Neonatal exposure to phenobarbital potentiates schizophrenia-like behavioral outcomes in the rat

Previous work has indicated an association between seizures early in life and increased risk of psychiatric disorders, including schizophrenia. However, because early-life seizures are commonly treated with antiepileptic drugs (AEDs) such as phenobarbital, the possibility that drug treatment may affect later-life psychiatric outcomes needs to be evaluated. We therefore tested the hypothesis that phenobarbital exposure in the neonatal rat increases the risk of schizophrenia-like behavioral abnormalities in adulthood. Thus, in this study, we examined the effects of a single acute neonatal exposure to phenobarbital on adult behavioral outcomes in the rat neonatal ventral hippocampal (nVH) lesion model of schizophrenia. We compared these outcomes to those in rats a) without nVH lesions and b) with nVH lesions, without phenobarbital. The tasks used for behavioral evaluation were: amphetamine-induced locomotion, prepulse inhibition, elevated plus-maze, and novel object recognition task. We found that neonatal phenobarbital treatment (in the absence of nVH lesions) was sufficient to disrupt sensorimotor gating (as tested by prepulse inhibition) in adulthood to an extent equivalent to nVH lesions. Additionally, neonatal phenobarbital exposure enhanced the locomotor response to amphetamine in adult animals with and without nVH lesions. Our findings suggest that neonatal exposure to phenobarbital can predispose to schizophrenia-like behavioral abnormalities. Our findings underscore the importance of examining AED exposure early in life as a potential risk factor for later-life neuropsychiatric abnormalities in clinical populations.

Developmental profile of neuregulin receptor ErbB4 in postnatal rat cerebral cortex and hippocampus

We investigated the cellular and subcellular distributions of neuregulin tyrosine kinase receptor ErbB4 in the postnatal rat frontal cortex and hippocampus by light-, confocal- and electron-microscopic immunocytochemistry. At birth, ErbB4-immunoreactivity (ErbB4-IR) was prominent in the apical cytoplasm and dendrites of cortical plate neurons and hippocampal pyramidal cells. Throughout postnatal development and in adulthood, ErbB4-IR in both regions remained confined to the somatodendritic compartment of neurons, which increased in number to reach the adult pattern by the end of the first postnatal month (P30). At all ages examined, double-labeling experiments revealed that ErbB4-IR always co-localized with the neuronal marker neuronal nuclei (NeuN) and never with glial markers Nestin or glial fibrillary acidic protein (GFAP). Immunoperoxidase labeling at the ultrastructural level confirmed the exclusive localization of ErbB4-IR in somatodendrites, and notably in dendritic spines. Immunogold labeling showed preponderant ErbB4-IR in the cytoplasm, where it was associated with microtubules. Furthermore, ErbB4-IR was abundant in the nucleus of adult cortical and hippocampal neurons, suggesting a role for ErbB4 nuclear signaling in the brain beyond embryonic development. Taken together, these results show that ErbB4 is expressed by neuronal somatodendrites in cerebral cortex and hippocampus from birth to adulthood, and support a role for neuregulins in dendritic growth and plasticity.

Alterations in dendritic morphology of prefrontal cortical and nucleus accumbens neurons in post-pubertal rats after neonatal excitotoxic lesions of the ventral hippocampus

Neonatal ventral hippocampal (nVH) lesions in rats result in adult onset of a number of behavioral and cognitive abnormalities analogous to those seen in schizophrenia, including hyperresponsiveness to stress and psychostimulants and deficits in working memory, sensorimotor gating and social interaction. Molecular and neurochemical alterations in the prefrontal cortex (PFC) and nucleus accumbens (NAcc) of nVH-lesioned animals suggest developmental reorganization of these structures following neonatal lesions. To determine whether nVH lesions lead to neuronal morphological changes, we investigated the effect of nVH lesion on dendritic structure and spine density of pyramidal neurons of the PFC and medium spiny neurons of the NAcc. Bilateral ibotenic acid-induced lesion of the VH was made in Sprague-Dawley pups at postnatal day 7 (P7); and at P70, neuronal morphology was quantified by modified Golgi-Cox staining. The results show that length of basilar dendrites and branching and the density of dendritic spines on layer 3 pyramidal neurons were significantly decreased in rats with nVH lesions. Medium spiny neurons from the NAcc showed a decrease in the density of dendritic spines without significant changes in dendritic length or arborization. The data, comparable to those observed in the PFC of schizophrenic patients, suggest that developmental loss of excitatory projections from the VH may lead to altered neuronal plasticity in the PFC and the NAcc that may contribute to the behavioral changes in these animals.

Neonatal ventral hippocampus lesion leads to reductions in nerve growth factor inducible-B mRNA in the prefrontal cortex and increased amphetamine response in the nucleus accumbens and dorsal striatum

Converging evidence in schizophrenia suggests prefrontal cortical neuronal deficits that correlate with exaggerated subcortical dopamine (DA) functions: Excitotoxic lesion of the ventral hippocampus (VH) in neonatal rats is widely considered a putative animal model of schizophrenia as they lead to characteristic post-pubertal emergence of behavioral and cognitive abnormalities suggesting a developmental change in the neural circuits comprising the prefrontal cortex (PFC) and subcortical DA. Nerve growth factor inducible-B (NGFI-B, also known as Nur77), an orphan nuclear receptor and transcriptional regulator, is constitutively expressed in the target structures of DA pathways. It acts as an immediate early gene with rapid modulation of its mRNA expression by stress, DA and antipsychotic drugs. The present study assessed the effects of neonatal VH (nVH) lesion and amphetamine treatment on the expression of NGFI-B mRNA in pre- and post-pubertal rats. Sprague-Dawley rat pups received bilateral injection of ibotenic acid or phosphate buffered saline in VH at postnatal (PD) 7. At PD35 and PD56, groups of sham and lesioned animals were administered with D-amphetamine (1.5 mg/kg) or saline and killed 20 min later. In situ hybridization analyses showed that the basal level of NGFI-B mRNA in saline-treated lesioned rats was significantly reduced in the medial PFC (mPFC) and cingulate cortex (CC) only at post-pubertal (PD56) age. No significant difference in NGFI-B mRNA levels was seen in the dorsal striatum or nucleus accumbens (NAcc). Amphetamine treatment increased the expression of NGFI-B mRNA in the mPFC, CC, striatum and NAcc in both control and lesioned animals of both ages. Interestingly, however, striatal and NAcc regions of lesioned rats showed a significantly greater effect of amphetamine at PD56. The data suggest that nVH lesions lead to delayed changes in PFC gene expression along with functional DAergic hyperactivity in subcortical regions.

