Mechanoreceptive neurons in an insect brain.

Staining deutocerebral nerves in locusts with cobalt chloride revealed a connective tissue strand innervated by the first side branch of the nervus scapalis medialis. The strand spans the joint between the basal segment of the antenna (scapus) and the head capsule (tentorium), parallel to the levator scapi muscle. It is shortest with the antenna completely elevated and becomes stretched during depression. The four to five neurons innervating the strand near its distal insertion are activated by mechanical stimuli such as direct elongation of the strand or depression of the antenna. As revealed by centripetal staining these neurons have their central arborizations in the posterior deutocerebrum, but their perikarya are located in the protocerebrum, close to the pars intercerebralis and the central body. These morphological and physiological characteristics identify the structure as a mechanoreceptive sense organ of the strand receptor class.