Effects of subacute capsaicin treatment on local cerebral glucose utilization in the rat

The autoradiographic 2-deoxy-D-[1-14C]glucose method was used to map the effect of subacute capsaicin administration on local cerebral glucose utilization, an index of brain function. After treatment with an 80 mg/kg, subcutaneous, cumulative dose of capsaicin over 3 days, a challenge dose of 20 mg/kg capsaicin stimulated glucose utilization in dorsal column and brainstem nuclei which receive primary sensory afferent input or are important in autonomic functions. Glucose utilization in the medial septum was simultaneously reduced. Following a 280 mg/kg cumulative dose of capsaicin over 5 days, a capsaicin challenge dose of 20 mg/kg did not stimulate glucose utilization in the hindbrain, but the decrement in the medial septum was maintained and extended into the lateral septum. The findings provide evidence for a central component of the stimulation and subsequent insensitivity observed with continued capsaicin treatment, and suggest that the deoxyglucose procedure is useful in elucidating the neuroanatomical areas involved in several of the sensory and autonomic effects of capsaicin.