title: Red pigment concentrating hormone strongly enhances the strength of the feedback to the pyloric rhythm oscillator but has little effect on pyloric rhythm period.
abstract: The neuropeptide, red pigment concentrating hormone (RPCH), strengthened the inhibitory synapse from the lateral pyloric (LP) neuron to the pyloric dilator (PD) neurons in the pyloric network of the stomatogastric ganglion (STG) of the lobster, Homarus americanus. RPCH produced several-fold increases in the amplitude of both action potential-mediated and non-impulse-mediated transmission that persisted for as long as the peptide remained present. Because the LP to PD synapse is the only feedback to the pacemaker kernel of the pyloric network, which consists of the electrically coupled two PD neurons and the anterior burster (AB) neuron, it might have been expected that strengthening the LP to PD synapse would increase the period of the pyloric rhythm. However, the period of the pyloric rhythm increased only transiently in RPCH, and a transient increase in cycle period was observed even when the LP neuron was hyperpolarized. Phase response curves were measured using the dynamic clamp to create artificial inhibitory inputs of variable strength and duration to the PD neurons. Synaptic conductance values seen in normal saline were ineffective at changing the pyloric period throughout the pyloric cycle. Conductances similar to those seen in 10(-6) M RPCH also did not evoke phase resets at phases when the LP neuron is typically active. Thus the dramatic effects of RPCH on synaptic strength have little role in modulation of the period of the pyloric rhythm under normal operating conditions but may help to stabilize the rhythm when the cycle period is too slow or too fast.
authors.affiliation: Volen Center for Complex Systems, Brandeis University, Waltham, MA, USA. vatsala@cshl.edu
authors.forename: Vatsala
authors.initials: V
authors.lastname: Thirumalai
authors.forename: Astrid A
authors.initials: AA
authors.lastname: Prinz
authors.forename: Christian D
authors.initials: CD
authors.lastname: Johnson
authors.forename: Eve
authors.initials: E
authors.lastname: Marder
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D001683:Biological Clocks / Q000187:drug effects / Q000502:physiology*; D005246:Feedback / Q000187:drug effects / Q000502:physiology; D066298:In Vitro Techniques; D017258:Medroxyprogesterone Acetate; D009046:Motor Neurons / Q000187:drug effects / Q000502:physiology*; D008121:Nephropidae / Q000187:drug effects / Q000502:physiology; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology; D009842:Oligopeptides / Q000494:pharmacology*; D010507:Periodicity; D011708:Pylorus / Q000187:drug effects / Q000294:innervation* / Q000502:physiology; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*
chemical_list: D009842:Oligopeptides; C022059:red pigment-concentrating hormone; D017258:Medroxyprogesterone Acetate; D011761:Pyrrolidonecarboxylic Acid