Functional organization of insect auditory sensilla
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Electrophysiological recordings from individual auditory sensilla in the tettigoniid (Caedicia simplex) ear (Fig. 1) show that spike potentials of two distinct amplitudes occur in the sensory neuron (Fig. 2). Generally, the smaller of the two classes of spike is observed as an inflection on the rising phase of the larger spike. In cases where the larger spike fails or is blocked, the smaller spike becomes distinct. In the attachment cell of the sensillum, negative-going monophasic, or biphasic spikes are recorded (Fig. 3). In biphasic spikes, the positive phase is of smaller amplitude and always follows the negative phase.
Simultaneous recordings from the sensory neuron and from its associated attachment cell, using two electrodes, show that the negative-going spike recorded from the attachment cell corresponds with the smaller spike recorded from the neuron (Fig. 4). The occurrence of a large spike in the neuron causes the positive-going potential in the attachment cell, immediately following the negative spike.
Injection of negative current into the attachment cell via a recording electrode elicits spikes in the sensory neuron. If large spikes in the neuron fail or are blocked by hyperpolarization of that cell, the injection of negative current into the attachment cell elicits small spikes in the neuron (Fig. 4).
Electrical stimulation of the tympanal nerve induces retrograde spikes in the soma of the sensory neuron. Such spikes show no inflection in the rising phase, indicating the absence of the small spike as a precursor to the retrograde spike (Fig. 6). Recordings from the attachment cell, when retrograde spikes are induced, show only a positive-going potential correlated with each retrograde spike. The positive deflections recorded in the attachment cell, resulting from retrograde spikes, generally are of greater amplitude than those specifically associated with large, orthograde spikes occurring in the sensory neuron.
These results confirm previous suggestions that, in insect auditory, chordotonal sensilla, spikes of relatively small amplitude occur at the apex of the sensory dendrite and subsequently, trigger spikes of conventional amplitude at a site more proximal in the dendrite. The occurrence of small spikes in the neuron implies novel equilibrium potentials at the apical dendritic membrane, which may result from the scolopale lumen functioning as a receptor lymph cavity.
KeywordsSensory Neuron Attachment Cell Negative Phase Positive Deflection Large Spike
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- Autrum H (1940) Über Lautäusserung und Schallwahrnehmung bei Arthropoden II. Das Richtungshören vonLocusta und Versuch einer Hörtheorie für Tympanalorgane vom Locustidentyp. Z Vergl Physiol 28:326–352Google Scholar
- Autrum H (1941) Über Gehör und Erschütterungssinn bei Locustiden. Z Vergl Physiol 28:580–637Google Scholar
- Erler G, Thurm U (1981) Dendritic impulse initiation in an epithelial sensory neuron. J Comp Physiol 142:237–249Google Scholar
- Fielden A (1960) Transmission through the last abdominal ganglion of the dragonfly nymph,Anax imperator. J Exp Biol 34:832–844Google Scholar
- Hill KG (1983) The physiology of locust auditory receptors. II. Membrane potentials associated with the response of the receptor cell. J Comp Physiol 152:483–493Google Scholar
- Kaissling KE, Thorson J (1980) Insect olfactory sensilla: Structural, chemical and electrical aspects of the functional organization. In: Satelle DB, Hall LM, Hildebrand JG (eds) Receptors for neurotransmitters, hormones and pheromones in insects. Elsevier/North-Holland Biomedical Press, Amsterdam, pp 261–282Google Scholar
- Moulins M (1976) Ultrastructure of chordotonal organs. In: Mill PJ (ed) Structure and function of proprioceptors in the invertebrates. Chapman and Hall, London New York, PP 387–425Google Scholar
- Oldfield BP (1982) Tonotopic organisation of auditory receptors in Tettigoniidae (Orthoptera: Ensifera). J Comp Physiol 147:461–470Google Scholar
- Oldfield BP (1984) Physiology of auditory receptors in two species of Tettigoniidae (Orthoptera: Ensifera). Alternative tonotopic organisations of the auditory organ. J Comp Physiol A155:689–696Google Scholar
- Schumacher R (1979) Zur funktionellen Morphologie des auditiven Systems der Laubheuschrecken (Orthoptera: Tettigonoidae). Entomol Gen 5:321–356Google Scholar
- Schwabe J (1906) Beiträge zur Morphologie und Histologie der tympanalen Sinnesapparate der Orthoptera. Zoologica (Stuttgart) 50:1–154Google Scholar
- Seyfarth E-A, Bohnenberger J, Thorson J (1982) Electrical and mechanical stimulation of a spider slit sensillum: outward current excites. J Comp Physiol 147:423–432Google Scholar
- Stewart WW (1978) Functional connections between cells as revealed by dye coupling with a highly fluorescent naphthalimide tracer. Cell 14:741–759Google Scholar
- Thurm U, Küppers J (1980) Epithelial physiology of insect sensilla. In: Locke M, Smith D (eds) Insect biology in the future. Academic Press, New York, pp 735–763Google Scholar