Instructive role of a peripheral pattern for the central patterning of the trigeminal projection at the brainstem and thalamus revealed by an artificially altered whisker pattern

The central patterning mechanism of neuronal circuits is an important issue in developmental neuroscience. We report here the role of a peripheral whisker pattern for the patterning of the trigeminal projection at the brainstem and thalamus in the mouse somatosensory system. The whisker pattern was manipulated by infecting the embryonic epidermis with adenovirus harboring Shh. The ectopic expression of Shh led to the induction of extra whiskers and displacement of whiskers, where these whiskers were histologically normal. The altered whisker pattern was isomorphically represented in the brainstem (barrelette: subnuclei principalis and subnuclei interpolaris), thalamus (barreloid) and cortex (barrel) as revealed by cytochrome oxidase staining. The barrelette-like pattern of the parvalbumin became discernible by immunostaining at P7 in subnuclei principalis and at P4 in subnuclei interpolaris in normal mice. These are the barrelette neurons projecting to the thalamus and the local circuit within the barrelette. The barrelette-like parvalbumin pattern also exhibits the altered whisker pattern induced by the adenovirus harboring Shh. These results highlight the role the peripheral whisker pattern for the central patterning of the brainstem, thalamus, and cortex in the mouse somatosensory system.