Morphology of a thermosensitive multipolar neuron in the infrared organ ofMerimna atrata (Coleoptera, Buprestidae)

Two pairs of infrared (IR) organs are situated ventrolaterally on the secon d and third abdominal sternites of the Australian fire beetle Merimna atrat a (Buprestidae). In ventral view, each IR organ has a round IR absorbing ar ea under which a sensory complex is attached to the epidermis. The main com ponent of the complex is a single large multipolar neuron and its mass of h ighly branched dendrites. All parts of this neuron are enveloped in glial c ells. The proximal primary dendrites, which arise from the soma, finally br anch into several hundred tightly packed terminal dendrites, which contain many mitochondria. We term this unusual morphology of the dendritic region a terminal dendritic mass (TDM). Additionally, two chordotonal organs were found in each sensory complex. Their somata are integrated in the complex a nd the dendrites extend to the periphery of the absorbing area. The bauplan of the dendritic region is reminiscent of the thermosensitive trigeminal n erve fibers innervating the absorbing structures in the IR receptors in boi d and crotalid snakes. Because this multipolar neuron also functions as a t hermoreceptor, another example of a functional analogy between insect and v ertebrate sensory systems could be demonstrated. (C) 2001 Elsevier Science Ltd. All rights reserved.