Short-Term Plasticity in Cortical GABAergic Synapses on Olfactory Bulb Granule Cells Is Modulated by Endocannabinoids

Area of Science:

• Neuroscience
• Olfactory System
• Synaptic Plasticity

Background:

• Olfactory bulb circuits are modulated by higher processing areas, influencing sensory processing and memory.
• Granule cells in the olfactory bulb receive both excitatory and inhibitory cortical inputs.
• Endocannabinoid signaling robustly modulates excitatory inputs to granule cells.

Purpose of the Study:

• To investigate endocannabinoid modulation of inhibitory cortical inputs to olfactory bulb granule cells.
• To determine if cannabinoid type 1 (CB1) receptors influence GABAergic projections from the HDB to granule cells.

Main Methods:

• Expressed channelrhodopsin-2 (ChR2) in GABAergic neurons of the HDB projecting to olfactory bulb granule cells.
• Used optical activation of ChR2 to induce GABAergic inhibitory postsynaptic currents (IPSCs).
• Administered CB1 receptor agonist (Win 55,212-2) and antagonist (AM 251) to assess receptor involvement.

Main Results:

• Optical activation of HDB projections caused frequency-dependent short-term depression of GABA-mediated IPSCs.
• CB1 receptor activation decreased IPSC amplitude and reduced short-term depression.
• CB1 receptor blockade increased individual IPSCs and enhanced short-term depression.

Conclusions:

• Tonic endocannabinoid activation modulates GABAergic HDB→granule cell synapses, similar to glutamatergic inputs.
• This modulation influences synaptic currents and short-term plasticity.
• Regulation of this inhibitory balance impacts olfactory bulb output and sensory processing.