Cocaine-taking and cocaine-seeking behaviors in rats remain stable after systemic administration of GYKI 52466: a non-competitive AMPA receptor antagonist

Given the posited role of enhanced AMPA-mediated synaptic transmission in relapse to drug seeking, we investigated whether systemic administration of the AMPA receptor antagonist GYKI 52466 inhibits cocaine-taking and cocaine-seeking behavior in rats. Rats were trained to self-administer cocaine until stable self-administration was achieved. Effects of GYKI 52466 (1, 3, or 10 mg/kg, i.v.) on cocaine self-administration were assessed. Animals were allowed to re-establish stable cocaine self-administration and were then behaviorally extinguished from drug taking. The effects of GYKI 52466 (3, 10 mg/kg, i.v.) on cocaine-induced reinstatement of drug-seeking behavior were assessed. We found that GYKI 52466 failed to inhibit cocaine-taking and cocaine-seeking in both the self-administration and reinstatement paradigms. We suggest that although AMPA receptors may be involved in cocaine reward and addiction, the AMPA receptor antagonist GYKI 52466 has low therapeutic potential for cocaine addiction treatment.     

Long-term behavioral and neurodegenerative effects of perinatal phencyclidine administration: implications for schizophrenia.

Both acute and chronic administration of N-methyl-D-aspartate (NMDA) receptor antagonists such as phencyclidine and dizocilpine have been proposed to mimic some of the symptoms of schizophrenia. The purposes of the present study were first, to characterize the long-term behavioral and neurodegenerative effects of subchronic administration of phencyclidine to perinatal rats and second, to determine whether pretreatment with olanzapine could attenuate these effects. On postnatal days 7, 9 and 11 rat pups were pretreated with either vehicle or olanzapine prior to administration of either saline or phencyclidine (10 mg/kg). Some pups were killed on postnatal day 12 for biochemical determinations and others were tested on postnatal days 24-28 for prepulse inhibition of acoustic startle, on postnatal day 42 for phencyclidine-induced locomotor activity and between postnatal days 33 and 70 for acquisition of a delayed spatial learning task. Phencyclidine treatment resulted in a substantial increase in fragmented DNA in the frontal and olfactory cortices consistent with neurodegeneration by an apoptotic mechanism. An increase in the NMDA receptor NR1 subunit mRNA was also observed in the cortex. Gel shift assays showed that phencyclidine also increased the nuclear translocation of nuclear factor-kappaB proteins in the prefrontal cortex. In tissue from the frontal cortex, western blot analysis revealed that phencyclidine treatment increased Bax and decreased Bcl-X(L) proteins. Later in development, it was observed that perinatal phencyclidine treatment significantly retarded baseline prepulse inhibition of acoustic startle measured shortly after weaning. In 42-day-old rats, it was found that challenge with 2 mg/kg phencyclidine increased locomotor activity to a significantly greater extent in the rats that had been pretreated with phencyclidine. Similarly, perinatal phencyclidine treatment significantly delayed the acquisition of a delayed spatial alternation task. Each of the aforementioned changes (except for the spatial learning task, which was not tested) was significantly inhibited by olanzapine pretreatment, an antipsychotic drug known to be effective against both positive and negative symptoms of schizophrenia. Further, olanzapine treatment for 12 days following the administration of phencyclidine was also able to reverse the phencyclidine-induced deficit in baseline prepulse inhibition.Together these data suggest that perinatal administration of phencyclidine results in long-term behavioral changes that may be mechanistically related to the apoptotic neurodegeneration observed in the frontal cortex. It is postulated that these deficits may model the hypofrontality observed in schizophrenia and that this model may be helpful in designing appropriate pharmacotherapy.     

AMPA receptor alterations precede mossy fiber sprouting in young children with temporal lobe epilepsy

