The Nuclei of origin of monoaminergic, peptidergic, and cholinergic afferents to the cat nucleus reticularis magnocellularis: A double-labeling study with cholera toxin as a retrograde tracer

Abstract

Using a sensitive double‐immunostaining technique with nonconjugated cholera toxin B subunit (CT) as a retrograde tracer, we examined the cells of origin and the histochemical nature of afferents to the cat nucleus reticularis magnocellularis (Mc) of the medulla oblongata. After injections of CT confined to the Mc, we found that the major afferents to the Mc arise from: (1) the lateral part of the bed nucleus of the stria terminalis, the nucleus of the anterior commissure, the preoptic area, the central nucleus of the amygdala, the posterior hypothalamus, and the nucleus of the fields of Forel; (2) the Edinger‐Westphal nucleus, the mesencephalic reticular formation, and the ventrolateral part of the periaqueductal grey; (3) the nuclei locus coeruleus α (LCα), peri‐LCα, locus subcoeruleus, and reticularis pontis oralis and caudalis; (4) the caudal raphe nuclei; and (5) the nucleus reticularis ventralis of the medulla. Further, we found that the Mc receives serotoninergic, noradrenergic, dopaminergic, cholinergic, as well as several peptidergic afferents: (1) serotoninergic afferents arise mainly from the nuclei raphe pallidus (B2), magnus (B3), obscurus (B1), and dorsalis (B7); (2) catecholaminergic afferents to the Mc originate mostly in the A11 dopamine cell group in the posterior hypothalamic area and A6 and A7 noradrenaline cell groups located in the locus coeruleus complex, the Kölliker‐Fuse nucleus, and the nucleus parabrachialis lateralis; (3) cholinergic afferents originate in the dorsal pontine tegmentum (ch5 and 6) located in the pedonculopontine tegmental nucleus or Area X, the nuclei LCα, peri‐LCα, locus subcoeruleus, and laterodorsalis tegmenti; (4) methionine‐enkephalin‐like inputs to the Mc arise from the nuclei peri‐LCα, LCα, the nucleus locus subcoeruleus, the ventrolateral part of the periaqueductal grey, and the nucleus raphe pallidus; (5) substance P‐like inputs arise principally from the ventrolateral part of the periaqueductal grey, the preoptic area, and in and around the Edinger‐Westphal nucleus; (6) corticotropin‐releasing‐factor‐like afferents were found in the middle portion of the nucleus peri‐LCα, in and around the Edinger‐Westphal nucleus, and in the perifornical area of the hypothalamus; (7) somatostatin‐like inputs originate principally from the ventrolateral part of the periaqueductal grey; (8) galanin‐like afferents to the Mc originate exclusively from galanin‐like immunoreactive cell bodies located in the preoptic area; (9) alpha melanocyte‐stimulating‐hormone‐like (α‐MSH) inputs arise from α‐MSH‐like immunoreactive cells distributed diffusely in the lateral, dorsal and posterior hypothalamic areas; (10) some cholecystokinin‐like afferents also were observed in the ventrolateral part of the periaqueductal grey and in the Edinger‐Westphal nucleus. In the light of these anatomical data, we discussed the functions of the Mc neurons underlying the generation of locomotion, analgesia, atonia, and paradoxical sleep.