Emx1-Cre Is Expressed in Peripheral Autonomic Ganglia That Regulate Central Cardiorespiratory Functions

Abstract

The Emx1-IRES-Cre transgenic mouse is commonly used to direct genetic recombination in forebrain excitatory neurons. However, the original study reported that Emx1-Cre is also expressed embryonically in peripheral autonomic ganglia, which could potentially affect the interpretation of targeted circuitry contributing to systemic phenotypes. Here, we report that Emx1-Cre is expressed in the afferent vagus nerve system involved in autonomic cardiorespiratory regulatory pathways. Our imaging studies revealed expression of Emx1-Cre driven tdtomato fluorescence in the afferent vagus nerve innervating the dorsal medulla of brainstem, cell bodies in the nodose ganglion, and their potential target structures at the carotid bifurcation such as the carotid sinus and the superior cervical ganglion (SCG). Photostimulation of the afferent terminals in the nucleus tractus solitarius (NTS) in vitro using Emx1-Cre driven ChR2 reliably evoked EPSCs in the postsynaptic neurons with electrophysiological characteristics consistent with the vagus afferent nerves. In addition, optogenetic stimulation targeting the Emx1-Cre expressing structures identified in this study, such as vagus nerve, carotid bifurcation, and the dorsal medulla surface transiently depressed cardiorespiratory rate in urethane anesthetized mice in vivo . Together, our study demonstrates that Emx1-IRES-Cre is expressed in the key peripheral autonomic nerve system and can modulate cardiorespiratory function independently of forebrain expression. These results raise caution when interpreting systemic phenotypes of Emx1-IRES-Cre conditional recombinant mice, and also suggest the utility of this line to investigate modulators of the afferent vagal system.

Early developmental deletion of forebrain Ank2 causes seizure-related phenotypes by reshaping the synaptic proteome

“…Previous studies have reported that Emx1-Cre is expressed in the afferent vagus nervous system, which regulates autonomic cardiorespiratory pathways. 15 To confirm the neuronal role in mortality, ANK2 −/− :NEX-Cre mice, in which ankyrin-B was removed from excitatory neurons in the neocortex and hippocampus (but not inhibitory neurons) during embryonic development, were observed, and they also showed similar lethality ( Figure 1A ). On the contrary, seizures were not observed in ANK2 −/− :CaMKIIα-Cre mice.…”

Perspectives on the basis of seizure-induced respiratory dysfunction

“…Despite this, only a small subset of these animals died prematurely (Aiba and Noebels, 2021 ). However, a caveat to these experiments is that Emx1 cre/+ is not restricted to cortical excitatory neurons but rather is also expressed by peripheral autonomic ganglia that provide modulatory feedback to cardiorespiratory centers (Ning et al, 2022 ). Excluding potential confounding effects of peripheral nerves, these results suggest compromised brainstem function is required for cortical seizure- or SD-induced respiratory arrest and premature death (see Section “III.…”