Neonatal deafferentation does not alter membrane properties of trigeminal nucleus principalis neurons

In the brain stem trigeminal complex of rats and mice, presynaptic afferent arbors and postsynaptic target cells form discrete modules ("barrelettes") , the arrangement of which duplicates the patterned distribution of whisker s and sinus hairs on the ipsilateral snout. Within the barrelette region of the nucleus principalis of the trigeminal nerve (PrV), neurons participati ng in barrelettes and those with dendritic spans covering multiple barrelet tes (interbarrelette neurons) can be identified by their morphological and electrophysiological characteristics as early as postnatal day 1. Barrelett e cells have focal dendritic processes, are characterized by a transient K conductance (I-A), whereas interbarrelette cells with larger soma and exte nsive dendritic fields characteristically exhibit low-threshold T-type Ca2 spikes (LTS). In this study, we surveyed membrane properties of barrelette and interbarrelette neurons during and after consolidation of barrelettes in the PrV and effects of peripheral deafferentation on these properties. D uring postnatal development (PND1-13), there were no changes in the resting potential, composition of active conductances and Na 1 spikes of both barr elette and interbarrelette cells. The only notable changes were a decline i n input resistance and a slight increase in the amplitude of LTS. The infra orbital (IO) branch of the trigeminal nerve provides the sole afferent inpu t source to the whisker pad. IO nerve transection at birth abolishes barrel ette formation as well as whisker-related neuronal patterns all the way to the neocortex. Surprisingly this procedure had no effect on membrane proper ties of PrV neurons. The results of the present study demonstrate that dist inct membrane properties of barrelette and interbarrelette cells are mainta ined even in the absence of input from the whiskers during the critical per iod of pattern formation.