Morphology of A beta hair follicle afferent collaterals in dorsal horn of cats with neonatal chronic denervation of digits.

1. The effect of neonatal denervation of two adjacent hindpaw digits (digits 3 and 4) in the cat on the morphology of spinal collaterals of identified A beta hair follicle afferents (HFAs) with receptive fields (RFs) on the neighbouring digits has been investigated using intra-axonal injection of horseradish peroxidase. 2. The morphology of collaterals of HFAs innervating intact digits (digit 2 or digit 5) was examined within the neonatally and chronically deprived region of dorsal horn by selectively injecting the afferents directly over this region. 3. Of a total of nine injected axons, seven had RFs on the distal part of digit 2, whereas two had RFs on the distal part of digit 5. With the exception of one of the digit 5 afferents, all injected afferents gave rise to stained collaterals throughout the chronically deprived digit representation. 4. Many collaterals within the chronically deprived region of dorsal horn gave rise to arborizations having relatively large numbers of boutons when compared with previously described somatotopically inappropriate (SIA) collaterals in the normal adult cat. 5. It is suggested that neonatal denervation of digits in the cat may lead to collateral sprouting and bouton formation by SIA collaterals of A beta HFAs innervating adjacent intact digits. This morphological plasticity could explain the previously reported functional reorganization of the RFs of spinocervical tract neurons that occurs in these neonatally deafferented animals.