Following neurological injury early in life numerous events, including excitotoxicity, neural degeneration, gliosis, neosynaptogenesis, and circuitry reorganization, may alone or in concert contribute to hyperexcitability and recurrent seizures in temporal lobe epilepsy. Our studies provide new evidence regarding the temporal sequence of key elements of hippocampal reorganization, mossy fiber sprouting and glutamate receptor subunit up-regulation, in a subset of young temporal lobe epileptic patients. Without evidence of mossy fiber sprouting, the youngest age group (3-10 years old) of mesial temporal lobe epileptic patients demonstrated enhanced glutamate receptor subunit profiles, suggesting that the dendritic change precedes axonal sprouting. However, sclerotic hippocampal specimens from epileptic patients ages 12-15 years old had the characteristic features of glutamate receptor up-regulation and mossy fiber sprouting first identified in the adult, indicating that reconstructed circuits appear early in the course of the disease. Non-sclerotic hippocampal specimens from lesion associated temporal lobe epileptic patients of all age groups showed minimal cell loss, sparse staining of glutamate receptor subunits in the dentate gyrus, and little or no mossy fiber sprouting. These compelling findings suggest a progressive sequence of events in the reorganization of the dentate gyrus of sclerotic hippocampal specimens. We suggest that cell loss and up-regulation of glutamate receptor subunits appear early in temporal lobe epilepsy and contribute to the synaptic plasticity that may facilitate the subsequent sprouting of mossy fiber collaterals which compound an already precipitous state of decline. The combination of pre-synaptic and post-synaptic changes serves as a potential substrate for hyperexcitability.     

Alterations in AMPA receptor phosphorylation in the rat striatum following acute and repeated cocaine administration

Protein phosphorylation is an important mechanism for the posttranslational modulation of ionotropic glutamate receptors and is subject to regulation by changing synaptic inputs. In this study, we investigated the regulation of α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor GluR1 subunit phosphorylation by cocaine exposure in the rat dorsal striatum in vivo. We found that acute cocaine challenge followed by 6 days of repeated systemic injections of cocaine (20 mg/kg once daily) enhanced the sensitivity of the GluR1 subunit in its phosphorylation at serine 831 (Ser831) in the dorsal striatum. This enhancement of the sensitivity of Ser831 phosphorylation was reduced, at the receptor and ion channel level, by blocking (1) group I metabotropic glutamate receptors (mGluRs), (2) N-methyl-d-aspartate receptors, and (3) L-type voltage-operated Ca²⁺ channels. Similar reduction of the enhancement was also induced, at the protein kinase level, by inhibiting (1) protein kinase C, (2) calcium/calmodulin-dependent protein kinases, and (3) c-Jun N-terminal kinases. In addition, inhibition of protein phosphatase 1/2A or calcineurin increased GluR1-Ser831 phosphorylation in the dorsal striatum of normal rats, whereas inhibition of these phosphatases did not further enhance the Ser831 phosphorylation in rats pretreated with 7 daily injections of cocaine. These data suggest that the phosphorylation of AMPA receptor GluR1 subunits at Ser831 is subject to upregulation by acute and repeated cocaine administration. Complex signaling integrations among glutamate receptors, Ca²⁺ channels, protein kinases, and protein phosphatases participate in this upregulation.     

Evidence for alterations in alpha2-adrenergic receptor sensitivity in rats exposed to repeated cocaine administration

It is well established that cocaine stimulates monoamine transmission by blocking reuptake of norepinephrine (NE), dopamine and serotonin into nerve cells, yet few investigations have addressed the effects of chronic cocaine on NE function. In the present study, we examined the effects of repeated cocaine injections on neuroendocrine responses evoked by the alpha2-adrenergic receptor agonist, clonidine. Previous findings show that clonidine increases pituitary growth hormone (GH) secretion by a central mechanism involving postsynaptic alpha2-adrenergic receptors. Male rats previously fitted with indwelling jugular catheters received two daily injections of cocaine (15 mg/kg, i.p.) or saline for 7 days. At 42 h and 8 days after treatment, rats were challenged with clonidine (25 microg/kg, i.v.) or saline, and serial blood samples were withdrawn. Plasma GH and corticosterone levels were measured by radioimmunoassay. Prior cocaine exposure did not affect basal levels of either hormone. However, cocaine-pretreated rats displayed a significant reduction in clonidine-evoked GH secretion at 42 h, and this blunted response was still apparent 8 days later. Corticosterone responses produced by clonidine were similar regardless of pretreatment. The present data suggest that withdrawal from repeated cocaine injections may be accompanied by desensitization of postsynaptic alpha2-adrenoreceptors coupled to GH secretion. Since human patients with depression often exhibit blunted GH responses to clonidine, our findings provide evidence that cocaine withdrawal might produce depressive-like symptoms via dysregulation of NE mechanisms.     

