Unconditioned behavioral effects of the powerful kappa-opioid hallucinogen salvinorin A in nonhuman primates: fast onset and entry into cerebrospinal fluid

Abstract

Salvinorin A is the main active component of the widely available hallucinogenic plant, Salvia divinorum. Salvinorin A is a selective high-efficacy kappa-agonist in vitro, with some unique pharmacodynamic properties. Descriptive reports show that salvinorin A-containing products produce robust behavioral effects in humans. However, these effects have not been systematically characterized in human or nonhuman primates to date. Therefore, the present studies focused on the characterization of overt effects of salvinorin A, such as sedation (operationally defined as unresponsiveness to environmental stimuli) and postural relaxation, previously observed with centrally penetrating kappa-agonists in nonhuman primates. Salvinorin A was active in these endpoints (dose range, 0.01-0.1 mg/kg i.v.) in nonhuman primates (n = 3-5), similar to the synthetic kappa-agonist U69,593 [(+)-(5alpha,7alpha,8beta)-N-methyl-N-[7-(1-pyrrolidinyl)-1-oxaspiro[4.5]-dec-8-yl]-benzeneacetamide], used for comparison herein. Salvinorin A effects could be prevented by a clinically available opioid antagonist, nalmefene (0.1 mg/kg), at doses known to block kappa-receptor-mediated effects in nonhuman primates. When injected intravenously, salvinorin A (0.032 mg/kg) could enter the central nervous system (as reflected in cisternal cerebrospinal fluid) within 1 min and reach concentrations that are in the reported range of the affinity (K(i)) of this ligand for brain kappa-receptors. Consistent with this finding, specific translationally viable behavioral effects (e.g., facial relaxation and ptosis) could also be detected within 1 to 2 min of injection of salvinorin A. These are the first studies documenting rapid unconditioned effects of salvinorin A in a primate species, consistent with descriptive reports of rapid and robust effects of this powerful hallucinogen in humans.

Fig. 1.

Sedative effects of intravenous salvinorin A (0.032 and 0.1 mg/kg) in chaired subjects (n = 3; dose ranging study) (left). Sedative effects of U69,593 (0.01, 0.032, and 0.056 mg/kg i.v.) (right). Abscissae, time from intravenous injection (minutes); ordinates, median sedation score. Points above “BL” represent median baseline preinjection values.

Fig. 2.

Sedative (left) and postural effects of intravenous salvinorin A in the home cage (0.01 and 0.032 mg/kg; n = 6; three males and three females). Other details as in Fig. 1.

Fig. 3.

Nalmefene prevention of the sedative (left) and postural (right) effects of intravenous salvinorin A (0.032 mg/kg; n = 5). Nalmefene (0.01 or 0.1 mg/kg) was administered as a pretreatment (PT) and compared with vehicle pretreatment. Other details as in Fig. 1.

Fig. 4.

Effects of intravenous salvinorin A on facial relaxation and ptosis (top left and bottom left, respectively; n = 5). Effects of intravenous U69,593 on facial relaxation and ptosis (top right and bottom right, respectively; n = 4). Abscissae, time from the end of intravenous injection (note axis break). Ordinates, mean (±S.E.M.) cumulative time for each behavior, within a 60-s time window.

Fig. 5.

Nalmefene prevention of salvinorin A-induced facial relaxation (top) and ptosis (bottom) (n = 5). Nalmefene (0.1 mg/kg s.c.) was administered as a 30-min pretreatment (PT) to salvinorin A (0.032 mg/kg). Other details as in Fig. 4.

Fig. 6.

Nalmefene reversal of ongoing salvinorin A-induced facial relaxation (top) and ptosis (bottom) (n = 5). Nalmefene (0.1 mg/kg i.v.) or vehicle were administered 11 min after salvinorin A (0.032 mg/kg). Therefore, observations after this nalmefene or vehicle treatment are used to evaluate the effectiveness of reversal. Note modified time windows to focus on postreversal period. Other details as in Fig. 4.

Fig. 7.

Time course of salvinorin A levels detected in CSF after intravenous injection (0.032 mg/kg) (n = 3). Abscissa, time from the end of intravenous injection (minutes). Ordinate, salvinorin A CSF levels quantified by LC-MS (mean ± S.E.M.).