PHYSIOLOGICAL-PROPERTIES OF AN IDENTIFIED GIANT INTERNEURON (GI4) AS RELATED TO THE ESCAPE AND FLIGHT CIRCUITRIES OF THE COCKROACH PERIPLANETA-AMERICANA

The cockroach's giant interneurons (GIs) are known to mediate escape a nd Right behaviors. The ventral group of giant interneurons (vGIs) (nu mbered 1, 2 and 3) mediates ground escape and the dorsal group (dGIs) (numbered 5, 6 and 7) mediates flight. Giant interneuron number 4 is t he only one of the seven abdominal identified giant interneurons of th e cockroach whose function in escape or Right has been hardly investig ated. It shows some morphological characteristics of a vental giant in terneuron while others are those of a dorsal giant interneuron. Likewi se, in this paper, T show that interneuron 4 presents some intermediat e physiological properties, some of which are characteristic of a vGI and others of a dGI. For instance: like the ventrals, interneuron 4 do es not fire strongly at the onset of Right and does not initiate Right . Like the dorsals, interneuron 4 is not inhibited during flight and i ts wind sensitivity is unchanged during flight. However, during flight , interneuron 4 fires spontaneously, unlike the dorsals which fire rhy thmically or the ventrals which are silent. To summarize then, the win d sensitive giant interneuron 4, which has so far been included in the ventral giant interneurons group, shows intermediate morphological an d physiological properties of both the ventral and the dorsal giant in terneurons.