Adeline Cathala

Midbrain dopamine (DA)‐neurons are slow pacemakers that continuously fire action potentials, maintaining basal extracellular DA levels in target regions. The sodium leak channel NALCN has been identified as a key contributor in the pacemaker control of these neurons. However, the consequences of a disrupted DA pacemaker activity remain largely unexplored. By generating mice lacking NALCN selectively in midbrain DA‐neurons, we investigated the impact of this deletion on the activity of ventral tegmental area DA‐neurons, D2R‐mediated signalling, reactivity to cues predicting threat and psychostimulant responsiveness in both males and females. Selective deletion of NALCN in midbrain DA‐neurons dampens their tonic activity, without reducing the basal extracellular DA levels in the nucleus accumbens. Mice with a loss of NALCN in DA‐neurons exhibit no impairments of basal motor responses, unaltered reactivity to cues predicting threat and risk assessment, while the neurochemical and behavioural responsiveness to psychostimulant drugs are enhanced and presynaptic D2R‐mediated signalling at DA terminals is altered. Together, our results emphasize the important role of NALCN conductance in controlling DA pacemaker activity, D2R‐mediated signalling and in modulating motor responses to psychostimulants. image Key points: The sodium leak channel NALCN is an important contributor to the spontaneous pacemaker activity in dopamine neurons, but the consequences of its loss in these neurons remain largely unknown. We investigated how selective deletion of NALCN in dopamine neurons affects neuronal activity, dopamine receptor signalling and behavioural responses in male and female mice. Loss of NALCN markedly reduced the spontaneous activity of dopamine neurons, yet basal motor function, reward‐related responses and reactivity to threat‐predicting cues remained largely preserved. In contrast, neurochemical and behavioural responsiveness to psychostimulant drugs are enhanced, probably through an altered presynaptic D2R‐mediated signalling at DA terminals. NALCN emerges as a key regulator of dopamine neuron activity, with disrupted pacemaker firing selectively enhancing psychostimulant sensitivity.

Post-traumatic stress disorder (PTSD) is a severe stress-related psychiatric condition triggered by traumatic life-threatening events, characterized notably by an altered memory profile. Although clinically well-documented, no specific biomarker exists. This translational study identifies plasminogen activator inhibitor-1 (PAI-1) as a brain risk factor for PTSD, thereby supporting its potential as a blood-derived biomarker. Mice with genetically ablated PAI-1 were protected from developing a PTSD-like memory profile. Conversely, mice exhibiting PTSD-like cognitive impairment showed increased blood PAI-1 levels, correlating with their profile severity. In the brain, PAI-1 levels were specifically increased in the dorsal hippocampus, a key region for cognitive functions and in the etiology of PTSD. Finally, a longitudinal study of soldiers revealed that those developing PTSD symptoms exhibit rising blood PAI-1 levels over a 12-month period. Its significant association with various indicators of PTSD-related psychological distress attests to PAI-1’s potential as a blood biomarker and brain therapeutic target for PTSD.

Post-traumatic stress disorder (PTSD) is a severe stress-related psychiatric condition triggered by traumatic life-threatening events, characterized notably by an altered memory profile. Although clinically well-documented, no specific biomarker exists. This translational study identifies plasminogen activator inhibitor-1 (PAI-1) as a brain risk factor for PTSD, thereby supporting its potential as a blood-derived biomarker. Mice with genetically ablated PAI-1 were protected from developing a PTSD-like memory profile. Conversely, mice exhibiting PTSD-like cognitive impairment showed increased blood PAI-1 levels, correlating with their profile severity. In the brain, PAI-1 levels were specifically increased in the dorsal hippocampus, a key region for cognitive functions and in the etiology of PTSD. Finally, a longitudinal study of soldiers revealed that those developing PTSD symptoms exhibit rising blood PAI-1 levels over a 12-month period. Its significant association with various indicators of PTSD-related psychological distress attests to PAI-1’s potential as a blood biomarker and brain therapeutic target for PTSD.

Administration of Δ ⁹ -tetrahydrocannabinol (THC), the main psychoactive component of the plant Cannabis sativa , can induce psychotic symptomatology in humans and a large spectrum of acute psychotic-like behaviors in mice, including hyperlocomotion observed at low dose of THC (0.3 mg/kg). The cellular and molecular substrates of this effect have not been fully identified yet. Here we demonstrate that THC-induced hyperlocomotion depends on plasma membrane CB1R, which regulate the β-arrestin 1/Akt/GSK3β signaling pathway in D2R-positive neurons of the dorsal striatum forming the striatopallidal pathway of the basal ganglia. Pregnenolone (PREG) and its clinically developed analog, AEF0117, which are signaling specific inhibitors of CB1R (CB1-SSi), prevented GSK3β-dependent psychomotor stimulation induced by THC. Overall, this work highlights a novel intracellular mechanism of CB1R, thereby revealing a neuronal pathway underlying an important but still underexplored effect of THC and cannabis consumption, which could help the development of innovative therapeutic concepts against psychotic conditions.

Summary: Salience attributed to stimuli predicting rewarding or aversive outcomes is critical for adaptive behavior. Dopamine (DA)-neurons play a central role in this process by modulating responses to both rewarding and aversive cues. DA-neurons are tightly and readily modulated by DA D2 autoreceptors (autoD2Rs), but their role in regulating responses to aversive stimuli remains unclear. In this study, we investigated the role of autoD2R in regulating the activity of VTA DA-neurons in response to salient aversive stimuli. Using Drd2 ^Slc6a3 mice, in which Drd2 is selectively deleted in DA-neurons, we observed enhanced excitatory and inhibitory responses of VTA DA-neurons to aversive stimuli, suggesting that autoD2R acts as a critical regulatory brake. Importantly, this modulation occurred independently of either the pacemaker activity of DA-neurons or their coupling to the non-selective sodium leak channel NALCN. Behaviorally, Drd2 ^Slc6a3 male mice showed enhanced discrimination between threat-predicting and non-predicting cues that persisted during extinction learning, highlighting a sex-biased role of autoD2R in threat processing. Our results provide new mechanistic insights through which autoD2R influence behavioral responses to aversive stimuli, with implications for understanding neuropsychiatric disorders characterized by maladaptive threat processing.