Objectives: 

In the transition from deep sleep to the awake state there is a massive activation of neurons in the cerebral cortex, modulated by the activating ascendant systems. The aim of this work was to discern the temporal role of the neuromodulator nitric oxide (NO), relative to two hemodynamic markers, during the cortical activation induced by the brainstem peribrachial region (PBR).

Materials: 

Using optical spectroscopy, we monitored the levels of oxy-, deoxy- and methemoglobin (oxyHb, deoxyHb and metHb respectively) in the somatosensory cortex of anesthetized and paralyzed cats. A bipolar electrode was used to record the electrocorticogram (ECoG). Data analysis included coherence and phase shift between signals in the range of 0.1 to 5 Hz.

Results: 

During spontaneous activity, deoxyHb showed a negative correlation both with oxyHb and metHb. Besides, a frequency dependent coherence was observed. Thus, deoxyHb had a 50% of coherence both with metHb and oxyHb for frequencies below 0.5 Hz. For frequencies greater than 0.5 Hz the coherence deoxyHb-oxyHb increased to 80% and the coherence deoxyHb-metHb decreased to 35%. On the other hand, metHb and oxyHb showed a positive correlation and a coherence of 15% in the whole frequency range. Phase shifts between signals were analyzed (by means of a complex wavelet analysis) before and after the activation of PBR. The ECoG showed no obvious correlation with any of the three markers, but temporal relationships were uncovered after grouping the data depending on the degree of coherence in different frequency sub-ranges. The group with coherence around 0.5 Hz showed a rapid recovery of hemodynamic markers after stimulation and an ECoG delayed from metHb at 0.5 Hz. The group with low coherence around 0.5 Hz showed a slower hemodynamic recovery.

Conclusions: 

These results suggest that the modulation of neuronal activity induced by PBR stimulation is mediated in part by a sustained and an alternating release of NO.

Supported by Xunta de Galicia, INCITE09 and MICINN, Spain