Deutocerebral interneurons responding to thermal stimulation on the antennae of the cockroach,Periplaneta americana L.

Abstract

Thermoreception is indispensable in insects to find desired temperature, to avoid lethal temperature, to thermally regulate their habitat, or to detect their host [1]. There have been a number of physiological and morphological studies on insect thermoreceptors [2]. Thus, we know now that all or most insects are equipped with thermoreceptors on antennae, with which they detect temperature and /o r temperature changes in their environments [3]. Furthermore, some models for the primary mechanism of thermoreception have been recently proposed [4]. However, only little is known about the processing of thermal information in insect brains [5]. Here we show some morphological and physiological characteristics of thermal responsive interneurons in the deutocerebrum of Periplaneta americana. An adult male cockroach reared at a constant temperature (25°C) was lightly anesthetized with CO2, and was waxed in an acrylic chamber. The brain was carefully exposed by opening the small rectangular window between the compound eyes on the head capsule, and was immersed in the saline. A reference electrode of AgCl-coated silver wire was placed under the brain. A glass microelectrode filled with cobaltlysine and 2.5 M KC1 mixture was used for intracellular recording and staining. The methods of thermal stimulation of the antennae were similar to those described in [6]. After intracellular recording of its thermal responses, we stained each neuron by iontophoretic injection of cobalt-lysine ( + 1 0 nA, 1 Hz, 500 ms duration, 5 1 5 min). Following diffusion of cobalt-lysine, the brain was dissected from the head and fixed in Carnoy's fixative. Thereafter the stain was intensified with silver [7], and the brain was dehydrated in ethanol and cleared with methyl sa-