Haydon Lab Interests

Astrocytes

Calcium-dependent Glutamate Release from Astrocytes

Glia outnumber neurons ten-to-one in the CNS. Despite their numerical superiority, the roles of glial cells are not yet fully understood. Rudolf Virchow (1894) described glia (Greek for 'glue') as the cement that holds together the nervous elements. It is now clear that glia play more dynamic roles. In 1994 four independent groups demonstrated that astrocytes can signal directly to neurons. We have shown that astrocytes and Schwann cells can release the excitatory amino acids glutamate and aspartate in response to elevated internal calcium levels. Furthermore, when neurons are co-cultured with astrocytes, calcium-dependent release of glutamate from astrocytes leads to an NMDA receptor-dependent elevation of neuronal calcium. We are using a combination of molecular genetics, electrophysiology, confocal imaging and photolysis to determine roles for astrocytes in information processing in the nervous system.

Astrocytes Modulate Synaptic Transmission

To study the regulation of synaptic transmission, we stimulated astrocytes locally either with mechanical or with electrical stimuli that can promote calcium waves. Recording from neurons with patch pipettes, we then monitored the effects on neuronal properties. We have shown that a calcium elevation in astrocytes is both necessary and sufficient to modulate synaptic transmission and to activate ionotropic glutamate receptors on hippocampal neurons. These data suggest that astrocytes can dynamically regulate neuronal excitability and synaptic transmission.