Robert E. Kay

Acoustic signalling and its possible relationship to assembling and navigation in the moth, Heliothis zea

Abstract Evidence for the use of sensory modes other than olfaction in the assembly of moths is discussed. It is proposed that a multitude of sensing and signalling methods may be used. To support this hypothesis the role of ultrasonic emissions in Heliothis zea from the standpoint of its usefulness to the animal in communication and navigation was investigated. It was found that H. zea emits a rapidly damped 50 kc ultrasonic burst every 25 msec in synchronization with the wing beat, but not automatically produced by the wing beat. The burst is composed of two 185 μ sec pulses of six oscillations each and the pulses are separated from each other by 190 μ sec. Ultrasonic emissions were sporadic during the morning and afternoon hours, but became very regular in the late afternoon and evening. The effective sound pressure was greatest in the topside direction and least below. At a distance of 1·5 cm the average effective sound pressure was 98·5 dB re 0·0002 μ bar. Using 0·02 μ bar as the threshold for hearing in the moth, an analysis of the moths acoustic capabilities was made. It was concluded that the ultrasonic emissions combined with the acoustic properties of the ears provided an echo-locating capability which could be used for the detection of large objects at a distance of over 2 m and the resolution of details down to 7 mm at distances up to 24 cm. Signalling for the purpose of assembling would be effective at distances of over 4 m and combined with olfactory information it should be of value in locating a mate.

Photoelectric reonses of lipid membranes.

Thin lipid membranes formed in aqueous solution from chloroform-methanol solutions of α-tocopherol or α-tocopherol plus sphingomyelin or sphingomyelin in decane gave photoelectric responses to μwatt energies of ultraviolet (UV) light of up to 160 mV and 1600 pA. The performance of all membranes was enhanced by placing an iodide solution on one side of the membrane. The location of the iodide solution was important in regard to the response obtained and specific differences were seen with membranes having different compositions. The action and absorption spectra of the membranes were determined, the effect of reversing the light direction ascertained and the current-voltage characteristics of the membranes examined before, after and during exposure to UV radiation. From data obtained it was hypothesized that changes in the membrane induced by UV radiation were an important part of the mechanism leading to the photoelectric effect.

Fluorescent materials in insect eyes and their possible relationship to ultra-violet sensitivity

It was suggested that insect eyes contain at least two light-sensitive pigment systems: one based on rhodopsin and the other on a non-rhodopsin complex. The rhodopsin system is responsible for sensitivity in the visible and for some sensitivity in the ultra-violet (u.v.), whereas the non-rhodopsin system functions only in the u.v. To support this hypothesis, experiments were conducted to find fluorescent substances in insect compound eyes which had excitation spectra compatible with the physiology of the insect eye in the u.v. In vivo fluorescence was demonstrated in flies, bees, and moths. Intensely u.v. fluorescent materials emitting in the visible were extracted in substantial quantities in all insect eyes examined. The excitation spectra of these materials were well within the insect u.v. sensitivity region and the u.v. excitation peak matched the u.v. eye sensitivity peak. Furthermore, histological sections of the eye revealed that the fluorescent material was present in the retinal cell. These results led to the proposal that the fluorescent material may appear in the insect eye in two forms; as a radiative system and as the chromophore of a non-radiative, non-rhodopsin, u.v.-sensitive pigment system. In the nonradiative system the chromophore is postulated to be present in a complex which directly couples the absorbed energy into a chemical system, whereas in the radiative system the chromophore is not part of this complex and the absorbed energy is dissipated by radiative means. The fluorescent materials were tentatively identified as hydroxy indole derivatives and its was suggested that they are absent in the mutant strains ‘chalky’ and ‘white-apricot’ of Calliphora erythrocephala since the eye pigment (ommochromes) missing from these mutants and hydroxy indoles are derived from a common precursor, tryptophan.

EFFECT OF X‐IRRADIATION ON GLUCOSE METABOLISM IN RAT CEREBRAL CORTEX SLICES

A NUMBER of studies has shown that a variety of lesions is histochemically demonstrable in the nervous system following exposure to various types and dosages of irradiation (HAYMAKER, 1961). Extensive alterations in structure are also evident when the immature mammalian brain is exposed to X-irradiation, and long term effects are seen following exposure of the adult brain (YAMAZAKI, BENNETT, MCFALL and CLEMENTE, 1960; CLEMENTE, YAMAZAKI, BENNETT and MCFALL, 1960). Of especial interest are the observations by KLATZO, MIGUEL, TOBIAS and HAYMAKER (1961) and WOLFE, KLATZO, MIGUEL, TOBIAS and HAYMAKER (1962). These investigators observed both histochemically and analytically an increase in brain glycogen in rats subjected to a brain surface dose of 6000 rad of alpha particle irradiation. They believe that the appearance of glycogen granules in the glial cells may be attributable to: (a) increased glucose supply from the circulation, (b) accumulation of glycogen due to the inhibition of aerobic glycolysis associated with a lowered metabolic rate as a result of radiation cell injury, and (c) disruption of tissue carbohydrates in the ‘Bragg-peak band’ in which the cell damage was most severe with release of the carbohydrate material into adjacent tissue and its subsequent uptake and conversion into glycogen by the glial cells. It appears that all of these factors may be operative and that a combination of such changes would be effective in causing the accumulation of glycogen in the brain. Although the work of KLATZO et al. (1961) indicates that an increase in glucose supply from the circulation due to change in vascular permeability is rather improbable, an increase in glucose supply due to radiation-induced hyperglycaemia is quite possible. If, following irradiation, the oxidation of glucose is inhibited and access to glucose is enhanced, due to hyperglycaemia, a situation conductive to an increase in the glycogen content of the brain exists. The radiation-induced hyperglycaemia has been well established in previous studies (KAY and ENTENMAN, 1956) and the data presented in this communication support the view that oxidation of glucose in the brain is inhibited by exposure to whole-body X-irradiation.