The nucleus paragigantocellularis lateralis in the rat

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Abstract
Injections of horseradish peroxidase (HRP) were placed in the middle or caudal portion of the nucleus paragigantocellularis lateralis (PGCL) and 24 h later the entire spinal cord and brain were processed and examined for labeled neurons. Spinal afferents arise from all levels of the cord. Rexed's lamination scheme was adapted to the spinal cord of the rat and labeled neurons were localized to laminae IV, V, VII, VIII and X mainly on the side contralateral to the injection. At cervical levels, labeled neurons were consistently found bilaterally. The medial reticular nuclei of the medulla and pons contained HRP-labeled perikarya, which were concentrated most heavily in the nuclei reticularis medullae oblongatae ventralis, gigantocellularis, and pontis caudalis predominantly ipsilateral to the injection. The medial vestibular nucleus was consistently labeled. HRP-labeled perikarya were found bilaterally within the commissural portion and in the medial part of the nucleus of the solitary tract on the side of the injection. The rostral portion of the PGCL receives afferents from some secondary auditory nuclei: the ipsilateral inferior colliculus and the posterior ventral cochlear nucleus bilaterally. Thus, the rostral PGCL may be involved in auditory feedback loops. The caudal raphe nuclei are a major source of afferents to the caudal PGCL. The lateral hypothalamic area, para ventricular nucleus, and zona incerta also contain labeled neurons when injections are centered in the caudal portion of the nucleus. Because of its connections, the PGCL may be divided into two subnuclei which roughly correlate with two cytoarchitecturally distinct regions (Andrezik et al. 1981). The rostral PGCL is involved in auditory reflexes. The entire PGCL but especially its caudal portion modulates autonomic reflexes which regulate the cardiovascular system and respiration. Analgesia resulting from electrical stimulation and injections of morphine or enkephalins probably are mediated by the caudal portion of the nucleus.