Neuroscience
-
5-Hydroxytrytamine (serotonin) type 3A receptors (5-HT3ARs), as the only ligand-gated ion channels in the serotonin receptor family, are known to regulate neuronal excitation and release of GABA in hippocampal interneurons. However, their physiological role in glutamatergic synaptic plasticity remains unclear. Here, we show that deletion of the 5-HT3AR gene in transgenic mice abolished N-methyl-d-aspartate (NMDA) receptor (NMDAR)-dependent long-term depression (LTD) induced by low-frequency stimulation (LFS) in hippocampal CA1 synapses in slices, whereas the metabotropic glutamate receptor (mGluR)-dependent LTD did not change in the 5-HT3AR knockout mice. ⋯ However, the deletion of 5-HT3ARs did not lead to loss of synapses and structural alteration of dendritic spines. Furthermore, the concentrations of 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) in the hippocampus were not affected by the deletion of 5-HT3ARs. These observations revealed an important role of 5-HT3ARs in NMDAR-dependent long-term depression, which is critical for learning behaviors.
-
We used a reporter mouse line in which green fluorescent protein (GFP) was inserted into the orexin-1 receptor (OX1) locus to systematically map the neuroanatomical distribution of the OX1 receptor in the mouse brainstem and pons. Here, we show that the OX1 receptor is expressed in a select subset of medullary and pontine nuclei. In the medulla, we observed OX1-GFP expression in the cuneate, gracile, dorsal motor nucleus of the vagus (10N), nucleus of the solitary tract and medullary raphe areas. ⋯ Double-staining with tyrosine hydroxylase revealed extensive co-expression in the LC, DRN and the lateral paragigantocellularis cell group in the ventral medulla. Our findings faithfully recapitulate the findings of OX1 mRNA expression previously reported. This is the first study to systematically map the neuroanatomical distribution of OX1 receptors within the mouse hindbrain and suggest that this OX1-GFP transgenic reporter mouse line might be a useful tool with which to study the neuroanatomy and physiology of OX1 receptor-expressing cells.
-
The tetrameric kainate receptors can be assembled from a combination of five different subunit subtypes. While GluK1-3 subunits can form homomeric receptors, GluK4 and GluK5 require a heteromeric partner to assemble, traffic to the membrane surface, and produce a functional channel. Previous studies have shown that incorporation of a GluK4 or GluK5 subunit changes both receptor pharmacology and channel kinetics. ⋯ In addition, mutation of the agonist binding site of GluK5 results in a heteromeric receptor with a glutamate sensitivity similar to homomeric GluK1 or GluK2 receptors, but which requires higher agonist concentrations to produce desensitization. This suggests that onset of desensitization in heteromeric receptors is determined more by the number of subunits bound to agonist than by the identity of those subunits. The distinct, concentration-dependent properties observed with heteromeric receptors in response to glutamate or kainate are consistent with a model in which either subunit can activate the channel, but in which occupancy of both subunits within a dimer is needed to allow desensitization of GluK2/K5 receptors.
-
Cell-type compartmentation of glucose metabolism in the brain involves trafficking of the oxidizable glycolytic end product, l-lactate, by astrocytes to fuel neuronal mitochondrial aerobic respiration. Lactate availability within the hindbrain medulla is a monitored function that regulates systemic glucostasis as insulin-induced hypoglycemia (IIH) is exacerbated by lactate repletion of that brain region. A2 noradrenergic neurons are a plausible source of lactoprivic input to the neural gluco-regulatory circuit as caudal fourth ventricular (CV4) lactate infusion normalizes IIH-associated activation, e.g. phosphorylation of the high-sensitivity energy sensor, adenosine 5'-monophosphate-activated protein kinase (AMPK), in these cells. ⋯ A1, C1, and A2 neurons, exhibit increased sensor activity in response to IIH. Moreover, hindbrain lactate repletion reversed hypoglycemic augmentation of pAMPKα1/2 content in A2 and C1 but not A1 cells, and normalized hypothalamic norepinephrine and epinephrine content in a site-specific manner. The present evidence for discriminative reactivity of AMPK-expressing medullary catecholamine neurons to the screened energy substrate lactate implies that that lactoprivation is selectively signaled to the hypothalamus by A2 noradrenergic and C1 adrenergic cells.
-
Striatal-enriched protein tyrosine phosphatase (STEP) is a brain-specific tyrosine phosphatase that has been shown to de-phosphorylate several key neuronal signaling proteins, including kinases (extracellular signal-regulated kinase (ERK1/2), FYN, PYK2) and glutamate receptor subunits (N-methyl-d-aspartate receptor subtype 2B (NR2B), glutamate receptor 2 (GLUR2)). Step knock-out mice have increased phosphorylation of these substrates in the brain, with potential functional consequences in synaptic plasticity and cognitive tasks. It is therefore of interest to identify the molecular pathways and downstream transcriptional targets that are impacted by Step knockdown. ⋯ Potential genes of interest identified by microarray were confirmed by quantitative real-time polymerase chain reaction (qRT-PCR) in the cortex and hippocampus, which shared several transcriptional alterations with the striatum. In order to evaluate Step knockdown in an in vitro system, a panel of genes were evaluated using qRT-PCR in rat cortical neurons that were transduced with lentivirus expressing short hairpin RNA against Step or a non-targeting control. Our data suggest that Step has a role in the expression of immediate early genes relevant to synaptic plasticity, in both in vitro and in vivo systems.