Anatomy of the Deep Cerebellar Nuclei Types of Neurons

THE INPUT TO THE DCN The DCN receive glutamatergic and GABAergic synaptic inputs, as well as a less-studied neuromodulatory input (see Gardette et al., 1987; Kitzman and Bishop, 1997; Saitow et al., 2009 for serotonergic innervations; and Jaarsma et al., 1997 for cholinergic innervations). The GABAergic input arises from PC axons. The glutamatergic input arises from the mossy fi ber (mf) collaterals carrying information from the spinal cord, diverse areas in the cerebral cortex (via the dorsal pontine nuclei) and several brainstem areas, and the climbing fi ber axon collaterals – the olivo-cerebellar (oc) fi bers – which carry information from the IO (Kandel et al., 2000). Each type of input forms a different varicosity on DCN neurons, making it possible to sort synapses according to their origin. The largest portion of synaptic connections is formed by PCs [about 60–85% of synapses, depending on the species and method used for counting (Chan-Palay, 1973b; Mezey et al., 1977; Palkovits et al., 1977; ANATOMY OF THE DEEP CEREBELLAR NUCLEI TYPES OF NEURONS The deep cerebellar nuclei (DCN) consist of three nuclei: the fastigial (medial) nucleus, the interposed nucleus and the dentate (lateral) nucleus. Together they form the sole output of the cerebellum. The total number of DCN neurons has been estimated at about 50–100,000 (Heidary, 1972; Beitz and Chan-Palay, 1979; Green et al., 2006). The neurons can be divided into three main sub-categories: excitatory projection neurons constituting approximately 50–60% of the population, that project to a variety of extra-cerebellar targets, including the cerebral cortex via the thalamus (Batini et al., 1992; Schwarz and Schmitz, 1997; Holdefer et al., 2000; Teune et al., 2000; Middleton and Strick, 2001; Dum and Strick, 2003; Kelly and Strick, 2003); inhibitory projection neurons constituting approximately 30–35% of the population, that project exclusively to the inferior olive (Tolbert et al., 1976; De Zeeuw et al., 1989; Fredette and Mugnaini, 1991); and local inhibitory interneurons constituting less than 10% of DCN neurons (Chan-Palay, 1977; Czubayko et al., 2001; Aizenman et al., 2003). These three subgroups are intermixed and spatially distributed heterogeneously throughout the DCN (Beitz and Chan-Palay, 1979; Kumoi et al., 1988; Batini et al., 1992). Recently, glycinergic projection neurons unique to the fastigial nuclei have been described Implications of functional anatomy on information processing in the deep cerebellar nuclei