This week we've been talking about the circuitry in the cholinergic, dopaminergic, and serotonergic pathways. This led me to consider the regulation of those pathways and whether certain areas down the line could regulate the entire system.
Nitrous oxide is a recent addition to our library of known neurotransmitters. Being a gas, it has properties different from those of the catecholamines. When released from a cell it diffuses more readily than a "normal" neurotransmitter. It has been implicated in retrograde synaptic transmission, meaning a message being sent from the post synaptic membrane to the pre synaptic.
In my Neuropharmacology class, we learned about the cannabinoid receptors CB1 and CB2. It seems that endogenous cannabinoids can serve as retrograde messengers, being released from the post synaptic cell and binding with CB1 on the pre synaptic cell.
I want to extrapolate this a little further. These are cases in which a definite signal (be it inhibitory or excitatory) is being sent. I am led to wonder whether there can be such a thing as an "off" signal in the brain. In other words, I consider a cell not firing to contain just as much information as a cell firing. I wonder if a tendency to give preference to circuits in which cellular firing (inhibitory or excitatory in nature) is a characteristic tone leads us down an alley when we would be better served going along the main roads.