Animal models of schizophrenia: a critical review

Current research into schizophrenia has remained highly fragmented, much like the clinical presentation of the disease itself. Differing theories as to the cause and progression of schizophrenia, as well as the heterogeneity of clinical symptoms, have made it difficult to develop a coherent framework suitable for animal modelling. However, a number of limited animal models have been developed to explore various causative theories and to test specific mechanistic hypotheses. Historically, these models have been based on the manipulation of neurotransmitter systems believed to be involved in schizophrenia. In recent years, the emphasis has shifted to targeting relevant brain regions in an attempt to explore potential etiologic hypotheses. The specific animal models developed within these frameworks are described in this review. Emphasis is placed on the critical evaluation of currently available models because these models help to shape the direction of future research.

Strain differences in the behavioural outcome of neonatal ventral hippocampal lesions are determined by the postnatal environment and not genetic factors

It has been demonstrated that not only do rats neonatally lesioned in the ventral hippocampus (VH) develop behavioural hypersensitivity to amphetamine postpubertally, but also that the expression of the sensitivity is strain specific. For example, excitotoxic VH lesions at postnatal day (PD) 7 lead to significant increases in amphetamine-induced locomotion in postpubertal Fischer rats, but not in Lewis rats. However, as it is likely that the effect of strain differences are due to a combination of genetics and environment, we examined the contributions of the environment of the pups in determining the behavioural outcome following neonatal VH lesions. Fisher and Lewis rat pups were cross-fostered at birth, and then at PD7 lesioned bilaterally in the VH with ibotenic acid. ANOVA analysis of postpubertal amphetamine-induced locomotor data revealed a significant effect of the strain of the dams raising the pups but no effect of the strain of the pup. In addition, a post hoc analysis revealed that lesioned Fisher or Lewis rats raised by Fisher, but not those raised by Lewis, dams demonstrated amphetamine-induced hyperlocomotion relative to nonlesioned controls. Observations of the maternal behaviour of Fischer and Lewis dams revealed significant differences in the frequency of arched-back nursing between the two strains. Interestingly, a correlation of the frequency of arched back nursing vs novelty- or amphetamine-induced locomotion revealed that the lesioned rats were significantly more affected by increases in arched-back nursing compared to the controls. The results suggest that the genetic background of the pups does not significantly affect the behavioural outcome following neonatal VH lesions; however, the results do suggest an important role of early environmental variables on the behavioural outcome of neonatal VH lesions.

DNA microarrays in neuropsychopharmacology

Recent advances in experimental genomics, coupled with the wealth of sequence information available for a variety of organisms, have the potential to transform the way pharmacological research is performed. At present, high-density DNA microarrays allow researchers to quickly and accurately quantify gene-expression changes in a massively parallel manner. Although now well established in other biomedical fields, such as cancer and genetics research, DNA microarrays have only recently begun to make significant inroads into pharmacology. To date, the major focus in this field has been on the general application of DNA microarrays to toxicology and drug discovery and design. This review summarizes the major microarray findings of relevance to neuropsychopharmacology, as a prelude to the design and analysis of future basic and clinical microarray experiments. The ability of DNA microarrays to monitor gene expression simultaneously in a large-scale format is helping to usher in a post-genomic age, where simple constructs about the role of nature versus nurture are being replaced by a functional understanding of gene expression in living organisms.

Differential changes in synaptic terminal protein expression between nucleus accumbens core and shell in the amphetamine-sensitized rat

Repeated, intermittent administration of psychostimulant drugs such as D-amphetamine (AMPH) produces a state of behavioral sensitization to the drug that can last up to weeks to months. The molecular basis of this enhanced sensitivity to AMPH is poorly understood; however, adaptive changes in the mesocorticolimbic dopamine system has been postulated to be of primary importance. In the present investigation we used Western blotting to examine the expression of candidate presynaptic proteins involved in regulating neurotransmitter release and synaptic plasticity. Specifically, syntaxin 1, synaptophysin and synapsin I protein levels were examined in the nucleus accumbens (Nacc) and ventral tegmental area (VTA) of Sprague-Dawley rats following AMPH-sensitization. Animals received five repeated administrations of AMPH (1.5 mg/kg, i.p. on alternate days) followed by 14 days of withdrawal. Levels of syntaxin 1 and synaptophysin were found to be significantly reduced in the Nacc core of sensitized animals compared to saline-treated and untreated controls. However, syntaxin 1 expression was significantly increased in the Nacc shell subregion of sensitized animals. No significant difference in the level of synapsin I was noted in any of the brain regions. Further, expression of none of the synaptic proteins was significantly altered in the VTA of sensitized animals. Given the importance of syntaxin and synaptophysin in learning and memory processes and in the regulation of neurotransmitter release, changes in these proteins suggest their involvement in the associative learning aspects of sensitization and differential neurotransmitter release in the Nacc subregions.

