Rhodes Dell L.PAIN: August 1979 doi: 10.1016/0304-3959(79)90106-4 Research report: PDF Only Buy Abstract Article MetricsMetrics Three areas within the periventricular system were studied: caudal periaqueductal gray (PAG), rostral PAG, and caudal midline thalamus. Rats were chronically prepared with a bipolar stimulating electrode in one of these areas and two lesion electrodes in another. Current thresholds for stimulation-produced analgesia in the tail-flick test were assessed. Then, lesions were made and thresholds for analgesia re-assessed.Destruction of the caudal PAG consistently produced large increases in thresholds for analgesia at rostral stimulation sites; however, destruction of the rostral areas did not affect thresholds at caudal PAG sites. Lesions in all 3 areas yielded significant reductions in baseline (pre-brain stimulation) tail-flick latencies. Both sham lesioned control animals and animals with small lesions maintained stable baseline latencies and analgesia thresholds.The data support the view that all 3 brain areas studied contribute to the same pain-inhibitory system. They further suggest that stimulation at rostral sites activates elements which connect to or pass through the caudal PAG. Accepted May 11, 1979. © Lippincott-Raven Publishers.