Fine structural features of the acetylcholine innervation in the developing neostriatum of rat

Abstract

The acetylcholine (ACh) innervation in the developing neostriatum of rat was examined by means of light and electron microscopic immunocytochemistry with a highly sensitive antibody against choline acetyltransferase (ChAT). ChAT-immunoreactive cell bodies and their emerging processes, located at birth in the lateral part of neostriatum, progressively pervaded the whole region, to give rise to an extremely dense axonal network. As visualized and measured in single thin sections, at postnatal (P) ages P8, P16, and P32, the intrinsic and relational features of ChAT-immunostained profiles of axon varicosities in the lateral and medial parts of neostriatum were similar to those previously described in the adult. At the three postnatal ages, the immunoreactive profiles were comparable in shape, size, and vesicular content, and displayed one or more mitochondria with increasing frequency (from 10% at P8 to 29% at P32). The proportion which showed a synaptic junction was low at the three ages (8-16%), indicating an average synaptic incidence of 22% for whole varicosities after stereological extrapolation. The observed junctions were relatively small, mostly symmetrical, and made with dendritic spines or branches. The frequency of synapses on spines versus branches increased with age, from 20% at P8 to almost 60% at P32. Thus, the relational features of the neostriatal ACh innervation were similar to adult as soon as it appeared, as previously observed to be the case in the developing cerebral cortex. The diffuse mode of transmission may therefore be characteristic of both ACh interneurons (neostriatum) and projection neurons (cerebral cortex) in the CNS, and could be determining their functional properties during development as well as at maturity.

Developmental Profile of the Aberrant Dopamine D2 Receptor Response in Striatal Cholinergic Interneurons in DYT1 Dystonia

“…Because developmental changes of both striatal cholinergic innervation as well as of torsinA expression occur during an early postnatal period [29], [39], we extended our electrophysiological analysis to two further ages: P10 and P20, in order to provide a more complete developmental profile. Consistently with data collected at P14 and P90, in interneurons recorded from hMT at P10 and P20, bath application of quinpirole (10 µM, 2 min) significantly depolarized the cells, increasing the rate of action potential discharge (Fig.…”

Cholinergic modulation of striatal microcircuits

“…Similar to dopaminergic axon varicosities, cholinergic ones, form few structurally defined synaptic connections, therefore favoring a slow cholinergic volume transmission (Descarries et al, 1997;Zhou et al, 2001;Aznavour et al, 2003;Coppola et al, 2016;Ovsepian et al, 2016;Dunant & Gisiger, 2017). The integration of a striatal cholinergic tone established by volume and synaptic transmission is considered to act within neuronal networks to change their balance of activity to possibly initiate neuronal ensembles with specific functions (Fuxe et al, 2012).…”

The cholinergic system and neostriatal memory functions

“…Cholinergic axons are often characterized by small varicosities [32]. In contrast to the very dense neostriatal cholinergic innervation, relatively few cholinergic synapses have been found [6,32]. This indicates that ACh acts mainly via non-synaptic (paracrine or non-junctional) and diffuse (volume) transmission, released by the varicosities, in addition to synaptic transmission (for review see [42]).…”