Neuronal diversity in the anteroventral cochlear nucleus of Mongolian gerbil

The cochlear nucleus is the first processing unit of the ascending auditory pathway, where various neuron types integrate spike trains from convergent auditory nerve fibres (ANF). It is known that the neurons in the anteroventral cochlear nucleus (AVCN) differ morphologically and are categorised electrophysiologically, based on the shape of their peri-stimulus-time-histogram (PSTH) in response to acoustic stimulation with pure tones. Previous study on cats (Felis catus) reported that most AVCN neurons increase their firing probability and precision relative to the ANFs that innervate them. This phenomenon has been termed “phase-locking enhancement” and surprisingly is not as common in the Mongolian gerbil (Meriones unguiculatus), a model organism of growing popularity in auditory research.Here, we aim to explore the functional and structural correlates of the phase-locking enhancement in gerbils. First, we recorded in vivo the response of gerbil single AVCN neurons to pure tones. To take into account the diversity in response, we developed an updated classification scheme relying on various metrics quantifying regularity of the spike trains. Next, we applied a high-throughput imaging approach, based on confocal images of the gerbil AVCN, to explore the histological diversity in this nucleus. Analysis was performed at different anatomical locations to take into account the tonotopic axis. Our results provide insights into complexity and ambiguity of categorisation of neurons in AVCN that has not been addressed in great detail until very recently.