CULTURED OLFACTORY INTERNEURONS FROM LIMAX-MAXIMUS - OPTICAL AND ELECTROPHYSIOLOGICAL STUDIES OF TRANSMITTER-EVOKED RESPONSES

1. The olfactory processing network in the procerebral (PC) lobe of th e terrestrial mollusk Limax maximus exhibits a coherent oscillation of local field potential that is modulated by odor input. To understand the cellular basis of this oscillation, we developed a cell culture pr eparation of isolated PC neurons and studied the responses of isolated cells to stimulation with neurotransmitters known to be present in th e PC lobe. 2. The distribution of PC soma diameters suggests at least two different populations of neurons. Approximately 95% of isolated ce lls had soma diameters of 7-8 mum, with the remaining cells having lar ger diameters (10-15 mum). 3. Extracellular measurements of action pot entials and optical measurements of intracellular calcium concentratio ns in fura-2-loaded cells were made. Serotonin and dopamine excited PC neurons and promoted transitions from steady to bursty activity. Both amines elicited increases in intracellular calcium, presumably concom itant with the increase in action-potential frequency. 4. Glutamate su ppressed action-potential firing and reduced intracellular calcium. Th is effect was seen most clearly when glutamate was applied to cells ex cited by high potassium medium. Quisqualate is an effective glutamate agonist in this system, whereas kainate is not. 5. Combined with anato mic and biochemical data and with studies of the effects of these neur otransmitters on the oscillating local field potential of the intact P C network, the data from isolated PC neurons are consistent with the h ypothesis that dopamine and serotonin modulate network dynamics, where as glutamate is involved in generating the basic oscillation of local field potential in the PC. 6. The optical studies of fura-2-loaded cel ls showed that several treatments that increase the rate of action-pot ential production lead to elevations in intracellular calcium. Optical studies of intracellular calcium may be useful for multisite measurem ents of activity in the intact, oscillating PC lobe network.