Rotundine

Rotundine displays a higher affinity to dopamine D1 than D2 receptor with K_i of 124 nM and 388 nM, respectively, while the IC50 values are 166 nM (D1) and 1.47 μM (D2), respectively. Rotundine exhibits a weak inhibitory activity against dopamine D3 with IC50 of 3.25 μM. Rotundine also potently inhibits 5-HT1A with IC50 of 374 nM and K_i of 340 nM. In addition to the antagonism of postsynaptic dopamine receptors, inhibition of presynaptic autoreceptors by Rotundine leads to increased dopamine release, which is probably attributed to lower affinity of Rotundine for D2 receptors. Along with dopamine receptors, Rotundine can interact with a number of other receptor types, including α-1 adrenergic receptors, at which it functions as an antagonist, and γ-aminobutyric acid receptors, at which it facilitates γ-aminobutyric acid binding through positive allosteric effects. ^[1]

Rotundine treatment does not affect the locomotor activity at the doses of 6.25 mg/kg, 12.5 mg/kg, or 18.75 mg/kg, but significantly antagonizes the hyperactivity induced by oxy-codone (5 mg/kg). ^[2] Oral administration of Rotundine (10-25 mg/kg) significantly increases hot-plate latency of mice, indicating that Rotundine exerts remarkable analgesic activity, which is associated with β-endorphin neurons in the arcute nucleus and supraspinal D2 receptor. ^[3] Administration of Rotundine (1-10 mg/kg) dose-dependently increases, while 20 mg/kg decreases the rate of cocaine self-administration under fixed-ratio (FR) reinforcement, due to a postsynaptic, rather than presynaptic, DA receptor blockade mechanism. In contrast to the effects on cocaine's actions, only the 10 mg/kg dose of Rotundine but not 1 mg/kg or 3 mg/kg produces inhibitory effect on sucrose self-administration and locomotion. ^[4] LD50: Mice 1160mg/kg (i.g.) ^[5]