[Corticofugal projections to the periaqueductal gray matter in the cat midbrain].

Stereotaxic microinjections of horseradish peroxidase (HP) were made into different parts of the rostral and caudal periaqueductal gray (PAG) in cats to study corticofugal projections to the PAG. The method of retrograde axonal transport of HP demonstrated labeled neurons in the I and II somatosensory areas, frontal, cingular and insular cortex of the brain. It was shown that the II somatosensory cortex projects to all the areas of the rostral and caudal PAG. The frontal cortex projects to the dorsolateral quadrant of the PAG. The findings obtained enabled the detection of the morphological substrate of the corticofugal effects on one of the antinociceptive brain structures--the PAG.