Cortical projections to the periaqueductal grey in the cat: a retrograde horseradish peroxidase study.

Stereotaxic fluid microinjections of horseradish peroxidase into different parts of the rostral and caudal periaqueductal grey (PAG) in cats have provided substantial retrograde evidence that the somatosensory cortex (I and II), frontal cortex, insular and cingular cortex are the principal sources of cortical-PAG projections. The somatosensory cortex II projects to all the regions of the rostral and caudal PAG. The frontal cortex projects to dorso-lateral quadrant of the PAG. The same projections were determined from insular and cingular cortex to PAG. The findings revealed a morphological substratum of corticofugal effects on PAG.

A study of the catecholaminergic systems of the lateral reticular nuclei and the serotoninergic systems of the raphe magnus in various types of analgesia.

The effects of catecholaminergic A-1 lateral reticular nuclei and serotoninergic neurons of NRM on pain reactions before and after various types of stimulation are presented. It was established that specific lesions of catecholaminergic (NE) neurons in A-1 nuclei using 6-hydroxydopamine, and of serotoninergic (5-HT) neurons of the nucleus raphe magnus using 5,7-dihydroxytryptamine caused a decrease in the respective levels of epinephrine and serotonin in the spinal cord. The baseline pain sensitivity did not change following surgery. Analgesia induced by cold swimming stress (CSS), auricular electroacupuncture (AEA) and vaginal probe (VP) was less in A-1-lesioned rats. Using stimulation of high intensity, such as CSS and VP, a decrease in pain sensitivity was determined, compared to the baseline. The AEA did not produce such an effect. The data obtained suggest that catecholaminergic systems of A-1 play an important role in pain regulation when CSS, AEA and VP are used. Other neurochemical mechanisms, as well as A-1 nuclei systems, are involved in analgesia, induced by CSS and VP. It was shown that lesion of 5-HT-ergic systems of NRM did not have any influence of antinociceptive mechanisms, when activated by AEA and VP.