Behavioral and neurochemical alterations following repeated phencyclidine administration in rats with neonatal ventral hippocampal lesions

Exposure to chronic phencyclidine (PCP) has been reported to mimic certain aspects of schizophrenia in normal subjects as well as to exacerbate symptoms in schizophrenic patients. Analogous to schizophrenics, adult rats with neonatal ventral hippocampal (VH) lesions have been shown to display enhanced sensitivity to both stress and psychostimulants. In order to examine whether repeated PCP treatment can modulate behavior when administered to neonatal VH-lesioned animals, we examined locomotor activity and immobility time in the forced swimming test (FST) in neonatal VH-lesioned rats following repeated PCP treatment. Receptor autoradiography studies were also performed for dopamine (DA) and N-methyl-D-aspartate (NMDA) receptors to identify neurochemical correlates of the altered behavior in these animals. Though repeated PCP administration resulted in increased levels of locomotor activity and rearing in both VH-lesioned as well as sham rats, the effects were much more enhanced in the lesioned rats compared to sham. However, repeated PCP treatment induced hypolocomotion during the habituation period in both sham and lesioned rats. In the FST paradigm, lesioned rats displayed an altered retention of acquired immobility. Repeated PCP administration increased DA D1-like receptors in the caudate-putamen in lesioned rats and decreased striatal D2-like receptors in both sham and lesioned rats. Moreover, repeated PCP administration in lesioned rats decreased NMDA binding sites in the prefrontal cortex while increasing labelling in the subcortical regions. These results suggest that repeated administration of PCP can qualitatively and quantitatively affect behaviors in neonatal VH-lesioned rats related to abnormal neurodevelopmental processes presumably via prefrontal glutamatergic and subcortical dopaminergic dysfunctions.

Olfactory bulbectomy alters NMDA receptor levels in the rat prefrontal cortex

Olfactory bulbectomized (OBX) rats show a variety of behavioral and biochemical deficits that parallel human depression. We investigated the expression of glutamate receptor subtypes in cortical and subcortical brain regions following bilateral olfactory bulbectomy in adult rats. Quantitative receptor autoradiography using [(125)I]MK-801 (NMDA receptor), [(3)H]AMPA (AMPA receptor), and [(3)H]kainate (kainate receptor) was performed on brain sections at 1-5 weeks following olfactory bulbectomy. Our results show an elevation of NMDA receptors in the medial prefrontal cortex within 1 week following bulbectomy, which persisted up to at least 5 weeks post-bulbectomy. Neither kainate nor AMPA receptors were altered in any brain region examined. The potential significance of these results is discussed in light of experimental findings supporting a role for NMDA receptors in the mechanism of action of antidepressant drugs and the pathophysiology of major depression.

Enhanced nucleus accumbens dopamine and plasma corticosterone stress responses in adult rats with neonatal excitotoxic lesions to the medial prefrontal cortex

The medial prefrontal cortex modulates the nucleus accumbens dopamine response to stress and has been implicated in feedback regulation of hypothalamic-pituitary-adrenal axis activation by stress. Here we report on the effects of bilateral neonatal (postnatal day 7) ibotenate-induced lesions to the medial prefrontal cortex on nucleus accumbens dopamine and neuroendocrine function in adult rats. Voltammetry was used to monitor the dopamine response to each of five, once-daily exposures to tail-pinch stress whereas alterations in neuroendocrine function were determined from the plasma corticosterone response to a single 20-min episode of restraint stress. Potential lesion-induced deficits in sensory-motor gating were assessed by measuring prepulse inhibition of the acoustic startle response before and after repeated stress. Our data show that each daily stress episode elicited larger and longer-lasting dopamine increases in prefrontal cortex-lesioned animals than in sham-lesioned controls. Furthermore, greater stress-induced elevations in plasma corticosterone were seen in lesioned animals than in their sham-lesioned counterparts. However, while repeated stress potentiated startle responses in animals of both groups, there was no effect of lesion on the amplitude or on prepulse inhibition of the startle response.Together, these findings indicate that neonatal prefrontal cortex damage can lead to changes in mesolimbic dopamine and neuroendocrine function during adulthood. They also add to a growing body of experimental and clinical evidence implicating abnormal prefrontal cortex neuronal development in the pathophysiology of schizophrenia and other disorders linked to central dopamine dysfunction.

Dopamine D-5 receptor modulates hippocampal acetylcholine release

Dopamine is intimately involved in cognitive processes in the brain. Of the several subtypes of dopamine receptors, the possible role of dopamine D1-like receptors in brain functions, especially in learning and memory, has recently generated much interest. However, molecularly the D1-like receptors are comprised of at least two subtypes, namely D-1 and D-5, and it has not been possible to ascertain which of these two receptor classes is responsible for these functions due to the lack of selective ligands. In the present study, utilizing a combined antisense-in vivo dialysis approach, we show that the D-5 subtype is the dopamine D1-like receptor involved in modulating hippocampal acetylcholine (ACh) release, a transmitter implicated in a variety of cognitive processes. This is one of the first evidence for a functional role for the D-5 receptor.

Expression of dopamine receptors in the subthalamic nucleus of the rat: characterization using reverse transcriptase-polymerase chain reaction and autoradiography

We analysed the expression of dopamine receptor subtypes in the subthalamic nucleus by means of reverse transcriptase-polymerase chain reaction. We also studied, using autoradiography, all pharmacologically characterized dopamine receptors in four subregions of the subthalamic nucleus. For comparison, dopamine receptor subtypes were also evaluated in brain regions where they are more abundant and well characterized. The radioligands used were: [3H]SCH-23390, [3H]emonapride and [3H]2-dipropylamino-7-hydroxy-1,2,3,4-tetrahydronaphthalene for dopamine D1, D2 and D3 receptors, respectively; and [3H]YM-09151-2 in the presence of raclopride for dopamine D4 receptors. Finally, we also evaluated the effect of unilateral 6-hydroxydopamine injection into the medial forebrain bundle on dopamine receptor levels expressed in the ipsilateral subthalamic nucleus. The lesion was estimated by decrease in the binding of [3H]WIN-35428, a specific dopamine transporter label. D1, D2 and D3 receptor messenger RNAs and binding sites were present in the subthalamic nucleus, but no messenger RNA for D4 receptors was found, although specific binding sites for these receptors were observed. As compared to the intact side, the 6-hydroxydopamine lesion did not change D1 receptors, increased D2 receptors, and decreased D3 receptors and the dopamine transporter. The results suggest that postsynaptic D1, D2 or D3 receptors can mediate the effect of dopamine on subthalamic nucleus neuronal activity. D4 receptors would mediate exclusively presynaptic effects. These results reinforce the idea that dopamine receptors in the subthalamic nucleus may play an important role in the physiology of the basal ganglia and in the pathophysiology of Parkinson's disease.

