Flumazenil-sensitive dose-related physical dependence in planarians produced by two benzodiazepine and one non-benzodiazepine benzodiazepine-receptor agonists

Abstract

Two benzodiazepine (midazolam and clorazepate) and one non-benzodiazepine (zolpidem) benzodiazepine-receptor agonists produced dose-related physical dependence, as evidenced by abstinence-induced decrease in planarian locomotor velocity (pLMV) when drug-exposed planarians were placed into drug-free water, but not when they were placed into drug-containing water (i.e., an abstinence-induced withdrawal, since the effect was only obtained in the removal of drug and not in the continued presence of drug). We have previously shown that the decrease in pLMV is associated with specific and transient withdrawal signs. In the present study, the selective benzodiazepine-receptor antagonist flumazenil significantly antagonized (P<0.05), by co-application, the ability of each agonist to produce the withdrawal. These results: (1) suggest that benzodiazepine-receptor agonists, for two different chemical categories, produce dose-related physical dependence manifested as abstinence-induced withdrawal in this simple and convenient model, and (2) in the absence of cloning or radioligand binding literature, suggest a possible specific interaction site (receptor?) for these compounds in planarians.

Fig 1

Dose-related decrease in pLMV, expressed as the mean ± S.E.M. cumulative number of gridlines crossed, following 1-h exposure to water (W) or midazolam (M) at 10 µM or concentration (µM) indicated, followed by testing in water (e.g., M(0.1)/W indicates 1-h immersion in 0.1 µM midazolam followed by testing in water.

Fig 2

Attenuation of the abstinence-induced withdrawal from midazolam (M) by co-treatment with flumazenil (F). Flumazenil alone had no effect on pLMV.

Fig 3

Dose-related decrease in pLMV (mean ± S.E.M.) cumulative number of gridlines crossed, following 1-h exposure to water (W) or clorazepate (C) at 10 µM or concentration (µM) indicated, followed by testing in water.

Fig 4

Attenuation of the abstinence-induced withdrawal from clorazepate (C) by co-treatment with flumazenil (F).

Fig 5

Dose- related decrease in pLMV (mean ± S.E.M.) cumulative number of gridlines crossed, following 1-h exposure to water (W) or zolpidem (Z) at 10 µM or concentration (µM) indicated, followed by testing in water.

Fig 6

Attenuation of the abstinence-induced withdrawal from zolpidem (Z) by co-treatment with flumazenil (F).

Fig 7

Dose-response curves of abstinence-induced withdrawal from 1-h exposure to midazolam, clorazepate, or zolpidem. Values are means ± S.E.M. cumulative pLMV compared to controls (drug-exposed planarians tested in drug-free water).