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Projections from the periaqueductal gray matter to the B 3 cellular area (nucleus raphe magnus and nucleus reticularis paragigantocellularis) as revealed by the retrograde transport of horseradish peroxidase in the rat
Author(s) -
Fardin V.,
Oliveras J. L.,
Besson J. M.
Publication year - 1984
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.902230403
Subject(s) - nucleus raphe magnus , dorsal raphe nucleus , periaqueductal gray , serotonergic cell groups , nucleus , neuroscience , raphe nuclei , stimulation , anatomy , horseradish peroxidase , axoplasmic transport , biology , chemistry , midbrain , central nervous system , serotonin , serotonergic , receptor , biochemistry , enzyme
Afferent projections from the periaqueductal gray matter (PAG) to the B 3 region (nucleus raphe magnus, NRM; and nucleus reticularis paragigantocellularis, NPG) were examined by means of the horseradish peroxidase (HRP) method revealed by using the tetramethylbenzidine (TMB) procedure. Following iontophoretic injection of HRP into the B 3 cellular area, numerous labeled neurons were found between the third oculomotor complex and the rostral part of the tegmental nucleus dorsalis of Gudden. The most densely labeled regions were the lateral parts of the dorsal raphe nucleus (wings of the DRN) and Hamilton's nucleus dorsalis of the PAG. Very few neurons were found within the medial part of the DRN. In contrast, results with control injections performed outside the B 3 area gave a different distribution of labeled neurons. The functional significance of these connections, particularly those emanating from the wings of the DRN which represent new information, is briefly discussed with regard to mechanisms operative in the control of pain. Although the major PAG‐B 3 direct projections could underlie a role for the B 3 area in PAG‐induced analgesia, the comparison of our anatomical and behavioral results points out some problems. Indeed, there is no strict correlation between the location of stimulation sites which induce analgesia in the freely moving rats and the distribution within the PAG of B 3 projections. These observations lead us to question the role of direct PAG‐B 3 connections in the antinociception induced by PAG stimulation and alternative hypotheses are proposed.