The Morphology of the Koniocellular Axon Pathway in the Macaque Monkey

Abstract

The key objective of this study was to determine the distribution and morphology of koniocellular (K) lateral geniculate nucleus (LGN) axons in primary visual cortex (V1) of the macaque monkey. In particular, we were interested in understanding whether subpopulations of K axons exist in this species and, if so, if these subpopulations arise from different K layers of the LGN. Restricted injections of the tracers, biotinilated dextran amine, or Phaseolus vulgaris leucoagglutinin were targeted to specific LGN K layers under electrophysiological guidance and immunocytochemistry was used to visualize labeled axons in cortex that were subsequently reconstructed through serial sections. A total of 36 complete axons and 166 axon segments were reconstructed. Our results identified at least 2 main subpopulations of K axons in macaque V1 based on branching patterns and bouton distribution. Axons that arise primarily from LGN layers K1 and K2 are morphologically simple and tend to branch in cortical layers 1 and 3A. These axons give rise to fewer boutons than seen in axons arising from the dorsal K LGN layers K3-K6. Axons that arise from LGN layers K3-K6 terminate as complex, focused arbors in the cytochrome oxidase (CO) blobs in layer 3Balpha, with only occasional simple projections to the more superficial layers of cortex. Combined with previous observations, our data suggest that there are at least 3 subclasses of K LGN axons in macaque monkey that are similar to K axons identified earlier in both nocturnal simian owl monkeys (Ding and Casagrande 1997) and in prosimian, bush babies (Lachica and Casagrande 1992) suggesting that the LGN K channels that terminate in the CO blobs and in layer 1 are not unique to macaque monkeys but are a common primate feature.

Differential expression patterns of OCC1-related, extracellular matrix proteins in the lateral geniculate nucleus of macaque monkeys

“…K layers of the dLGN, especially K3-K6, have been characterized by blue-color processing, and have been shown to project to blobs of V1 (Casagrande et al, 2007;Martin et al, 1997). Since we have revealed that SC1 mRNA is abundantly expressed in blobs as well (Takahata et al, 2009b), our previous studies and this study raise an interesting possibility that SC1 mRNA is selectively expressed in this particular circuitry.…”

Parallel information processing channels created in the retina

“…This system has been extensively studied; several reviews describe it in detail (91)(92)(93)(94)(95)(96)(97)(98). Many of the K ganglion cells have bistratified dendritic arbors, as a result of which they receive both ON and OFF inputs from bipolar cells.…”

Retinal ganglion cell inputs to the koniocellular pathway

“…Many cells in the koniocellular division show neurochemical signatures (patterns of immunoreactivity) that are distinct from those of cells in the parvocellular and magnocellular divisions, supporting the koniocellular pathway as a distinct part of the afferent visual stream (Hendry and Yoshioka, 1994;Goodchild and Martin, 1998;Hendry and Reid, 2000;Solomon, 2002;Casagrande and Xu, 2003). It is customarily assumed that ganglion cell input to the koniocellular layers comes from non-midget, non-parasol cells with relatively large ("widefield") dendritic fields and diverse cortical projections (Rodieck and Watanabe, 1993;Hendry and Reid, 2000;Casagrande et al, 2007). The diverse morphological properties of wide-field cells could thus potentially be mapped onto the diverse physiological ("W-like") properties of koniocellular cells (Norton and Casagrande, 1982;Irvin et al, 1986;White et al, 2001;Xu et al, 2001;Solomon et al, 2002;Casagrande and Xu, 2003).…”