NEUROTENSIN MODULATION OF ULTRASONIC VOCALIZATION USING SYSTEMIC NEONATAL SEPSIS MODEL

Abstract

Neonatal sepsis is the leading cause of morbidity and mortality in newborns. The presence of non-specific signs and symptoms caused by invading pathogens hinders early recognition and diagnosis in neonatal sepsis. The brainstem neural circuits that maintain automatic breathing become disrupted in response to sepsis-induced neuroinflammation, leading to respiratory dysfunction. In addition, breathing circuits interact with eliciting vocalizations during the crying phase in newborns, showing a fundamental coordination of both circuits. Therapeutic hypothermia is defined as a 2-6°C reduction in body temperature that can act as neuroprotective for sepsis-induced encephalopathy. Neurotensin is a 13 amino acid peptide that binds to NTSR1 and NTSR2, promoting hypothermia in rodents. A poorly understood interaction exists between therapeutic hypothermia, neurotensin, and inflammation for breathing-vocalization circuits. Our hypothesis states that therapeutic hypothermia could provide neuroprotection and ultimately preserve the brainstem functions, including the respiratory-vocalization circuit integrity. This thesis investigated the potential of therapeutical hypothermia using neurotensin agonist (PD149163) to modulate respiratory circuit integrity following sepsis. We utilized a preclinical experimental model utilizing TLR ligands such as LPS (TLR4 agonist) and PAM3CSK4 (TLR1/2 agonist) to mimic systemic inflammatory response promoted by gram-negative and gram-positive bacterial infection. Postnatal day 5 CD1 mouse pups were exposed to either saline or neurotensin pretreatment, followed by sepsis induction. Physiological and behavioral assessments were performed 3 hours following the TLR ligands administration. We leveraged ultrasonic vocalizations (USVs) and whole-body plethysmography (WBP) to assess respiratory circuit integrity. USVs and WBP were used as noninvasive approaches to provide a readout of intact respiratory-vocalization circuits in rodent models. Data analysis utilized machine-learning pipelines including MUPET and VocalMat in MATLAB for USVs recordings. R programming language and environment were utilized for statistical computing and graphics. Neurotensin agonist was effective inducing hypothermia in PD5 control pups. As previously reported by our lab, LPS also induced hypothermic effects. PD149163 paired with LPS further reduced the body temperature whereas PAM3CSK4 or paired with PD149163 did not promote changes. Maternal retrieval time increased in response to LPS, and it was aggravated by PD149163. USV complexity was deeply affected by neonatal sepsis changes due to LPS, reducing total calls, syllable variety, and repertoire units. PD149163 further exacerbated these vocal deficits with LPS-induced sepsis but partially restored complex call types in the PAM3CSK4 group. The WBP assessed the respiratory changes due to sepsis and hypothermia. The minute ventilation was depressed in baseline recordings of LPS and LPS + PD149163 groups. Hypercapnia was used to evoke a central ventilatory response; sepsis results in a depressed minute ventilation response which was further amplified with PD149163. The hypothermic effects due to PD149163 resulted in depressed minute ventilation during hypercapnia. Together, these findings demonstrate that neurotensin modulates brainstem respiratory-vocalization circuitry which might not be beneficial upon gram-negative bacterial induced inflammation. This work provides new insight into how thermoregulation, immune activation, and neural control of breathing and communication interact in early life. By revealing the conditions under which neurotensin signaling is protective or detrimental, this thesis establishes a foundation for future studies exploring neurotensin modulation as a potential regulator of neonatal responses during infection.No embargoAcademic Major: Microbiolog