Excitatory amino acids in the cerebellum

In recent years, it has been shown diat the class of excitatory amino acid transmitters is very important for neurotransmission throughout the nervous system. Glutamate and aspartate are the most common endogenous transmitters of this class, but it is now known that they exert their actions through a multitude of receptor subtypes. Furthermore, modifications of excitatory amino acid transmission are believed to underlie many forms of sensory and motor learning in the brain, whereas perturbations of these systems underlie many neuropathologies. Since the cerebellum is involved with motor coordination and the cerebellar Purkinje cell forms a crucial link in the formation of motor learning, a thorough understanding of excitatory amino acid neurotransmission would be desirable.

Extracellular recording techniques were coupled with microiontophoretic application of drugs to test the effectiveness of several endogenously and exogenously occurring excitatory amino acids in exciting cerebellar Purkinje cells in the anesthetized rat. Also, further characterization of N-methyl-D-aspartate (NMDA)-mediated responses was done as some studies have suggested that Purkinje cells do not have NMDA receptors.

Results from these studies indicate that agents from all classes of excitatory amino acids are enable of exciting Purkinje cells and that NMDA-induced excitations are mediated through the classically defined NMDA receptor. Additionally, serotonin was shown to depress responses elicited by some but not all of the excitatory amino acids. These results suggest that all classes of excitatory amino acids are important for neurotransmission within the cerebellum and that serotonin may selectively modulate some of these pathways, thus affecting motor learning and coordination.