Voltage sensitive dye imaging and population activity in the pedunculopontine nucleus - effects of carbachol (CAR)

HYDE JR; URBANO FJ; GARCIA-RILL E

Washington DC, USA, Nov 12-16, 2011

Congreso; 41th Society for Neuroscience Annual Meeting; 2011

Society for Neuroscience

The pedunculopontine nucleus (PPN) is involved in the activated states of waking and paradoxical sleep, forming part of the reticular activating system. The PPN receives cholinergic input from both the contralateral PPN and the laterodorsal tegmental nuclei, and has been found to manifest gamma band activity. These studies tested the hypothesis that evoked voltage sensitive dye (VSD) activation patterns and population responses will a) show stimulation frequency-dependence, and b) be modulated by cholinergic input. We used the nonspecific cholinergic agonist CAR to activate cholinergic input to the PPN. VSD signals and event related spectral perturbations (ERSPs) from population recordings were studied in 9-20 day old rat brainstem slices. Slices were stained for 20 min with 200µM di-4-ANEPPS and placed in an interface chamber. VSD signals were recorded with an Evolve 512 (512x512 pixel) back illuminated EMCCD camera equipped with the appropriate optics. Slices were stimulated using concentric bipolar electrodes attached to a constant current unit. 8 pulse trains of 1Hz, 10Hz, and 40Hz, 100-750µA in amplitude were applied to the ventral edge of the PPN. ΔF/F processed VSD images and ERSPs were compared between control and after perfusion with CAR (50 microM). VSD responses in the PPN showed little activation at 1Hz, slight posterior activation at 10Hz, and greater activation at 40Hz. ERSPs showed little activation at 1Hz stimulation, 10Hz produced slight low frequency responses (delta-beta), and 40Hz stimulation produced higher amplitude delta-beta responses. Responses showed little difference in VSD signal intensity between control and CAR perfusion, but CAR exposure showed an increase in activation area, particularly after 40Hz stimulation. We showed that gamma band activity appears to be part of the intrinsic properties of PPN neurons. This study showed that VSD imaging is a viable method of measuring overall PPN gamma band activity. Given sufficient cholinergic excitation, the PPN may impart gamma band activation on its targets.