Peptidergic and adrenergic innervation of the lachrymal gland in the euryhaline turtle, Malaclemys terrapin.

The controlling factors of lachrymal gland secretions were examined in the euryhaline turtle, Malaclemys terrapin. Histochemical and immunocytochemical methods were used to localize some of the possible neurotransmitters involved. There was no immunoreactivity to choline acetyltransferase, the enzyme synthesizing acetylcholine, nor did the histochemical technique for acetylcholinesterase produce positive results. Immunofluorescence and immunoperoxidase labels revealed vasoactive intestinal peptide (VIP)- and neuropeptide Y (NPY)-like immunoreactivity in high concentrations surrounding the secretory tubules and ducts. Substance P produced a weak immunoreactivity in the interstitial space surrounding the ducts. Dopamine beta-hydroxylase, the enzyme synthesizing norepinephrine and epinephrine, was localized around the blood vessels. Immunogold labeling confirmed the presence of VIP- and NPY-like reactivity in nerve varicosities close to the basement membrane of the secretory epithelium, and double-labeling showed VIP and NPY are co-localized within the same nerve terminals. The results suggest that the secretory epithelium may be primarily under peptidergic control while the vascular system is under adrenergic control. This is possibly a new pattern of innervation for exocrine glands and may be related to the particular function of this salt gland in an euryhaline turtle.