Opiates acting upon receptors in brainstem and spinal cord will inhibit the transmission or spinal nociceptive transmission by a direct effect at the spinal level and indirectly in brainstem by the activation of bulbospinal monoamine pathways. Employing systems which permit local perfusion of the mesencephalic aqueduct (adjacent to the periaqueductal gray: PAG) and a novel spinal perfusion procedure developed in our laboratory, we demonstrated, under the auspices of NS16541-1 and 2, that high, but not low intensity stimulation of somatic afferents will release serotonin (5-HT) and norepinephrine (NE) from spinal cord and methionine-enkephalin-like immunoreactivity (MELI) from PAG and cord. Preliminary data using column-coupled radioreceptor assays further has indicated that other fractions, appearing to resemble the hepta- and hexa-enkephalinoid peptides and a second class resembling the dynorphin-related peptides are released into spinal perfusates by somatic stimulation. In light of the work we have thus far carried out, we will continue using mesencephalic and spinal superfusion to study the physiology and functional connectivity of the brainstem systems from which a) the spinal monoamines are released and b) the brainstem and spinal systems from which the distinguishable classes of enkephalinoid peptides are released in vivo. Particular emphasis will be placed on the relationship between ascending and descending systems and endorphin release. We will seek to compare the relative quantities of each of the several endorphin fractions released from brain and cord after a variety of physiological manipulations including stimulation of primary afferents and direct activation of descending pathways. Frequency dependency of this release and that of the spinal monoamines will be compared. These observations obtained with our superfusion procedures provide, firstly, novel insights into the connectivity of pharmacologically defined spinally-directed modulatory systems which appear to be reflexly activated to modulate rostrad sensory transmission. Secondly, our ability to measure these novel materials will permit us to extend, in vivo in a relatively simple and accessible system--the spinal cord--the essential question of whether these materials meet one of the primary criteria for a neurotransmitter, e.g. are they released in consequence to neural activity? Thirdly, our understanding of the pharmacology of spinal modulatory systems provides insight into CNS pain mechanisms.
Showing the most recent 10 out of 99 publications
