.European Journal of Pharmacology 431 2001 201207www.elsevier.comrlocaterejphar
Rapid tolerance to D9-tetrahydrocannabinol and cross-tolerance betweenethanol and D9-tetrahydrocannabinol in mice
George E. da Silva, Gina S. Morato, Reinaldo N. Takahashi)Departamento de Farmacologia, Centro de Ciencias Biologicas, Uniersidade Federal de Santa Catarina, UFSC, R. Ferreira Lima, 82,
88015-420 Florianopolis, SC, Brazil
Received 1 October 2001; accepted 5 October 2001
Motor incoordination in the rota-rod test was used to assess the development of rapid tolerance to D9-tetrahydrocannabinol and rapidcross-tolerance between ethanol and D9-tetrahydrocannabinol in mice. Further, the influence of the cannabinoid receptor antagonist SR
. . .141716A N- piperidin-1-yl -5- 4-chlorophenyl -4-methyl-1H-pyrazole-3-carboxyamide on the motor impairment induced by both drugs9 . was examined. Mice were injected on day 1 with equipotent doses of D -tetrahydrocannabinol 28 mgrkg, i.p. and ethanol 2.25 grkg,
. 9i.p. and tested at 30, 60 and 90 min after the injections. On day 2, control groups received ethanol or D -tetrahydrocannabinol, somegroups received the same treatment as the day before, while the remaining groups switched the treatment. All groups were tested toevaluate tolerance. The development of rapid tolerance to D9-tetrahydrocannabinol was observed and pretreatment with ethanol resulted in
9 .rapid cross-tolerance to D -tetrahydrocannabinol. SR 141716A 2 mgrkg, i.p. failed to block the development of rapid tolerance to bothdrugs, ethanol and D9-tetrahydrocannabinol. These results suggest that D9-tetrahydrocannabinol, similarly to ethanol, can induce rapidtolerance to motor incoordination in mice. They also support the use of the 2-day protocol as an effective procedure to reduce the lengthof drug exposure necessary to induce tolerance. q 2001 Elsevier Science B.V. All rights reserved.
Keywords: Rapid tolerance; Cross-tolerance; Rota-rod; D9-Tetrahydrocannabinol; Ethanol; SR 141716A
The repeated exposure to Cannabis satia or its princi-pal psychoactive constituent, D9-tetrahydrocannabinol, hasbeen reported to induce tolerance in several species, in-cluding mice, using different measures such as hypother-mia, antinociception, catalepsy, depression of locomotoractivity, hypotension, anticonvulsant activity, cortico-
steroid release and schedule-controlled behavior reviewed.by Adams and Martin, 1996 . However, within the last
decade, the research on cannabis has undergone dramaticadvances due to developments such as the identification,cloning and expression of selective cannabinoid CB and1
.CB receptors Matsuda et al., 1990; Munro et al., 1993 ,2the isolation of the endogenous cannabinoid receptor lig-
ands anandamide and 2-arachidonyl glycerol Devane et.al., 1992; Stella et al., 1997 and, most recently, the
availability of a selective cannabinoid CB receptor antag-1 .onist, SR 141716A Rinaldi-Carmona et al., 1994 .
) Corresponding author. Tel.: q55-48-331-9764; fax: q55-48-222-4164.
.E-mail address: email@example.com R.N. Takahashi .
Although drug tolerance, in many situations, is rathereasily demonstrated and measured, there is an increasingawareness of the fact that the development of this responseis a complex event which is influenced by both behavioraland environmental factors. For instance, there are severalreports showing that tolerance to D9-tetrahydrocannabinoloccurs in different species, but many of these studies have
been conflicting and ambiguous Carlini, 1968; McMillan.et al., 1970; Kaymakcalan et al., 1974 . As mentioned
.recently by Bass and Martin 2000 , a possible source fordiscrepancies among studies may be the length of exposureto D9-tetrahydrocannabinol during tolerance induction.Moreover, studies designed to assess the rate of develop-ment of chronic tolerance to ethanol indicate that this rate
is highly dependent upon the test measure examined Bitran.and Kalant, 1991 . The phenomenon designated as rapid
tolerance to ethanol has been reported to occur within824 h, after the effect of the first dose has disappeared .Crabbe et al., 1979 . One of the most interesting aspectsof rapid tolerance is that the magnitude of the observedtolerance is often not significantly different from that
observed following chronic ethanol treatment Khanna et.al., 1997 . In addition, both rapid tolerance and chronic
0014-2999r01r$ - see front matter q 2001 Elsevier Science B.V. All rights reserved. .PII: S0014-2999 01 01449-2
( )G.E. da Sila et al.rEuropean Journal of Pharmacology 431 2001 201207202
tolerance have been shown to be influenced by, or torequire, the activation of a process related to learning and
.memory Bitran and Kalant, 1991 .Alcohol and marijuana are two of the most widely used
psychoactive drugs in the world. There is a growingliterature, mainly consisting of human studies, document-ing that D9-tetrahydrocannabinol and ethanol share some
. central nervous system CNS depressant effects Hollister.and Gillespie, 1970; Ng et al., 1973 and that there are
certain doses of these drugs that may produce comparable .behavioral effects Heishman et al., 1997 . It is important
to note in the context of the present study the early .findings of Sprague and Craigmill 1976 that ethanol and
D9-tetrahydrocannabinol injected over 12 and 7 days, re-spectively, produce a similar type of behavioral impair-ment in mouse performance measured on a rota-rod ap-paratus as well as the development of cross-tolerancebetween these two drugs.
