Regulation of body volume by salivation in a tick challenged with fluid loads

Injection into the hemolymph of 1.2% NaCl, 11.2% sucrose, 2.3% urea (all approximately isosmotic to hemolymph), or distilled water induced salivary fluid secretion in the ixodid tick Amblyomma hebraeum Koch. Saline gave the largest response at high doses. Injection of hyperosmotic NaCL into the hemolymph did not induce salivation but led to the drinking of distilled water in amounts sufficient to dilute the salt load to isosmolarity. Atropine only partially inhibited salivation induced by NaCl, sucrose, and distilled water. Reserpine markedly inhibited salivation induced by NaCl. We propose that at least two sensory pathways (one cholinergic, one not) converge on the secretory nerve. The physiological significance of the cholinergic pathway is not known. The other pathway probably mediates the regulation of hemolymph volume, possibly via stretch receptors, but its transmitter is not known.