ULTRASTRUCTURAL RELATIONSHIPS OF SPINAL PRIMARY AFFERENT-FIBERS WITH NEURONAL AND NONNEURONAL CELLS IN THE MYENTERIC PLEXUS OF THE CAT ESOPHAGOGASTRIC JUNCTION

Spinal primary afferent fibres innervating the myenteric area in the o esophago-gastric junction of the cat were selectively labelled by ante rogradely transported cholera toxin B subunit-horseradish peroxidase c onjugate injected into thoracic dorsal root ganglia. The ultrastructur e of these labelled primary afferent fibres was studied in order to de termine whether they display close relationships with specific cell ty pes in the myenteric plexus. Horseradish peroxidase was revealed with tetramethylbenzidine stabilized with ammonium heptamolybdate or with t he tetramethylbenzidine/tungstate reaction in order to visualize the c ytoplasmic organelles and the axolemma, respectively. The labelled pri mary afferent fibres were unmyelinated. Two kinds of profiles of label led fibres containing vesicles and mitochondrial accumulations were fo und: (i) fibres running in myenteric connectives in isolated nerve bun dles, and (ii) fibres within the myenteric ganglia. The first kind had small areas of axolemma with no glial cell covering, whereas the seco nd kind had little or no glial cell covering (termed naked primary aff erent fibres). In addition, labelled fibres containing few vesicles an d mitochondria and running in nerve bundles surrounded by perineurium were numerous. Within the myenteric ganglia, naked primary afferent fi bres contacted myenteric neurons. The contacts were mainly axosomatic. No synaptic specializations were distinguished. In the interganglioni c area, some labelled fibres terminated close to blood vessels. The in traganglionic naked primary afferent fibres are suggested to be mechan oreceptors. Their exposed axolemma might allow both mechanotransductio n and release of neurotransmitters which could act on myenteric neuron s. Because they are protected by their glial cell sheath and by bundle s of collagen fibrils, interganglionic primary afferent fibres are lik ely to be less exposed to deformation. (C) 1997 IBRO. Published by Els evier Science Ltd.