66 ± 0.37 mm and 7.36 ± 0.71 mm, respectively). The two cell types were indistinguishable in terms of number of primary dendrites and dendritic segments, total dendritic length, and highest branch order

(data not shown). All neurons bore dendritic spines (of various forms), and highly-varicose branching ramifications (Bevan et al., 1998 and Sadek et al., 2007) were present at some distal dendrites. On average, the dendrites of GP-TA neurons bore spines at a significantly higher density than those of GP-TI neurons (Table 1). Altogether, our anatomical analyses of GP-TI and GP-TA neurons showed that physiological dichotomy in GPe is supported by cell-type-specific differences in the structure of dendrites, local axon collaterals, and, most strikingly, GDC-0449 nmr long-range axonal selleck products projections. We provide the first direct correlation of the electrophysiological properties of individual GPe neurons in vivo with their molecular profiles and structure. In doing so, we elucidate key features that together constitute the foundations of a dichotomous functional organization of GPe. Two GPe cell types are thus specialized to release GABA, with or without a neuropeptide, on largely distinct

BG neuronal populations in different temporal patterns according to brain state. Neurons of the same cell type deliver identical neuroactive substances to a matching range of postsynaptic targets in the same temporal patterns (Somogyi,

2010). Our data are unique in establishing that GP-TI and GP-TA neurons are Megestrol Acetate different cell types as defined at several requisite levels of function. Our electrophysiological recordings readily distinguished two GABAergic GPe neuron populations with distinct neurochemical and structural properties. Most GP-TI neurons express PV, whereas almost all GP-TA neurons do not. While GP-TA neurons express PPE protein, suggesting they use enkephalin as a co-transmitter, GP-TI neurons do not. This physiological and molecular diversity is mirrored in cell structure. Thus, GP-TI neurons are prototypic in always innervating downstream BG nuclei like STN, whereas GP-TA neurons exclusively provide a massive input to striatum. The diverse electrophysiological properties of GPe neurons (Kita, 2007 and Mallet et al., 2008a) suggest different functions, but to firmly establish this, physiological diversity must be put into context with structure. By correlating spike timing in vivo with neurochemistry and outputs, we provide a good working definition of a functional dichotomy in GPe. Examination of synaptic transmission dynamics, causal interactions, and other parameters in the future will help to fully characterize this dichotomy. Molecular and structural diversity of GPe neurons has been reported at the population level (Kita, 2007) but has not been related to activity in vivo.