Search

Nitric oxide (NO) is a neuronal messenger molecule that mediates pathway refinement in some brain regions. We used nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) histochemistry to examine the development of NO expression in the superior colliculus (SC) of kittens aged E28-E58 and P2-P57 and adults in order to determine if NO expression is correlated with pathway refinement. At E28, labeled cells were seen only within the subventricular zone (SVZ). At E36-E41, labeled cells were also found within the deep gray layer (DGL) of SC. At E51 and E58, a few labeled neurons were also present in the intermediate gray layer (IGL). These neurons already had extensive dendritic fields and well-developed morphologies at the time that they first expressed nitric oxide synthase (NOS). The number of neurons labeled in the DGL and IGL increased postnatally, reaching a peak density between P14 and P35. Neurons within the optic (OL) and superficial gray layers (SGL) were first visible at P7 and increased slightly in number until adulthood. However, SGL-labeled neurons were relatively limited in number and lightly labeled at all ages examined. We conclude that (1) NADPHd expression occurs in SC beginning in the second trimester in kittens and progresses in a ventral to dorsal pattern between E36-P35; (2) few neurons in kitten SGL are labeled by NADPHd and these appear relatively late in postnatal development; and (3) there is no correlation between NOS expression and retinocollicular pathway refinement in kittens, a result different from that seen in rodents.

The distribution and ultrastructure of neurons and neuropil labeled by an antiserum to gamma-aminobutyric acid (GABA) were examined in the lateral geniculate nucleus (LGN) of the tree shrew (Tupaia belangeri). The LGN of this species segregates center type and cell class into three distinct pairs of laminae: a medial pair (laminae 1 and 2) containing ON-center cells, a more lateral pair (4, 5) containing OFF-center cells, and 2 laminae (3, 6) containing W-like cells. The relationship between this laminar segregation and the distribution of GABA immunoreactivity was investigated in the present study. GABA-immunoreactive neurons and neuropil were present in all six of the laminae. However, both the density of labeled cells (adjusted for neuronal density across laminae) and the density of labeled neuropil showed a medial-to-lateral gradient. The adjusted density of labeled cells was higher laterally than medially, and the density of labeled neuropil was significantly greater in the more lateral OFF-center laminae and W-like laminae than in the medial two ON-center laminae. Thus, inhibitory, GABAergic influences may modulate to different degrees the visual signals in the ON, OFF, and W pathways. Labeled cells had a mean cross-sectional area (107 microns 2) approximately one-half that of unlabeled cells (216 microns 2). They constitute 16-34% of the neurons in the LGN. At the electron microscope level, three different kinds of labeled profile were observed. Vesicle containing profiles like the F2 profiles of cat were postsynaptic to retinal terminals and presynaptic to conventional dendrites. F1 axon terminals with dense clusters of vesicles were also labeled as were some myelinated axons. Another labeled profile, which we suggest should be called an F3 process, was a large dendrite of irregular caliber with punctate groups of vesicles near the synapse. Our results suggest that GABAergic circuitry is an important part of the functional organization in the LGN of the tree shrew.

Cat-301 is a monoclonal antibody which recognizes a cell surface associated antigen of selected neurons in the central nervous system (CNS). In the visual system, cat-301 selectively labels Y-like cells in several visual structures, including portions of the lateral geniculate nucleus complex and visual cortex. The cat superior colliculus (SC) also receives Y input and contains cells driven by Y input which are selectively distributed in the deep superficial gray and deeper laminae. If cat-301 is selective to the Y-cell system in SC, labeled cells should be restricted to those laminae. To test this hypothesis, we have examined quantitatively the laminar distribution, percentage, size, and morphology of cells in SC labeled by the cat-301 antibody. Cat-301 labeled a variety of cells in the cat SC. Labeled cells were found within the deep portion of the superficial gray layer (6.6%), optic layer (27.6%), intermediate gray layer (26.9%), and the deep gray and white layers (38.5%). By contrast, only 2 of 667 labeled cells (0.3%) were found within that part of the upper superficial gray layer innervated exclusively by W input and thought to contain only W-driven cells. When considered as a percentage of the total cell population, cat-301 labeled cells represented less than 3% of cells in the superficial gray layer and approximately 15% in the deeper layers. Neurons labeled by cat-301 were all of medium to large size (mean average diameter = 33.3 microns; range = 15-84 microns) and included vertical fusiform and stellate cells in the upper layers and the very large neurons found in the intermediate gray and deeper layers. These results provide further evidence that the cat-301 antibody selectively recognizes the Y channel of the cat visual system.