of the endocrine system (release of oxytocin, vasopressin or CRH). Almost complete colocalization of D1 receptors with pCREB protein suggests that these receptors are likely functional (active). The presence of D1 receptors and pCREB protein in studied structures of rat brain, as well as the specificity of applied antibodies were confirmed by Western Blot method. It was demonstrated that antibodies against D1 receptor and pCREB protein recognized main bands with molecular weight approximately 40 and approximately 46 kDa, respectively, what correlates well with the literature data.

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.

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.

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.

[The involvement of 5-HT1a serotonin receptors in the pathophysiology and pharmacotherapy of schizophrenia]

Many studies of schizophrenic brains indicate the dysfunction of dopamine and glutamate systems in the prefrontal and frontal cortex. It seems that better understanding of mechanisms regulating functions of these neuronal cortical systems could contribute to creation of new drugs acting in the cortex selectively. This might be profitable in cognition of dysfunction and negative symptoms in schizophrenia. This article presents preclinical data concerning the role of 5-HT1A serotonin receptors in the modulation of cortical dopamine system and in psychotomimetic effects of non-competitive NMDA receptor antagonists. Neurochemical studies have shown that 5-HT1A receptor agonists increase dopamine release in the rat prefrontal cortex on the one hand, and they inhibit the augmentation of dopamine release induced by stress or amphetamine, on the other. However, the increase of dopamine release induced by non-competitive NMDA receptor antagonists is blocked by 5-HT1A receptor antagonists. Blockade of 5-HT1A receptors seems to be important also in reduction of most psychotomimetic effects induced by non-competitive NMDA antagonists both involving (locomotor hyperactivity, working memory impair) and not involving (sensorimotor gating deficits) dopamine mechanism. Thus, binding with 5-HT1A receptors can be an important site for the regulation of cortical dopamine system, both in physiological conditions and in disregulation of the system induced by stress, psychostimulants or psychotomimetics. On the other hand, 5-HT1A receptors modulate most of psychotomimetic effects of non-competitive NMDA receptor antagonists. The above results of preclinical investigations indicate that 5-HT1A receptor can be involved in the pathology of schizophrenia, what is partly confirmed by clinical postmortem studies of schizophrenic brains. These studies showed the increase of 5-HT1A receptor density in prefrontal and frontal cortex in schizophrenic brains. It also seems that 5-HT1A receptors might be a good target for the antipsychotic drugs. Although the clinical studies have demonstrated controversial data, maybe further studies using substances with selectivity to 5-HT1A receptors would help to determine more precisely the role of these receptors in pathology and pharmacotherapy of schizophrenia.

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.

NMDA receptor antagonists acting at the glycineB site in rat models for antipsychotic-like activity

Several partial agonist and full antagonists acting at the glycine site of the NMDA receptors were tested for potential antipsychotic-like properties in rats. As models, amphetamine- and phencyclidine (PCP)-induced locomotor activation in the open field and PCP-induced impairment of prepulse inhibition of the acoustic startle response were employed. In the open field test, partial agonists, D-cycloserine failed to show any effect, aminocyclopropane carboxylic acid (ACPC) enhanced the action of PCP (but not that of amphetamine) and R(+)HA-966 attenuated the locomotor activation produced by both amphetamine and PCP. Both full glycineB antagonists, L-701,324 and MRZ 2/576 attenuated the action of amphetamine and PCP but at the doses that also produce transient behavioural inhibition in naive animals. A competitive NMDA receptor antagonist CGP 39551 was ineffective. In the prepulse inhibition test neither L-701,324 nor MRZ 2/576 changed sensorimotor gating in naive animals nor attenuated the disrupting effects of PCP. The present data do not support antipsychotic profile of glycineB full antagonists. However, psychotomimetic potential of glycineB antagonists seems to be low.

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.

GlycineB antagonists as potential therapeutic agents. Previous hopes and present reality

It is not clear what therapeutic application is most likely for agents blocking glycine site of the NMDA receptors (glycineB). Majority of the studies to date used either glycineB antagonists with doubtful brain penetration or partial agonists. Following systemic administration to rats of our newly developed glycineB antagonists (MRZ 2/570; 2/571 and 2/576) and L-701,324 (MSD) as a reference agent the following behavioural effects were observed: weak (if any) antiparkinsonian-like effects, lack of anxiolytic activity, inhibition of physical and motivational aspects of morphine dependence and neuroprotective activity in global ischaemia. The side effects include: sedation, ataxia, and myorelaxation. We detected neither vacuolisation in the cingulate cortex nor impairment of pre-pulse inhibition indicating lack of psychotomimetic potential.

Effect of EMD 57445, the selective sigma receptor ligand, on the turnover and release of dopamine

EMD 57445 (1, 3 and 10 mg/kg, po), a selective sigma receptor ligand without an affinity to dopamine receptors, induced potent, dose-dependent increases in the tissue DOPAC and HVA levels in the rat brain cortex, nucleus accumbens and striatum. The extracellular DOPAC and HVA levels after EMD 57445 and (3 and 10 mg/kg, po) administrations, measured by microdialysis in the rat prefrontal cortex, were also increased, without significant effects on the outflow of dopamine.

