The inducible serotonergic 1C115-HT cell line expresses a defined set of serotonergic receptors of the 5-HT2B, 5-HT1B/D and 5-HT2A subtypes, which sustain a regulation of serotonergic-associated functions through G-protein dependent signaling. 1C115-HT cells have been instrumental to assign a signaling function to the cellular prion protein PrPC. Here, we establish that antibody-mediated ligation of PrPC concomitant to agonist stimulation of 5-HT receptors modulates the couplings of all three serotonergic receptors present on 1C115-HT cells. Specific impacts of PrP antibodies were monitored depending on the receptor and pathway considered. PrPC ligation selectively cancels the 5-HT2A-PLC response, decreases the 5-HT1B/D negative coupling to adenylate cyclase and potentiates the 5-HT2B-PLA2 coupling. As a result, PrPC ligation disturbs the functional interactions occurring between the signaling pathways of the three receptor subtypes. In 1C115-HT cells, antagonizing crosstalks arising from 5-HT2B and 5-HT2A receptors control the 5-HT1B/D function. PrPC ligation reinforces the negative regulation exerted by 5-HT2B on 5-HT1B/D receptors. On another hand it abrogates the blocking action of 5-HT2A on the regulatory loop linking 5-HT2B and 5-HT1B/D receptors. We propose that the ligation of PrPC affect the potency or dynamics of G-protein activation by agonist-bound serotonergic receptors. Finally, the PrPC-dependent modulation of 5-HT receptor couplings is restricted to 1C115-HT cells expressing a complete serotonergic phenotype. It critically involves a PrPC-caveolin platform implemented on the neurites of 1C115-HT cells during differentiation. Our findings define PrPC as a modulator of 5-HT receptor coupling to G-proteins and thereby as a protagonist contributing to the homeostasis of serotonergic neurons. They provide a foundation for uncovering the impact of prion infection on serotonergic functions.