Neuroendocrine bag cells of Aplysia are activated by bag cell peptide-containing neurons in the pleural ganglion.
1. The generation of egg-laying behavior in the marine mollusk Aplysia involves a prolonged burst discharge in the neuroendocrine bag cells, which secrete neuropeptides derived from the egg-laying hormone/bag cell peptide (ELH/BCP) precursor protein. 2. Besides the bag cells, which are located in the abdominal ganglion, small clusters of neurons in the cerebral and pleural ganglia also express the ELH/BCP neuropeptides. We made intracellular recordings from 32 of these ELH/BCP cells in right pleural ganglia, in 18 preparations, to characterize their physiological properties and their functional relationship to the bag cells. 3. The identification of these ELH/BCP cells was confirmed by pressure injection of Lucifer yellow and subsequent immunocytochemical processing for alpha-BCP immunoreactivity. 4. The basic electrophysiological properties of the pleural ELH/BCP cells were similar to those of the bag cells. These pleural cells were directly demonstrated to be electrically coupled, and direct intracellular stimulation of individual pleural ELH/BCP cells initiated prolonged, synchronous burst discharges in the entire cluster through a positive feedback mechanism. 5. Burst discharges elicited in the pleural ELH/BCP cells consistently initiated burst discharges in the bag cells. Bag cell burst discharges were less effective in initiating burst discharges in the pleural ELH/BCP cells, indicating that there were reciprocal but asymmetrical connections. 6. The results show that the pleural ELH/BCP cells are functionally coupled to the bag cells. They support the hypothesis that the pleural ELH/BCP cells are part of the descending pathway that initiates bag cell activity and egg-laying behavior, in vivo.
Brown
R O
RO
Department of Physiology, University of California, San Francisco 94143-0444.
Pulst
S M
SM
Mayeri
E
E
D000200:Action Potentials; D000818:Animals; D001048:Aplysia / Q000502:physiology*; D005724:Ganglia / Q000378:metabolism / Q000502:physiology*; D007150:Immunohistochemistry; D007447:Invertebrate Hormones / Q000378:metabolism*; D008839:Microelectrodes; D009474:Neurons / Q000502:physiology*; D010994:Pleura / Q000166:cytology / Q000502:physiology*
D007447:Invertebrate Hormones; C026880:egg-laying hormone, Mollusca