Histamine H3 receptor inverse agonists/antagonists influence intra-regional cortical activity and inter-regional synchronization during resting state: an exploratory cortex-wide imaging study in mice

The histaminergic system plays a key role in modulating learning and memory, wakefulness, and energy balance. Histamine H₃ receptors constitutively inhibit the synthesis and release of histamine and other neurotransmitters. Therefore, H₃ receptor inverse agonists/antagonists increase the synthesis and release of these neurotransmitters, enhancing cognitive functions, including memory consolidation and retrieval. Spontaneous neural activity across the cerebral cortex is essential for cognitive function, including memory consolidation. Abnormal spontaneous activity has, in fact, been associated with cognitive dysfunctions and psychiatric disorders. Given the cognitive improvement achieved with the use of H₃ receptor inverse agonists/antagonists, we examined the effects of two inverse agonists/antagonists - thioperamide and pitolisant - on spontaneous cortical activity, using in vivo wide-field Ca²⁺ imaging. Changes in cortical activity, across multiple cortical regions and in inter-regional connectivity, from pre- to post-administration were evaluated using a linear support vector machine decoder. Thioperamide and pitolisant both modified the amplitude distribution of calcium events across multiple cortical regions, including a reduction in the frequency of low-amplitude calcium events in the somatosensory cortex. Graph theory analysis revealed increases in centrality measures in the somatosensory cortex with the use of both thioperamide and pitolisant, indicative of their importance in the organization of cortical networks. These findings indicate that H₃ receptor inverse agonists/antagonists influence intra-regional cortical activity and inter-regional synchronization of activity in the cerebral cortex during the resting state.