No abstract

Breathing requires precise control of respiratory muscles to ensure adequate ventilation. Neurons within discrete regions of the brainstem produce oscillatory activity to control the frequency of breathing. Less is understood about how spinal and pontomedullary networks modulate the activity of respiratory motor neurons to produce different patterns of activity during different behaviors (i.e., during exercise, coughing, swallowing, vocalizing, or at rest) or following disease or injury. Here, we use a chemogenetic approach to inhibit the activity of glutamatergic V2a neurons in the brainstem and spinal cord of neonatal and adult mice to assess their potential roles in respiratory rhythm generation and patterning respiratory muscle activity. Using whole-body plethysmography (WBP), we show that V2a neuron function is required in neonatal mice to maintain the frequency and regularity of respiratory rhythm. However, silencing V2a neurons in adult mice increases respiratory frequency and ventilation, without affecting regularity. Thus, the excitatory drive provided by V2a neurons is less critical for respiratory rhythm generation in adult compared to neonatal mice. In addition, we used simultaneous EMG recordings of the diaphragm and extradiaphragmatic respiratory muscles in conscious adult mice to examine the role of V2a neurons in patterning respiratory muscle activity. We find that silencing V2a neurons activates extradiaphragmatic respiratory muscles at rest, when they are normally inactive, with little impact on diaphragm activity. Thus, our results indicate that V2a neurons participate in a circuit that serves to constrain the activity of extradiaphragmatic respiratory muscles so that they are active only when needed.

Basal-like breast carcinomas (BLCs) present with extratumoral lymphovascular invasion, are highly metastatic, presumably through a hematogenous route, have augmented expression of CD44 oncoprotein and relatively low levels of retinoblastoma (Rb) tumor suppressor. However, the causal relation among these features is not clear. Here, we show that Rb acts as a key suppressor of multiple stages of metastatic progression. Firstly, Rb suppresses collective cell migration (CCM) and CD44-dependent formation of F-actin positive protrusions in vitro and cell-cluster based lymphovascular invasion in vivo. Secondly, Rb inhibits the release of single cancer cells and cell clusters into the hematogenous circulation and subsequent metastatic growth in lungs. Finally, CD44 expression is required for collective motility and all subsequent stages of metastatic progression initiated by loss of Rb function. Altogether, our results suggest that Rb/CD44 pathway is a crucial regulator of CCM and metastatic progression of BLCs and a promising target for anti-BLCs therapy.

Our prior studies suggested that one subset of V2a neurons activates accessory respiratory muscles whereas another subset of V2a neurons actively prevents their activation at rest. However, since these studies altered V2a neuron excitability throughout the spinal cord and brainstem, it was not clear whether the V2a neurons that activate accessory respiratory muscles are located in the same region of the neuraxis as V2a neurons that prevent activation of accessory respiratory muscles at rest. Therefore, we used a Cre‐dependent AAV virus injected into a Chx10Cre/+ mouse to selectively target either the excitatory (Gq)‐ or inhibitory (Gi)‐DREADD receptor to cervical spinal V2a neurons on one side or both sides of the cord in order to alter V2a neuron excitability. Whole breath plethysmography (WBP) and electromyography (EMG) were recorded in conscious mice at rest to measure ventilation and respiratory muscle activity before and after altering V2a neuron excitability. We found that bilaterally increasing the excitability of cervical spinal V2a neurons increases accessory respiratory muscle (scalene) activity, diaphragm EMG peak amplitude, and ventilation. Although V2a neurons project ipsilaterally, increasing their excitability on one side of the cord is able to synchronously activate scalene muscles on both sides of the body. Bilaterally silencing cervical spinal V2a neurons also activates scalene muscle activity, but does not impair diaphragm function. Our results are consistent with the hypothesis that one subset of V2a neurons in the cervical spinal cord activates accessory respiratory muscles whereas another subset of cervical V2a neurons inhibits accessory respiratory muscles at rest. Support or Funding Information 1RO1NS112255T32NS5007453University of Cincinnati Dean’s Dissertation Completion Fellowship

Accessory respiratory muscles (ARMs) can be recruited to maintain respiration when the diaphragm is impaired or weakened, such as patients with Amyotrophic Lateral Sclerosis (ALS) or spinal cord injury. We chronically record mouse diaphragm electromyography (EMG), ARM EMG, and whole body plethysmography to assess the effect of activating and silencing V2a neurons with DREADDs on respiratory muscle activity and ventilation. Increasing the excitability of glutamatergic V2a neurons in the brainstem and/or the spinal cord recruits ARMs and enhances ventilation. Interestingly, silencing V2a neurons also activates ARMs. We hypothesize that V2a neurons participate in both excitatory and inhibitory pathways controlling activation of ARMs for breathing.Support or Funding InformationUniversity of Cincinnati T32 Training Grant 2016–2017This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.