Glial hyperpolarization upon nerve root stimulation in the leech Hirudo medicinalis

Area of Science:

• Neuroscience
• Glial Cell Biology
• Neurophysiology

Background:

• Glial cells in the leech central nervous system (CNS) primarily show depolarizing responses to neuronal activity.
• Previous studies indicated that glial cells respond to nerve stimulation with depolarization, but hyperpolarizing responses were less understood.

Purpose of the Study:

• To investigate hyperpolarizing responses in leech neuropil glial cells evoked by nerve root stimulation.
• To elucidate the underlying neuron-glial communication pathways and neurotransmitters involved.

Main Methods:

• Intracellular recording and extracellular stimulation techniques were employed in the isolated CNS of the leech Hirudo medicinalis.
• Glial cell responses were measured before and after application of specific antagonists and altered ionic concentrations.

Main Results:

• Nerve root stimulation induced significant hyperpolarization in glial cells (mean -8.6 mV from -60.5 mV resting potential).
• The ionotropic glutamate receptor antagonist CNQX partially blocked this hyperpolarization, suggesting a role for glutamate.
• High divalent cation concentrations reduced hyperpolarization, while bath-applied glutamate and kainate elicited CNQX-sensitive hyperpolarizations.

Conclusions:

• Leech glial membranes respond to neuronal activity with both depolarizing and hyperpolarizing potentials.
• Glutamate acts as a neurotransmitter in an indirect neuron-glial communication pathway mediating these hyperpolarizing responses.
• These findings expand the understanding of neuron-glial interactions in the CNS.