Effects of monoamine oxidase inhibitors and dopamine agonists on the behavior of mammal- and frog-eating snakes

Skin mucus of the frog, Xenopus laevis, induces climbing and attenuates tongue flicking in Nerodia sipedon; these effects are induced alone and are potentiated by L-deprenyl, a monoamine oxidase type B inhibitor (MAO-Bi), but not by clorgyline, an MAO type A inhibitor (MAO-Ai). Both MAO-A and MAO-B metabolize dopamine, with MAO-B having the higher affinity; MAO-A selectively metabolizes serotonin and norepinephrine and MAO-B is selective for phenylethylamine. It was hypothesized that clorgyline and L-deprenyl would differentially modulate tongue flicking and climbing in frog-eating (Nerodia erythrogaster) and mammaphagous (Elaphe o. obsoleta) snakes, based on physiological differences between the species. L-Deprenyl caused a decrease in tongue flicking and climbing by Elaphe and an increase in climbing by Nerodia, whereas clorgyline did not alter tongue flicking, climbing, or locomotor activity in either species. To further assess the role of dopamine, hybrid black/gray rat snakes, E. o. spiloides, were administered the D1 and D2 dopamine receptor agonists SKF 77434 (SKF 38393, N-allyl) and quinpirole, respectively. SKF 77434 and quinpirole attenuated climbing, but only SKF 77434 attenuated tongue flicking in Experiment 3; neither drug affected locomotor activity. Results suggest that dopaminergic stimulation by MAO-Bi and dopamine agonists modulates tongue flicking and climbing behaviors in snakes, and that the contrasting climbing reactions induced by MAO-Bi between Elaphe and Nerodia may be linked to quantitative differences in endogenous catecholamine levels and/or to the numbers and sensitivity of receptors.

MAO-A and -B inhibitors selectively alter Xenopus mucus-induced behaviors of snakes

Skin mucus of the frog Xenopus laevis, contacted orally by snakes, induces dyskinetic oral movements and climbing behavior that promote escape. The mucus contains peptides and indoleamines known to produce drug-induced movement disorders in other species. We hypothesized that inhibition of monoamine oxidase-A (MAO-A) by N-methyl-N-propargyl-3-(2,4-dichlorophenoxy)-propylamine [clorgyline (CLG)] and MAO-B by R(-)-N, alpha-Dimethyl-N-2-propynyl-benzene-ethanamine [L-deprenyl (LDL)] would selectively modify mucus-induced behaviors by elevating norepinephrine and serotonin (with CLG), phenylethylamine (with LDL), or dopamine (with both drugs). In Experiment 1 (EXP1), adult snakes received mucus and/or 20 micrograms/g (IP) of both drugs. In EXP2, juveniles received mucus and/or 5, 10, and 20 micrograms CLG or LDL. CLG given alone had no effect on tongue flicking, activity, and climbing (EXP1,2). LDL alone decreased tongue flicking in EXP2 and increased climbing (EXP1,2). Given with mucus, both drugs further lowered the tongue flicking rates attenuated by mucus (EXP1,2); only LDL potentiated mucus-induced climbing. Yawning was the only mucus-induced dyskinesia attenuated (20 micrograms CLG, adults; 20 micrograms LDL, juveniles). We suggest that dopamine and/or phenylethylamine, the substrates for MAO-B, may promote mucus-induced climbing and tongue flicking but may have some protective role against mucus-induced yawning in water snakes.

SCH 23390: D-1 modulation of oral dyskinesias induced in snakes by Xenopus skin mucus

