Labellar Sensilla Research Articles

The sensory control of motor output in fly proboscis extension

Proboscis extension, the initial sequence of feeding behavior in the blowfly, Phormia regina, can be induced by sucrose stimulation of a single labellar sensillum. Exploiting the ability to record single unit sensory input from labellar sensilla and single unit motor output from the extensor of the haustellum, I have investigated the degree of control exerted by the sensory spike train from the sugar receptors on motor output. Extension of the proboscis can be triggered by temporal summation of sensory activity during a 20 millisecond period after the first sensory spike (Fig. 1, Tables 1, 2). The duration and number of muscle spikes per motor response are determined in part by the sensory frequency and duration of sensory input (Figs. 2, 3). Habituation of the motor response to repeated stimulation of a single sugar receptor occurs and is independent of activity in other sugar receptors (Fig. 4). A role for receptor adaptation and habituation at central synapses in determining the duration and number of spikes per motor response is postulated. Nonlinear summation between spatially separate sensory inputs was found and is discussed in terms of the findings from stimulation of single receptors. (Figs. 5, 6) A minimal neuronal model to account for motor activity in response to labellar sugar receptor activity is proposed (Fig. 7).

The effect of aqueous solutions of some 1:1 electrolytes on the electrical response of the type 1 (‘salt’) chemoreceptor cell in the labella of Phormia

The former classification of the four known chemoreceptor cells in the labellar sensilla trichodea of Phormia regina (salt, sugar, water, and anion receptors) is rejected as too teleological and replaced by types 1, 2, 3, and 4 respectively. The effects of solutions of monovalent ion-pair (1:1) electrolytes on both action potential and receptor potential modulated electrical responses of the type 1 cell are re-examined. Unstimulated response with the sensillum can only be detected in types 1 and 3 cells; in the former the mean frequency of discharge of action potentials (APGF) is 2·5 impulses/sec. The APGF of the type 1 cell is plotted against stimulus activity of KCl, KBr, KI, and NaCl at constant temperature for an instant 0·35 sec after the commencement of stimulation. Mean time-courses of APGF are plotted against elapsed stimulation time for several activities of NaCl and KCl stimulus solutions. A build-up of APGF is always observed in the initial 10 to 30 msec of response before the adapting decline. Relative d.c. displacements representing changes in potential across the receptor membrane are plotted against the activity of stimulus electrolyte for KCl, KBr, and KI. Solutions of choline chloride suppress unstimulated discharge of the type 1 cell at high concentrations (1–3 M), and cause hyperpolarization of the receptor membrane. This may be due to excess chloride ion on the outside of the receptor membrane in the presence of large, non-permeant cations. Abbreviations and symbols: APGF Frequency of generation of action potentials f i , f i Individual and mean APGF at any given instant f s , f s Individual and mean APGF at t s = 0·35 sec representing ‘steady state’ of response f u , f u Individual and mean APGF when receptor is not stimulated t s Time elapsed since the commencement of stimulation a ± Mean electrolytic activity of a given component of the stimulus solution Other symbols are defined where they appear in the text

Mode of action of straight chain hydrocarbons on primary chemoreceptors of the blowfly, Phormia regina.

AbstractThe fundamental actions of straight‐chain hydrocarbons on the three known primary chemoreceptor cell types of the blowfly, Phormia regina, were studied in quantitative terms. Lower alcohols and long‐chain amines act in two stages: first a reversible inhibition, and then injury, of the salt, water, and sugar receptors in the labellar sensilla. The primary effects on salt and water receptors resemble hydrocarbon narcosis of nerve. Effects on sugar receptors, when analyzed kinetically, superficially resemble competitive inhibition. Other evidence, however, indicates that a non‐specific effect on sugar receptor sites is more likely. The electrophysiological results from labellar chemoreceptors indicate that the previously reported hydrocarbon behavioral rejection thresholds are best explained by the inhibition of the sugar receptors. This conclusion is strengthened by further electrophysiological and behavioral tests on tarsal chemoreceptors.