INTRACELLULAR CHARACTERIZATION OF IDENTIFIED SENSORY CELLS IN A NEW SPIDER MECHANORECEPTOR PREPARATION

We have developed an isolated mechanoreceptor-organ preparation in whi ch the intact sensory structures are available for mechanical stimulat ion and electrical recording. The anterior lyriform slit sense organ o n the patella of the spider, Cupiennius salei Keys., consists of seven or eight cuticular slits, each innervated by a pair of large bipolar sensory neurons. The neurons are fusiform, and the largest somata are less than or equal to 120 mu m long. The innervation of the organ was characterized by light microscopy of neurons backfilled with neuronal tracers. Intracellular recording was used to measure the passive and a ctive electrical properties of the neurons, in several cases followed by identification with Lucifer yellow injection. Both neurons of each pair from one slit responded with action potentials to depolarization by a step current injection. Approximately half of the sensory neurons adapted very rapidly and generated only one or two action potentials in response to a sustained depolarizing step, while a second group pro duced a burst of action potentials that adapted to silence in similar to 1 s or less. Recordings from identified neuron pairs indicated that each pair consists of one rapidly adapting and one bursting neuron. M easurements of cell membrane impedances and time constants produced es timates of neuronal size that agreed with the morphological measuremen ts. This new preparation offers the possibility of characterizing the mechanisms underlying transduction and adaptation in primary mechanose nsory neurons.