Biomedical subjects

Andrei B Belousov

Publications and source records attributed to Andrei B Belousov.

4 recordsLinked to original sources

PubMed2005

NMDA receptors regulate developmental gap junction uncoupling via CREB signaling.

Signaling through gap junctions (electrical synapses) is important in the development of the mammalian central nervous system. Abundant between neurons during postnatal development, gap junction coupling subsequently decreases and remains low in the adult, confined to specific subsets of neurons. Here we report that developmental uncoupling of gap junctions in the rat hypothalamus in vivo and in vitro is associated with a decrease in connexin 36 (Cx36) protein expression. Both developmental gap junction uncoupling and Cx36 downregulation are prevented by the blockade of NMDA glutamate receptors, action potentials and the calcium-cyclic AMP response element binding protein (CREB), and are accelerated by CREB overexpression. Developmental gap junction uncoupling and Cx36 downregulation are not affected by blockade of non-NMDA glutamate receptors, and do not occur in hypothalamic neurons from NMDA receptor subunit 1 (NMDAR1) knockout mice. These results demonstrate that NMDA receptor activity contributes to the developmental uncoupling of gap junctions via CREB-dependent downregulation of Cx36.

Action Potentials↗

PubMed2004

Non-cholinergic excitation in neurons after a chronic glutamate receptor blockade.

Previous experiments revealed a dramatic increase in excitatory acetylcholine transmission in hypothalamic cultures during a chronic decrease in glutamate activity. Data suggested that in the absence of glutamate excitation, acetylcholine becomes the major excitatory neurotransmitter. However, non-cholinergic excitatory activity was also detected in some neurons. Here, using calcium imaging in hypothalamic cultures chronically subjected to the glutamate receptor blockade, we demonstrate the contribution of metabotropic glutamate receptors, P2-purinoreceptors, histamine receptors, adrenoreceptors, and gap junctions, but not nitric oxide to this non-cholinergic excitation. We also show that the sensitivity of neurons to receptor agonists is increased following the blockade. Data suggest that multiple components contribute to the excitatory activity in hypothalamic neurons during a long-term decrease in glutamate activity.

Action Potentials↗

PubMed2003

Glutamate-dependent regulation of cholinergic phenotype in hypothalamic neurons.

Glutamate NMDA receptor antagonists are used clinically. However, they have serious side effects, some of which are presumably due to an increase in acetylcholine transmission. Our previous experiments revealed acetylcholine-dependent excitation in rat hypothalamic cultures after a chronic glutamate receptor blockade. Dextromethorphan, amantadine, and eliprodil are NMDA receptor antagonists. Lamotrigine inhibits synaptic glutamate release. These drugs are used clinically. Here, using calcium imaging and immunocytochemistry, we demonstrate that a chronic treatment with each of these drugs induced acetylcholine activity and choline acetyltransferase immunoreactivity in rat hypothalamic (but not cortical) cultures. These data support the possibility that some side effects of anti-glutamate drugs in vivo may be due to the increase in cholinergic properties in certain regions of the CNS.

Acetylcholine↗

PubMed2002

Calcium-dependent regulation of cholinergic cell phenotype in the hypothalamus in vitro.

Glutamate is a major fast excitatory neurotransmitter in the CNS including the hypothalamus. Our previous experiments in hypothalamic neuronal cultures showed that a long-term decrease in glutamate excitation upregulates ACh excitatory transmission. Data suggested that in the absence of glutamate activity in the hypothalamus in vitro, ACh becomes the major excitatory neurotransmitter and supports the excitation/inhibition balance. Here, using neuronal cultures, fura-2 Ca(2+) digital imaging, and immunocytochemistry, we studied the mechanisms of regulation of cholinergic properties in hypothalamic neurons. No ACh-dependent activity and a low number (0.5%) of cholinergic neurons were detected in control hypothalamic cultures. A chronic (2 wk) inactivation of N-methyl-D-aspartate (NMDA) ionotropic glutamate receptors, L-type voltage-gated Ca(2+) channels, calmodulin, Ca(2+)/calmodulin-dependent protein kinases II/IV (CaMK II/IV), or protein kinase C (PKC) increased the number of cholinergic neurons (to 15-24%) and induced ACh activity (in 40-60% of cells). Additionally, ACh activity and an increased number of cholinergic neurons were detected in hypothalamic cultures 2 wk after a short-term (30 min) pretreatment with bis-(o-aminophenoxy)-N,N,N',N'-tetraacetic acid tetrakis(acetoxy-methyl) ester (BAPTA AM; 2.5 microM), a membrane permeable Ca(2+)-chelating agent that blocks cytoplasmic Ca(2+) fluctuations. An increase in the number of cholinergic neurons following a chronic NMDA receptor blockade was likely due to the induction of cholinergic phenotypic properties in postmitotic noncholinergic neurons, as determined using 5-bromo-2'-deoxyuridine (BrdU) labeling. In contrast, a chronic inactivation of non-NMDA glutamate receptors or cGMP-dependent protein kinase had little effect on the expression of ACh properties. The data suggest that Ca(2+), at normal intracellular concentrations, tonically suppresses the development of cholinergic properties in hypothalamic neurons. However, a decrease in Ca(2+) influx into cells (through NMDA receptors or L-type Ca(2+) channels), inactivation of intracellular Ca(2+) fluctuations, or downregulation of Ca(2+)-dependent signal transduction pathways (CaMK II/IV and PKC) remove the tonic inhibition and trigger the development of cholinergic phenotype in some hypothalamic neurons. An increase in excitatory ACh transmission may represent a novel form of neuronal plasticity that regulates the activity and excitability of neurons during a decrease in glutamate excitation. This type of plasticity has apparent region-specific character and is not expressed in the cortex in vitro; neither increase in ACh activity nor change in the number of cholinergic neurons were detected in cortical cultures under all experimental conditions.

Acetylcholine↗