Suprapontine Structures Modulate Brainstem and Spinal Networks

Abstract

Several spinal motor output and essential rhythmic behaviors are controlled by supraspinal structures, although their contribution to neuronal networks for respiration and locomotion at birth still requires better characterization. As preparations of isolated brainstem and spinal networks only focus on local circuitry, we introduced the in vitro central nervous system (CNS) from neonatal rodents to simultaneously record a stable respiratory rhythm from both cervical and lumbar ventral roots (VRs).Electrical pulses supplied to multiple sites of brainstem evoked distinct VR responses with staggered onset in the rostro-caudal direction. Stimulation of ventrolateral medulla (VLM) resulted in higher events from homolateral VRs. Stimulating a lumbar dorsal root (DR) elicited responses even from cervical VRs, albeit small and delayed, confirming functional ascending pathways. Oximetric assessments detected optimal oxygen levels on brainstem and cortical surfaces, and histological analysis of internal brain structures indicated preserved neuron viability without astrogliosis. Serial ablations showed precollicular decerebration reducing respiratory burst duration and frequency and diminishing the area of lumbar DR and VR potentials elicited by DR stimulation, while pontobulbar transection increased the frequency and duration of respiratory bursts. Keeping legs attached allows for expressing a respiratory rhythm during hindlimb stimulation. Trains of pulses evoked episodes of fictive locomotion (FL) when delivered to VLM or to a DR, the latter with a slightly better FL than in isolated cords.In summary, suprapontine centers regulate spontaneous respiratory rhythms, as well as electrically evoked reflexes and spinal network activity. The current approach contributes to clarifying modulatory brain influences on the brainstem and spinal microcircuits during development. Graphical Abstract Novel preparation of the entire isolated CNS from newborn rats unveils suprapontine modulation on brainstem and spinal networks. Preparation views (A) with and without legs attached (B). Successful fictive respiration occurs with fast dissection from P0-P2 rats (C). Decerebration speeds up respiratory rhythm (D) and reduces spinal reflexes derived from both ventral and dorsal lumbar roots (E).

A focal traumatic injury to the spinal cord causes an immediate and massive spreading depolarization sustained by chloride ions, with transient network dysfunction and remote cortical glia changes

“…Spontaneous rhythmic motor discharges recorded from cervical VRs, with a period of 24.27 ± 16.13 s, were attributed to respiratory bursts that were also derived synchronous among bilateral lumbar VRs (Mohammadshirazi et al, 2023;Apicella and Taccola, 2023). The coefficient of variation (CV), an indicator of response consistency, was determined by the ratio between standard deviation and mean value (Taccola et al, 2020).…”

“…Experiments were performed on in vitro preparations of the entire isolated central nervous system (CNS; (Mohammadshirazi et al, 2023)). Newborn rats were subjected to cryoanesthesia (Danneman and Mandrell, 1997).…”

“…To investigate the immediate events following a contusive spinal cord injury, a custom-made impactor was employed to induce a physical impact at thoracic spinal cord level of an in vitro preparation of entire CNS (Mohammadshirazi et al, 2023). The careful design of the impactor included a proper shielding to minimize any electrical interference during operation, to allow simultaneous electrophysiological recordings during the impact.…”

“…This temporal limitation sums up to the effects of anesthetics that depress neuronal excitability and are used in preclinical models at the time of the physical trauma. A solution to avoid any technical artifacts, as well as any consequences of anesthetics, is the adoption of the neonatal preparation of the entire central nervous system in vitro (CNS; (Mohammadshirazi et al, 2023;Apicella and Taccola, 2023)), which does not require the administration of any drugs. In addition, the rodent spinal cord can be optimally damaged through a low-noise calibrated micro impactor recently designed in the laboratory.…”

Cycle-frequency content EEG analysis improves the assessment of respiratory-related cortical activity

“…Breathing is the only vital function controlled both automatically and voluntarily (Horn & Waldrop, 1998; Mohammadshirazi et al, 2023). The involvement of the brain in breathing control ranges from increased attentional resources (Moore et al, 2012), to voluntary modification of the breathing pattern (Pouget et al, 2018), as well as compensatory mechanisms in the presence of ventilatory constraints that hinder adequate airflow (Raux et al, 2007).…”