INPUT FROM CENTRAL NUCLEUS OF THE AMYGDALA EFFERENTS TO PERICOERULEARDENDRITES, SOME OF WHICH CONTAIN TYROSINE-HYDROXYLASE IMMUNOREACTIVITY

Light microscopic anterograde tracing studies indicate that neurons in the central nucleus of the amygdala (CNA) project to a region of the dorsal pontine tegmentum ventral to the superior cerebellar peduncle w hich contains noradrenergic dendrites of the nucleus locus coeruleus ( LC), However, it has not been established whether the efferent termina ls from the CNA target catecholamine-containing dendrites of the LC or dendrites of neurons from neighboring nuclei which may extend into th is region, To examine this question, we combined immunoperoxidase labe ling of the anterograde tracer biotinylated dextran amine (BDA) from t he CNA with immunogold-silver labeling of the catecholamine-synthesizi ng enzyme tryrosine hydroxylase (TH) in the rostrolateral LC region of adult rats, By light microscopy, BDA-labeled processes were dense in the dorsal pens within the parabrachial nuclei as well as in the peric oerulear region immediately ventral to the superior cerebellar peduncl e, Higher magnification revealed that BDA-labeled varicose fibers over lapped TH-labeled processes in this pericoerulear region, By electron microscopy, anterogradely labeled axon terminals contained small, clea r as well as some large dense core vesicles and were commonly apposed to astrocytic processes along some portion of their plasmalemma, BDA-l abeled terminals mainly formed symmetric type synaptic contacts charac teristic of inhibitory transmitters, Of 250 BDA-labeled axon terminals examined where TH immunoreactivity was present in the neuropil, 81% c ontacted unlabeled and 19% contacted TH-labeled dendrites, Additionall y, amygdala efferents were often apposed to unlabeled axon terminals f orming asymmetric (excitatory type) synapses. These results demonstrat e that amygdaloid efferents may directly alter the activity of catecho laminergic and non-catecholaminergic neurons in this pericoerulear reg ion of the rat brain, Furthermore, our study suggests that CNA efferen ts may indirectly affect the activity of pericoerulear neurons through modulation of excitatory afferents, Amygdaloid projections to noradre nergic neurons may help integrate behavioral and visceral responses to threatening stimuli by influencing the widespread noradrenergic proje ctions from the LC. (C) 1996 Wiley-Liss, Inc.