|Parvalbumin (PV)-containing cortical GABA neurons include chandelier cells (PVChCs) and basket cells (PVBCs), which innervate the axon initial segment (AIS) and soma/proximal dendrites of pyramidal cells, respectively. In monkey prefrontal cortex (PFC), the density of PVChC axon cartridges detectable by PV immunoreactivity peaks prior to the onset of puberty before declining markedly to adult levels, whereas the density of PV-immunoreactive (IR) puncta (presumed PVBC terminals) increases during adolescence. These inverse developmental changes in axon terminal density could explain why an electron microscopy study found no change in the density of symmetric, presumably GABAergic, synapses between infancy and adulthood in monkey PFC. Alternatively, the inverse developmental trajectories of PVChC and PVBC axon terminals could represent cell type-specific differences in the maturation of PV protein levels. To differentiate between these two alternatives, multi-label confocal microscopy was used to identify pre- and post-synaptic proteins at PVChC and PVBC appositions to pyramidal neurons (figure) in the PFC of 3 mo old and adult monkeys. The mean number of PVChC appositions per pyramidal neuron AIS was 32% significantly lower in adult compared to 3 mo monkeys, whereas the density of PVBC connections per pyramidal neuron did not differ between age groups. In contrast, relative levels of PV protein were two-fold higher in PVBC appositions in adult animals, whereas PV levels in PVChC appositions did not differ between age groups. These findings suggest cell type-specific mechanisms of maturation of PV-containing GABAergic axon terminals in monkey PFC.
|Fish K, Hoftman G, Sheikh W, Kitchens M, Lewis DA: Parvalbumin-containing chandelier and basket cell axon terminals have distinctive modes of maturation in monkey prefrontal cortex. J Neurosci, 8 May 2013, 22(19):8352-8358.