Gamma-aminobutyric acid ( GABA ) is a widely occurring inhibitory neurotransmitter in vertebrate and invertebrate neural tissue. To explore the role of GABA as a putative neurotransmitter in the optic lobes of the crab Hemigrapsus nudus,
light microscope autoradiography ( LM ARG ), light microscope immunocytochemistry ( LM ICC ), and neurochemical techniques were employed. ARG labeling of 3H-GABA was observed over specific neuronal cell bodies and axon fibers in the two outer optic neuropils, the lamina ganglionaris and the medulla externa. Biochemical analysis of 3H-GABA uptake revealed little surface receptor binding as picrotoxin and bicuculline did not appear to effect uptake. Similar biochemical experiments showed little glial . involvement. 2,4-diaminobutyrate ( L-DABA ), shown in other studies to preferentially inhibit uptake by neurons but not glia, matched the degree of inhibition of uptake seen by unlabeled GABA, which affects uptake by neurons and glia equally. p-Alanine, which has the reverse effect of L-DABA, reduced uptake only slightly more than seen in untreated eyes. Hence, ARG labeling was primarily intracellular and confined to neurons.
LM ICC staining of GABA was found in specific neurons in the same regions of the neuropils which tested positive by ARG. In addition to verifying the presence of endogenous GABA, ICC findings support the assumption that uptake of exogenous GABA occurs in cells that contain and presumably use that transmitter.
Neurochemical analysis of uptake describe a high-affinity, sodiumdependent, metabolically active process, findings similar to uptake mechanisms described for GABA in vertebrate central nervous system and retinal tissue. Release of label from preloaded eyes was effected in a dose-dependent manner using high concentrations of potassium. Neither uptake nor release appeared to involve the cytoskeletal elements actin or tubulin as cytochalasin B and colchicine did not effect either process.
Results described above establish GABA as a putative neurotransmitter in the optic lobes of the eye of Hemigrapsus nudus.
Demonstration of the presence of endogenous GABA in specific neurons, uptake of 3H-GABA into specific neurons by a high-affinity, sodium-dependent, metabolically active process, and demonstration of release of 3H-GABA satisfy half of the criteria for establishing a substance as a neurotransmitter.
Robert W. Teel
Ramon G. Gonzalez
Robert L. Schultz
John W. Patrickson
Doctor of Philosophy (PhD)
Year Degree Awarded
Date (Title Page)
Library of Congress/MESH Subject Headings
Crabs -- physiology; Gaba; Neuroregulators
Loma Linda University Libraries
This title appears here courtesy of the author, who has granted Loma Linda University a limited, non-exclusive right to make this publication available to the public. The author retains all other copyrights.
Fulenwider, Carol L., "GABA as a Putative Neurotransmitter in the Optic Lobes of the Crab HEMIGRAPSUS NUDUS" (1991). Loma Linda University Electronic Theses, Dissertations & Projects. 581.
Loma Linda University Electronic Theses and Dissertations
Loma Linda University. Del E. Webb Memorial Library. University Archives