Enkephalin-like immunoreactivity in the mossy fiber pathway of the hippocampal formation of the tree shrew ( Tupaia glis)

Abstract

The distribution of enkephalin-like immunoreactivity within the hippocampal formation of the tree shrew ( Tupaia glis) has been investigated. By far the most conspicuous immunoreactive structures within the hippocampal formation were components of the mossy fiber pathway. Immunoreactive granule cells within the dentate gyrus could often be seen sending dendrites into the molecular layer and axons into the hilus of the dentate gyrus. Within the regio inferior of Ammon's horn, massive immunoreactive terminal swellings associated with thin fibers were located in the zone just above the pyramidal cell layer. While the mossy fiber pathway was the most intensely labeled portion of the hippocampal formation, occasionally sparse terminals and lightly immunoreactive cell bodies were noted in regio superior. These results indicate that the mossy fiber system may be an important pathway for opiate modulation of hippocampal activity.