THE LACTOSERIES CARBOHYDRATE ANTIGEN, Gal[beta]1-4GlcNAc-R, IS EXPRESSED BY A SUBPOPULATION OF CAPSAICIN SENSITIVE RAT SENSORY NEURONS. Del Mar, Lucinda P. and Reese S. Scroggs. University of Tennessee College of Medicine, Department of Anatomy and Neurobiology, 855 Monroe Avenue, Memphis, TN 38163.
APStracts 3:0125N, 1996.
SUMMARY AND CONCLUSIONS
1. The membrane properties of dorsal root ganglion (DRG) cells expressing the lactoseries carbohydrate antigen Gal[beta]1-4GlcNAc-R were studied and compared to those of DRG cells lacking this antigen. Acutely dissociated rat DRG cells which expressed Gal[beta]1-4GlcNAc-R on their outer cell membranes were detected using a primary monoclonal mouse IgM antibody (A5), directed against Gal[beta]1-4GlcNAc-R, and a fluorescent secondary antibody (fluorescein-conjugated goat anti-mouse IgM). 12.8 [mu] g/ml of A5 was found to be a saturating concentration of primary antibody, which labeled approximately 19% of the DRG cells. A battery of membrane properties including; AP duration, sensitivity to capsaicin, expression of I H , I A , Ca 2+ current subtypes (L, N, and T), and inhibition of high-threshold Ca 2+ currents by 5HT or 8-OH-DPAT was measured in DRG cells labeled (A5 + ) and unlabeled (A5 - ) by a saturating concentration of A5. 2. There was a significant difference in the number of capsaicin sensitive DRG cells and a significant difference in the magnitude of the capsaicin induced inward current in A5 + versus A5 - DRG cells. Thirty-three of 35 A5 + cells tested were sensitive to 1 [mu]M capsaicin, which produced an inward current averaging 4 nA 0.46 (n=33). In contrast, only 12 of 33 A5 - cells were sensitive to 1 [mu]M capsaicin, which produced an inward current averaging 1.2 nA +/- 0.52 (n=12). 3. There were also significant differences between A5 + and A5 - cells regarding average AP duration, N- and T-type Ca 2+ current amplitude, and number of cells which expressed I H and I A . A5 + cells had significantly larger N-type Ca 2+ currents, and expressed I A more frequently than A5 - cells. Conversely, A5 - cells had significantly longer AP duration, larger T-type Ca 2+ currents, and expressed I H currents more frequently compared to A5 + cells. 4. A5 + and A5 - cells differed regarding the inhibition of high-threshold Ca 2+ currents by maximal concentrations of 5HT 1A agonists (10 [mu]M 5HT or 1 [mu]M 8-OH-DPAT). Inhibition of Ca 2+ currents in A5 + cells by 1 [mu]M 8-OH-DPAT (n=15) or 10 [mu]M 5HT (n=18) averaged 4% +/- 0.9. In contrast, inhibition of Ca 2+ currents in A5 - cells by 10 [mu]M 5HT (n=33) averaged 20% +/- 3.8. 5. Cells for which sufficient data was collected were categorized as type 1, 2, 3, or 4 based on sensitivity to capsaicin, expression of I H , I A , and T-type Ca 2+ current amplitude, as described earlier (Cardenas et al., 1995), and the distribution of A5 + and A5 - cells among the various groups was observed. The categories were defined as follows: type 1 (capsaicin sensitive, no I H or I A ); type 2 ( capsaicin sensitive, significant I A ); type 3 (capsaicin insensitive, T-type Ca 2+ currents less than 1 nA, significant I H but no I A ); type 4 (capsaicin insensitive, T-type Ca 2+ currents greater than 2.4 nA). Based on this criteria, 6 of 15 type 1 cells, and all type 2 cells (n=19) were A5 + . All type 3 cells (n=8) and all type 4 cells (n=11) were A5 - . 6. As indicated above, the expression of the Gal[beta]1-4GlcNAc-R antigen differentiated two subgroups of DRG cells in the type 1 category (A5 + , n=6 and A5 - , n=9). These two groups varied regarding the sensitivity of Ca 2+ currents to maximally effective concentrations of 5HT 1A agonists. In type 1 A5 + DRG cells, high-threshold Ca 2+ currents were not significantly inhibited by 1 [mu]M 8-OH-DPAT (average inhibition = 1.2% +/- 0.8, n=6). However, in type 1 A5 - cells, high-threshold Ca 2+ currents were reduced 47% +/- 6.0 (n=9) by 10 [mu]M 5HT. 7. The several significant differences in membrane properties between A5 - and A5 + DRG cells suggests that the Gal[beta]1-4GlcNAc-R antigen is expressed by a distinct subset of DRG cells, consisting predominately of type 1 and type 2 cells. The observation that most A5 + DRG cells were capsaicin sensitive suggests that the Gal[beta]1-4GlcNAc-R antigen is expressed primarily by nociceptors. This idea is consistent with a previous study (Dodd and Jessell, 1985) which observed the Gal[beta]1-4GlcNAc-R antigen on a subpopulation of DRG neurons with afferent terminals in lamina I and II of the spinal cord, an important relay area for nociceptive information. 

Received 16 February 1996; accepted in final form 29 May 1996.
APS Manuscript Number J95-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 17 June 96