Neurones in the adult rat anterior medullary velum

The presence of neurones in the rat anterior medullary velum (AMV) has been investigated by using antibodies to the calcium-binding proteins, parvalbu min (PV), calretinin (CR), and calbindin-D28k (CB). Disparate populations o f mainly GABAergic neurones were located in the rostral and caudal regions of the AMV. The rostral region of the AMV was characterised by GABAergic CR -labelled or W-labelled neurones. CR-labelled neurones were bipolar or mult ipolar with round to ovoid somata (diameters between 8 and 12 mu m) and ros trocaudally running dendrites forming a network. PV-labelled neurones had r ound somata (diameters between 6 and 10 mu m) and were bi-tufted, with bead ed dendrites. Both CR-labelled and PV-labelled dendrites formed punctate pe ricellular associations with unlabelled somatic profiles. In the caudal reg ion of the AMV, PV-labelled neurones were GABAergic, multipolar cells, havi ng round somata (diameters between 9 and 12 mu m), with either beaded or no n-beaded dendrites forming a network of interconnecting dendrites. PV-label led pericellular associations were made around both PV-labelled and unlabel led somatic profiles. CR labelled unipolar brush cells (UBCs) were not GABA ergic. UBCs were characterised by a round to oval somata (10-15 mu m in dia meter) from which a single primary dendrite emerged to form a distal expans ion having small terminal dendrites. From the distal expansion, there also appeared to be CR-labelled processes emanating and extending for up to 250 mu m. CB occasionally labelled "Purkinje-like cells" TPLCs). The rat ARN is a more complex structure than first envisaged with the presence of predomi nantly inhibitory neurones expressing different calcium-binding proteins. F unctional and anatomic aspects of this circuitry are further discussed. J. Comp. Neurol. 419:122-134, 2000. (C) 2000 Wiley-Liss, Inc.