Opposing effects of striatonigral feedback pathways on midbrain dopamine cell activity

Area of Science:

• Neuroscience
• Neurophysiology

Background:

• The striatonigral GABAergic pathway is anatomically and biochemically established.
• Dopaminergic (DA) neurons in the substantia nigra are crucial for motor control and reward.
• Understanding the precise mechanisms of striatal influence on DA neurons is vital.

Purpose of the Study:

• To investigate the functional properties of the striatonigral GABAergic pathway.
• To elucidate the direct and indirect effects of striatal stimulation on DA neurons and substantia nigra reticulata (SNR) neurons.
• To determine the role of interneurons in mediating striatal effects on DA cell firing.

Main Methods:

• Intracellular and extracellular recordings from identified DA neurons and SNR neurons in vivo.
• Electrical stimulation of the striatum.
• Pharmacological manipulation using picrotoxin.
• Intracellular chloride injection to assess chloride conductance.

Main Results:

• Striatal stimulation elicits chloride-mediated inhibitory postsynaptic potentials (IPSPs) in DA neurons with a short latency.
• SNR neurons receive larger and longer-duration IPSPs from striatal stimulation, without a rebound depolarization.
• Low-level striatal stimulation increases DA cell firing, potentially by inhibiting GABA-sensitive SNR interneurons.

Conclusions:

• Striatal cells project to both DA neurons and SNR neurons via branched, fast-conducting GABAergic pathways.
• DA neuron excitation by low-level striatal stimulation is mediated by preferential inhibition of more sensitive SNR interneurons.
• The striatonigral pathway exhibits complex modulatory effects on DA neuron activity.