α-Latrotoxin Indirectly Stimulates Melanophore-stimulating Hormone Secretion From Melanotrophs of the Neurointermediate Lobe of the Lizard Anolis carolinensis

Objective. To determine the effect of α-Latrotoxin (α-Ltx), a toxin known to cause transmitter release from CNS neurons, on melanophore-stimulating hormone (MSH) secretion from the neurointermediate lobe (NIL) of the anole. Background. MSH secretion from the anole melanotrophs is considered to be under stimulant control exerted by factors released from neurons in the neural lobe. Since α-Ltx induces transmitter release from such neurons it was tested on MSH secretion from the anole NIL. Methods. NILs were either used acutely or placed in culture in a medium containing a 50:50 mixture of Hams F12 and Hams F10 in a humidified atmosphere of 5% CO2/95%O2 at 25o C for 7 - 10 days to allow nerve terminals in the neural lobe to degenerate. The freshly excised or cultured NILs were placed in a perifusion chamber and the MSH content of the perifusate measured by the Anolis skin bioassay. Results. α-Ltx (3 nM) stimulated MSH secretion from freshly excised NILs but not from cultured NILs. In both preparations high [K+] (50 mM) administered 20 min after α-Ltx exposure, produced a robust secretory response of up to 16 times basal level. Conclusion. The stimulant effect of α-Ltx on MSH secretion from freshly excised NILs and the lack of effect on cultured (denervated) NILs suggest that the stimulation is neurally mediated and is thus consistent with the suggestion that stimulant factors, released from nerve endings in the neural lobe, are involved in the control of MSH secretion from melanotrophs of the lizard Anolis carolinensis.