Processing of gustatory information by spiking local interneurons in the locust

Despite the importance of gustation, little is known of the central pathway s responsible for the processing and coding of different chemical stimuli. Here I have analyzed the responses of a population of spiking local interne urons, with somata at the ventral midline of the metathoracic ganglion, dur ing stimulation of chemo- and mechanoreceptors on the legs of locusts. Vola tile acidic stimuli were used to selectively activate the chemosensory neur ons. Different members of the population of local interneurons received dep olarizing or hyperpolarizing inputs during chemosensory stimulation. Many o f the same interneurons that received chemosensory input also received mech anosensory inputs from tactile hairs on the leg, but others received exclus ively mechanosensory inputs. Chemosensory inputs occurred with a short and constant latency, typical of monosynaptic connections. The chemosensory rec eptive fields of the spiking local interneurons mapped the surface of a hin d leg so that spatial information relating to the location of a taste recep tor was preserved. The amplitude of potentials in interneurons during chemo sensory stimulation varied in a graded manner along the long axis of the le g, thus creating gradients in the chemosensory receptive fields of inteneur ons. Some interneurons were depolarized to a greater extent by chemical sti muli applied to basiconic sensilla on distal parts of the leg, whereas othe rs were depolarized more by chemical stimulation of more proximal sensilla.