Developmental changes in the expression of GABAA receptor subunits alpha1, alpha2, and alpha3 in brain stem nuclei of rats

Gamma-aminobutyric acid (GABA)(A) receptor subunit switching is a suggested postnatal mechanism for changes in GABA transmission from depolarization to hyperpolarization. Previously, we found an apparent switch between GABA(A) alpha3 and alpha1 subunit expression in the rat pre-B?tzinger complex (PBC) on postnatal day (P) 12, a presumed peak critical period of respiratory nuclei development. The present study aimed at determining if GABA(A) subunit switching occurred in another respiratory nucleus, the ventrolateral subnucleus of the solitary tract nucleus (NTS(VL)), and in a non-respiratory cuneate nucleus (CN) of P0 to P21 rats. In both nuclei: (1) the expression of GABA(A) alpha1 subunit was relatively low at birth but increased with development; (2) that of GABA(A) alpha3 was relatively high at birth but declined with age; and (3) GABA(A) alpha2 remained relatively low and constant throughout development. However, the specific patterns differed between the two nuclei, but were similar between the NTS(VL) and the PBC. In the NTS(VL), GABA(A) alpha1 expression gradually increased from birth and peaked at P12, whereas that in the CN sharply rose from P7 and peaked at P10. GABA(A) alpha3 expression had a prominent decrease from P11 to P12 in the NTS(VL), whereas that in the CN only gradually declined from P10 to P12. The developmental trends of alpha1 and alpha3 in the NTS(VL) intersected close to P12, whereas those in the CN intersected at P10. Despite differences in timing, GABA(A) alpha subunit switching may be a common theme in the brain stem that may mediate different functional properties of GABA transmission.     

Quantitative autoradiography of 5-HT1D and 5-HT1E binding sites labelled by [H]5-HT, in frontal cortex and the hippocampal region of the human brain

In human cortex and hippocampus area, [³H]5-HT (5 nM) labels 5-HT_1A, 5-HT_1D and 5-HT_1E sites. After masking 5-HT_1A receptors by 0.1 μM 8-OH-DPAT, the binding displaced by 0.1 μM 5-CT presumably represented 5-HT_1D sites and the remaining binding 5-HT_1E sites. In frontal cortex, 5-HT_1A receptors represented the main binding in layers II and VI and a lower fraction on other layers. 5-HT_1D and 5-HT_1E sites, were more homogeneously distributed in layers II to VI (21–34% of specific [³H]5-HT binding). 5-HT_1E sites were of similar affinities (K_D close to 6–8 nM) in the cortical layers II to VI. In CA1 field of hippocampus, (pyramidal layer, stratum radiatum, molecular layer), CA2 and dentate gyrus, 5-HT_1A receptors represented the major fraction, 5-HT_1D sites a significant fraction and 5-HT_1E a minor fraction of the specific [³H]5-HT binding. In CA3–CA4 fields, 5-HT_1A receptors were less densely present, 5-HT_1D sites were predominant and 5-HT_1E sites represented a significant fraction (27%). The highest densities of 5-HT_1E sites have been measured in subiculum, where 5-HT_1A, 5-HT_1D, and 5-HT_1E binding sites were equally represented and in entorhinal cortex where 5-HT_1E sites represented the major binding in layer III. They were also present in layers II and IV (29 and 24%) and, to a lesser extent, in layers V and VI. 5-HT_1A sites were predominant in layer VI, II and V and were less abundant in other layers. 5-HT_1D were homogeneously present in layers II, III, IV and were present in low amounts in other layers. No 5-HT_1E were detected in choroid plexus, where [³H]5-HT was dramatically reduced by mesulergine (5-HT_2C receptors). No significant displacement of [³H]5-HT by mesulergine was measured in other structures.     

Comparison of the binding of nicotinic agonists to receptors from human and rat cerebral cortex and from chick brain (α4β2) transfected into mouse fibroblasts with ion channel activity

(−)-Nicotine, cytisine and carbachol evoked⁸⁶Rb efflux from mouse fibroblasts stably transfected with α₄β₂ chick brain nicotinic subunits. This response to (−)-nicotine was inhibited by mecamylamine and dihydro-β-erythroidine and was mirrored by a rise in intracellular Ca²⁺ measured by microspectrofluorimetry. Lobeline and isoarecolone methiodide evoked no significant⁸⁶Rb from cells and unlike the above agonists displayed significantly different IC₅₀ values for the displacement of [³H]nicotine from mammalian (rat and human cerebral cortex) and transfected fibroblast membranes.     

TNF deficiency causes alterations in the spatial organization of neurogenic zones and alters the number of microglia and neurons in the cerebral cortex

BackgroundAlthough tumor necrosis factor (TNF) inhibitors are used to treat chronic inflammatory diseases, there is little information about how long-term inhibition of TNF affects the homeostatic functions that TNF maintains in the intact CNS.Materials and methodsTo assess whether developmental TNF deficiency causes alterations in the naïve CNS, we estimated the number of proliferating cells, microglia, and neurons in the developing neocortex of E13.5, P7 and adult TNF knock out (TNF^−/−) mice and wildtype (WT) littermates. We also measured changes in gene and protein expression and monoamine levels in adult WT and TNF^−/− mice. To evaluate long-term effects of TNF inhibitors, we treated healthy adult C57BL/6 mice with either saline, the selective soluble TNF inhibitor XPro1595, or the nonselective TNF inhibitor etanercept. We estimated changes in cell number and protein expression after two months of treatment. We assessed the effects of TNF deficiency on cognition by testing adult WT and TNF^−/− mice and mice treated with saline, XPro1595, or etanercept with specific behavioral tasks.ResultsTNF deficiency decreased the number of proliferating cells and microglia and increased the number of neurons. At the same time, TNF deficiency decreased the expression of WNT signaling-related proteins, specifically Collagen Triple Helix Repeat Containing 1 (CTHRC1) and Frizzled receptor 6 (FZD6). In contrast to XPro1595, long-term inhibition of TNF with etanercept in adult C57BL/6 mice decreased the number of BrdU⁺ cells in the granule cell layer of the dentate gyrus. Etanercept, but not XPro1595, also impaired spatial learning and memory in the Barnes maze memory test.ConclusionTNF deficiency impacts the organization of neurogenic zones and alters the cell composition in brain. Long-term inhibition of TNF with the nonselective TNF inhibitor etanercept, but not the soluble TNF inhibitor XPro1595, decreases neurogenesis in the adult mouse hippocampus and impairs learning and memory after two months of treatment.