EFFECTS OF CHOLINERGIC DEPLETION ON GLUTAMIC-ACID DECARBOXYLASE IMMUNOREACTIVITY IN THE SOMATOSENSORY CORTEX OF RATS

The purpose of these experiments was to determine the effects of choli nergic depletion on the morphology and staining density of barrels for med by glutamic acid decarboxylase-positive neuropil in the posteromed ial barrel subfield of the somatosensory cortex. The density and distr ibution of glutamic acid decarboxylase immunoreactive neuropil were ex amined after highly selective lesions of cholinergic neurons in the nu cleus basalis of Meynert with an immunotoxin, IgG 192-saporin. Glutami c acid decarboxylase immunoreactivity was also examined in animals sub jected to a whisker-pairing experience and lesion of acetylcholine inp uts from the nucleus basalis of Meynert. Seven to 9 weeks after intrav entricular injection of the immunotoxin, animals were perfused with a zinc aldehyde fixative and glutamic acid decarboxylase immunoreactivit y was examined in 30-mu m tangential sections. Cholinergic depletion c aused reduced glutamic acid decarboxylase immunoreactivity in selectiv e regions of the posteromedial barrel subfield. The density of neuropi l and cell bodies immunoreactivie for glutamic acid decarboxylase was significantly reduced in septa and perimeters of barrel walls. The len gth, width, and area of barrels were reduced 10-20% in cholinergic-dep leted animals compared with controls. The density of glutamic acid dec arboxylase immunoreactivity in the hollow of barrels was not affected by this treatment. Whisker pairing did not significantly change the de nsity of glutamic acid decarboxylase immunoreactivity in barrels. Thes e observations are discussed in regard to how long-term cholinergic de pletion affects the function of different fiber systems in the postero medial barrel subfield cortex and how some sensory functions may be co mpromised.