When amphetamine enters a neuron and interacts with VMAT2, the transporter reverses its direction of transport, thereby releasing stored monoamines inside synaptic vesicles back into the neurons intracellular fluid. Meanwhile, when amphetamine activates TAAR1, the receptor causes the neurons cell membrane-bound monoamine transporters (i.e., the dopamine transporter, norepinephrine transporter, or serotonin transporter) to either stop transporting monoamines altogether (via transporter internalization) or transport monoamines out of the neuron; in other words, the reversed membrane transporter will push dopamine, norepinephrine, and serotonin out of the neurons intracellular fluid and into the synaptic cleft. In summary, by interacting with both VMAT2 and TAAR1, amphetamine releases neurotransmitters from synaptic vesicles (the effect from VMAT2) into the intracellular fluid where they subsequently exit the neuron through the membrane-bound, reversed monoamine transporters (the effect from TAAR1). Pharmacokinetics
The oral bioavailability of amphetamine varies with gastrointestinal pH; it is well absorbed from the gut, and bioavailability is typically over 75% for dextroamphetamine. Amphetamine is a weak base with a pKa of 9.9; consequently, when the pH is basic, more of the drug is in its lipid soluble free base form, and more is absorbed through the lipid-rich cell membranes of the gut epithelium. Conversely, an acidic pH means the drug is predominantly in a water-soluble cationic (salt) form, and less is absorbed. Approximately 20% of amphetamine circulating in the bloodstream is bound to plasma proteins.
Symptoms include upper gastrointestinal tract dysfunction such as delayed gastric emptying or lower gastrointestinal dysfunction, such as constipation and prolonged stool transit time.Urinary retention, waking at night to urinate, increased urinary frequency and urgency, and over- or underactive bladder are common in people with synucleinopathies. Sexual dysfunction usually appears early in synucleinopathies, and may include erectile dysfunction, and difficulties achieving orgasm or ejaculating. Diagnosis
Differential diagnosis
Persons with PD are typically less caught up in their visual hallucinations than those with DLB. There is a lower incidence of tremor at rest in DLB than in PD, and signs of parkinsonism in DLB are more symmetrical. In MSA, autonomic dysfunction appears earlier and is more severe, and is accompanied by uncoordinated movements, while visual hallucinations and fluctuating cognition are less common than in DLB. Urinary difficulties are one of the earliest symptoms with MSA, and are often severe. DNA damage
Alpha-synuclein modulates DNA repair processes, including the repair of DNA double-strand breaks by the non-homologous end joining pathway. The DNA repair function of alpha-synuclein appears to be compromised in Lewy body inclusion bearing neurons, and this may trigger cell death. Study of synucleinopathy mouse models of Parkinson’s disease indicates that alpha-synuclein pathogenesis is associated with increased DNA damage and activation of the DNA damage response. See also
Proteopathy
Lewy body


== References ==