Anum Qassam   Cornell University College Of Engineering

Brief Introdution to Neuromodulators 

Neuromodulators are neurotransmitters that illicit a long-term response in the post-synaptic cell, often through changes in the conductances of ion channels caused by a transduction process initiated by G-protein coupled receptors on the post-synaptic cell.  Essentially, neuromodulators provide an adaptive mechanism by which one generated pattern can switch to another depending on the varying external (or internal) conditions. They can change the strength of synapses as well as the intrinsic firing properties of the neuron. 

Neuromodulators have several characteristics (taken from Professor Harris-Warrick's lecture):
(1) Neuromodulators have a slow time course, often lasting seconds, minutes, hours, or even days. 
(2)Consistent with Professor Harris-Warrick's analogy in lecture, the modulator's effects are subtle, and often not witnessed until another synapse comes along.
(3) They can change the intrinsic properties of the the neuron
(4) They often work through a complex biochemical pathway.


 The image above shows the specific pathways involved in three different neuromodulators, each of which activates a G-Protein Coupled Receptor (GPCR).  Each of the neuromodulators activates a G-Protein, which in turn activates an effector protein, like Adenylyl cyclase in the case of Dopamine. The effector protein is Kinase A for Dopamine, which then results in a decrease of protein physphorylation for that specific receptor. This change in protein phosphorylation directly influences the membrane proteins and affects  the membrane potential and possibly the ultimate firing pattern of the neuron, as is the case in the pyloric circuit of the stomatogastric ganglion. 

In the simulation of the pyloric circuit I focus upon the effects of dopamine, but most importantly it is crucial to recognize that it is the effector protein and NOT the neuromodulator which affects the specific neuronal response. This will be witnessed directly in the next section on the Pyloric Circuit. 

Specifically in the Pyloric Circuit, experimentation has shown the following 

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