Chemo-discriminatory neurones in the sub-oesophageal ganglion of Locusta migratoria

The sub-oesophageal ganglion of Locusta migratoria was searched for neurone s responsive to stimulation of the maxillary palps using intracellular reco rding techniques. Two plant stimuli were used: wheat, a host plant and cabb age, an unacceptable non-host plant. The stimuli were presented to the palp as both intact leaf tissue and as droplets of aqueous solutions of plant e xtracts. All the sampled neurones that responded to stimulation of the palp also responded to simple mechanical stimulation. However, 25% of the neuro nes exhibited consistent differences in response to the two plants when pre sented as both leaf tissue and droplets, strongly suggesting that they also received a chemosensory input. These differential responses most commonly took the form of differences in the duration of cell activity and/or variat ion in the latency of the onset of response. The receptive fields of differ entially responding neurones were confined to the maxillary palp, or at mos t to the maxillary and labial palps.