Nucleus basalis of Meynert modulates signal processing in rat layer 5 somatosensory cortex but leads to memory impairment and tactile discrimination deficits following lesion.

ABSTRACT

In rodents, exploring through continuous whisking is a process resulted from sensorimotor networking among different layers of somatosensory cortex (SC) such as layer 5 (L5) or barrel field, and regions like the nucleus basalis of Meynert (NBM). NBM is densely packed with cholinergic fibers and its dysfunction leads to diminished acetylcholine release within SC, tactile deficits and Alzheimer's disease (AD)-like memory impairment. Using extracellular single-unit recording, we investigated mechanisms underlying changes in response characteristics of L5b neurons to single or paired deflection of selected principle and adjacent whiskers (PW and AW), following NBM electrical stimulation in normal rats or ibotenic acid-induced NBM lesion leading to potential tactile deficiency and memory loss during passive avoidance learning (PAL) in AD-like neuropathology. Our results indicated that NBM electrical stimulation decreased ON and OFF response magnitude in nearly half of the units upon vibrissal deflection. The larger the response was evoked to whisker deflection before NBM stimulation, the smaller it gets after stimulation. Neuronal spontaneous activity was not changed with NBM stimulation or lesion. Leading to more sublinear response summation and decreased condition-test ratio, NBM lesion decreased ON response magnitude and facilitation, increased AW surround inhibition in paired whisker deflection, increased excitatory and decreased inhibitory receptive fields, weakened information processing during whisking, and resulted in AD-like declined PAL performance. These findings provide further understandings to develop translational approaches in precision therapeutics to target highly specific regions such as NBM or SC, and pathways like cholinergic system involved in tactile and memory deficits in AD.