Blood flow changes in chicken brain stem auditory nuclei following cochlea removal

Abstract

Cochlea removal results in rapid and persistent metabolic and morphological changes in avian brain stem auditory nuclei. Because such changes in the central nervous system are often associated with changes in local blood flow, we examined blood flow in second-order auditory nucleus magnocellularis (NM) and third-order nucleus laminaris (NL). The diffusible tracer [ 14C]-iodoantipyrine was infused intravenously into 20- to 26-day-old chickens either 30 min or 6 h after unilateral cochlea removal. This tracer rapidly equilibrates between blood and tissue in proportion to local blood flow. Unoperated animals served as controls. Thirty seconds after tracer infusion, brains were removed and frozen. Cryostat sections were prepared for quantitative film autoradiography. Blood flow in normal and deafferented areas within NM and NL was compared. Nucleus magnocellularis receives its only excitatory input from the ipsilateral cochlea via the eighth nerve. Axons from NM bifurcate and project to the ipsilateral dorsal dendritic region of NL (NLd) and the contralateral ventral dendritic region of NL (NLv). Thirty minutes after cochlea removal, blood flow in ipsilateral NM decreases by 30%. This decrease persists at 6 hours. Blood flow in NL does not change in accordance with the pattern of afferent input from NM. Rather, blood flow in NLd and NLv ipsilateral to cochlea removal is significantly decreased 6 h post lesion. These results are in contrast to the pattern of morphological and metabolic changes observed in NL after cochlea removal.