The Effects of Cooling on an Identified Reflex Pathway in the Cockroach (Periplaneta Americana), in Relation to Chill-Coma

Abstract

1. The effects of cooling were studied in relation to (a) the impairment of locomotion (i.e. chill-coma) and (b) the functioning of various components of the monosynaptic trochanteral hair plate reflex in the cockroach, Peri-planeta americana. 2. The mean temperature for onset of chill-coma was 10.5 °C. At this temperature animals were unable to right themselves and visible tremors of the legs and body occurred. 3. Extracellular recordings from metathoracic nerve 5 indicated that cooling from 24 to 15 °C caused a decrease in the background spiking rate of motor neurone Ds. However, cooling from 12 to 9 °C caused a marked increase in the spiking frequency of both Ds and other unidentified neurones. This increase in spiking activity is the probable basis of leg and body tremors that occur during chill-coma. 4. Monosynaptic coupling between hair plate afferent spikes and Ds spikes (following electrical stimulation of the hair plate) was markedly affected by cooling. At 25 °C, hair plate afferent and Ds spikes were always tightly coupled to one another, whereas at 10 °C coupling was very weak. Several lines of evidence suggest that this loss of coupling was the result of failure of central synaptic transmission. The reduced effectiveness of central synaptic transmission during cooling may be a critical factor in the impairment of locomotor ability associated with chill-coma.