Age-associated alterations in catecholaminergic concentrations, neuronal activity, and alpha 1 receptor densities in female rats

The density of alpha 1-adrenergic receptors and catecholamine concentrations and neuronal activity were assessed in selected estrogen-responsive regions of the hypothalamus and pineal glands. The results of this study demonstrate that the densities of alpha 1-adrenergic receptors and norepinephrine and epinephrine concentrations and activity rate constants are altered in aged rats. The direction and extent of the change depend on the specific brain region and reproductive state of the animals. No widespread decline with increased age was observed in any of the parameters measured.     

Maternal immune activation during pregnancy increases limbic GABAA receptor immunoreactivity in the adult offspring: implications for schizophrenia

Prenatal exposures to a variety of infections have been associated with an increased incidence of schizophrenia. We have reported that a single injection of the synthetic cytokine releaser PolyI:C to pregnant mice produced offspring that exhibited multiple schizophrenia-related behavioral deficits in adulthood. Here, we characterized the effect of maternal inflammation during fetal brain development on adult limbic morphology and expression of GABAA-receptors. The PolyI:C treatment did not induce morphological abnormalities but resulted in a significant increase in GABAA receptor subunit alpha2 immunoreactivity (IR) in the ventral dentate gyrus and basolateral amygdala in adult treated compared to control subjects. Correlative analyses between the a2 subunit IR in the ventral dentate gyrus and the performance in the prepulse inhibition paradigm revealed a significant correlation in controls that was however absent in the pathological condition. These results suggest that prenatal immune activation-induced disturbances of early brain development result in profound alterations in the limbic expression of GABAA receptors that may underlie the schizophrenia-related behavioral deficits in the adult mice.     

Regional alterations in brain amino acids after administration of the N-methyl-D-aspartate receptor antagonists MK-801 and CGP 39551 in rats.

The effects of the non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 and the novel competitive NMDA receptor antagonist CGP 39551 on levels of 11 amino acids, including several excitatory and inhibitory neurotransmitters, were studied in 12 brain regions of rats. Both drugs were administered at doses which produced comparable behavioural effects (ataxia, hyperactivity). Amino acids were determined in brain tissue by high-performance liquid chromatography after o-phthaldialdehyde precolumn derivatization. MK-801 (0.1 mg/kg, i.p.) moderately increased the concentration of glutamate and GABA in several brain regions. Other amino acids (glutamine, taurine, asparagine, alanine, serine) were only altered in single brain regions, or were not altered at all (aspartate, glycine, threonine, arginine). In contrast to MK-801, CGP 39551 (10 mg/kg, i.p.) increased glutamate levels only in the cerebellum, and produced no significant alterations in levels of GABA. The data demonstrate differences in alterations of amino acid levels in response to competitive and non-competitive NMDA receptor antagonists and support the assumption that competitive NMDA antagonists may be more selective than non-competitive antagonists.     

Blood-brain barrier permeability: regional alterations after acute and chronic administration of ethinyl estradiol

In this study we measured the effect of acute and chronic estrogen treatment on cerebrovascular permeability to sucrose and inulin. Animals were subcutaneously injected once with 0.1 micrograms/rat of ethinyl estradiol or injected daily with the same drug dose for 3 weeks. Control rats received the same amount of arachis oil vehicle. Three weeks treatment but not the single injection of ethinyl estradiol produced significant increases in the cerebrovascular permeability-surface area product for sucrose and inulin in almost all brain regions.     

Immunologic alterations in MRL/lpr mice after chronic dimethyl sulfoxide administration

Dimethyl sulfoxide (DMSO) in 1 and 2% concentration was added to the drinking water of 30-100 day MRL/lpr mice. In comparison to control mice, the DMSO treated mice had a 78% increase in their response to exogenous IL-2 and a 64% increase in production of IL-2. Con A stimulated cells had a net help effect in the untreated mice, which was suppressed from 82-26% after DMSO treatment. There was no marked change in Thy 1.2, Lyt 1 and Lyt 2 percentages after treatment. The anti-DNA decreased from 29.0 +/- 17.0% to 13.2 +/- 7.8% after DMSO treatment. We conclude that chronic DMSO administration to MRL/lpr mice can induce immunologic alterations with possible clinical implications.     

