Immunohistochemical analysis of the relation between 5-hydroxytryptamine- and neuropeptide-immunoreactive elements in the spinal cord of an amphibian (Xenopus laevis).
In mammals, a large proportion of the bulbospinal 5-hydroxytryptamine (5-HT) neurons also contain neuropeptides, such as substance P (SP) and galanin (GAL). To examine whether a similar coexistence occurs in an amphibian, an immunofluorescence double-labelling technique was employed on sections of the Xenopus laevis spinal cord. Antisera raised against SP, GAL, enkephalin (ENK), corticotropin-releasing factor (CRF), calcitonin gene-related peptide (CGRP), and cholecystokinin (CCK) produced a labelling of fibers at all rostrocaudal levels of the spinal cord, with the highest fiber densities for SP and ENK and intermediate densities for GAL, CCK, and CGRP, while CRF-immunoreactive fibers were barely detectable in intact animals. 5-HT-immunoreactive fibers were widely distributed in the spinal cord, and they often occurred in the vicinity of different types of peptide-immunoreactive fibers. However, no coexistence between 5-HT and the different peptide immunoreactivities could be detected, although SP and GAL immunoreactivities were sometimes found to be colocalized in the same fiber. Similar negative results were obtained when 5-HT+SP- and 5-HT+GAL-labelled sections were examined in single focal planes with a confocal microscope. After a spinal transection, (survival period 6 weeks to 4 months), almost all 5-HT-immunoreactive fibers below the lesion were lost, and a build-up of immunoreactive material occurred in fibers just rostral to the cut. In contrast, no significant loss of peptide-immunoreactive fibers occurred, although some swollen SP-, GAL-, ENK-, CRF-, and CCK-immunoreactive fibers were present rostral to the cut. The distribution of swollen peptide-immunoreactive fibers did not overlap with that of the swollen 5-HT-immunoreactive fibers. Although negative immunohistochemical data must be interpreted with caution, in conjunction with previous studies (Brodin et al. [1988] J. Comp. Neurol. 271:1-18; Sakamoto and Atsumi [1991] Cell Tissue Res. 264:221-230), the present results indicate that bulbospinal 5-HT neurons in nonmammalian vertebrates cocontain neuropeptides to a lesser extent than in mammals.
Pieribone
V A
VA
Department of Histology and Neurobiology, Karolinska Institute, Stockholm, Sweden.
Brodin
L
L
Hökfelt
T
T
D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000032:analysis; D002766:Cholecystokinin / Q000032:analysis; D003346:Corticotropin-Releasing Hormone / Q000032:analysis; D004745:Enkephalins / Q000032:analysis; D005260:Female; D019004:Galanin; D007150:Immunohistochemistry; D008297:Male; D009412:Nerve Fibers / Q000737:chemistry; D009479:Neuropeptides / Q000032:analysis*; D010455:Peptides / Q000032:analysis; D012701:Serotonin / Q000032:analysis*; D013116:Spinal Cord / Q000737:chemistry*; D013373:Substance P / Q000032:analysis; D014982:Xenopus laevis / Q000378:metabolism*
D004745:Enkephalins; D009479:Neuropeptides; D010455:Peptides; D012701:Serotonin; D013373:Substance P; D019004:Galanin; D002766:Cholecystokinin; D003346:Corticotropin-Releasing Hormone; D015740:Calcitonin Gene-Related Peptide