Metabolism of histamine in the CNS of Aplysia californica: Cellular distribution of γ-glutamylhistamine synthetase

Abstract

1. The cellular distribution of the histamine-metabolizing enzyme, γ-glutamylhistamine synthetase, was studied in the CNS of Aplysia californica. 2. Enzyme activity was assayed in single, re-identifiable neuronal cell bodies, clusters of nerve cells and neuropil and capsule tissue surrounding the ganglia. 3. The “histaminergic” C-2 cells and all other single nerve cell bodies contained measurable γ-glutamylhistamine synthetase activity. 4. The cerebral E cluster, which houses the C-2 cells and several of its post-synaptic neurons, had an apparently higher specific enzyme activity than other neuronal clusters. 5. The rinding of measurable enzyme activity in the histamine-rich C-2 cell bodies and in clusters of cells responsive to this imidazoleamine supports the hypothesis that one function for γ-glutamylhistamine synthetase is in the disposal of neuronally released histamine. 6. The average specific activity of γ-glutamylhistamine synthetase in single cells was 3.64 ±0.32 μmol/g protein/hr. This represented only 5% of the enzyme activity measured in the whole ganglion. 7. The bulk of synthetase activity was found to reside in the capsule tissue.