Changes in AMPA receptor phosphorylation in the rostral ventromedial medulla after inflammatory hyperalgesia in rats

To study the glutamatergic mechanisms underlying changes in excitability in the brain stem pain modulatory circuitry after injury, we examined GluR1 serine 831 phosphorylation in the rostral ventromedial medulla (RVM) after complete Freund's adjuvant-induced hindpaw inflammation. Western blots indicated a rapid and prolonged (30 min and 7 days post-inflammation) increase in phosphoserine 831 GluR1 protein levels in the RVM. The upregulated GluR1 phosphorylation was blocked by pretreatment, but not by post-treatment, with the local anesthetic, lidocaine, at the site of inflammation. The upregulation of phosphoserine 831 GluR1 was attenuated by pretreatment with chelerythrine, a selective PKC inhibitor, KN-93, a selective CaMKII inhibitor, and two NMDA receptor antagonists, MK-801 and APV. These findings provide new evidence linking in vivo AMPA receptor phosphorylation in the RVM pain modulatory circuitry to the enhanced descending pain modulation after inflammation.     

Repeated apomorphine administration alters dopamine D1 and D2 receptor densities in pigeon basal telencephalon

When pigeons are repeatedly administered a dose of apomorphine they show an increasing behavioral response, much as rodents do. In birds this expresses itself in an augmented pecking response. This sensitization is assumed to be largely due to a conditioning process. Here we present evidence that sensitization is accompanied by an alteration of the D₁ to D₂ dopamine receptor densities. An experimental group of pigeons was repeatedly injected with apomorphine, and a control group with saline. The basal forebrain tissue, known to be rich in dopamine receptors, was subjected to binding assays using tritiated specific D₁ and D₂ dopamine receptor antagonists. There was a trend towards an increase in D₁ and a significant decrease in D₂ receptor densities in apomorphine-treated birds compared to the saline-treated controls. We conclude that extended apomorphine treatment modifies the D₁ dopamine receptor density in the opposite manner to the D₂ dopamine receptor density.     

Age- and region-dependent alterations in Abeta-degrading enzymes: implications for Abeta-induced disorders

Accumulation of amyloid beta-protein (Abeta) is a fundamental feature of certain human brain disorders such as Alzheimer's disease (AD) and Down syndrome and also of the skeletal muscle disorder inclusion body myositis (IBM). Emerging evidence suggests that the steady-state levels of Abeta are determined by the balance between production and degradation. Although the proteolytic processes leading to Abeta formation have been extensively studied, less is known about the proteases that degrade Abeta, which include insulin-degrading enzyme (IDE) and neprilysin (NEP). Here we measured the steady-state levels of these proteases as a function of age and brain/muscle region in mice and humans. In the hippocampus, which is vulnerable to AD pathology, IDE and NEP steady-state levels diminish as function of age. By contrast, in the cerebellum, a brain region not marked by significant Abeta accumulation, NEP and IDE levels either increase or remain unaltered during aging. Moreover, the steady-state levels of IDE and NEP are significantly higher in the cerebellum compared to the cortex and hippocampus. We further show that IDE is more oxidized in the hippocampus compared to the cerebellum of AD patients. In muscle, we find differential levels of IDE and NEP in fast versus slow twitch muscle fibers that varies with aging. These findings suggest that age- and region-specific changes in the proteolytic clearance of Abeta represent a critical pathogenic mechanism that may account for the susceptibility of particular brain or muscle regions in AD and IBM.     

Contribution of inflammatory mast cell mediators to alterations in macrophage function after malathion administration

Recent studies using mast cell-deficient mice showed that the presence of mast cells was necessary for the increase in macrophage function observed after oral administration of malathion and reconstitution with bone marrow-derived mast cells restored the ability of malathion to increase macrophage function. In addition, the release of mast cell mediators (blocked by cromolyn) and histamine (action blocked by pyrilamine) was shown to be involved in the action of malathion on macrophage function. In the present study, the contribution of inflammatory mediators (i.e. arachidonic acid metabolites and tumor necrosis factor [TNF]) which may be generated by mast cells after oral administration of malathion, was examined. Controls in this study included the effect of the agent to be examined on: (1) resident peritoneal macrophages; and (2) macrophages elicited with pristane, an agent shown previously to stimulate macrophage function in the absence of mast cells. Intraperitoneal administration of indomethacin, an inhibitor of cycloxygenase, or neutralizing antibody to TNF 30 h before and 4 h after oral malathion blocked the ability of malathion to increase macrophage function, as measured by the generation of respiratory burst activity and the production of cathepsin D. On the other hand, administration of these agents to mice injected intraperitoneally with pristane did not affect the observed increase in cathepsin D production. Respiratory burst function after elicitation with pristane was slightly decreased (indomethacin) or not affected (antibody to TNF). The effect of intraperitoneal administration of nordihydroguaiaretic acid (NDGA), an inhibitor of both cycloxygenase and lipoxygenase, was also examined. Intraperitoneal administration of NDGA partially blocked the effects of oral administration of malathion on peritoneal macrophage function, but did not affect the function of resident or pristane-elicited peritoneal macrophages. These data suggest that inflammatory mediators (potentially released from mast cells upon stimulation) contribute to the elevation in macrophage function observed after oral malathion administration.     

