title: Effect of raised Mg2+ on the antidromic activation of immature rat spinal motoneurones in vitro.
abstract: Currents elicited by electrical stimulation of the ventral root were recorded from motoneurones of the immature rat spinal cord in vitro using the patch pipette technique. Control medium contained Ca2+ (1.5 mM) and Mg2+ (0.75 mM). In nine preparations the mean amplitude of antidromic current responses was 5.12 +/- 0.41 nA. Raising Mg2+ (EC50 9.6 +/- 1.1 mM) to levels up to 50 mM produced an all-or-none maximal depression of the current responses by 69 +/- 1%. These levels of Mg2+ depressed currents elicited by depolarizing command steps by only 30% and compound action potentials recorded in ventral roots by only 17%. It is concluded that raised Mg2+ caused conduction block from the initial segment to the soma dendritic region of motoneurones. This non-synaptic depressant action of raised Mg2+ should be considered when raised Mg2+ is used in order to specifically block synaptic activity in vitro.
authors.affiliation: Department of Pharmacology, School of Medical Sciences, University of Bristol, UK.
authors.forename: C Q
authors.initials: CQ
authors.lastname: Cao
authors.forename: R H
authors.initials: RH
authors.lastname: Evans
authors.forename: P M
authors.initials: PM
authors.lastname: Headley
mesh_terms: D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology*; D009046:Motor Neurons / Q000187:drug effects*; D018408:Patch-Clamp Techniques; D051381:Rats; D011919:Rats, Inbred Strains; D013116:Spinal Cord / Q000187:drug effects*
chemical_list: D008274:Magnesium; D002118:Calcium