Nociception is enhanced by the intrathecal injection of 5-methoxy-N,N-dimethyltryptamine in the rat

Nem~osc~enceLetter$, 33(1~82} 3 2 ~ 3 2 8 .

323

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~'~e~f:i.;O~Veieti~p~B~'oloi~,y,.Uoiv*mity , , ~li~nesota,. St, Paul, MN 55108 (U.S.A,) ( R ~ i v ~ i i i y : : 6 t h , :~198:~ RGviscd:version r~eived arid accepted October lst~ 1982)

Key words: nociception - serotonin - tryptami-,e - 5-methoxy-N,N-dimethyltryptamine - imratheeal injection - spinal cord •

The~ffect Of 5-methoxy-N,N,dimethyltryptamii~e (5-MeODMT) at the spinal cord level on nociceptive reflexes was:tested :using =the tail-flick assay in rats. 5.MeODMT was injected d~rect!y imo the spinal subarachnoid space of.consciou~ rats via a pernmnendyindwe~ling intrathecal cannula, Administration of 100~.~g/rat of 5-M¢ODMT into the thoracic re#on, using a 4 cm long eannula, reduced the average percent.of contrc.' reaction time by 14~70. The injection of the same dose. of 5-MeODMT i.~tc the !umb0sacrai re#on, via an-8.6 em long cannula, decreased the average percent ofcontrol reaction t~me by 25 go, Th~ ability of'5=MeODMT'to mimic th6 facili ta~.ory(hyperalgesic) effect on nocicepfion of similar doses of tryptamine, in contrast-to theantinocieepfive ~analgesie) effect of serotoni:a, suggests an interaction of ~,MeODMT with tryptaminergi¢ rather than serotonergic receptors in th~.~ ~;pinal cord.

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It has been reported that Jntrac~:rebroventficuh~rinjections of h~w do.~es (3. !-.50 t~g/rat) of 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) enhance neciceptf~on i n rats;'whilehi~er do~es (t~:and 400#g,/rat)of 5-MeODMT prod~ce antinocicepti#e effeclZ [2]. The enhan~,~d:nocicepfio:a' induced by 5-MeODMT was postulated by Berge et al. [2] to result from interaction with presynaptic serotoner#¢ receptors, f0t Whieh,~5-M,~<)DMT:has a high affinity[1]. The analgesic effect ,of 5-MeODMT~ on:the:0ther ~hand, wasattfibu~ed:to diffusion of the drug and subsequent binding tO:po~tsyriapti¢ :Ser0tonergic receptors; ]x~ssibty located i n the spinal cord area. Several lines o~evidence suggest that acfivationof descending serotonergic pathways can directly caUseantinocicepfion and.that such activity is, in part, res~0onsible for opiate=itidu~ed analgesia [ i 8], Injected intratheCally~.i.e. directly into the spinal st!ba~aehnOJd' spaCo, serotonin,produces a dose-related increase ia the latency of response to noxious thermal stimuli [14, .25]. Ir,~.contras~ ~o the antinoci¢~ptive effect of serotoni~, we have recer~fiy observed i~tqit~:ra~h~ and :~mraeereb~oventricnlar injections of tow: dose,J of tryptami~e (::i~! aad:200~/eat)~:ualiy enhance :nocicepfion as md~ca,e~a by decreased latchties in ~ai] flick and hot place responses [i2] In ;pite of their stri/ctara[ similarity, 030~3940/82/0900-0000/$ 02."5 © t982 Elsevier Scientific Publishers IrelarM l_,tck.

