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Modifications in the distribution of met-enkephalin in the cat spinal
cord after administration of clonidine. An immunocytochemical study
J. Vázquez1, R. Coveñas2, M. Muñoz3,
J.A. García3 and A. Victoria4
1Department of Morphological Sciences, School of Medicine,
University of Sevilla, Sevilla, 2Department of Cell Biology and Pathology,
School of Medicine, University of Salamanca, Salamanca, 3Service of Pediatry,
Children's Hospital, Sevilla and 4Department of Morphological Sciences,
School of Medicine, University of Valencia, Valencia, Spain
Offprint requests to: Prof.
Dr. José Vázquez, Departamento de Ciencias Morfológicas,
Facultad de Medicina, Universidad de Sevilla, Avda. Sánchez Pizjuan
s/n, 41009-Sevilla, Spain
Summary. We have studied the
modifications in the distribution of methionine-enkephalin in the cat spinal
cord after intravenous or intrathecal administration of clonidine by using
an immunocytochemical technique. In animals not treated with the substance,
a very high density of immunoreactive fibers was found in layers I and II;
a high density in the dorso-lateral funiculus and in the reticular formation;
a moderate density in layers III, IV and V; and a low density in layer VI.
However, after intravenous or intrathecal administration of clonidine a
decrease in fibers containing met-enkephalin was observed in layers I and
II (high or moderate density), the dorso-lateral funiculus, and the reticular
formation (moderate or low density), and in layers IV and V (low or very
low density). In all cases, the decrease in the immunoreactivity was more
marked when clonidine was administered intrathecally. Our results suggest
that clonidine induces the release of met-enkephalin in the spinal cord.
They further suggest that the opioid peptide released could be involved
in the control of nociceptive transmission by inhibiting the release of
neurotransmitters (e.g., substance P). In summary, our study shows that
clonidine could be involved in antinociceptive mechanisms in the cat spinal
cord. Histol. Histopathol. 13, 955-959 (1998)
Key words: Met-enkephalin,
Clonidine, Spinal cord, Immunocytochemistry, Cat
DOI: 10.14670/HH-13.955
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