Parvalbumin immunoreactivity is enhanced by brain-derived neurotrophic factor in organotypic cultures of rat retina

The rodent retina undergoes considerable postnatal neurogenesis and phenoty pe differentiation, and it is likely that diffusible neurotrophic factors c ontribute to this development and to the subsequent formation of functional retinal circuitry. Accordingly, perturbation of specific neurotrophin liga nd-receptor interactions has provided valuable information as to the fundam ental processes underlying this development. Tn the present studies we have built upon our previous observation that suppression of expression of trk( B), the high-affinity receptor for brain-derived neurotrophic factor (BDNF) , in the postnatal rat retina results in the alteration of a specific inter neuron in the rod pathway-the parvalbumin (PV)-immunoreactive AII amacrine cell. Here, we isolated retinas from newborn rats and maintained them in or ganotypic culture for up to 14 days (approximating the time of eye opening, in vivo) in the presence of individual neurotrophins [BDNF or nerve growth factor (NGF)]. We then examined histological sections of cultures for PV i mmunoreactivity, In control cultures, only sparse PV-immunostained cells we re observed. In cultures supplemented with NGF, numerous lightly immunostai ned somata were present in the inner nuclear layer (INL) at the border of t he inner plexiform layer (IPL). Many of these cells had rudimentary dendrit ic arborizations in the IPL. Cultures supplemented with BDNF displayed nume rous well-immunostained somata at the INL/IPL border that gave rise to elab orate dendritic arborizations that approximated the morphology of mature AI I amacrine cells in vivo. These observations indicate that neurotrophins ha ve specific effects upon the neurochemical and, perhaps, morphological diff erentiation of an important interneuron in a specific functional retinal ci rcuit. (C) 1999 John Wiley & Sons, Inc.