Vesicular and cytoplasmic localization of neurotensin-like immunoreactivity (NTLI) in neurons postsynaptic to terminals containing NTLI and/or tyrosine hydroxylase in the rat central nucleus of the amygdala

Abstract

Neurotensin and catecholamines in the central nucleus of the amygdala (CNA) have both been implicated in the integration of autonomic responses to stress. We examined whether there might be a cellular substrate for interactions involving these putative neurotransmitters in the CNA. Sections of acrolein-fixed rat brain were processed either (1) for the ultrastructural localization of a rat antiserum against neurotensin using the peroxidase-antiperoxidase (PAP) method, or (2) for the dual localization of rat neurotensin antiserum and rabbit antiserum against the catecholamine-synthesizing enzyme, tyrosine hydroxylase (TH), using the PAP method and immunoautoradiography. The rat polyclonal antiserum against neurotensin was shown in immunoblots to recognize neuromedin N and Lys-Arg-neurotensin (LANT-6) in addition to neurotensin. In single and dual labeling studies, the neurotensin-like immunoreactivity (NTLI) was detected in perikarya and processes. The NTLI was localized predominantly to dense core vesicles in one group of perikarya and dendrites, while a second group had labeling both in dense core vesicles and more diffusely throughout the cytoplasm. Terminals also showed NTLI, particularly in association with dense core vesicles. The labeled terminals formed primarily symmetric junctions with both cell bodies and dendrites. In the dual labeling study, perikarya contained only NTLI while terminals contained TH and/or NTLI. Terminals containing TH or NTLI separately innervated cell bodies and dendrites displaying NTLI, and formed separate or convergent inputs onto unlabeled neuronal targets. Terminals colocalizing both TH and NTLI formed junctions only on unlabeled dendrites. These findings show that in the rat CNA two populations of neurons differ with respect to their distribution of NTLI, and that the output from neurons containing NTLI is modulated by direct synaptic input from terminals containing neurotensin and/or catecholamines. Release of neurotensin and catecholamines, most likely dopamine, from the same or separate terminals on common targets in the CNA may account for certain similarities in their stress-related functions.