ABSTRACT
Studies of invertebrate sensory receptors have been greatly aided by the use of compounds, such as cobalt salts, which can diffuse or be transported in peripheral nerves, to characterize morphologically and to label identified exteroceptive and proprioceptive sense organs (Bräunig, et al. 1981). However, most of these methods require the maintenance of live preparations, which can be difficult when attempting to fill axons over long distances. We have mapped sense organs of the cockroach leg using the carbocyanine dye, diI. This lipid-soluble dye, recently developed for use in vertebrates (Honig and Hume, 1989), diffuses passively in neuronal membranes and can be used in fixed tissues. However, because of its lipid solubility, it has the disadvantage that it dissolves in standard organic clearing agents. We have developed methods of applying diI and clearing cockroach preparations that permit the visualization of both sensory neuron somata under fluorescent illumination and their associated cuticular specializations by conventional light microscopy. These experiments have confirmed the location of many receptors previously identified by serial sectioning and light microscopy (Dresden and Nijenhuis, 1958; Nijenhuis and Dresden, 1952, 1956). We have also mapped sense organs on the distal leg segments and demonstrated the widespread presence of multiply innervated, chemoreceptor-like sense organs on all segments of the cockroach mesothoracic and metathoracic legs.