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tryptamine does not n~nic the aminociceptive effect of intrathecalty administered serotonin until a much higher dose of tryptamine (400 #g/raQ is ad~nister~:l. Pretreatv~nt with serotom a n ~ g o n i ~ was found to iblock tHS antinociceptive efby lower doses of tryptamine.: ~! : r , :~::: !:: ri~! r~!::ii ~ii:: :~ /~ i :::!: ~:~~:!/i~:i~ Tryptamine is lound in afllmajor regions o f the~brain and in all species exan~ned thus far [4, 16, 19, 20], however the spinal cord i~ reported to contort significantly higher concentrations of tryptamine than the wh,c)le brain [22]. Inve~t~ators:ha;,'e previously postulated the ~stence of atryptsminergic system m r~he CNS [!5' 1I7, Ell. Based on tryptami.ne's apparent h ~ r ~ _ g ~ i c effect, we have propose d that, while a descending serotonergic system il)hibits nociceptive elements in the spinai cord, a trypt~inergic system may act to potentiate nociception in the process of pain perception [13]. -In light of the hyperalgesJc and analgesic potential of tryptamine applied intrathecally, the dual effects produced by 5-MeODMT could result from binding to the same receptor populations as those which produce the antinoc';ceptive and enhanced nociceptive effects of tryptamine. The present studyrwas initiated to determine whether the antinociceptive effect of 5-MeODMT is due t o an action on postsynaptic serotonergic receptors located in the spinal cord as proposed by Berge et al. [2], or whether 5-MeODMT, like tryptamine, can cause an enhancement of nociceptive activity in spinal as well as supraspinal are~. Opposite effects of serotor~in in spinal versus ~upraspinal areas have previously been demonstrated by depression of the acoustic startle areas have previously been demonstrated by depression of the acoustic ~;tartle reflex after infusions of serotonin er 5-MeODMT into forebrain areas, compared to enhancement of startle ,:eflexes m ter [ntrathecal ir.jections of serotonin [9] c,r 5-MeODMT [8]. 5-MeODMT was thus injected directly into the spin~ ~ubarachnoid spacein conscious rats: at a dose reported to enhance tail-flick latencies when injected intracerebrove.'.,tric.ularty [2]. The eff~t of these injections on pare reflex activity was then determined :by measuring the latency of the tail-flick response to radiant heat. Male Sprague-Dawley rats weighing between 375 and 425 g were anesthetized with ether and chronically implanted with int~athecal cmmulas constructed of PE 10 tubing (Clay Adams, Parsipanny, NJ), according to the method described by Yaksh and ~;.udy [2g]. Such catheterization of the spinal subarachnoid space allowed: for the ~'epeated in,iecfion of drugs into either the thoracic or lumhosacr~ areas of the spinat cord. Rats were anesthetized with ether during cannulation through the cisterna magna. An injection of saline was routinely made to clear the catheter of any po~sible debri.~ accumulated during the insertion, ,Thereafter, rats were housed ~ndividually, fe~ ad libitum and allo~ed a minimum of 7 days to: recover frorn::the surgical procedure, Rats :exhibitingar~yobserv~le motor or sensory deficit "~ete.not used i,a the st v,~y, Rats receiving more than one dn~g injection were allowed: t 4 d~ys re~t between experiments, r "

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Drug ,~olutlons were prepared fresh daffy in distil.led water. The rear, mum volume of drug administered was 20 el, followed by a 12. l~t flush with distilled water. ]t should.be noted thatmost authors usearfificial CSF or an isotonic solution to avoid 1 ~ d ~ a g e to neurons~ T ~ p ~ e IWdroc~oride and 5-MeODMT
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Fig. i. Time course of the effect of 5-MeODMT after its ~ntrathecal injection into ~oracic:(4.0 cm long cannulas) or lumbosacral (8.6 cm long ¢~annl~) areas of the rat spinal cord. The intrathee.al injection of 100 ~g of 5-MeODMT imo these two areas each produced a significam decrease (*P,~0.05) in thete.ilflick lateneies for at least 15 rain following its injection. Vertical bars indicatethe S.E.M. calculated from groups of seven rats at various times after their injection with 5-MeODMT,

