Sex-Specific Relationships between Cerebral Cortex Metabolism, Behavior, and ECG Parameters in Rats under...

Sex-specific interactions between neurosignaling systems, which generate, propagate, and terminate signals in nervous tissue, and metabolic pathways that support these processes may underlie sex differences in adaptation and therapeutic efficacy. This study aimed to characterize these interactions as systemic indicators of sex-specific adaptive responses in a rat model of metabolic stress induced by the inhibition of pyruvate dehydrogenase complex (PDC), which catalyzes the key reaction linking anaerobic glycolysis to aerobic glucose oxidation. To inhibit brain PDC, we used a single intranasal administration of methyl acetylphosphinate (MeAcP), a phosphinate analog of pyruvate, or dimethyl acetylphosphonate (AcPMe₂), a membrane-permeable precursor of phosphonate pyruvate analogs. Effects were assessed 24 h post-administration by measuring biochemical and physiological parameters in the cerebral cortex, including glutamate levels, glutamine synthetase (GS) activity, and activities of enzymes in the tricarboxylic acid (TCA) cycle and affiliated pathways. Neurosignaling was evaluated using surrogate indicators: ECG (electrocardiogram) parameters and spontaneous behavior in the open field test. Relationships between measured parameters were analyzed using Spearman's rank correlation coefficients, with the correlation strength classified according to the Chaddock's scale. In control animals, no sex differences were observed in the mean values of biochemical or ECG parameters. However, behavioral parameters (e.g., grooming and locomotion) and the overall structure of correlations between the studied parameters exhibited marked sex dependence. In control females, strong correlations were detected between ECG parameters and GS activity, whereas in males, ECG parameters were strongly associated with malic enzyme (ME) activity. Male controls also showed strong correlations between locomotor/exploratory behavior and activities of ME, PDC, and 2-oxoglutarate dehydrogenase complex (OGDC). Administration of PDC inhibitors induced a sex-specific reorganization of relationships between neurosignaling indicators and glutamate metabolism, which eliminated pronounced sex differences in locomotor activity observed in controls, while revealing new sex-related differences in glutamate levels, glutamate dehydrogenase (GDH) and ME activities, grooming bout duration, and freezing time. The reduction in glutamate levels observed in females following PDC inhibition was consistent with the established decrease in de novo glutamate synthesis from glucose under conditions of impaired substrate flux through the TCA cycle. Overall, these findings demonstrate that the relationships among metabolic, behavioral, and ECG parameters are inherently sex-specific. Moreover, the homeostatic response of the cerebral cortex to PDC inhibition reshapes these relationships, thereby modifying sex-dependent biochemical and behavioral characteristics observed under control conditions.