Research paperSpinal pharmacology of antinociception produced by microinjection of μ or δ opioid receptor agonists in the ventromedial medulla of the rat
Section snippets
Abbreviations used in the figures
- dcn
dorsal cochlear nucleus
- icp
inferior cerebellar peduncle
- ngc
nucleus reticularis gigantocellularis
- nV
spinal trigeminal nucleus
- nVII
facial motor nucleus
- P
pyramid
- tb
trapezoid body
- 7g
genu of the seventh cranial nerve
- 7t
tract of the seventh cranial nerve
Experimental procedures
These experiments were approved by the Institutional Animal Care and Use Committee of the University of Chicago. All procedures were conducted in accordance with the “Guide for Care and Use of Laboratory Animals” published by the National Institutes of Health and the ethical guidelines of the International Association for the Study of Pain. Every effort was made to minimize animal suffering and to limit the number of animals used.
Microinjection sites
Histological analysis revealed a comparable distribution of injection sites throughout the rostral-caudal extent of the NRM and NGCpα in each treatment group. Some sites that impinged on the rostral edge of the nucleus reticularis paragigantocellularis lateralis were included in the NGCpα for purposes of data analysis. Fig. 1 illustrates the distribution of injection sites for a representative treatment group. Microinjection of DPDPE, DELT or DAMGO at sites outside these two nuclei, such as the
Activation of δ1, δ2 or μ opioid receptors in the rvm produces antinociception
The NRM and NGCpα are often considered to be a functional unit because electrical or chemical activation of neurons in either region can produce similar antinociceptive effects. However, substantial pharmacological and anatomical evidence indicates that the afferent and efferent connections of these two nuclei and their neurotransmitter content are not identical. For example, the antinociception produced by electrical stimulation or microinjection of L-glutamate in the NRM or NGCpα can be
Acknowledgements
This study was supported by U.S. Public Health Service grants DA06736 (D.L.H.) and DA05784 (R.W.H.) from the National Institute on Drug Abuse. We thank Sanjay N. Thorat, Kenneth Park, and Laura Skrocki for their assistance with aspects of this work.
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