Evidence against a neurotransmitter role of aspartate in primary afferent terminals
Field:	Sensory systems
Authors:	Larsson, Max Broman, Jonas
Address of presenting author:	Dept of Physiological Sciences Sölvegatan 19 S-223 62 LUND Sweden
E-mail:	max.larsson.351@student.lu.se
Phone:	+46 46 2227781
Fax:	+46 46 2224546
Text of abstract:	Since L-aspartate is a potent agonist of NMDA receptors, it has been proposed to act alongside glutamate as an excitatory neurotransmitter. However, the role of L-aspartate as a neurotransmitter in primary afferent synapses in the spinal cord dorsal horn is disputed. To further investigate this issue, we have used immunogold labeling to examine the presence of aspartate-like immunoreactivity in primary afferent nerve terminals and other tissue components in laminae I-IV of the rat dorsal horn, as well as the correlation between aspartate-like immunoreactivity and the density of synaptic vesicles in primary afferent terminals in laminae II-IV. Low levels of aspartate, similar to those detected in presumed inhibitory terminals and lower than those of neuronal cell bodies, were found in primary afferent terminals in laminae I and III-IV (identified by anterograde transport of choleragenoid-horseradish peroxidase conjugate) and in presumed C fiber terminals in lamina II. No significant correlation between the density of gold particles and synaptic vesicles was detected in any of the examined terminal populations. These results indicate low levels and a non-vesicular localization of aspartate in primary afferent terminals and suggest that aspartate does not function as a primary afferent neurotransmitter.
Keywords:	immunogold, dorsal horn, pain, choleragenoid

Created 2000-03-15