Syntaxin 1A and 1B display distinct distribution patterns in the rat peripheral nervous system.

Syntaxin 1 has been shown to play an outstanding role in synaptic vesicle exocytosis. Two isoforms of this protein are expressed in neurons, syntaxin 1A and 1B. However, the physiological significance of the occurrence of such closely related isoforms is not still understood. Here, by means of isoform-specific immunocytochemistry, we show that syntaxin 1A and 1B display different patterns of expression in the rat peripheral nervous system. Nerve terminals of sensory neurons reaching the spinal cord were clearly enriched in immunoreactive syntaxin 1A. Both isoforms were detected in cell bodies of sensory neurons at the dorsal root ganglia, although specific immunolabelling displayed very different patterns at the cellular level. Motor endplates and muscle spindles were only immunostained for syntaxin 1B. Syntaxin 1A was mainly associated with nerve fibres reaching small blood vessels. In addition, nerve plexuses of the enteric nervous system showed immunostaining for both syntaxin isoforms. The different distribution pattern of the two neuronal syntaxin isoforms in the rat peripheral nervous system could be related to isoform-specific biochemical properties involved in the exocytotic process.