Diagnostic Utility of Sodium Lactate Infusion and CO2-35% Inhalation for Panic Disorder

Locus coeruleus noradrenaline depletion and its differential impact on CO2-induced panic and hyperventilation in male and female mice

CO2 exposure has been used to investigate the panicogenic response in patients with panic disorder. These patients are more sensitive to CO2, and more likely to experience the "false suffocation alarm" which triggers panic attacks. Imbalances in locus coeruleus noradrenergic (LC-NA) neurotransmission are responsible for psychiatric disorders, including panic disorder. These neurons are sensitive to changes in CO2/pH. Therefore, we investigated if LC-NA neurons are differentially activated after severe hypercapnia in mice. Further, we evaluated the participation of LC-NA neurons in ventilatory and panic-like escape responses induced by 20% CO2 in male and female wild type mice and two mouse models of altered LC-NA synthesis. Hypercapnia activates the LC-NA neurons, with males presenting a heightened level of activation. Mutant males lacking or with reduced LC-NA synthesis showed hypoventilation, while animals lacking LC noradrenaline present an increased metabolic rate compared to wild type in normocapnia. When exposed to CO2, males lacking LC noradrenaline showed a lower respiratory frequency compared to control animals. On the other hand, females lacking LC noradrenaline presented a higher tidal volume. Nevertheless, no change in ventilation was observed in either sex. CO2 evoked an active escape response. Mice lacking LC noradrenaline had a blunted jumping response and an increased freezing duration compared to the other groups. They also presented fewer racing episodes compared to wild type animals, but not different from mice with reduced LC noradrenaline. These findings suggest that LC-NA has an important role in ventilatory and panic-like escape responses elicited by CO2 exposure in mice.

Adaptation of Threat Responses Within the Negative Valence Framework

External threats are a major source of our experience of negatively valanced emotion. As a threat becomes closer and more real, our specific behavior patterns and our experiences of negative affect change in response to the perceived imminence of threat. Recognizing this, the National Institute of Mental Health's Research Domain Criteria (RDoC) Negative Valence system is largely based around different levels of threat imminence. This perspective describes the correspondence between the RDoC Negative Valence System and a particular neurobiological/neuroecological model of reactions to threat, the Predatory Imminence Continuum (PIC) Theory. Using the COVID-19 pandemic as an illustration, we describe both adaptive and maladaptive behavior patterns from this perspective to illustrate how behavior in response to a crisis may get shaped. We end with suggestions on how further consideration of the PIC suggests potential modifications of the negative valence systems RDoC.

Salt: The paradoxical philosopher's stone of autonomic medicine

Sodium chloride, or common table salt, for millennia has played a prominent role in human affairs. Salt is also a key molecule for regulating intravascular fluid volume in patients with orthostatic disorders. In this first article of a special issue of the journal focusing on salt and the autonomic nervous system, the historical and physiologic significance of salt is reviewed, highlighting its importance to society and to medicine. The relevance of salt both for civilization and for autonomic physiology penetrates into nearly every aspect of life and health. Replacing salt that has been depleted or administering salt to expand intravascular volume is considered standard treatment for patients with orthostatic hypotension and syndromes of orthostatic intolerance. The potential longterm effects of added salt, including effects unrelated to intravascular volume, have been insufficiently studied in patients with autonomic disorders. A salient concern is the potential increased risk of developing hypertension. Underappreciated aspects of salt include its ability to increase anxiety and through nonosmotic mechanisms to contribute to local tissue inflammation. Salt may be either salubrious or detrimental, or possibly both at the same time, depending on the clinical conditions. Reconciling these opposite effects in clinical practice requires weighing benefits against potential risks, assessing what is known alongside what is uncertain, and titrating treatment decisions to the particular needs of each individual patient.

Mouse model of panic disorder: Vulnerability to early environmental instability is strain-dependent

Early life experiences and genetic background shape phenotypic variation. Several mouse models based on early treatments have evaluated short- and long-term phenotypic alterations and explored their molecular mechanisms. The instability of maternal cues was used to model human separation anxiety in outbred mice, one of the etiopathogenetic factors that predict panic disorder (PD). Application of the repeated cross-fostering (RCF) protocol to inbred strains (C57 and DBA) allowed us to measure differential responses to the same experimental manipulation. Ultrasounds emitted during isolation indicated that after RCF, pups from both strains lose their ability to be comforted by nest cues, but the frequency modulation of separation calls increased in RCF-C57 and decreased in RCF-DBA mice. No strain-specific difference in olfactory ability explained these responses in RCF-exposed mice. Rather, disruption of the infant-mother bond may differentially affect separation calls in the two strains. Moreover, the RCF-associated increased respiratory response to hypercapnia-an endophenotype of human PD documented among mice outbred strains-was replicated in the C57 strain only. We suggest that RCF-induced instability of the early environment affects emotionality and respiratory physiology differentially, depending on pups' genetic background. These strain-specific responses provide a lead to understand differential vulnerability to emotional disorders.