The granular gland skin secretion of Xenopus laevis induces seven involuntary oral dyskinesias and climbing behavior in the water snake Nerodia sipedon. In a previous study the D-2 receptor antagonist, haloperidol (HAL), selectively potentiated mucus-induced yawning and chewing but attenuated fixed gaping; other oral behaviors were unaffected; HAL alone induced no dyskinesias and failed to modify mucus-induced decreases in tongue flicking, cage climbing and activity. As skin compounds have neuroleptic properties known to induce human and animal dyskinesias, we hypothesized that D-1 receptor antagonism may modulate the four of seven mucus-induced dyskinesias and the climbing not altered by HAL. We found that, like HAL, SCH 23390 (SCH) potentiated mucus-induced yawning, attenuated fixed gaping and had no effect on climbing. Unlike HAL's potentiation of chewing, SCH attenuated chewing and potentiated writhing tongue movements. SCH alone, like skin mucus, attenuated tongue flicking and activity but, given with mucus, SCH increased tongue flicking and activity to control levels. Compared to the HAL study, results suggest that mucus-induced yawning and fixed gaping are similarly modulated by both HAL and SCH, while these drugs have opposite effects on writhing tongue and chewing. SCH given alone or with frog mucus had unique effects on activity and normal tongue flicking.

Neuroleptic modulation of oral dyskinesias induced in snakes by Xenopus skin mucus

The skin mucus of the African clawed frog Xenopus laevis promotes escape from the American water snake Nerodia sipedon by inducing oral dyskinesias. As Xenopus mucus contains peptides and indoleamines with known neuroleptic properties, and because neuroleptics are the chief cause of drug-induced orofacial dyskinesias in humans, the hypothesis was tested that the neuroleptic haloperidol (HAL) would induce oral dyskinesias when given alone and would potentiate dyskinesias in Nerodia if injected prior to oral application of Xenopus mucus. Mucus alone induced yawning, gaping, fixed yawning, fixed gaping, writhing tongue movements, gular and chewing movements, and climbing behavior, but attenuated locomotor activity. HAL given IP alone at 0.05 and 0.5 microgram/g was ineffective. However, HAL greatly potentiated mucus-induced yawning but attenuated the fixed gaping seen when only mucus was applied. Data support the hypothesis that Xenopus skin mucus has neuroleptic properties and that Xenopus' antipredatory defense is in part related to chemical induction of orofacial and climbing behavior in snake predators.

Xenopus skin mucus induces oral dyskinesias that promote escape from snakes

African clawed frogs fed to American water snakes induced yawning and gaping which slowed ingestion and facilitated the frogs' escape without inducing flavor aversion. The peptide and/or indolealkylamine contents of the frog's poison glands caused the effect because frogs with purged glands did not induce these behaviors and rarely escaped. Poison gland mucus, applied orally, elicited similar oral movements. The frog's clear lubricating mucus was inactive. As several compounds in the poison glands have known neuroleptic properties, the oral behaviors may be induced by neural mechanisms reported to govern neuroleptic-induced orofacial dyskinesia in schizophrenics.

Cyclic amines are selective cytotoxic agents for pigmented cells

We have shown that morpholine, a cyclic amine, exerts a selective inhibition of growth on melanocytic pigmented cell lines compared to nonpigmented cells. The ID50 of morpholine for the pigmented B-16 cell line HFH was 1200 micrograms/ml, compared to values greater than 2400 micrograms/ml for baby hamster kidney, Chinese hamster ovary and NP, an unpigmented primate cell line. Two other cyclic amines piperazine and piperidine, were similarly found to be selectively toxic to melanocytes. This selective toxicity could be synergistically enhanced by pretreatment of the cells with theophylline, a stimulator of tyrosinase activity, which indicates that the selective toxicity may be associated with melanin synthesis. Low passage HFH, high passage HFH and Syrian hamster melanoma RPMI 1846 cells that were pretreated with theophylline showed between 13 and 29% greater toxicity compared to controls treated with theophylline or morpholine alone. Unpigmented NP primate cells, Chinese hamster ovary and mouse fibroblast L929 remained unaffected. These cyclic amines join a list of other amines that have also been shown to be melanocytotoxic.

Combined effects of ethanol and diazepam on performance and acquisition of serial position sequences by pigeons

The effects of diazepam and ethanol, alone and in combination, were studied in pigeons responding under acquisition and performance chain schedules. Both diazepam and ethanol increased the number of pecks on the incorrect key (errors). Under the acquisition schedule both diazepam and ethanol increased errors at doses lower than those under the performance schedule. Under both schedules effects of combinations of ethanol and diazepam were usually greater than the sum of the effects of the individual drugs.