Comorbidity of schizophrenia and substance abuse: implications for treatment.

The problem of substance abuse disorders in schizophrenia patients is reviewed, including the prevalence of co-morbid disorders, assessment, hypothesized mechanisms underlying abuse, and the clinical effects of abuse on the course of illness and cognitive functioning. The principles of treatment for dual-diagnosis schizophrenia patients are outlined, and the limitations of existing interventions are noted. Gaps in current knowledge about the impact of substance abuse on schizophrenia and its treatment are identified, and suggestions are made regarding promising avenues of research in this area.     

AMPA receptor subunit expression in the cuneate nucleus of adult squirrel monkeys after peripheral nerve injury

The primate somatosensory system provides an excellent model system with which to investigate adult neural plasticity. Here, we report immunohistochemical staining data for the GluR1 and GluR2/3 AMPA receptor subunits in the cuneate nucleus of adult squirrel monkeys one week after median nerve compression. These data are compared to subunit changes in the area 3b cortex of the same animals. We report differences between control and deprived brainstem implying that deprivation induced changes in subunit expression mirror those reported in the cortex. There are significant increases in GluR1 receptor subunit staining intensity and significant decreases in GluR2/3 receptor subunit staining intensity. This pattern of expression resembles receptor configurations reported in developing sensory systems. Taken together, these results suggest that the brainstem and the cortex initially progress through a phase of developmental recapitulation prior to the onset of NMDA mediated adult somatosensory reorganization.     

Increase in AMPA receptor-mediated miniature EPSC amplitude after chronic NMDA receptor blockade in cultured hippocampal neurons

Synaptic scaling has been reported as scaling up of AMPA receptors (AMPAR)-mediated miniature excitatory postsynaptic currents (mEPSCs) induced by blockade of action potentials or AMPAR. Here, we show a novel type of synaptic scaling induced by N-methyl-D-aspartate receptors (NMDAR) blockade. In the present study, we analyzed AMPAR-mediated mEPSCs of D-(-)-2-amino-5-phosphonopentanoic acid (AP5)-treated hippocampal neurons (16 days in vitro) for 48 h in low-density cultures, using a whole-cell patch-clamp technique. The mEPSC amplitudes recorded from chronic AP5-treated neurons (25.5+/-0.3 pA; n=30 neurons) were significantly larger than that recorded from control neurons (21.6+/-0.2 pA; n=30 neurons, p<0.05), whereas the frequency of mEPSCs was not changed. Immunocytochemistry showed that the number of synapsin I clusters of AP5-treated neurons was not different from that of control neurons. Cumulative amplitude histograms revealed that the amplitude of mEPSCs was scaled multiplicatively after AP5 treatment. GluR2-lacking AMPAR were not involved in the scaling observed here. Together, our data indicate that NMDAR activity, as well as AMPAR activity, is involved in the negative feedback plasticity of AMPAR-mediated synaptic activity.     

Oxidative stress in schizophrenia: pathogenetic and therapeutic implications

Over a century, a wide-ranging variety of pathophysiological models and causal hypotheses have been conceptualized for schizophrenia. One among these is the role for free radical-mediated pathology in schizophrenia, indicating impaired antioxidant defense system (AODS) and presence of oxidative stress in patients with schizophrenia. For the past two decades, the whole investigative domain of AODS and oxidative stress has broadened to include the wider AODS components, direct central nervous system assays of AODS, chemical imaging studies, proteomics, genetics of AODS, and, of importance to sufferers of schizophrenia, antioxidant therapeutics. These are some of the perspectives that are reviewed by several articles in this Forum. Overall, there has been growing recognition of the importance of oxidative stress in the pathophysiology of schizophrenia and in treatment-related side effects. The totality of the evidence from biochemistry, metabolomics, proteomics, genetics, and in vivo brain imaging points to the presence of multifarious abnormalities in the AODS and redox signaling in schizophrenia.