Neonatal ventral hippocampal lesions attenuate the nucleus accumbens dopamine response to stress: an electrochemical study in the adult rat

Neonatal damage to the ventral hippocampus (VH) can lead, during adulthood, to behaviours that are believed to reflect enhanced mesocorticolimbic dopamine (DA) transmission. In the present study, the effects of neonatal excitotoxic lesions to the VH on spontaneous locomotor activity and stress-elicited increases in extracellular nucleus accumbens (NAcc) DA levels were examined in adult rats. Male pups received, on postnatal day 7, bilateral injections of either an ibotenic acid solution (lesioned) or vehicle (sham-lesioned) into the VH. At 3-4 months of age, animals were assessed during five daily sessions for changes in spontaneous locomotor activity associated with habituation to a novel environment. Voltammetry was used in separate groups of sham- and VH-lesioned animals to monitor the NAcc DA response to each of five once-daily exposures to tail-pinch stress. The results indicate that while VH-lesioned animals seem to habituate to novelty, they remain hyperactive relative to sham-lesioned controls. In contrast, however, stress consistently elicited in VH-lesioned animals smaller and shorter-lasting increases in NAcc DA than in sham-lesioned controls. These data suggest that neonatal excitotoxic damage to VH leads to changes in DA function that persist into adulthood. The blunted response to stress seen in VH-lesioned animals indicates that one consequence of such damage is a functional hyporeactivity in meso-NAcc DA neurons. The fact that these animals are spontaneously more active suggests compensatory changes in DA function that are efferent to DA terminals in NAcc.

Antisense oligodeoxynucleotides against the muscarinic m2, but not m4, receptor supports its role as autoreceptors in the rat hippocampus

Antisense oligodeoxynucleotides against muscarinic m2 and m4 receptors were used to investigate the role of these receptor subtypes as negative autoreceptors in the regulation of acetylcholine (ACh) release in the rat hippocampus. Following the continuous infusion of antisenses into the third ventricle (1 microgram microliter-1 h-1, 3 days), 3H-AF-DX 384/muscarinic M2-like binding was significantly decreased in the medial septum by the antisense against the m2 receptor whereas M2-like binding in the dorsal striatum was decreased by the antisense against the m4 receptor. In contrast, 3H-pirenzepine/muscarinic M1-like binding was unaffected by either antisense treatment in any of the brain areas investigated. When perfused into the hippocampus via a dialysis probe, the purported muscarinic M2 receptor antagonist AF-DX 384 (100 nM) increased hippocampal ACh release in freely moving rats. This effect of AF-DX 384 was significantly attenuated by the m2, but not the m4, receptor antisense treatment. Hippocampal choline acetyltransferase activity was not affected by either antisense treatments. Taken together, these results suggest that the molecularly defined muscarinic m2 receptor regulates hippocampal ACh release by acting as a negative autoreceptor. In contrast, the molecularly defined m4 receptor is unlikely to be directly involved in the negative regulation of ACh release in the rat hippocampus. Therefore, inhibiting muscarinic m2 receptor function may be an alternative approach to regulate the release of ACh in neurodegenerative diseases associated with impaired cholinergic functions.

Lewis and Fischer rats: a comparison of dopamine transporter and receptors levels

Previous reports have shown that the inbred strains of rat, Lewis (LEW) and Fischer 344 (F344), differ in several behavioural and biochemical indices of mesolimbic dopamine (DA) function. Specifically, these two strains differ in their behavioural and neurochemical response to novel environments, and acute amphetamine or cocaine challenge as well as in their susceptibility to addiction. To investigate if differences in DA D1-like, D2-like, D3 receptors and DA transporter could be correlated with these behavioural differences between strains, a comparative autoradiographic study of DA receptors and transporter within the striatal and accumbal regions was undertaken. We observed strain and region specific differences in binding levels for DA D2-like and D3 receptors and for the DA transporter. Namely, DA transporter levels in the striatum, nucleus accumbens and olfactory tubercle of LEW rats were significantly lower than in F344 rats. DA D3 densities in the shell of the nucleus accumbens and olfactory tubercle of LEW rats were lower than the levels found in the F344 rats. Finally, LEW rats have a lower levels of D2-like receptors in the striatum and the core of the nucleus accumbens compared to F344 rats. These data suggest that differences in DA transporter and DA receptors may in part contribute to differences in DA related behaviour seen between these two strains.

NCAM-180 knockout mice display increased lateral ventricle size and reduced prepulse inhibition of startle

NCAM-180 knockout mice, which have documented deficits in neural migration, were used to determine whether developmental abnormalities could lead to morphological changes and alterations in sensory motor gating mechanisms. Measurement of the lateral ventricle showed that NCAM-180-/- mice had marked increases in both the left and right anterior horns of the lateral ventricle. Furthermore, these mice also displayed a reduction of prepulse inhibition that was differentially affected by the dopamine agonist apomorphine. These results are discussed in light of the known increase in lateral ventricle size and reduction in prepulse inhibition that are seen in schizophrenia.

