ESTABLISHMENT OF PATTERNED THALAMOCORTICAL CONNECTIONS DOES NOT REQUIRE NITRIC-OXIDE SYNTHASE

Subplate neurons are early-generated neurons that project into the ove rlying neocortex and are required for the formation of ocular dominanc e columns. A subset of subplate neurons express nitric oxide synthase (NOS) and produce nitric oxide (NO), a neuronal messenger thought to b e involved in adult hippocampal synaptic plasticity and also in the es tablishment of certain specific connections during visual system devel opment. Here, we examine whether the NOS-containing subplate neurons a re involved in ocular dominance column formation in the ferret visual system. Ocular dominance columns form in ferrets between postnatal day 35 (P35) and P60. NOS expression in the visual subplate is low at bir th, increases to a maximum at the onset of ocular dominance column for mation, and falls thereafter. Nevertheless, blockade of NOS with daily injections of nitroarginine from P14 to P56 fails to prevent the form ation of ocular dominance columns, although NOS activity is reduced by >98%. To test further a requirement for NOS in the patterning of conn ections during CNS development, we examined the cortical barrels in th e somatosensory system of mice carrying targeted disruptions of NOS th at also received injections of nitroarginine; cortical barrels formed normally in these animals. In addition, barrel field plasticity induce d by whisker ablation at birth was normal in nitroarginine-injected NO S knock-out mice. Thus, despite the dynamic regulation of NOS in subpl ate neurons, NO is unlikely to be essential for the patterning of thal amocortical connections either in visual or somatosensory systems.