The synergetic modulation of the excitability of central gray matter by a neuropeptide: two protocols using excitation waves in chick retina.
The isolated chick retina provides an in vitro tissue model, in which two protocols were developed to verify the efficacy of a peptide in the excitability control of the central gray matter. In the first, extra-cellular potassium homeostasis is challenged at long intervals and in the second, a wave is trapped in a ring of tissue causing the system to be under self-sustained challenge. Within the neuropil, the extra-cellular potassium transient observed in the first protocol was affected from the initial rising phase to the final concentration at the end of the five-minute pulse. There was no change in the concomitants of excitation waves elicited by the extra-cellular rise of potassium. However, there was an increase on the elicited waves latency and/or a rise in the threshold potassium concentration for these waves to appear. In the second protocol, the wave concomitants and the propagation velocity were affected by the peptide. The results suggest a synergetic action of the peptide on glial and synaptic membranes: by accelerating the glial Na/KATPase and changing the kinetics of the glial potassium channels, with glia tending to accumulate KCl. At the same time, there is an increase in potassium currents through nerve terminals.
Lima
Vera M F de
VM
Departamento de Medicina, Universidade Federal de São João del Rei, Divinópolis, MG, Brasil, 35501-296.
Piqueira
José R C
JR
Hanke
Wolfgang
W
D000818:Animals; D002645:Chickens; D004558:Electric Stimulation; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D010487:Periaqueductal Gray / Q000187:drug effects / Q000502:physiology*; D011188:Potassium / Q000378:metabolism*; D012160:Retina / Q000187:drug effects / Q000502:physiology*; D013004:Somatostatin / Q000494:pharmacology*
D013004:Somatostatin; D011188:Potassium