Integration of hydrodynamic and odorant inputs by local interneurons of the crayfish deutocerebrum

Intracellular electrodes were used to record from local interneurons in the olfactory lobes of the midbrain in the crayfish Procambarus clarkii. Cells that resembled previously studied central targets of olfactory receptor neurons on the lateral antennular flagellum were specifically examined for their responses to hydrodynamic stimuli. Initiation of water movement past the antennular flagellum, confined within an olfactometer, evoked a triphasic excitatory-inhibitory-excitatory postsynaptic potential lasting up to 2 s that generated spikes on depolarizing phases of the response sequence. Odorant pulses seamlessly imbedded in the water pulse past the antennule evoked purely excitatory, dose-dependent postsynaptic responses and associated spike trains. The latency of the initial phase of the response to water was approximately half as long as the latency of the response to odorant, suggesting that different afferent pathways are involved in responses to hydrodynamic and odorant stimuli, respectively. In some olfactory lobe interneurons that resembled previously described cells classified as Type I, conjoint stimulation of fluid onset and odorant evoked responses that were twice the amplitude of the summed response to either hydrodynamic or odorant stimulation alone, suggesting that the olfactory responses were potentiated by hydrodynamic input. Individuals of at least one other class of first-order interneuron that responded to both hydrodynamic and odorant stimulation were occasionally recorded from. These results indicate that multimodal integration of chemical and mechanical information occurs at the level of first-order sensory interneurons in the crayfish brain.