HTR1A and cerebrovascular disorder: When the deep cortex, including the substantia nigra and striatum, is impaired due to cerebrovascular disease, the ability to synthesize dopamine is also impaired, leading to a decrease in swallowing function.[9] Acupuncture stimulation of the neck improves swallowing function and the expression of 5-HT1A in the arcuate nucleus.[19] Studies that directly investigate the mechanism of dopamine synthesis in the nigrostriatal striatum, as described above, are lacking.