Amino Acid Transmitters in the Adult and Developing Cerebellum

The cerebellum is a part of the brain in which amino acid transmitters are particularly abundant. Attempts to allocate transmitters to units in the cerebellar circuits have been facilitated by the fact that structural organization in the whole cerebellum is remarkably similar in different vertebrates and involves a limited number of nerve cell types [1,2]. The only efferent cell in the cerebellum is the Purkinje cell, which conveys inhibition onto nerve cells in the deep cerebellar nuclei. Impulse traffice from the cerebellum is determined by two major circuits, the climbing fiber-Purkinje cell and the mossy fiber-granule cell-Purkinje cell circuits, whose activities are modulated by inhibitory interneurones. There is good evidence that the major transmitter of Purkinje cells is gamma-aminobutyric acid (GABA), although the co-existence of this amino acid with certain neuropeptides has also been documented (see Section 5.2.1). The inhibitory interneurones, and basket, stellate, and Golgi cells also seem to operate primarily with GABA. However, it has been proposed that taurine (Tau) may be associated with some of the inhibitory cerebellar neurones (see Section 5.2.2). It seems that the transmitter of the only excitatory nerve cells in the cerebellum, the granule cell, is also an amino acid, most of the evidence favoring glutamate (Glu). In addition to the intrinsic nerve cells, some of the cerebellar afferents are also aminoacidergic.