DENDRITES OF LOCUS-COERULEUS NEURONS EXTEND PREFERENTIALLY INTO 2 PERICOERULEAR ZONES

The intrinsic cytoarchitecture and neurochemical organization of the n ucleus locus coeruleus have been characterized extensively, but there is little information about the organization of locus coeruleus neuron al processes extending outside of the nucleus proper. Light and electr on microscopic immunocytochemical techniques were used to investigate the distribution of dopamine-beta-hydroxylase- or tyrosine-hydroxylase -labeled extranuclear processes in the rat pericoerulear region. The v ast majority of these processes extended preferentially into two zones : (1) the pontine tegmentum medial and rostral to locus coeruleus, her e termed the rostromedial pericoerulear region; and (2) a narrow regio n adjacent to the IVth ventricle caudomedial to locus coeruleus, desig nated here as the caudal juxtaependymal pericoerulear region. Far fewe r labeled processes extended into the lateral and ventral pericoerulea r regions. Seventy-seven percent of the labeled profiles in the perico erulear region were dendrites. All labeled profiles in the rostromedia l pericoerulear region and 94% of the labeled profiles in the caudal j uxtaependymal zone were dendrites. By contrast, in the rostroventral p ericoerulear region, 25% of the labeled profiles were axons. Locus coe ruleus extranuclear dendrites were never presynaptic to other structur es but were often contacted by several unlabeled presynaptic terminals . These results indicate that the dendrites of locus coeruleus neurons extend preferentially into two pericoerulear zones. Extranuclear dend rites in all pericoerulear regions receive extensive, nonnoradrenergic synaptic contacts. Thus, pericoerulear dendrites, particularly in the rostromedial and caudal juxtaependymal zones, are important sites for the integration of inputs to locus coeruleus neurons. (C) 1996 Wiley- Liss, Inc.