Aim: 

We study the coupling between blood flow and neuronal responses in the visual thalamus and try to shed some light in the mechanisms that mediate such a coupling. This is a fundamental question to our understanding of brain function since non invasive optical techniques such as fMRI are based on it, and blood flow regulatory mechanisms might have an enormous impact in neural activity.

Methods: 

Experiments were carried out in the LGN of 7 anesthetized and paralyzed adult cats. All the procedures conformed to the Spanish Physiology Society and the International Council for Laboratory Animal Science and the European Union (statute nr 86/809). We simultaneously recorded extracellular neuronal activity and oxyhaemoglobin (an indicator of blood flow) and metahaemoglobin (nitric oxide indicative) by spectrophtometry during control and different visual stimulation protocols.

Results: 

Despite of a clear difference in temporal response (neuronal activity operates in a much faster time scale) both, neuronal response and blood flow, show increase with stimulus intensity (contrast-response curves), presenting signs of saturation at high contrasts and both are heavily influenced by nitric oxide. It seems clear that, at least in the thalamus, NO has two different sources based on the stimulation intensity: endothelial NO for low intensity and neuronal NO for high stimulation intensity.

Conclusion: 

In the visual thalamus of the cat blood flow and neuronal activity shown a degree of correlation higher than observed in other brain areas, with a prominent role for NO as mediator.