ORTHODROMICALLY AND ANTIDROMICALLY EVOKED LOCAL-FIELD POTENTIALS IN THE CRAYFISH OLFACTORY LOBE

A local field potential, consistent in form and duration, can be recor ded from the olfactory lobe of crayfish following electrical stimulati on of the outer flagellum of the antennule. The field potential is rev ersibly blocked by perfusion of the brain with low-[Ca2+] saline or ga mma-aminobutyric acid and, to a lesser extent, histamine. Paired shock s to the antennule and antidromic electrical stimulation of olfactory lobe output neurones also partially block the field potential. Compari ng the field potential with simultaneously recorded intracellular resp onses of olfactory interneurones reveals a coincidence between excitat ory and inhibitory effects in the interneurones and the appearance of identifiable components of the field potential. We interpret the held potential to reflect the response of neural elements in the olfactory lobe to orthodromic activity in the axons of the olfactory receptor ne urones on the antennule, We conclude from the blocking experiments tha t the greater part of the field potential stems from neurones in the o lfactory lobe that are postsynaptic to olfactory receptor neurones. As such, it provides a robust indication of olfactory neurone activity.