How do serotonin cause constriction and dilation of blood vessels in the brain?

Serotonin secreted from the enterochromaffin cells eventually finds its way out of tissues into the blood. There, it is actively taken up by blood platelets, which store it. When the platelets bind to a clot, they release serotonin, where it serves as a vasoconstrictor and helps to regulate hemostasis and blood clotting.

It does this by binding to the 5-HT1B receptor or the 5-HT1D receptor. 5-HT1B receptors are widely distributed throughout the CNS with the highest concentrations found in the frontal cortex, basal ganglia, striatum, and the hippocampus. The function of the 5-HT1B receptor differs depending upon its location. In the frontal cortex, it is believed to act as a postsynaptic receptor inhibiting the release of dopamine. In the basal ganglia and the striatum, evidence suggests 5-HT signaling acts on an autoreceptor, inducing the release of serotonin and decreasing glutamatergic transmission by reducing miniature excitatory postsynaptic potential frequency, respectively.

Outside the brain, 5-HT1B receptor activation also has vascular effects, such as pulmonary vasoconstriction. Furthermore, blocking 5-HT1B receptor signaling decreases the number of osteoblasts, bone mass, and the bone formation rate.

Based on your description, for the body internal process, do you have any suggestions on how positive ionization cause the release of excessive serotonin into the bloodstream?

Do you have any suggestions?
Thank you very much for any suggestions :>