THE LOCAL CEREBRAL METABOLIC EFFECTS OF MORPHINE IN RATS EXPOSED TO ESCAPABLE FOOTSHOCK

The 2-deoxy-D-[1-C-14]glucose (2-DG) method was used to examine the ef fects of morphine sulfate (MS) on local cerebral metabolic rates for g lucose (LCMR(glu)) in male F-344 rats required to turn a wheel manipul andum in order to escape from nociceptive footshock. Four groups of ra ts were studied: control-saline, control-MS, footshock-saline and foot shock-MS. All animals were administered MS (4 mg/kg, s.c.) or saline 7 days, 3 days and 10 min prior to the start of the 2-DG experiment. In agreement with its well-known effect on the emotional component of pa in, MS administered to rats exposed to footshock caused a significant decrease in LCMR(glu) compared to footshock-saline rats in limbic stru ctures such as the diagonal band of Broca, lateral septum, bed nucleus of the stria terminalis, horizontal limb of the diagonal band, habenu lar complex and medial amygdala. Additionally, two components of the m idline thalamus with extensive connections with the limbic system, the paraventricular and paratenial thalamic nuclei, were similarly affect ed by morphine. Footshock caused an overall increase in cerebral metab olism as 52 of 73 measured structures demonstrated increases in activi ty compared to saline control, however, statistically significant effe cts in specific structures were limited. These results identify limbic and midline thalamic structures important in morphine-induced analges ia and indicate that footshock tends to have a generalized stimulatory effect on LCMR(glu).