- Email: [email protected]
Peptide coexistence in axon terminals within the superficial laminae of the rat spinal cord
S198
EFFECTS OF ALPHA ADRENOCEPTOB AGONISTS ON THE EXCITABILITY OF PRIMARY AFFERENT TERMINALS OF CUTANEOUS FIBRES IN THE CAT SPINAL CORD. 0. Calvillol, M. Ghignone*l, L. Quintin* Dept. of Anesthesiologyl,TTUHSC, Lubbock, TX. 79430 Aim of Investigation: Alpha adrenoceptor agonists have well defined antinociceptive properties, however their mechanism of action is not well understood. Changes in excitability of primary afferent terminals of cutaneous C fibres could help explain the mechanism of antinociceptionof alpha adrenoceptor agonists. Experiments were done on cats (n=22) anesthetizedwith Methods: Nembutal. The lumbosacral spinal cord was exposed and transected at T13. Primary afferent terminal excitability was tested using conventional techniques. Results: Clonidine (an alpha 2 agonist) i.v. in doses of l-5 ng/kg increased the excitabilitv of C fibre terminals bv about 60% in 12 cats (r= .62, p= 0.0011, yohimbine i.v. (loo-iOOpg/kg) in 6 cats, and phentolamine i.v. (100-500 pg/kg) in 6 other cats reversed the effects of clonidine to near control values. ST587 (an alpha 1 agonist) in doses of lo-50 pg/kg decreased the excitability of both A and C fibres terminal by about 20% (r=.48 p= 0.001) in 10 cats. These effects of ST587 were reversed to control valves by prazosin (15-50 ug/kg). Discussion: Clonidine increased the excitability of C fibres thus signaling primary afferent depolarization (PAD) therefore probably leading to presynaptic inhibition. ST587 decreased terminal excitability indicating primary afferent hyperpolarization (PAH). PAH is usually associated with presynaptic facilitation thus it is not immediately obvious how alpha 1 agonists cause antinociception. It is possible that a 20% reduction in C fibre terminal excitability could lead to inhibition, since C fibres have low safety factor of transmission. PEPTIDE COEXISTENCE IN AXON TERMINALS WITHIN THE SUPEHFICIAL jC4 Poster LAMINAE OF THE RAT SPINAL CORD. M.B. Plenderleith*,C. 'Tues.Room 3 Haller*, A.A. Cameron* and P.J. Snow, Department of Anatomy, Board 144 I Queensland University, St. Lucia, 4067, Australia. Aim of Investigation: Although a number of neuroactive peptides have been shown to coexist within the cell bodies of some unmyelinated primary afferent fibres (C-fibres),there appears no obvious correlation between the nature of the stimuli which activate a cell and the pattern of peptides it contains. However, the possibility still exists that these multiple peptide containing cells may only express a single peptide at their central terminals. The aim of this study was to address this question directly by determining whether the peptides substance P (sP1 and Calcitonin GeneRelated Peptide (CGRP) coexist within single axon terminals within the superficial laminae of the rat spinal cord. Methods: The Protein A-gold technique was used to locate both sP and CGRwimmunoreactivity (-LI) on ultrathin sections cut from resin embedded portions lof the dorsal horn of the rat spinal cord. Gold probes were freshly prepared using the Tannic acid technique. Results: Using different sized gold particles to label antisera to SP and CGRP we have found a high degree of coexistence of these peptides within axon terminals within the superficial laminae. Most (althoughnot all) terminal profiles examined showing CGRP-LI also exhibited sP-LI. Conclusion: Previously it has been shown that SP and CGRP coexist within cells in the rat dorsal root ganglia. The size, location and morphology of some of the terminal boutons in which we have found sP- and CGPP-LI would suggest that they are of primary afferent origin. It thus seems likely that the central terminals of C-fibres, like their parent cell bodies, exhibit peptide coexistence.
EFFECTS OF ALPHA ADRENOCEPTOB AGONISTS ON THE EXCITABILITY OF PRIMARY AFFERENT TERMINALS OF CUTANEOUS FIBRES IN THE CAT SPINAL CORD. 0. Calvillol, M. Ghignone*l, L. Quintin* Dept. of Anesthesiologyl,TTUHSC, Lubbock, TX. 79430 Aim of Investigation: Alpha adrenoceptor agonists have well defined antinociceptive properties, however their mechanism of action is not well understood. Changes in excitability of primary afferent terminals of cutaneous C fibres could help explain the mechanism of antinociceptionof alpha adrenoceptor agonists. Experiments were done on cats (n=22) anesthetizedwith Methods: Nembutal. The lumbosacral spinal cord was exposed and transected at T13. Primary afferent terminal excitability was tested using conventional techniques. Results: Clonidine (an alpha 2 agonist) i.v. in doses of l-5 ng/kg increased the excitabilitv of C fibre terminals bv about 60% in 12 cats (r= .62, p= 0.0011, yohimbine i.v. (loo-iOOpg/kg) in 6 cats, and phentolamine i.v. (100-500 pg/kg) in 6 other cats reversed the effects of clonidine to near control values. ST587 (an alpha 1 agonist) in doses of lo-50 pg/kg decreased the excitability of both A and C fibres terminal by about 20% (r=.48 p= 0.001) in 10 cats. These effects of ST587 were reversed to control valves by prazosin (15-50 ug/kg). Discussion: Clonidine increased the excitability of C fibres thus signaling primary afferent depolarization (PAD) therefore probably leading to presynaptic inhibition. ST587 decreased terminal excitability indicating primary afferent hyperpolarization (PAH). PAH is usually associated with presynaptic facilitation thus it is not immediately obvious how alpha 1 agonists cause antinociception. It is possible that a 20% reduction in C fibre terminal excitability could lead to inhibition, since C fibres have low safety factor of transmission. PEPTIDE COEXISTENCE IN AXON TERMINALS WITHIN THE SUPEHFICIAL jC4 Poster LAMINAE OF THE RAT SPINAL CORD. M.B. Plenderleith*,C. 'Tues.Room 3 Haller*, A.A. Cameron* and P.J. Snow, Department of Anatomy, Board 144 I Queensland University, St. Lucia, 4067, Australia. Aim of Investigation: Although a number of neuroactive peptides have been shown to coexist within the cell bodies of some unmyelinated primary afferent fibres (C-fibres),there appears no obvious correlation between the nature of the stimuli which activate a cell and the pattern of peptides it contains. However, the possibility still exists that these multiple peptide containing cells may only express a single peptide at their central terminals. The aim of this study was to address this question directly by determining whether the peptides substance P (sP1 and Calcitonin GeneRelated Peptide (CGRP) coexist within single axon terminals within the superficial laminae of the rat spinal cord. Methods: The Protein A-gold technique was used to locate both sP and CGRwimmunoreactivity (-LI) on ultrathin sections cut from resin embedded portions lof the dorsal horn of the rat spinal cord. Gold probes were freshly prepared using the Tannic acid technique. Results: Using different sized gold particles to label antisera to SP and CGRP we have found a high degree of coexistence of these peptides within axon terminals within the superficial laminae. Most (althoughnot all) terminal profiles examined showing CGRP-LI also exhibited sP-LI. Conclusion: Previously it has been shown that SP and CGRP coexist within cells in the rat dorsal root ganglia. The size, location and morphology of some of the terminal boutons in which we have found sP- and CGPP-LI would suggest that they are of primary afferent origin. It thus seems likely that the central terminals of C-fibres, like their parent cell bodies, exhibit peptide coexistence.