Neural Mechanism of 5-HT4R-Mediated Memory Enhancement in Hippocampal-Prefrontal Circuits in a Mouse Model of Schizophrenia.

We investigated the cellular and neurophysiological mechanisms underlying the pro-cognitive effects of 5-HT4R activation in hippocampal-prefrontal pathways. Our findings show that, in addition to pyramidal neurons, 30-60% of parvalbumin+ interneurons in the CA1, CA3, and dentate gyrus (DG) of the hippocampus and the anterior cingulate (ACC), prelimbic (PL), and infralimbic (IL) regions of the prefrontal cortex co-express 5-HT4Rs. Additionally, 15% of somatostatin+ interneurons in CA1 and CA3 express 5-HT4Rs. Partial 5-HT4R agonist RS-67333 (1 mg/kg, i.p.) exerted anxiolytic effects and ameliorated short-term (3-min) and long-term (24-h) memory deficits in a mouse model of schizophrenia-like cognitive impairment induced by sub-chronic phencyclidine (sPCP) but did not enhance memory in healthy mice. At the neurophysiological level, RS-67333 normalized sPCP-induced disruptions in hippocampal-prefrontal neural dynamics while having no effect in healthy animals. Specifically, sPCP increased delta oscillations in CA1 and PL, leading to aberrant delta-high-frequency coupling in CA1 and delta-high-gamma coupling in PL. RS-67333 administration attenuated this abnormal delta synchronization without altering phase coherence or signal directionality within the circuit. Collectively, these results highlight the therapeutic potential of 5-HT4R activation in pyramidal, parvalbumin+, and somatostatin+ neurons of hippocampal-prefrontal pathways for mitigation of cognitive and negative symptoms associated with schizophrenia.