LARGE SEGMENTAL DIFFERENCES IN THE SPINAL PROJECTIONS TO THE PERIAQUEDUCTAL GRAY IN THE CAT

The periaqueductal gray (FAG) is involved in motor activities, such as movements of the neck, back and hind limbs, cardiovascular regulation , micturition, vocalization, and mating behavior, as well as in nocice ption control. To accomplish these functions the FAG uses information from other parts of the limbic system, from the lower brainstem, and f rom the spinal cord. To study the ascending projections from the spina l cord to the PAG, tracer was injected in different parts of the FAG, and the number of retrogradely labeled neurons were counted for each s pinal segment. Results show that large segmental differences exist in the number of FAG projecting neurons throughout the length of the spin al cord and that different parts of the spinal cord project to specifi c areas in the FAG. (C) 1997 Elsevier Science Ireland Ltd.