GluN2D Subunit in Parvalbumin Interneurons Regulates Prefrontal Cortex Feedforward Inhibitory Circuit and Molecular Networks Relevant to Schizophrenia.

BACKGROUND: Parvalbumin interneuron (PVI) activity synchronizes the medial prefrontal cortex circuit for normal cognitive function, and its impairment may contribute to schizophrenia (SZ). NMDA receptors in PVIs participate in these activities and form the basis for the NMDA receptor hypofunction hypothesis of SZ. However, the role of the GluN2D subunit, which is enriched in PVIs, in regulating molecular networks relevant to SZ is unknown. METHODS: Using electrophysiology and a mouse model with conditional deletion of GluN2D from PVIs (PV-GluN2D knockout [KO]), we examined the cell excitability and neurotransmission in the medial prefrontal cortex. Histochemical, RNA sequencing analysis and immunoblotting were conducted to understand molecular mechanisms. Behavioral analysis was conducted to test cognitive function. RESULTS: PVIs in the medial prefrontal cortex were found to express putative GluN1/2B/2D receptors. In a PV-GluN2D KO model, PVIs were hypoexcitable, whereas pyramidal neurons were hyperexcitable. Excitatory neurotransmission was higher in both cell types in PV-GluN2D KO, whereas inhibitory neurotransmission showed contrasting changes, which could be explained by reduced somatostatin interneuron projections and increased PVI projections. Genes associated with GABA (gamma-aminobutyric acid) synthesis, vesicular release, and uptake as well as those involved in formation of inhibitory synapses, specifically GluD1-Cbln4 and Nlgn2, and regulation of dopamine terminals were downregulated in PV-GluN2D KO. SZ susceptibility genes including Disc1, Nrg1, and ErbB4 and their downstream targets were also downregulated. Behaviorally, PV-GluN2D KO mice showed hyperactivity and anxiety behavior and deficits in short-term memory and cognitive flexibility. CONCLUSIONS: These findings demonstrate that GluN2D in PVIs serves as a point of convergence of pathways involved in the regulation of GABAergic synapses relevant to SZ.

Glutamate delta 1 receptor regulates autophagy mechanisms and affects excitatory synapse maturation in the somatosensory cortex.

The glutamate delta family of receptors is composed of GluD1 and GluD2 and serve as synaptic organizers. We have previously demonstrated several autism-like molecular and behavioral phenotypes including an increase in dendritic spines in GluD1 knockout mice. Based on previous reports we evaluated whether disruption of autophagy mechanisms may account for these phenotypes. Mouse model with conditional deletion of GluD1 from excitatory neurons in the corticolimbic regions was utilized. GluD1 loss led to overactive Akt-mTOR pathway, higher p62 and a lower LC3-II/LC3-I ratio in the somatosensory cortex suggesting reduced autophagy. Excitatory elements were increased in number but had immature phenotype based on puncta size, lower AMPA subunit GluA1 expression and impaired development switch from predominantly GluN2B to mixed GluN2A/GluN2B subunit expression. Overactive Akt-mTOR signaling and impaired autophagy was also observed in dorsal striatum upon conditional ablation of GluD1 and in the prefrontal cortex and hippocampus in constitutive knockout. Finally, cognitive deficits in novel object recognition test and fear conditioning were observed in mice with conditional ablation of GluD1 from the corticolimbic regions. Together, these results demonstrate a novel function of GluD1 in the regulation of autophagy pathway which may underlie autism phenotypes and is relevant to the genetic association of GluD1 coding, GRID1 gene with autism and other developmental disorders.

Agmatine attenuates nicotine induced conditioned place preference in mice through modulation of neuropeptide Y system.

The purpose of the present study was to examine the effect of agmatine on nicotine induced conditioned place preference (CPP) in male albino mice. Intra-peritoneal (ip) administration of nicotine (1mg/kg) significantly increased time spent in drug-paired compartment. Agmatine (20 and 40 mg/kg, ip) co-administered with nicotine during the 6 days conditioning sessions completely abolished the acquisition of nicotine-induced CPP in mice. Concomitant administration of neuropeptide Y (NPY) (1 pg/mouse, icv) or [Leu(31), Pro(34)]-NPY (0.1 pg/mouse, icv), selective NPY Y1 receptor agonist potentiated the inhibitory effect of agmatine (10 mg/kg, ip) on nicotine CPP. Conversely, pretreatment with NPY Y1 receptor antagonist, BIBP3226 (0.01 ng/mouse, icv) blocked the effect of agmatine (20 mg/kg, ip) on nicotine induced CPP. In immunohistochemical study, nicotine decreased NPY-immunoreactivity in nucleus accumbens shell (AcbSh), bed nucleus of stria terminalis, lateral part (BNSTl), arcuate nucleus (ARC) and paraventricular nucleus (PVN). Conversely, administration of agmatine prior to the nicotine significantly reversed the effect of nicotine on NPY-immunoreactivity in the above brain nuclei. This data indicate that agmatine attenuate nicotine induced CPP via modulation of NPYergic neurotransmission in brain.

Neuroprotective effect of cocaine- and amphetamine-regulated transcript peptide in spinal cord injury in mice.

We explored the effect of cocaine- and amphetamine-regulated transcript peptide (CART), alone and in combination with methylprednisolone (MP), on the cellular pathology and locomotor recovery of mice following spinal cord injury (SCI). While cellular pathology was evaluated in terms of spinal cord histology and profile of astrocytes following immunolabeling with antibodies against glial fibrillary acidic protein (GFAP), locomotor recovery was monitored using hindlimb motor function scoring system. At 24 h post-SCI, there was a massive loss of motor function and cysts formation in the spinal cord. The SCI mice, following 3 days and onwards, showed a significant (P < 0.001) increase in the population and hypertrophy of GFAP + astrocytes, suggesting the occurrence of reactive astrogliosis. Intra-fourth ventricular administration of CART (54-102) or intravenous treatment with MP, dose dependently improved motor function score, while CART-antibody (intra-fourth ventricular) was ineffective. This neuroprotective effect of MP was potentiated by the subeffective dose of CART and antagonized by CART-antibody. CART or MP treatment not only prevented the cysts formation, but also significantly attenuated the population of GFAP + astrocytes at days 3, 7, 14, 21 and 28 post-SCI and the hypertrophy of astrocytes at day 14 and 28. The histological consequence of SCI, like cysts formation in the spinal cord, was rapidly improved by CART and/or MP. Taken together, the data suggest that CART may exert its neuroprotective effect via inhibition of post-SCI astrogliosis and participate in the MP mediated neuroprotection.