Immunocytochemical localization of choline acetyltransferase in rat cerebral cortex: A study of cholinergic neurons and synapses

Abstract

Choline acetyltransferase (ChAT), the acetylcholine-synthesizing enzyme and a definitive marker for cholinergic neurons, was localized immunocytochemically in the motor and somatic sensory regions of rat cerebral cortex with monoclonal antibodies. ChAT-positive (ChAT+) varicose fibers and terminal-like structures were distributed in a loose network throughout the cortex. Some immunoreactive cortical fibers were continuous with those in the white matter underlying the cortex, and many of these fibers presumably originated from subcortical cholinergic neurons. ChAT+ fibers appeared to be rather evenly distributed throughout all layers of the motor cortex, but a subtle laminar pattern was evident in the somatic sensory cortex, where lower concentrations of fibers in layer IV contrasted with higher concentrations in layer V. Electron microscopy demonstrated that immunoreaction product was concentrated in synaptic vesicle-filled profiles and that many of these structures formed synaptic contacts. ChAT+ synapses were present in all cortical layers, and the majority were of the symmetric type, although a few asymmetric ones were also observed. The most common postsynaptic elements were small to medium-sized dendritic shafts of unidentified origin. In addition, ChAT + terminals formed synaptic contacts with apical and, probably, basilar dendrites of pyramidal neurons, as well as with the somata of ChAT-negative nonpyramidal neurons.ChAT+ cell bodies were present throughout cortical layers 11-VI, but were most concentrated in layers 11-111. The somata were small in size, and the majority of ChAT-t neurons were bipolar in form, displaying vertically oriented dendrites that often extended across several cortical layers. Electron microscopy confirmed the presence of immunoreaction product within the cytoplasm of small neurons and revealed that they received both symmetric and asymmetric synapses on their somata and proximal dendrites. These observations support an identification of ChAT+ cells as nonpyramidal intrinsic neurons and thus indicate that there is an intrinsic source of cholinergic innervation of the rat cerebral cortex, as well as the previously described extrinsic sources.

BACE1 gene deletion prevents neuron loss and memory deficits in 5XFAD APP/PS1 transgenic mice

“…In this regard, it is interesting to note that neuron loss is also observed in both of these regions in AD brain (Bobinski et al, 1997;Giannakopoulos et al, 1996). Importantly, it is plausible that ablation of these neurons contributes to memory decline, since layer 5 pyramidal neurons receive the highest density of cholinergic innervation (Houser et al, 1985) and greater atrophy in the subiculum (which is part of the hippocampus) is associated with increased risk for conversion from mild cognitive impairment to AD (Apostolova et al, 2006). Our finding that BACE1 deletion prevents neuronal loss, amyloidosis, astrogliosis, and spatial working memory deficits in the Y-maze in 5XFAD mice of advanced age suggests a beneficial effect of BACE1 inhibition and Aβ reduction on later phases of cognitive impairments and AD-related pathologies.…”

Input-specific effects of acetylcholine on sensory and intracortical evoked responses in the “barrel cortex” in vivo

“…Evidence suggests that muscarinic receptors are localized presynaptically on intrinsic cortical fibers (Sabin et aL, 1992) and postsynaptically on cortical neurons (Houser et al, 1985;McCormick " Prince, 1985). Depression of the intracortical response produced by low doses of exogenous Ac~, high doses of endogenous Ach and muscarine were aIl accompanied by an enhancement in pp ratio.…”

“…• • • V and 1, whereas lower densities were observed in layers II, mand VI (Houser et al, 1985;Kristt, 1979a, b).…”

“…Muscarinic receptors are distributed profusely throughout the cerebral cortex and are generally present in both superficial and deep cortical layers (Lidow et al, 1989;Sabin et al, 1992). In general, the rec:eptors are localized postsynaptically on cortical neurons (Houser et al, 1985;McCormick & Prince, 1985). However, evidence exists for presynaptie locaiization on intrinsie (Sabin et al, 1992), thalamocortical (Vo~1984), and basal forebraincholinergie (Mash & Potter, 1986) tibers in the cortex.…”

Lack of Sympathetic and Cholinergic Influences on Cerebral Vasodilation Caused by Sciatic Nerve Stimulation in the Rat

“…, 1980;Johnston et aI. , 198 1;Houser, 1985). The basal forebrain has been shown to mediate increase in CBF produced by stimulation of the rat fastigial nucleus (Iadecola et aI.…”