Visually evoked potentials are differently modulated by the basal forebrain and the nucleus cuneiformis of freely...

Different modulatory influences on visually evoked potentials (VEPs) of freely moving rats from two different cholinergic brain regions, the basal forebrain (bf, nucleus basalis magnocellularis) and the mesencephalic parabrachial nucleus cuneiformis (Cnf) are described. Bipolar stimulating electrodes were implanted in both regions and recording electrodes on the visual cortex, the frontal cortex, the olfactory bulb, and in the nasal bone. Serial electrical stimulations with increasing intensities, a series duration of 1 s, and frequencies of 100 and 10 cps, and single impulses were applied within both cholinergic regions 100 ms before light flashes. Lesions of the stimulated sites were produced to test whether modulations disappear. The bf revealed heterogeneous effects on the evoked potentials depending on the stimulation modes and on the electrode localization inside the bf whereas the Cnf modulated the evoked potentials rather uniformly. All stimulation modes in the Cnf reduced the N 30-amplitude of the primary VEP in the visual cortex simultaneously with a decrease of their peak times, and reduced the trigger rate of photically evoked afterdischarges (PhAD). 100 and 10 cps stimulation of the Cnf decreased also the PhAD amplitude and the number of PhAD per flash when stimulation intensity was above the threshold of behavioural activation. The bf stimulation with 100 cps modulated all investigated parameters differently in their quantity: with 10 cps stimulation VEP amplitude and PhAD trigger rate were differently modulated. Single impulses within the bf 100 ms before flash were ineffective on the evoked potentials. No peak time alterations of the VEP were evoked with 10 cps stimulation within the bf in contrast to Cnf stimulation. The bf seems to be heterogeneous in its physiological effects on the visual cortex.