Cloning and in situ hybridization analysis of the expression of polysialyltransferase mRNA in the developing and adult rat brain

Polysialyltransferase (PST) is an enzyme that catalyzes the addition of polysialic acid (PSA), a homopolymer of alpha-2,8-linked sialic acid residues, onto neural cell adhesion molecule (NCAM). The expression of PSA-NCAM in the brain is developmentally regulated and is of critical importance; however, the temporal and spatial developmental expression of brain PST, a potential key player in the control of PSA-NCAM levels, remains unclear. In the present study, we have cloned the coding region of rat PST cDNA by reverse transcription-polymerase chain reaction, using primers based on the hamster PST-1 cDNA sequence. A 39-mer oligonucleotide complementary to rat PST cDNA was synthesized to investigate the distribution of its mRNA in the developing and adult rat brain by Northern blot and in situ hybridization. In the embryonic rat brain, PST mRNA was detected abundantly throughout the neuroepithelia of most brain regions. At post-natal days 1 and 14, PST was detected throughout the neocortex, in the pyramidal cells (PC) of the hippocampus proper, the granule cell layer (GCL) of the dentate gyrus, the anterior ventral nucleus of the thalamus (AVNT) and the GCL and external germinal layer of the cerebellum. Finally, from PD21 until adulthood, expression of PST mRNA was restricted to the PC layer of the hippocampus proper, the GCL of the dentate gyrus, the AVNT, the GCL of the cerebellum and the dorsal and lateral nucleus of the anterior olfactory bulb. The developmental profile of PST mRNA is paralleled in some structures by that of the PSA-NCAM, there are, however, notable exceptions. Therefore, our results demonstrate that expression of rat PST mRNA is developmentally regulated, is present in the adult rat brain in restricted areas and may be involved in regulating temporal and spatial expression of PSA-NCAM.

Identification and localization of dopamine receptor subtypes in rat olfactory mucosa and bulb: a combined in situ hybridization and ligand binding radioautographic approach

Olfactory bulb (OB) of mammals contains a large population of dopaminergic interneurons within the glomerular layer. Dopamine has been shown in vivo to modulate several aspects of olfactory information processing. The dopamine receptors of olfactory bulb and mucosa are assessed here at the levels of mRNAs and radioligand binding sites with presently available tools. D1A mRNA was found in OB glomerular-, plexiform-, mitral-cell and granular layers, but not in olfactory mucosa. D1B mRNA was absent in olfactory bulb and mucosa. D1-like binding sites were detected with two distinct radioligands, in glomerular-, plexiform-, mitral cell- and granular layers of OB but not in olfactory mucosa. We thus demonstrate the previously doubtful presence of D1-like receptors in OB. D2 mRNAs were localized in the glomerular and granular layers of OB and in olfactory mucosa; lesser amounts of D3 mRNAs were found in OB glomerular and granular layer, but not in olfactory mucosa. No D4 mRNA was detected in either structure. High densities of D2-like, [125I]Iodosulpride-labelled binding sites, were revealed within lamina propria of olfactory mucosa, and confirmed in the olfactory nerve- and glomerular layers of OB. A faint but significant density of [3H]7-hydroxy-dipropyl-aminotetralin (OH-DPAT) labelled, D3 binding sites was detected in olfactory nerve- and glomerular layers of OB, but not in olfactory mucosa. Competition of [125I]Iodosulpride specific binding by three D2/D3 selective drugs yielded kinetics typical of the D2 receptor subtype in olfactory bulb and mucosa. Olfactory nerve- and glomerular layers of OB are proved thus to contain a predominant contingent of D2 receptors and a minor population of D3 receptors, while olfactory mucosa expresses only D2 receptors.

Enhanced amphetamine sensitivity and increased expression of dopamine D2 receptors in postpubertal rats after neonatal excitotoxic lesions of the medial prefrontal cortex

Functional and structural abnormalities in the medial prefrontal cortex (MPFC) and overactive dopamine (DA) neurotransmission are thought to be the key pathologies in schizophrenia. To understand the role of MPFC in the pre- and postpubertal development of the subcortical DA system, the effects of neonatal [postnatal day 7 (PD7)] MPFC excitotoxic lesions on locomotor behaviors and the expression of DA receptor subtypes and DA transporter were investigated in Sprague Dawley rats at PD35 and PD56, respectively. No significant differences in the novelty of d-amphetamine-induced locomotion were observed between sham-operated and ibotenic acid-lesioned rats at PD35. Postpubertally (at PD56), however, the locomotor activity of lesioned rats in the novel environment and after d-amphetamine administration was enhanced significantly compared with controls. The expressions of DA D1, D2, D3, and D4 receptors and DA transporter were then estimated in MPFC-lesioned and sham-operated rats at PD59 and PD60. The levels of DA D2 receptors, measured using [3H]-YM-09151-2 binding, and its mRNA by in situ hybridization, were observed to be significantly increased at PD60 in striatal and limbic areas of lesioned rats. Levels of other DA receptor subtypes were not significantly affected at any time points. Lesioned rats at PD39 show a small increase in DA transporter level in the shell of nucleus accumbens; however, this effect seems to wear off at PD60. The data suggest that neonatal MPFC lesions may alter the functional development and maturation of mesolimbic/nigrostriatal DA systems in that neonatally lesioned rats grow into a behavioral/neurochemical deficit.

Decreased binding of dopamine D3 receptors in limbic subregions after neonatal bilateral lesion of rat hippocampus

Neonatal, bilateral lesion of the ventral hippocampus (VH) in rats recently has been proposed as a model of schizophrenia because these animals show postpubertal hypersensitivity to stress and to dopamine (DA) agonists that can be reversed by neuroleptic treatment. In search of the mechanisms of postpubertal emergence of hyperdopaminergic behavior in this model, we investigated developmental expressions of DA D1, D2, and D3 receptors in various striatal and limbic subregions of rats that had received bilateral ibotenic acid lesion of the VH at postnatal day 7 (PD7). D-Amphetamine-, apomorphine-, and stress-induced changes in locomotor activity were measured and, in accordance with previous reports, we observed an increased locomotor activity at PD56 in the hippocampal-lesioned group. The expression of DA D1, D2, and D3 receptors was then estimated in these rats by ligand autoradiography at PD41 and PD62. We observed that the levels of DA D3 receptors, as measured by tritiated 7-hydroxy-N,N-di-n-propyl-2-amino-tetralin ([3H]7-OH-DPAT) binding, are markedly reduced at PD62 in the limbic areas of lesioned rats compared with sham controls particularly in the nucleus accumbens, olfactory tubercles, and islands of Calleja. A small but significant increase in D1 receptors was also seen in the caudate-putamen of the lesioned animals at PD62, whereas no significant change in the overall expression of D2 receptors ([3H]spiperone binding) was noted. In view of the inhibitory role of D3 receptors on locomotion and, presumably, other DA-mediated behaviors, it is suggested that behavioral changes in the neonatally hippocampal-lesioned rats may be mediated by altered D3 receptor levels.

