Abstract
The well known muscarinic slow excitatory polysynaptic potential (s-EPSP) of rabbit superior cervical ganglion (SCG) peaking at about 1–2 s and lasting 5–10 s, is immediately followed by an abrupt change in slope to a longer, lower depolarizing phase. A brief dip in the level of depolarization (DP) often separates the two depolarizing phases. The secondary phase of s-EPSP rises to its own peak at about 25 s; total duration 60–120 s. With repetition of orthodromic volleys secondary s-EPSP builds up more gradually than initial s-EPSP, but more rapidly than slow-slow (ss-) EPSP. The later ‘secondary’ depolarizing phase along with the antecedent ‘dip in DP’ are, like the ‘initial’ s-EPSP, eliminated by a muscarinic antagonist, quinuclinidyl benzilate hydrochloride (QNB). This distinguishes secondary s-EPSP from the even slower rising non-cholinergic ss-EPSP. The ss-EPSP, although relatively small in the responses to the usual 3-pulse test stimuli, rises to an extraordinary amplitude (equal to the compound action potential) during a 10 s–120 s train of pulses. Gallamine blocked most of the slow IPSP component in test responses but not initial or secondary s-EPSP. A preganglionic conditioning train (10/s for 2 min) induced a long-term-enhancement (LTE) of secondary s-EPSP lasting > 3 h, with maximum postconditioning percentage increases greater than for initial s-EPSP. Also enhanced was the dip in DP, now forming a deeper notch between initial and secondary s-EPSPs; this attains a maximum at about 30 min postconditioning but thereafter progressively loses the enhancement by about 90 min. The dip in DP appears to represent some delayed, perhaps hyperpolarizing process that may overlap with the initial and secondary phases of s-EPSP and affect their forms and peak amplitudes. This would not exclude the possibility that the initial and secondary phases of s-EPSP reflect multiple muscarinically activated electrogenic mechanisms having differing time-courses.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.