Ultracryotomy of nerve-electroplaque synapses for immunocytochemistry

In order to carry out ultrastructural immunocytochemical localization of acetylcholinesterase at cholinergic synapses, ultrathin frozen sections of aldehyde-fixed electric organs of Electrophorus and Torpedo were obtained by a modified ultracryotome technique. Dry frozen sections, picked up with rabbit serum and negatively stained, revealed, in the postsynaptic regions of the neuro-electroplaque junction, the presence of numerous rod-like or pin-headed protrusions (30 X 40 A) attached perpendicularly at 60 A intervals to the hydrophobic lamina of the plasma membrane, forming a comb-like structure oriented toward the synaptic cleft. A possible correlation is suggested between this comb-like structure and the 'acetylcholine receptors' observed by other authors with high resolution electron microscopy either after classical preparative techniques or after freeze-etching, of the postsynaptic membrane of vertebrae cholinergic synapses.