Decreased expression of the embryonic form of the neural cell adhesion molecule in schizophrenic brains

The regulated expression of neural cell adhesion molecule (NCAM) isoforms in the brain is critical for many neurodevelopmental processes including neurulation, axonal outgrowth, and the establishment of neuronal connectivity. We have investigated the expression of the major adult isoforms of NCAM (NCAM-180, NCAM-140, and NCAM-120) and its embryonic highly polysialylated isoform (PSA-NCAM) in the hippocampal region of postmortem brains from 10 schizophrenic and 11 control individuals. Immunohistochemical analysis with a monoclonal antibody recognizing the PSA-NCAM revealed immunoreactivity primarily in the dentate gyrus and in a subset of cells in the hilus region. We have observed a 20-95% reduction in the number of hilar PSA-NCAM-immunoreactive cells in the great majority of schizophrenic brains. The change in PSA-NCAM immunoreactivity is not obvious in other hippocampal subfields. Western blots of tissues from the hippocampal region (as well as from the frontal cortex) probed with a polyclonal antibody recognizing all NCAM isoforms did not reveal significant changes in the overall expression of NCAM, suggesting that the decrease in PSA-NCAM-immunoreactive cells may be related to post-translational processing of the molecule. The expression of this embryonic form of NCAM has been proposed to be related to synaptic rearrangement and plasticity. Therefore, the decrease in PSA-NCAM immunoreactivity in schizophrenic hippocampi may suggest an altered plasticity of this structure in a large proportion of schizophrenic brains. These findings may bear significance to the "neurodevelopmental hypothesis" of schizophrenia.

Functional modifications of the coupling of solubilized dopamine D2 receptors to guanine-nucleotide-binding proteins

The molecular basis for the regulation of high-affinity agonist, [3H]N-n-propylnorapomorphine ([3H]NPA), binding to cholate-solubilized dopamine D2 receptors was characterized using cations, guanine nucleotides and sulfhydryl-modifying agents. [3H]NPA binding displayed an absolute requirement for divalent cations in the solubilized preparation. Removal of Na+ from the solubilized preparation caused an apparent reconstitution of soluble receptors resulting in a reduced sensitivity of the agonist binding to divalent cations. The pharmacological profile of [3H]NPA binding was found to be similar in membrane and solubilized preparations. N-ethylmaleimide (NEM) and thermal exposure mimicked the effects of guanine nucleotides in reducing the proportion of high-affinity agonist sites in the solubilized state. [3H]NPA binding was much more susceptible to NEM-induced alkylation or heat inactivation compared to the antagonist [3H]spiroperidol binding. Pertussis-toxin-catalyzed ADP-ribosylation of G-proteins in the solubilized preparation resulted in the labelling of only one protein with the apparent molecular weight of 39-41 kDa. Both NEM and heat treatments caused the loss of ADP-ribosylation in the solubilized preparations. A consistent pattern of correlation between receptor binding data and ADP-ribosylation response suggests functional coupling of dopamine D2 receptors to the components of the effector system in solution.

Ontogeny of dopamine D2 receptor mRNA in rat brain

The postnatal development of rat brain dopamine D2 receptor gene expression was investigated in animals 1 day to 1 year old. The level of expression of the striatal D2 mRNA was appreciable at birth (day 1), steadily increased to a maximum at day 28, and showed declines at ages 6 months and one year. The mRNA development profile was similar to that of [3H]spiroperidol binding in striatal membranes except that there was a lack of correlation between mRNA levels and [3H]spiroperidol binding during the early developmental periods. For example, although the mRNA expression at day 1 is about 75% of the 28-day value, the corresponding level of [3H]spiroperidol binding is only 15% of the value observed at day 28. Polymerase chain reaction (PCR) analysis of alternatively spliced forms of D2 receptor mRNA showed that the developmental expression of the two isoforms proceeded in parallel as the ratio of D2L and D2S mRNAs remained more or less constant in different age group of rats. In situ hybridization revealed a differential developmental profile of D2 mRNA for major dopaminergic regions of rat brain such as caudate putamen, nucleus accumbens, olfactory tubercle and substantia nigra.

Effect of haloperidol on expression of dopamine D2 receptor mRNAs in rat brain

Chronic administration of the neuroleptic drug haloperidol previously has been shown to increase the density of striatal dopamine D2 receptor, which is believed to be the underlying factor in neuroleptic-induced tardive dyskinesia. To search for the mechanism of receptor upregulation, the expression of the isoforms of dopamine D2 receptor mRNA in rat striatum was analyzed by Northern, solution, and in situ hybridizations in haloperidol-treated rats (1-35 days). Northern blot analysis of poly(A)+ RNA hybridized with a probe common for both isoforms as well as an insert-specific probe for the long isoform of the receptor revealed no significant difference in hybridization signal between the control and any of the haloperidol-treated groups of rats. The receptor density, however, was increased by 30-40% in animals receiving haloperidol for 7-35 days. Solution hybridization with an antisense riboprobe specific for a consensus sequence as well as in situ hybridization with a consensus oligonucleotide probe similarly failed to detect any increase in the expression of receptor mRNA following haloperidol treatment. The results suggest that post-transcriptional mechanisms may be responsible for regulating the haloperidol-induced increase in dopamine D2 receptors.

