ED Sciences de la Vie et de la Santé
Cannabinoid type-1 receptor signalling and its role in regulating brain lactate dynamics in freely moving mice
by Tommaso DALLA TOR (Neurocentre Magendie)
The defense will take place at 12h00 - Sala riunioni Torre Biologica Torre Biologica Via Santa Sofia, 97 - 95123 - Catania
in front of the jury composed of
- Giovanni MARSICANO - Directeur de recherche - Université de Bordeaux - Directeur de these
- Riccardo BRAMBILLA - Full professor - University of Pavia - Examinateur
- Marco RIVA - Full professor - Università degli Studi di Milano, Dipartimento di Scienze Farmacologiche e Biomolecolari - Examinateur
- Roberto CICCOCIOPPO - Full professor - University of Camerino - Examinateur
- Filippo DRAGO - Directeur de recherche - Università di Catania, Scienze Biomediche e Biotecnologiche - CoDirecteur de these
The brain is one of the most active metabolic organs in the body. Despite accounting for only ~2% of total body weight, it consumes up to 20% of the body's energy. This energy is primarily derived from glucose metabolism, which produces both ATP and lactate. In the central nervous system (CNS), astrocytes are the main source of lactate, generated mostly via aerobic glycolysis. Neurons, in contrast, rely largely on oxidative phosphorylation for ATP production and preferentially utilize lactate as an energy substrate in a process known as the astrocyte-to-neuron lactate shuttle (ANLS). Beyond its metabolic role, lactate also functions as a key signalling molecule involved in neuronal plasticity, memory, and behavioural regulation. However, the mechanisms controlling lactate production and release in the brain remain poorly understood. Recent findings have implicated the cannabinoid receptor type 1 (CB1R) in the regulation of astrocytic metabolism. Persistent activation of astroglial mitochondrial CB1Rs (mtCB1Rs) for 24 hours has been shown to suppress lactate production. In contrast, our recent work reveals that transient (5 minutes) stimulation of CB1Rs in astrocytes triggers a transient increase in lactate levels. While these effects have been observed in vitro, the impact of CB1R activation on brain lactate dynamics in vivo has yet to be directly examined. In this thesis, we address this gap using fiber photometry (FP) and eLACCO2.1, a genetically encoded fluorescent biosensor for extracellular lactate. We successfully established a protocol to monitor lactate dynamics in freely moving mice and validated the responsiveness of the sensor to exogenous lactate administration. Our in vivo experiments revealed that lactate levels are modulated not only by cannabinoid exposure but also by behavioural state, particularly locomotor activity. Specifically, we observed brain region-specific patterns in lactate fluctuations during periods of immobility and following Δ⁹-THC administration, suggesting that CB1R activation alters the timing and dynamics of lactate regulation in a circuit-dependent manner. In parallel, we investigated the intracellular signalling mechanisms underlying CB1R-dependent regulation of lactate in cultured astrocytes, with a particular focus on the switch between the transient and persistent effects induced by WIN55 stimulation. Using the broad PKC inhibitor Go 6983, we found that PKC activity is required for both the transient lactate increase and the later suppression induced by CB1R stimulation. Blocking PKC abolished both effects, indicating that it serves as a critical molecular switch within the CB1R-lactate signalling axis. Interestingly, a progressive accumulation of lactate was observed when PKC was inhibited in the presence of CB1R activation. Control experiments with PKC inhibition alone did not show changes in baseline lactate levels, although technical limitations prevented full quantification. Together, these findings establish a new in vivo method for studying lactate dynamics in freely moving mice, demonstrate that Δ⁹-THC alters brain lactate dynamics specifically during periods of immobility, suggesting that CB1R signalling reshapes neurometabolic responses in relation to behavioural state and brain region, and uncover a previously not fully characterized role for PKC in astrocyte metabolic regulation. This work advances our understanding of the complex interplay between cannabinoid signalling, astrocyte function and behaviour, and sets the stage for future studies into the neurometabolic consequences of CB1R activity.