GABA and Dopamine

The following films are from the Multimedia Neuroscience Education Project at Williams College

This cross section of the brain shows the Limbic System and focuses in on the amydgdala the area most responsible for feelings of fear and anxiety.

If enough excitatory action potentials arrive at the axon terminal simultaneously, the membrane potential will rise above threshold, and a the nerve will fire. The presence of inhibitory signals (from a nerve releasing GABA for example) will lower the membrane potential. If enough inhibitory nerves have fired, they will stop the neuron from firing. In this video the neuron in the middle is an inhibitory neuron, stopping the firing in the output neuron generated by the other two excitatory neurons.

The action potential in the inhibitory interneuron travels to the end of the axon, Here we find vesicles containing the neurotransmitter GABA, waiting to be released. The vesicles fuse with the presynaptic membrane, and release the GABA molecules into the synaptic cleft, where they can diffuse to the GABA receptors on the postsynaptic side.

When two molecules of GABA bind to the receptor, the channel in the middle opens up, and chloride ions rush into the receiving neuron. The chloride has an inhibiting effect on the firing of the nerve.

rotation of the subunits of the receptor causes the channel in the middle to open up allowing the passage of chloride

The GABAa receptor has a second recognition site at which can Benzodiazepines can bind. These drugs such as Librium Valium and Xanax, are tranquilizers which work to reduce fear and anxiety.

The Benzodiazepines do not bind directly to the GABA recognition site, instead they alter the GABAreceptor in such a way as to allow GABA to bind more easily to its own binding site increasing its effectiveness.

The natural effector that binds the diazepam site has the opposite effect of the drugs it decreases the effectiveness of GABA, and acts as an anxiogenic

The dopamine receptor works in a very different way. When dopamine binds to the receptor changes in the receptpr initiate a series of reactions leading to cAMP formation (similar to what happens with adrenaline). cAMP triggers phosphorylations that among other things changes the sensitivity of the neuron to stimuli.