Ultrastructural effects of 4-aminopyridine on the presynaptic membrane in the rat spinal cord.
The effects of 4-aminopyridine (4-AP, 1 mg/kg, i.v.) on the ultrastructure of synapses in the ventral horn of the spinal cord were examined in rats anesthetized with 50 and 100 mg/kg, i.p., pentobarbital sodium and alpha-chloralose respectively. The presynaptic membrane of the 4-AP-treated animals, in both S- and F-type synapses, was wrinkled and gave frequently rise to omega-shaped profiles. However, it was not prominently lifted in comparison with the controls. In both extracellular (EF) and protoplasmic fracture faces (PF) of freeze-etched replicas, the frequency of the presynaptic membrane modulations (PMM) per unit area rose significantly under the influence of 4-AP. The ratio of open (crater-like) to total PMM in EF increased almost twice under the experimental condition. No differential 4-AP effects were seen between pentobarbital- and chloralose-treated animals. The morphological evidence is consistent with electrophysiological data showing that 4-AP facilitates the transmitter release at synaptic endings.
D000632:Aminopyrine / Q000494:pharmacology*; D000818:Animals; D005614:Freeze Fracturing; D051381:Rats; D013116:Spinal Cord / Q000187:drug effects / Q000648:ultrastructure*; D013570:Synaptic Membranes / Q000187:drug effects / Q000648:ultrastructure*; D013572:Synaptic Vesicles / Q000648:ultrastructure
D000632:Aminopyrine