Peptidergic modulation of a multioscillator system in the lobster. I. Activation of the cardiac sac motor pattern by the neuropeptides proctolin and red pigment-concentrating hormone

1. The cardiac sac motor pattern consists of slow and irregular impulse bursts in the motor neurons [cardiac sac dilator 1 and 2 (CD1 and CD2)] that innervate the dilator muscles of the cardiac sac region of the crustacean foregut. 2. The effects of the peptides, proctolin and red pigment-concentrating hormone (RPCH), on the cardiac sac motor patterns produced by in vitro preparations of the combined stomatogastric nervous system [the stomatogastric ganglion (STG), the paired commissural ganglia (CGs), and the oesophageal ganglion (OG)] were studied. 3. Bath applications of either RPCH or proctolin activated the cardiac sac motor pattern when this motor pattern was not already active and increased the frequency of the cardiac sac motor pattern in slowly active preparations. 4. The somata of CD1 and CD2 are located in the esophageal and stomatogastric ganglia, respectively. Both neurons project to all four of the ganglia of the stomatogastric nervous system. RPCH elicited cardiac sac motor patterns when applied to any region of the stomatogastric nervous system, suggesting a distributed pattern generating network with multiple sites of modulation. 5. The anterior median (AM) neuron innervates the constrictor muscles of the cardiac sac. The AM usually functions as a part of the gastric mill pattern generator. However, when the cardiac sac is activated by RPCH applied to the stomatogastric ganglion, the AM neuron becomes active in antiphase with the cardiac sac dilator bursts. This converts the cardiac sac motor pattern from a one-phase rhythm to a two-phase rhythm. 6. These data show that a neuropeptide can cause a neuronal element to switch from being solely a component of one neuronal circuit to functioning in a second one as well. This example shows that peptidergic "reconfiguration" of neuronal networks can produce substantial changes in the behavior of associated neurons.

A HISTOCHEMICAL PROCEDURE FOR THE LOCALIZATION OF CHOLINE ACETYLTRANSFERASE ACTIVITY

A histochemical procedure has been developed for the demonstration of choline acetyltransferase activity. This procedure is based upon the formation of an insoluble lead mercaptide from coenzyme A (CoASH), a product of the enzymatic reaction. Optimal conditions for the precipitation of the lead mercaptide are defined. The localization of the reaction product in the rat spinal cord is restricted to the neuronal element. Heavy deposition of reaction product in the perikaryon was noted for the anterior motor neurons; some of the other neurons were negative. Boutons terminaux were visible on the surface of all neurons studied. A combination of quantitative radiochemical data, enzyme solubilization, copper inhibition and the histologic distribution of the reaction product is discussed in relation to the specificity of the procedure for the differential localization of choline acetyltransferase and nonspecific acetyl-CoA hydrolase activities.