MAINTAINING TEMPORAL PRECISION: SPECIES-DEPENDENT BIOPHYSICAL ADAPTATIONS IN THE MNTB

The medial nucleus of the trapezoid body is a well-studied model for exceptionally fast and reliable synaptic transmission, due to its unique synaptic input from the calyx of Held and conserved role in providing inhibition to binaural centres across species. Thus, the MNTB serves as a temporally precise relay station within the superior olivary complex to facilitate binaural detection. With its somatic location, size and high number of active zones the calyx of Held elicits a postsynaptic action potential reliably in a one-to-one connectivity. The rapid action potential generation in the postsynaptic MNTB neuron is aided through finely tuned biophysical properties, supporting rapid integration and short latencies. While this functionality appears to be stable across species, varying functional demands, compensating for differences in hearing range, head size or ecological and metabolic requirements, might promote highly specific adaptations.
In this study we quantify the biophysical properties of MNTB neurons, using whole-cell electrophysiology, across a wide range of animal models, including mice, mongolian gerbils, etruscan shrews, gray short tailed opossums and mouse lemurs.
We find that not only do MNTB neurons across different species vary in soma size but more importantly they show adaptations in voltage-gated conductances governing their firing properties and action potential kinetics to maintain temporal precision of input-output function.
Our findings demonstrate that even within highly conserved neuronal structures, subtle yet meaningful adaptations emerge. These results challenge the assumption that rodent models fully capture the diversity of mammalian neuronal biophysics and highlight the importance of comparative approaches.