Dopamine enhances both electrotonic coupling and chemical excitatory postsynaptic potentials at mixed synapses

Area of Science:

• Neuroscience
• Cellular Neuroscience
• Synaptic Plasticity

Background:

• Dopamine modulates neuronal excitability and synaptic transmission in various systems.
• Retinal horizontal cells show reduced electrotonic coupling and increased glutamate sensitivity with dopamine.
• Mixed electrotonic and chemical synapses are common, but dopamine's effect on them is less understood.

Purpose of the Study:

• To investigate the effect of dopamine on mixed electrotonic and chemical excitatory synapses.
• To determine the receptor and intracellular mechanisms underlying dopamine's action on Mauthner cell input.
• To characterize the dopaminergic innervation of the Mauthner cell.

Main Methods:

• Local application of dopamine near the goldfish Mauthner cell lateral dendrite.
• Monitoring excitatory postsynaptic potentials and currents evoked by eighth nerve stimulation.
• Pharmacological manipulation using dopamine D1 receptor antagonist (SCH-23390) and protein kinase A inhibitor (PKI5-24).
• Immunohistochemistry for dopamine and tyrosine hydroxylase, and electron microscopy.

Main Results:

• Dopamine persistently enhanced both electrotonic and chemical components of the postsynaptic response.
• Dopamine increased Mauthner cell input conductance.
• These effects were blocked by SCH-23390 and PKI5-24, indicating D1 receptor and cAMP-dependent kinase involvement.
• Dopaminergic fibers innervate the Mauthner cell but lack direct synaptic contact.

Conclusions:

• Dopamine enhances the gain of primary sensory input to the Mauthner cell.
• The mechanism involves D1 receptor activation, leading to a cAMP-dependent phosphorylation cascade.
• Dopamine acts as a volume transmitter, modulating synaptic transmission from a distance.