Solubilization and reconstitution of dopamine D1 receptor from bovine striatal membranes: effects of agonist and antagonist pretreatment

The bovine striatal dopamine D1 receptor was solubilized with a combination of sodium cholate and NaCl in the presence of phospholipids, following treatment of membranes with a dopaminergic agonist (SKF-82526-J) or antagonist (SCH-23390). The solubilized receptors were subsequently reconstituted into lipid vesicles by gel-filtration. A comparison of ligand-binding properties shows that the solubilized and reconstituted receptors bound [3H]SCH-23390 to a homogeneous site in a saturable, stereospecific and reversible manner with a Kd of 0.95 and 1.1 nM and a Bmax of 918 and 885 fmol/mg protein respectively for agonist- and antagonist-pretreated preparations. These values are very similar to those obtained for membrane-bound receptors. The competition of antagonists for [3H]SCH-23390 binding exhibited a clear D1 dopaminergic order in the reconstituted preparation obtained from either agonist or antagonist-pretreated membranes, except that (+)butaclamol was about four-fold more potent than cis-flupentixol in displacing [3H]SCH-23390 binding in preparation obtained from agonist-pretreated membranes compared to antagonist-pretreated membranes. The agonist/[3H]SCH-23390 competition studies revealed the presence of a high-affinity component of agonist binding in both the reconstituted receptor preparations. The number of high-affinity agonist binding sites, however, is 40-80% higher in reconstituted preparation obtained from antagonist-treated membrane compared to that obtained from the agonist-treated membrane. In both the preparations, 100 microM guanylylimidodiphosphate (Gpp(NH)p) completely abolished the high-affinity component of agonist binding compared to partial abolition in the native membranes, indicating a close association of a G-protein with the solubilized receptors. Whether the receptor was solubilized following agonist or antagonist preincubation of the membranes, the receptor-detergent complex eluted from a steric-exclusion HPLC column with an apparent molecular size of 360,000. Preincubation of the solubilized preparations with Gpp(NH)p had virtually no effect on the elution profile suggesting a lack of guanine nucleotide-dependent dissociation of G-protein receptor complex.

Dopamine receptor modulation by conformationally constrained analogues of Pro-Leu-Gly-NH2

Two series of conformationally constrained analogues of Pro-Leu-Gly-NH2 (PLG) have been synthesized. In one series of analogues, the Leu-Gly-NH2 dipeptide segment of PLG was replaced with the gamma-lactam residues 3(S)- and 3(R)-amino-2-oxopyrrolidineacetamide and the delta-lactam residue 3(S)-amino-2-oxopiperidineacetamide. The corresponding gamma-lactam analogues of less than Glu-Leu-Gly-NH2 were also synthesized. In a second series of analogues, the glycinamide residue of PLG was replaced with the 2-ketopiperazine, 3(S)-amino-2-pyrrolidone, and 3(S)-amino-2-piperidone residues. The above analogues were tested for their ability to enhance the binding of the dopamine receptor agonist 2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthalene (ADTN) to striatal dopamine receptors. Of the conformationally constrained analogues of PLG synthesized in this study, only the gamma-lactam analogue 3(R)-(N-L-prolylamino)-2-oxo-1-pyrrolidineacetamide (3) was found to possess significant activity. This analogue was 10,000 times more active than PLG, under preincubation conditions. It significantly enhanced the binding of ADTN at concentrations of 10(-9) and 10(-10) M.

Interaction of L-prolyl-L-leucyl glycinamide with dopamine D2 receptor: evidence for modulation of agonist affinity states in bovine striatal membranes

The role of the hypothalamic tripeptide L-prolyl-L-leucyl-glycinamide (PLG) in modulating the agonist binding to bovine striatal dopamine D2 receptor was investigated using a selective high-affinity agonist, n-propylnorapomorphine (NPA). PLG caused an enhancement in [3H]NPA binding in striatal membranes in a dose-dependent manner, the maximum effect being observed at 10(-7)-10(-6) M concentration of the tripeptide. The Scatchard analysis of [3H]NPA binding to membranes preincubated with 10(-6) M PLG revealed a significant increase in the affinity of the agonist binding sites. In contrast, there was no effect of PLG on the binding pattern of the antagonist [3H]spiroperidol. The antagonist versus agonist competition curves analyzed for agonist high- and low-affinity states of the receptor displayed an increase in the population and affinity of the high-affinity form of the receptor with PLG treatment. The low-affinity sites concomitantly decreased with relatively small change in the affinity for the agonists. Almost similar results were obtained when either NPA or apomorphine was used in the competition experiments. A partial antagonistic effect of PLG on 5'-guanylylimidodiphosphate [Gpp(NH)p]-induced inhibition of high-affinity agonist binding was also observed, as the ratio of high- to low-affinity forms of the receptor was significantly higher in the PLG-treated membranes compared to the controls. Direct [3H]NPA binding experiments demonstrated that PLG attenuated the Gpp(NH)p-induced inhibition of agonist binding by increasing the EC50 of the nucleotide (concentration that inhibits 50% of the specific binding). No effect of PLG on high-affinity [3H]NPA binding, however, could be observed when the striatal membranes were preincubated with Gpp(NH)p.(ABSTRACT TRUNCATED AT 250 WORDS)

Reconstitution of affinity-purified dopamine D2 receptor binding activities by specific lipids

The role of lipids in maintaining ligand binding properties of affinity-purified bovine striatal dopamine D2 receptor was investigated in detail. The receptor, purified on a haloperidol-linked Sepharose CL6B affinity column, exhibited low [3H]spiroperidol binding unless reconstituted with soybean phospholipids. In order to understand the role of individual phospholipids in maintaining the receptor binding activity, the purified preparation was reconstituted separately with individual phospholipids and assayed for [3H]spiroperidol binding. Except for phosphatidylcholine and phosphatidylethanolamine, that respectively restored 30 and 20% binding as compared to that obtained with soybean lipids, reconstitution with other lipids had very little effect. When various combinations of phospholipids were used for reconstitution, a phosphatidylcholine and phosphatidylserine mixture seemed to almost fully restore the receptor binding. A mixture of phosphatidylcholine and phosphatidylethanolamine was as effective as phosphatidylcholine alone in reconstituting ligand binding; however, when phosphatidylserine was also included in the mixture, there was a pronounced increase in binding (about 2-fold compared to the soybean lipids and about 6-fold compared to the phosphatidylcholine-phosphatidylethanolamine mixture). Substitution of other phospholipids or cholesterol for phosphatidylserine in phosphatidylcholine and phosphatidylethanolamine mixture had little effect. Maximal reconstitution of [3H]spiroperidol binding was obtained with phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine mixture (2:2:1, w/w) at a concentration of 0.5 mg/ml. The reconstituted receptor exhibited high affinity binding for [3H]spiroperidol which was comparable to that obtained with membrane or solubilized preparations. Various dopaminergic antagonists and agonists showed appropriate order of potency for the reconstituted receptor. The presently described reconstitution data suggest a role of specific phospholipids in preserving the binding properties of dopamine D2 receptor and should prove useful in studies on functional reconstitution of the receptor.