The cannabinoid CB receptor antagonist SR 141716A1has been reported to antagonize many of the acute effectsof cannabinoids including hypothermia, analgesia and lo-
comotor activity Rinaldi-Carmona et al., 1994; Compton. 9et al., 1996 . Following chronic D -tetrahydrocannabinol
administration, SR 141716A precipitated a withdrawalsyndrome in rats, mice and dogs Cook et al., 1998;
.Lichtman et al., 1998 . In addition, there are studies pre-sumably investigating the role of the cannabinoid CB1
receptor in the reinforcing effects of ethanol Arnone et al.,.1997; Colombo et al., 1998 .
In view of the above, the purpose of the present studywas to examine whether, similarly to ethanol, a rapidmodel for the development of tolerance to D9-tetrahydro-cannabinol-induced motor impairment in mice could beachieved. To explore this possibility, we have compared amotor-impairing doses of D9-tetrahydrocannabinol andethanol on the rota-rod test. In addition, the developmentof rapid cross-tolerance between these two drugs wasassessed using the same test. Further, the influence of acannabinoid CB receptor antagonist on the development1of rapid tolerance by ethanol and D9-tetrahydrocannabinolwas investigated.
2. Materials and methods
.Male Swiss albino mice 2535 g, 68 weeks old weremaintained in groups in the colony room of the Depart-ment of Pharmacology, under a lightdark cycle of 12 h .lights on at 6:00 a.m. with food and water ad libitum. Allprocedures used in the present study complied with theguidelines on animal care of the Brazilian Society ofNeuroscience and Behavior.
Ethanol was purchased from Merck Darmstadt, Ger-. 9many . D -Tetrahydrocannabinol was obtained from the
.National Institute of Drug Abuse Bethesda, USA at 200 . mgrml in alcohol. SR 141716A N- piperidin-1-yl -5- 4-
. .chlorophenyl -4-methyl-1H-pyrazole-3-carboxyamide was .kindly supplied by Sanofi Recherche Montpellier, France .
Ethanol was diluted with saline to a concentration of 14%wrv. The appropriate concentration of D9-tetrahydro-cannabinol was prepared immediately before use by evapo-rating the alcohol and emulsifying the residue with Tween-
.80 Takahashi and Singer, 1979 . One drop of Tween-80per 10 ml was added for the preparation of the SR141716A suspension. Control solution was prepared withthe corresponding vehicle. All solutions were administeredby i.p. route.
Motor impairment was measured on a rota-rod appara- .tus Rotamex-V-EEr85; Columbus Instruments, USA
controlled through a computer and as described previously .Barreto et al., 1998 . Briefly, mice were trained under
.continuous acceleration 1 rpmrs in 1-min sessions.Whenever the animal falls off the rotating bar, it receives a
.foot shock 0.3 mA . The speed of the rotating bar whenthe animal falls off is taken as the performance score.
.Animals that did not reach a stable baseline at least 20 sin 15 trials were discarded. After the selection, experimen-
.tal and control groups Ns10 were matched according totheir body weight and mean performance during the lastsession. With this procedure, animals presented similarbaseline values on both days for all groups.
2.3.1. Effect of different doses of D9-tetrahydrocannabinolon the deelopment of rapid tolerance
On day 1, four groups of trained mice received different9 .doses of D -tetrahydrocannabinol 8, 15 or 28 mgrkg or
control solution. Then, they were tested on the rota-rod 30,60 and 90 min later. Mice were then returned to their homecages. On day 2, each animal received exactly the sametreatment that it received on the previous day, and 30, 60and 90 min later, all animals were tested on the rota-rod toevaluate the development of rapid tolerance.
2.3.2. Comparison between the deelopment of rapid toler-ance to ethanol and D9-tetrahydrocannabinol and cross-tolerance between these drugs
Previous experiments in this laboratory have shown thata single dose of 2.25 grkg ethanol caused a significant
.tolerance in this paradigm Barbosa and Morato, 2001 . . 9Therefore, ethano