Adrenergic transmission in hippocampus-locus coeruleus double grafts in oculo: demonstration by in vivo electrochemical detection.

In vivo electrochemical detection was used to study transmitter release from a synaptically or pharmacologically stimulated noradrenergic isolated pathway formed by double in oculo brain tissue grafts. Retinal illumination, which activates cholinergic nerve fibers that grow into intraocular grafts from the autonomic ground plexus of the iris, produced increases in the concentration of electroactive species in the hippocampal portion of intraocular locus coeruleus-hippocampus double grafts. This response was potentiated after cholinesterase inhibition, and mimicked by perfusion of carbachol, a muscarinic agonist. Much smaller increases in the electroactive species were measured in reserpinized animals, and this minimal response was completely eliminated by the subsequent inhibition of catecholamine synthesis with alpha-methyl-p-tyrosine. Taken together, the data suggest that synaptically released transmitter in these isolated brain circuits can be measured using in vivo electrochemical detection techniques, and lend further support to the hypothesis that in oculo locus coeruleus grafts develop a functional catecholaminergic input to sequentially grafted hippocampus.