Amine modulation of the neurogenic Limulus heart.

(1) The biogenic amines octopamine (OCT), dopamine (DA), epinephrine (E), and norepinephrine (NE) cause dose-dependent increases in both the rate and amplitude of contractions of the isolated Limulus heart-cardiac ganglion. Their relative ability to produce this excitation is OCT greater than DA approximately the same as E greater than NE. (2) The excitatory effects of all these amines are antagonized by the alpha-adrenergic blocker phentolamine and the dopaminergic antagonist haloperidol.

The neuropeptide proctolin acts directly on Limulus cardiac muscle to increase the amplitude of contraction.

The pentapeptide proctolin increases the amplitude of contraction but not heart beat frequency of the isolated heart of Limulus polyphemus. It acts directly on the heart muscle and has no effects on the neurones of the cardiac ganglion or on the cardiac neuromuscular EJPs. A peptide with molecular weight, enzymatic susceptibilities and physiological effects similar to those of proctolin occurs in the Limulus cardiac ganglion.

Neurotransmitter release from a vertebrate neuromuscular synapse affected by a food dye.

The food dye erythrosine (Erythrosin B; FD & C No. 3) was applied to isolated neuromuscular synapses in the frog, and its effects on the spontaneous quantal release of acetylcholine were examined with electrophysiological techniques. At concentrations of 10 muM or greater this anionic dye produced an irreversible, dose-dependent increase in neurotransmitter release.