The Effects of Some Neuronal Drugs On the Settling Behaviour of Hemileucine Moths

Abstract

Abstract1. The walking behaviour of Automeris aspera was examined as one of the factors which contribute to the variability of the rocking score in this species. When walking precedes settling it potentiates the rocking score, so that the further an animal has walked the more likely it is to give its maximum response. However, the strength of walking does not determine that maximum. It is argued that walking acts by priming the rocking system directly. 2. The administration of physostigmine to some species of Hemileucine moths will quantitatively alter the rocking response, so that the number of rocks an animal will give at any time is increased (lowest dose used: 5 microlitres 1 : 25,000 W/V). The qualitative form of the response is unaltered. The effect is dosage dependent: higher concentrations raise the score more rapidly than lower. At low concentrations the maximum response induced by physostigmine appears to be stable for several hours. There is a correlation between the maximum response obtained before the drug is given and that obtained after, though the two ranges scarcely overlap. 3. Except when the increment is very great, the potentiation imposed by physostigmine does not prevent a further potentiation of the rocking score by walking. Similarly, despite the action of physostigmine (a) factors inhibiting rocking continue to do so, (b) inter-specific variations in the form of the response are still present. However, response waning in Hylesia nigricans, which in this species is shown to be partially a property of the rocking system, was not apparent after preparations had been treated with physostigmine. 4. Nicotine does not affect the rocking score at low concentrations, while at higher concentrations rapid knockdown precludes the observation of any change. 5. Pilocarpine (lowest dose 10 microlitres 1 : 10,000 W/V) raises the rocking score, though the increment wanes rapidly, and large increments appear to result from successive re-excitations of the response. 6. Atropine (threshold dose 5 microlitres 1 : 15,000 W/V) reduces the rocking score, and the reduction is dosage dependent. The decrement may be partially, though unreliably obviated by the prior occurrence of walking, or by the administration of physostigmine. 7. Automeris nyctimane leucane differs from Automeris aspera; whereas the rocking response of both species is similarly affected by atropine, physostigmine only affects Automeris aspera. 8. The effects of all these drugs, unlike those produced by the metabolic inhibitors previously examined (BLEST and COLLETT, 1963), are not dependent on the performance of the response.