Electrical activity of the sinus gland of the terrestrial isopod, Oniscus asellus: characteristics of identified potentials recorded extracellularly from neurosecretory terminals.

Spontaneously occurring neurosecretory action potentials recorded extracellularly from the sinus gland (SG) of the terrestrial isopod. Oniscus asellus, are of 5 types (A through E) identified by their amplitudes and patterns of discharge. Type A have the largest (200-450 microV) and type E the smallest (25-50 microV) amplitude. Types A, B and C originate from the bulb of the SG, and discharge at high frequencies (30-60 Hz) in coordinated bursts ranging from seconds to several minutes in duration. Coordination of their discharges suggests a mechanism for synchronizing bursting activity among different cell types. Types D and E originate from the lateral extension of the SG, and discharge at low frequencies (0.5-1.0 Hz) for prolonged periods (5-10 min). Their activity is not synchronized with discharges of other potentials. Following transection of the brain through the lateral part of the central protocerebral neuropile, A, B and C potentials are eliminated whereas D and E potentials remain active. This result suggests A, B and C potentials arise from neurosecretory cells (NSCs) whose cell bodies are located in the medial protocerebrum, and D and E potentials arise from NSCs identified in the optic lobe. Alterations in the appearance of action potentials following exposure to salines deficient in Na+ or Ca2+, or containing tetrodotoxin or cobalt, reveal that A and B potentials are primarily Ca2+ dependent whereas C potentials are both Ca2+ and Na+ dependent.