NEUROTRANSMITTER MODULATION OF HIGH AND LOW FREQUENCY INPUTS IN SOMATOSENSORY CORTEX: AN IN VITRO OPTICAL IMAGING STUDY

E. LEZNIK; F.J. URBANO; R. LLINAS.

New York, USA

Conferencia; Optical Monitoring of activity in the brain and heart. A celebration of Merocyanine-540.; 2002

We used somatosensory cortical slices from 2-5 week old rats to investigate the role of neuromodulators on the interactions between low (2 to 10Hz) and high (40 Hz) frequency cortical inputs. Slices were stained with the voltage-sensitive dye RH795 and their fluorescent activity was recorded using a CCD camera (Fujix HRDeltaron 1700). Electrical stimulation was delivered by two concentric bipolar electrodes positioned over the surface of white matter with a 1-2 mm separation. Application of 5-20M of carbachol (a muscarinic ACh receptor agonist) facilitated both the low and high frequency-induced cortical responses. A significant increase in amplitude and duration of the responses within the deep cortical layers was observed (n=5). However, the characteristic spatial profiles generated by the low and high frequency cortical activation remained unmodified (see the accompanying abstract Urbano et al., 2002; Contreras & Llinas, 2001; J. Neuroscience). Indeed, during high frequency stimulation, the area of initial cortical excitation was laterally reduced to a small radial column. Furthermore, in the presence of carbachol a single shock applied during the 40Hz stimulation was able to further facilitate the cortical signals induced by the 40Hz train. A 50-75 % increase in the slope of the rising phase of the 40Hz train responses was observed after the single shock stimulation (n=6). These results suggest that interactions between high and low frequency cortical activity could be significantly influenced by the muscarinic cholinergic system.Supported by: NIH-NINDS grant NS13742