Biology subjects

Anair, J. D.

Publications and source records attributed to Anair, J. D..

2 recordsLinked to original sources

bioRxiv2022

Inhibitory NPY neurons provide a large and heterotopic commissural projection in the inferior colliculus

Located in the midbrain, the inferior colliculus (IC) plays an essential role in many auditory computations, including speech processing and sound localization. The right and left side of the IC are interconnected by a dense fiber tract, the commissure of the IC (CoIC), that provides each IC with one its largest sources of input (i.e., the contralateral IC). Despite its prominence, the CoIC remains poorly understood. Previous studies using anterograde and retrograde tract-tracing showed that IC commissural projections are predominately homotopic and tonotopic, targeting mirror-image locations in the same frequency region in the contralateral IC. However, it is unknown whether specific classes of neurons, particularly inhibitory neurons which constitute [~]10-40% of the commissural projection, follow this pattern. We therefore examined the commissural projections of Neuropeptide Y (NPY) neurons, the first molecularly identifiable class of GABAergic neurons in the IC. Using retrograde tracing with Retrobeads in NPY-hrGFP mice of both sexes, we found that NPY neurons comprise [~]11% of the commissural projection. Moreover, focal injections of Retrobeads showed that NPY neurons in the central nucleus of the IC exhibit a more divergent and heterotopic commissural projection pattern than non-NPY neurons. Thus, commissural NPY neurons are positioned to provide cross-frequency, lateral inhibition to the contralateral IC. Through this circuit, sounds that drive activity in limited frequency bands on one side of the IC might suppress activity across a larger number of frequency bands in the contralateral IC.

neuroscience↗

bioRxiv2019

Neuropeptide Y expression defines a novel class of GABAergic projection neurons in the inferior colliculus

Located in the midbrain, the inferior colliculus (IC) integrates information from numerous auditory nuclei and is an important hub for sound processing. Despite its importance, little is known about the molecular identity and functional roles of defined neuron types in the IC. Using a multifaceted approach in mice, we found that neuropeptide Y (NPY) expression identifies a major class of inhibitory neurons, accounting for approximately one-third of GABAergic neurons in the IC. Retrograde tracing showed that NPY neurons are principal neurons that can project to the medial geniculate nucleus. In brain slice recordings, many NPY neurons fired spontaneously, suggesting that NPY neurons may drive tonic inhibition onto postsynaptic targets. Morphological reconstructions showed that NPY neurons are stellate cells, and the dendrites of NPY neurons in the tonotopically-organized central nucleus of the IC cross isofrequency laminae. Immunostaining confirmed that NPY neurons express NPY, and we therefore hypothesized that NPY signaling regulates activity in the IC. In crosses between Npy1rcre and Ai14 Cre-reporter mice, we found that NPY Y1 receptor (Y1R)-expressing neurons are glutamatergic and were broadly distributed throughout the rostro-caudal extent of the IC. In whole-cell recordings, application of a high affinity Y1R agonist led to hyperpolarization in most Y1R-expressing IC neurons. Thus, NPY neurons represent a novel class of inhibitory principal neurons that are well poised to use GABAergic and NPY signaling to regulate the excitability of circuits in the IC and auditory thalamus.

neuroscience↗