The immunocytochemical localization of enkephalin in the central nervous system of the rat

TLDR

Enkephalin‑like immunoreactivity in the rat CNS is implicated in diverse functions beyond nociception, including neuroendocrine, respiratory, auditory, vestibular, and olfactory regulation. The study aimed to map the distribution of enkephalin‑like immunoreactivity throughout the rat central nervous system. ELI was detected using colchicine‑treated brains, pronase proteolytic pretreatment, and a double‑bridge staining technique. ELI was found in perikarya, processes, and terminals across many CNS regions, with novel perikarya localization in numerous nuclei and the cervical spinal cord, indicating heterogeneous interneuron and projection neuron populations.

Abstract

Abstract The immunocytochemical localization of enkephalin‐like immunoreactivity (ELI) throughout the rat central nervous system (CNS) was investigated. The detection of ELI‐containing structures was facilitated through the use of (1) brains from colchicine‐treated rats, (2) the proteolytic pretreatment of sections with pronase and (3) the “double‐bridge” staining technique. Our findings confirm the presence of ELI in perikarya, neuronal processes and terminals in many areas of the CNS. In addition, the localization of ELI‐containing perikarya is reported for the first time in the following areas: the olfactory bulb, the olfactory tubercle, the lateral preoptic nucleus, several nuclei within the amygdaloid nuclear complex, the hippocampus, the neocortex, the cingulate cortex, the posterior mammillary nucleus, the medial nucleus of the optic tract, the brachium of the inferior colliculus, the ventral tegmental nucleus, the locus ceruleus, the subceruleal region, the lateral trapezoid nucleus, the nucleus reticularis lateralis, and lamina VII of the cervical spinal cord. Our results demonstrate ELI in neurons which are heterogeneous in size, some probably functioning as interneurons and others as projection neurons in different areas of the CNS. The location of these neurons within the brain suggests that these pentapeptides serve diverse functions which include, in addition to nociception, the regulation of neuroendocrine, respiratory, auditory, vestibular, and olfactory functions.