An 125I-labeled binding probe for the muscarinic cholinergic receptor

Effects of intracellular antibodies to cGMP on responses of cortical neurons of awake cats to extracellular application of muscarinic agonists

Intracellular injection of specific antibody to cyclic 3',5'-guanosine monophosphate (cGMP-Ab) produced substantial decreases in input resistance (Rm) selectively in neurons of the motor cortex that had responded with increased resistance to prior application of muscarinic agents. Intracellular injection of nonspecific immunoglobulins (IgG) did not produce this effect. (Some nonspecific effects on spike production occurred in cells given IgG or cGMP-Ab.) The decrease in Rm may be interpreted as being consequential to a reduction in baseline amounts of active cGMP due to binding of cGMP with the injected antibody. In cells which demonstrated a prior increase in Rm following extracellular application of the muscarinic agonist, aceclidine, or acetylcholine, injection of antibody to cGMP also resulted in suppression of the increase in Rm to subsequent applications of these muscarinic agents. Some increases in firing rate to these agents continued to be observed after injection of cGMP-Ab. The results support the hypothesis that cGMP mediates effects of muscarinic neurotransmission on the conductances of neurons of the motor cortex of awake cats. Intracellular injection of antibodies to specific cellular elements is shown to be feasible in cortical neurons of awake cats and may prove a useful adjunct to future studies of neurotransmitter mechanisms.

Putative 51,000-Mr protein marker for postsynaptic densities is virtually absent in cerebellum

Cerebrum and cerebellum contain numerous asymmetric synapses characterized by the presence of a postsynaptic thickening prominently stained by phosphotungstic acid and other electron-dense stains suitable for electron microscopy. A 51,000-Mr protein, copurified in postsynaptic density-enriched fractions from cerebrum, is considered to be a well established marker for the postsynaptic density. On the basis of two criteria, our studies demonstrate that the 51,000-Mr protein marker for postsynaptic densities is virtually absent in cerebellum, First, it is present in negligible amounts in deoxycholate-insoluble fractions from cerebellum but abundant in parallel fractions from cerebrum. Secondly, the 51,000-Mr protein, which binds 125I-calmodulin after SDS PAGE is readily visualized in membrane samples from cerebrum but is virtually undetectable in cerebellar samples. It is apparent that these results require reexamination of the role of the 51,000-Mr protein in postsynaptic density structures.