Recently a number of complex electrophysiological responses to neurotransmitters have been observed that cannot be described as simple excitation or inhibition. These responses are often characterized as modulatory, although there is no consensus on what defines modulation. Morphological studies reveal certain neurotransmitters stored in what might be release sites without synaptic contact. There is no direct evidence for nonsynaptic release from CNS sites, although such release does occur in the periphery and in invertebrates. Nonsynaptic release might provide a basis for (...) diffuse one-cell-to-many communication, but it might also simply be a means of sending the transmitter to a broader area of a single neuron than occurs in typical synapses. Several kinds of macromolecules have been found to be transported in a retrograde direction – and in some cases transsynaptically. There have been suggestions that some neurons may release more than one type of transmitter. Particularly intriguing is the possibility of release of substances that modulate actions of a primary transmitter. Taken together this range of evidence suggests that neurons may use a variety of forms of molecular communication in addition to traditionally described synaptic transmission.Several authors have suggested modes of communication distinct from classical synaptic transmission and have classified released substances using terms such as neurohumor, neurohormone, neuroregulator, and modulator. These suggestions have the heuristic value of drawing together diverse kinds of data, but it remains to be established that the pieces fit together in that fashion – for example, that complex electrophysiological effects are associated with substances released nonsynaptically. In order to reduce confusion, a flexible, generic approach to nomenclature for substances released from neurons and for hypothetical modes of communication is recommended. Some behavioral implications of nonconventional transmission are considered. (shrink)

Philosophical controversy about the mind has flourished in the thin air of our ignorance about the brain. The humble toad, it now seems, may provide our first instance of a creature whose whole brain is within the reach of our scientific understanding. What will happen to the traditional philosophical issues as our theoretical and factual ignorance recedes? Discussion of the issues explored in the target article is, as Ewert says, "often too theoretical, sometimes philosophical and even [as if that weren't (...) bad enough?--DCD] emotion-laden." The research reported by Ewert has interesting philosophical implications, as he probably recognizes, but he wisely leaves the philosophy to the philosophers. Being one, I would like to draw some of the conclusions he eschews. (shrink)