cGMP: the wayward child of the cyclic nucleotide family.

An informal poll of neurobiologists indicates the following widely-held misconceptions about cGMP: (1) we know very little about it; (2) it must not be very different from cAMP; and (3) no new biological principles are likely to emerge from studying it. In fact, despite these prejudices, our understanding of the cGMP second messenger cascade has increased dramatically in the last few years. We now know that it is very different from the cAMP system in almost every particular, and the differences reveal interesting and novel solutions to the biological problem of receptor-effector coupling.