Characterization of high-affinity dopamine D2 receptors and modulation of affinity states by guanine nucleotides in cholate-solubilized bovine striatal preparations

3,4-Dihydroxyphenylethylamine (dopamine) D2 receptors, solubilized from bovine striatal membranes using a cholic acid-NaCl combination, exhibited the typical pharmacological characteristics of both agonist and antagonist binding. The rank order potency of the agonists and antagonists to displace [3H]spiroperidol binding was the same as that observed with membrane-bound receptors. Computer-assisted analysis of the [3H]spiroperidol/agonist competition curves revealed the retention of high- and low-affinity states of the D2 receptor in the solubilized preparations and the proportions of receptor subpopulations in the two affinity states were similar to those reported in membrane. Guanine nucleotide almost completely converted the high-affinity sites to low-affinity sites for the agonists. The binding of the high-affinity agonist [3H]N-n-propylnorapomorphine ([3H]NPA) was clearly demonstrated in the solubilized preparations for the first time. Addition of guanylyl-imidodiphosphate completely abolished the [3H]NPA binding. When the solubilized receptors were subjected to diethylaminoethyl-Sephacel chromatography, the dopaminergic binding sites eluted in two distinct peaks, showing six- to sevenfold purification of the receptors in the major peak. Binding studies performed on both peaks indicated that the receptor subpopulation present in the first peak may have a larger proportion of high-affinity binding sites than the second peak. The solubilized preparation also showed high-affinity binding of [35S]guanosine-5'-(gamma-thio)triphosphate, a result suggesting the presence of guanine nucleotide binding sites, which may interact with the solubilized D2 receptors. These data are consistent with the retention of the D2 receptor-guanine nucleotide regulatory protein complex in the solubilized preparations and should provide a suitable model system to study the receptor-effector interactions.

Changes in phosphofructokinase and pyruvate kinase in rat brain following thyroidectomy

Changes in the profile of phosphofructokinase (PFK) and Pyruvate kinase (PK) from rat brain regions were studied following thyroidectomy. A regional variation of thyroidectomy on brain was observed; cerebral hemispheres and cerebellum showed decreased activity of phosphofructokinase and pyruvate kinase. The activity in the brain stem did not change. Administration of triiodothyronine to the thyroidectomized rats restored the activity to near control levels. The results suggest a role of the thyroid hormones in the regulation of glycolysis in brain.

Purification and properties of rat brain pyruvate kinase

Rat brain pyruvate kinase was purified to near homogeneity by a three-step process involving ammonium sulfate precipitation and phosphocellulose and Blue-Sepharose CL-6B column chromatography. The enzyme migrated on polyacrylamide gel along with a commercial sample of rabbit muscle pyruvate kinase. The enzyme showed a hyperbolic relationship with phosphoenolpyruvate and ADP, with apparent Km's of 0.18 and 0.42 X 10(-3) M, respectively. The enzyme was inhibited by ATP, the effect being more pronounced at unsaturating concentrations of phosphoenolpyruvate. L-Phenylalanine was found to be a strong inhibitor of the enzyme, with the Ki for inhibitor being 0.11 mM. The inhibition by phenylalanine was more pronounced at pH 7.4 than at pH 7.0, and appeared to be competitive with phosphoenolpyruvate. L-Alanine and fructose 1,6-bisphosphate prevented the inhibition of the enzyme by phenylalanine. Ca2+ was found to be a strong inhibitor of the enzyme, and the inhibition was more marked at saturating phosphoenolpyruvate concentrations. The kinetic properties of the purified brain pyruvate kinase suggest that the enzyme may be distinct from the muscle or liver enzymes.

Glyoxalase-I activity and cell cycle regulation in yeast

The status of glyoxalase-I was explored in exponentially growing and G1 arrested temperature sensitive (ts) cell division cycle (cdc) mutants of Saccharomyces cerevisiae. It was observed that the specific activity of this enzyme was correlated with overall growth status. The activity was high in actively growing cells and was low in G1 arrested cells. Specific activities of glyoxalase-I were also low in G1 arrested prolonged stationary phase (PSP) cells of S. cerevisiae and Candida albicans. The activity of glyoxalase-I recovered when G1 arrested S. cerevisiae (ts) cells were allowed to regrow under permissive conditions. Results demonstrate that although glyoxalase-I activity is a good indicator of cell growth status, it is not involved in cell cycle regulation of this eukaryotic organism.

Changes in phosphofructokinase and pyruvate kinase in rat brain regions during alloxan-induced diabetes

Changes in the profile of two glycolytic enzymes, phosphofructokinase and pyruvate kinase, in different regions of rat brain were studied under alloxan-induced diabetes. A regional variation of the effect of diabetes on brain was noted - the cerebral hemispheres and cerebellum showed decreased activity of the enzymes, while the brain stem remained relatively unaffected. The changes in enzyme activities in the brain regions were more pronounced at the early days of diabetes, particularly at 8 days. Insulin administration to the diabetic animals restored the activity of the enzymes. The results indicate a regionally variable effect of diabetes on the two key glycolytic enzymes, and bring out a role of insulin in the regulation of brain glycolysis.