title: Periventricular system lesions and stimulation-produced analgesia.
abstract: 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.
mesh_terms: D000698:Analgesia; D000818:Animals; D004027:Diencephalon / Q000502:physiology*; D004558:Electric Stimulation / Q000295:instrumentation / Q000379:methods; D008297:Male; D009433:Neural Inhibition; D010146:Pain / Q000503:physiopathology; D051381:Rats; D012684:Sensory Thresholds; D013788:Thalamus / Q000502:physiology