en Physiology Physiology Original Research: Basic Science in Medicine Original Research: Basic Science in Medicine The effects of formalin as a peripheral noxious stimulus on the activity of lateral paragigantocellularis nucleus (LPGi) neurons were examined. Spontaneous activity ofLPGi neurons was recorded after confirmation of their responsiveness to acute pain, and thereafter formalin (50 µL, 2.5%) was injected in the contralateral hindpaw. The response of the LPGi neurons was monitored for 60 min. A biphasic response with a peak lasting 3 to 5 min post-injection, and a second more prolonged tonic excitatory response were obtained which corresponds to the nature and time course of behavioral studies. It is concluded that LPGi neurons may be involved in the processing of nociceptive information related to formalin as a noxious stimulus. Nucleus paragigantocellularis, Formalin test, Multiple unit recording, Rat. 231 236 http://mjiri.iums.ac.ir/browse.php?a_code=A-10-298-243&slc_lang=en&sid=1 E SOLEIMAN-NEJAD 20031947532846006814 20031947532846006814 No From the Dept. of Physiology. Faculty of Medicine. Army University of Medical Sciences. Po. Box: 14185- 611. Tehran Y FATHOLLAHI 20031947532846006815 20031947532846006815 No The Dept. of Physiology. School a/Medical Sciences. Tarbiat Modarres University. Po. Box: 14115-111. Tehran. S SEMNANIAN 20031947532846006816 20031947532846006816 Yes the Institute of Biochemistry and Biophysics. Tehran University. Po.Box: 13145-1384. Tehran.l.R. Iran.