Identification of active thoracic spinal segments responsible for tonic and bursting sympathetic discharge in neonatal rats.
The isolated thoracic cord of a neonatal rat in vitro generates tonic sympathetic activities in the splanchnic nerves. This tonic sympathetic nerve discharge (SND) has a prominent quasi-periodic oscillation at approximately 1-2 Hz. Bath application of bicuculline and strychnine, which removes endogenous GABA(A) and glycine receptor activities, transforms the quasi-periodic tonic SND into synchronized bursts (bSND). Picrotoxin, another GABA(A) receptor antagonist, also induces bSND. Serial transections of the thoracic cord (T1-12) were performed to identify the cord segments responsible for these tonic and bursting SNDs. Removal of T1-5 did not affect tonic SND. Nerve-cord preparation with either T6-8 or T10-12 segments could generate a substantial amount of tonic SND that retained comparable oscillating patterns. On the other hand, removal of T1-5 significantly reduced bSND amplitude without affecting its rhythmicity. Either T6-8 or T10-12 segments alone could generate bSND. Mid-point transection of T6-12 at T9 might split bSND rhythmogenesis, leading to the occurrence of bSND that could be attributed to two independent oscillators. Our results demonstrated that three segments within the T6-12 cord were sufficient to generate a rudimentary tonic and bursting SNDs. The thoracic cord segments, however, are dynamically interacting so that a full size bSND could only be produced with the intact thoracic cord.
Su
Chun-Kuei
CK
Institute of Biomedical Sciences, Academia Sinica, 11529, Taipei, Taiwan.
Phoon
Sau-Leong
SL
Yen
Chen-Tung
CT
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D000831:Animals, Newborn; D001640:Bicuculline / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004594:Electrophysiology / Q000379:methods; D018756:GABA Antagonists / Q000494:pharmacology; D018684:Glycine Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D009991:Oscillometry; D010852:Picrotoxin / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013116:Spinal Cord / Q000033:anatomy & histology / Q000502:physiology*; D013119:Spinal Cord Injuries; D013153:Splanchnic Nerves / Q000187:drug effects / Q000502:physiology; D013331:Strychnine / Q000494:pharmacology; D013564:Sympathetic Nervous System / Q000187:drug effects / Q000502:physiology*; D013904:Thoracic Vertebrae / Q000033:anatomy & histology / Q000187:drug effects
D001640:Bicuculline; D018756:GABA Antagonists; D018684:Glycine Agents; D008274:Magnesium; D010852:Picrotoxin; D013331:Strychnine