Functional activation in the auditory system of the rat produced by arousing reticular stimulation: a 2-deoxyglucose study.

The 2-deoxyglucose (2-DG) autoradiographic method was used to map the activity in the auditory pathway during behaviorally arousing electrical stimulation of the mesencephalic reticular formation (RET). Uptake of 2-DG during RET stimulation was compared to the effect of a frequency-modulated tone (4-5 kHz, 60 dB SPL) and to controls without stimulation. The major finding was a specific pattern of increased metabolic activation throughout the auditory pathway evoked during RET stimulation. The observed increases in 2-DG uptake were always greater in RET-stimulated rats as compared to sound-stimulated or control rats. The dorsal cochlear nucleus (DCN) showed the largest incorporation of 2-DG among the auditory nuclei of the brainstem in RET-stimulated rats. In the central nucleus of the inferior colliculus a layered pattern made of 3 discrete bands of high 2-DG uptake was visible in RET-stimulated rats. The medial geniculate (MG) and the auditory cortex (AC) also showed highly significant increases in 2-DG uptake induced by RET stimulation. The method provided correlations between classical morphological schemes of parcellation on nuclei and functionally defined areas of increased 2-DG uptake. Our observations represent the first anatomical demonstration of the activating effects of RET stimulation in a sensory system, and they support the concepts of arousing reticular mechanisms for sensory control.