I am looking further into the Smith and Darlington article, and this is a real gold mine of information. I believe that this research gives us some understanding about how migraine can cause both episodic and chronic vestibular symptoms.
“If a sudden change in serotonin levels in the VNC is the cause of dizziness following SSRI withdrawal, then there are several important implications for vestibular function. First, it suggests that in cases where the natural levels of serotonin in the brain are altered, such as in depression, the change in serotonin levels in the VNC may affect vestibular function. In fact, Soza Ried and Aviles [20] reported that patients with major depression who were not medicated exhibited a significant decrease in the slow phase velocity of the vestibulo-ocular reflex for rotation to the right side, suggesting hypoactivity of the right VNC.”
“Serotonin has been found in the peripheral vestibular system, in the vestibular labyrinth, although its function there is poorly understood (see Smith and Darlington [11] for a review). Serotonin is also known to be an important neurotransmitter in the brainstem vestibular nucleus, which along with the cerebellar flocculus, is the only area of the brain to receive direct input from the vestibular nerve carrying vestibular sensory information from the inner ear. Serotonin exists in high concentrations in the vestibular nucleus complex (VNC) and an important source of serotonergic projections to the VNC comes from the dorsal raphe nucleus”
“Interestingly, approximately one-eighth of the serotonergic dorsal raphe neurons projecting to the VNC also project into the central amygdaloid nucleus [13], suggesting a surprising connection between the vestibular system and anxiety.”
“Since glutamate is the major excitatory neurotransmitter in the VNC and the neurotransmitter mediating input from the vestibular nerve [11], this suggests that the impact of changes in serotonin levels on VNC neurons could be dramatic. Consistent with this evidence, 5-HT1F receptors have recently been reported to be co-localized with glutamate in the VNC [14].”
“the decrease in serotonin may result in the reduced activation of the 5-HT1F receptors, thereby increasing glutamate release by VNC neurons. If this happened bilaterally, as would be expected with a systemically administered drug, then both the left and right VNCs would send increased vestibular signals to the rest of the brain. This hypothesis would be consistent with the evidence that patients discontinuing SSRIs do not experience vertigo (which would require unilateral increased activation of the VNC) but only dizziness, and that the dizziness is exacerbated by head movement.”
Link: xa.yimg.com/kq/groups/1920818/73 … ziness.pdf