1 Gamma band unit activity and population responses 1 in the pedunculopontine nucleus ( PPN ) 2

27 The pedunculopontine nucleus (PPN) is involved in the activated states of waking and 28 paradoxical sleep, forming part of the reticular activating system (RAS). The studies described 29 tested the hypothesis that single unit and/or population responses of PPN neurons are capable 30 of generating gamma band frequency activity. Whole-cell patch clamp recordings (immersion 31 chamber) and population responses (interface chamber) were conducted on 9-20 days old rat 32 brainstem slices. Regardless of cell type (I, II or III) or type of response to the nonselective 33 cholinergic receptor agonist carbachol (excitation, inhibition, biphasic), almost all PPN neurons 34 fired at gamma band frequency, but no higher, when subjected to depolarizing steps (50 +/2 35 Hz, mean +/SE). Non-accommodating neurons fired at 18-100 Hz throughout depolarizing 36 steps, while most accommodating neurons exhibited gamma band frequency of action 37 potentials followed by gamma band membrane oscillations. These oscillations were blocked by 38 the sodium channel blocker tetrodotoxin (TTX), suggesting that at least some are mediated by 39 sodium currents. Population responses in the PPN showed that carbachol induced peaks of 40 activation in the theta and gamma range, while glutamatergic receptor agonists induced overall 41 increases in activity at theta and gamma frequencies, although in differing patterns. Gamma 42 band activity appears to be a part of the intrinsic membrane properties of PPN neurons, and the 43 population as a whole generates different patterns of gamma band activity under the influence 44 of specific transmitters. Given sufficient excitation, the PPN may impart gamma band activation 45 on its targets. 46 47