The distribution of the NMDA R1 subunit in the rat hippocampus--an immunocytohistochemical study

In the present study we examined immunocytochemically the distribution of the R1 subunit of NMDA receptors in rat hippocampus. The applied antibody directed against the III-IV transmembrane region of the R1 subunit of NMDA receptors revealed a heterogeneous distribution of NMDA R1 protein which was highest in the CA1 pyramidal layer and lowest in the stratum lacunosum moleculare. The high immunoreactivity that corresponded to the presence of NMDA R1 receptor subunits was observed mainly in layers of cell bodies of hippocampal neurons, such as deep pyramidal layers of CA1, CA2 and CA3 regions and a granular cell layer of the dentate gyrus. The obtained data are discussed in terms of correlation between the receptor localization and the vulnerability of hippocampal neurons to overstimulation associated with activation of NMDA 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.

Presence and function of dopamine D1 receptors in the rat ventral tegmental area

In the recent years there is a growing number of reports suggesting that dopamine D1 receptors are involved in the phenomenon of sensitization. In this article we are reviewing the data suggesting the crucial role of dopamine D1 receptors, localized in the rat ventral tegmental area in this phenomenon.

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.

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.

Competitive and non-competitive NMDA receptor antagonists induce c-Fos expression in the rat anterior, cingulate cortex

In the present study we tried to find out whether the competitive NMDA receptor antagonist CGP 40116 was capable of inducing c-Fos expression in the rat cingulate cortex in a manner similar to that described previously for the non-competitive NMDA receptor antagonist MK-801. Induction of fast early genes by MK-801, especially in the rat cortex, has recently been linked with the neurotoxic effects of non-competitive NMDA receptor antagonists on cortical neurones, hence it was of interest to extend those studies to another class of NMDA receptors antagonists i.e., competitive one. It was found that CGP 40116 (2.5 and 5 mg/kg) induced c-Fos expression in the rat anterior cingulate cortex. That effect was dose-dependent and was shown as an increase in the number of cells expressing the c-Fos immunoreactivity. A qualitatively similar, but quantitatively stronger, effect was observed after administration of MK-801 (0.2 and 0.4 mg/kg), which also caused a dose-dependent increase in the number of c-Fos positive neurones. The described dose-dependent effects of CGP 40116 and MK-801 are shown as an increase in the number of c-Fos-positive neurones, but not as an increase in the optical density of c-Fos immunostaining in c-Fos positive neurones. In control, vehicle-injected rats, the constitutive c-Fos immunoreactivity was not found in the rat anterior cingulate cortex. The obtained data indicate that both competitive and non-competitive NMDA receptor antagonists may induce similar effects on the c-Fos immunoreactivity in the rat anterior cingulate cortex, and that their administration may lead to similar functional consequences resulting form activation of fast, early genes.

Adaptive changes in the rat dopaminergic transmission following repeated lithium administration

In the present study the alterations in the contents of dopamine (DA) and metabolites, as well as in the levels of mRNA coding for DA receptor D2, were determined in the rat striatum (STR) and nucleus accumbens septi (NAS), in correlation with the duration of lithium administration. Single or subchronic (3 days) administration of lithium produced less consistent effects as far as the levels of DA and metabolites are concerned; however, following 7 or 14 days of lithium administration, the DA release from terminals was significantly attenuated and the effect was more pronounced in NAS. After the same time of treatment, the increase in the levels of mRNA coding for the D2 receptor was increased; this might be interpreted as an adaptive change to the decreased dopaminergic transmission following the prolonged administration of lithium.

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.

Imipramine increases the 5-HT1A receptor-mediated inhibition of hippocampal neurons without changing the 5-HT1A receptor binding

The effect of repeated treatment with imipramine on the 5-HT1A receptor-mediated inhibition of a population spike was studied in the rat CA1 hippocampal region ex vivo. Serotonin (5-hydroxytryptamine, 5-HT) and the selective 5-HT1A receptor agonist 8-hydroxy-2-(dipropylamino)tetralin (8-OH-DPAT) decreased dose-dependently the amplitude of population spikes; this effect was blocked by the selective 5-HT1A receptor antagonist (S)-N-tert-butyl-3-[4-(2-methoxyphenyl)piperazin-1-yl]-2-phenylpro panamide dihydrochloride [(S)-WAY 100135]. Repeated (14 days, twice daily), but not single, administration of imipramine (10 mg/kg) shifted the dose-response curves for serotonin and 8-OH-DPAT to the left. Repeated treatment with imipramine did not change the density of 5-HT1A receptors in the hippocampus as measured by autoradiography using [3H]8-OH-DPAT as a ligand. The latter findings indicate that the imipramine-induced increase in the responsiveness of hippocampal neurons to stimulation of 5-HT1A receptors may not involve an increase in the density of this receptor subtype. To find out whether the efficacy of the postreceptor transduction mechanism is changed by repeated treatment with imipramine, we examined the effect of baclofen. The baclofen-induced inhibition of the population spike was not changed by imipramine. Our results suggest that repeated treatment with imipramine induces sensitization to the inhibitory effects of 5-HT1A receptor agonists in the hippocampus.

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.