The injection of low doses of tryptamine into both spina~ and supr~p~na| areas i~as been ~,~hownto produce an enhanced nocic~tive cff~t in rats [1.]. Thus, for ex~mple, an injection of 100~g of tryptamine-HCl (0.414 ~mol tryptarzrine base) produces an immediate and transient decrease in tail-flick r ~ t i o n thnes,(Table l). However the htency of the tail~fllck response returns to control ~:by tO rnln postinjection, a time at which the effect :ofS-MeODMT appears to be maximal, (Fig. 1). Endogenously formed tryptamine is localized i n nerve termin~ds :[5].and,inhibition of monoamine oxidase (MA,O)has shown that it has a'very rapid turnover ~[6, I0, 20, 23]. While tryptamine's effectis rspidly terminated b y M A O , 5 : M ~ D M T appears to have a longer duration of action in the CNS: The dis~repancy between the time courses of these two compound~ may thus lie in the differenl: rstes oftheir metabolism. Our results showing an apparent hyperalgesia produced by intrath,~:alt~ injected 5-MeODMT are compatible with the enhanced no¢iceptiveeffec~s of !Ow doses of 5-MeODMT administered supraspinally [3]. In light o f 5-McODMT's and tryp, tarnine's similar activity ~n nocieeptive :refle×es,:at both spinat~r~d isupr~spinai and tryptarnme s l~sslble role in ~the ~ S - a s a neurotn~nsmit~:er, tt: aS tempting to speculate that low doses :ofS*MeODMT mimic the:effectof tryptami~e ~in

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HYPERALGESIC ~EFFECTS O F 5-MeODMT AND TRYPTAMINE HCI iN RATS the lumbo~cral region, of.the spinal cord vi~ an 8.6 cm imra~hecai cannula. T~flT~¢g laten~des,~ere measured at 10~minafter rejection unless otherwise stated..Values in parencheses in-

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theCNS. Although a receptor population having saturable and high affinity binding to [3H]tryptam~ne has been describe,~l i n the rat cortex [I1], the ability of 5-MeODMT to displace this binding was reported to be low in that system. Thus the exact receptGr with which 5-MeODMT and tryptamine interact to produce these effects on pain reflexes is not clear at ~his time. In summary, our data indicate that direct apphcadon of 5-MeODMT to the spinal cord of rats produces enhanced ncciception. Thus, in spite o f their slructura[ similarity, the effect of intratheca|ly administered 5-MeODMT on nociception is opposite that of serotonin; however, the effect, of 5-MeODMT is similar to that of low doses of tryptamine.

1 Berge, O.G. and Hole, K., In3uene¢ of descending 5-hydroxy~r~.p~amine Ci-HT) pathways on a reflex response to radiant heat, Neurosci. Lett., Suppl. 3 0979) $257. 2 Bcrge, O.G., Hole, K. and DaMe, H., Nociception is~.~ha~cedafterlow dose~ an~ reduced afterhigh doses of the serotonin rvceptor agonist 5-methoxy-N,N-dimethyltryptamhhe, Neurosci. Left., 19 (1980) 219-223. 3 Bj6rklund, A. and Wiklund, L., Mechanisms cf regrowth of the bulbospir~l serotonin system following 5,6-DHT induced axotomy I. Biochemical effects, Brain Rcs., 191 (1980) 109-127. 4 Boulton, A.A., Identification, metabolism, and function of meta- and p,:ra4yramine, ph~nylethylamin¢ and h3,ptamine in brain, Advane. Biochem. Psychopharmacol, 15 (1976) 57-67. 5 Boulton, A.A. and Baker, G.B., The subcel~u]ardistributionof ~°phenyleth'~lamine,p4yramine and tryptamine in rat brain, J. Neurochem, 25 (1975) 477-481. 6 Boutton, A.A., Juorio, AoV., Philips, S.R. and Wu, P., Some arylalkyIamines in rehbit brain, Brain Res., 16 (1975) 212-216. 7 D'Amour, F.E. told Smith, D.L., A method for determining loss of pain sensation, 3o Pharmacol. Thor., 72 (|941) 8 Davis, M., Astrachan~ D3., glendetman, P.M. and Glende]man, D.S., 5-Methoxy-N,N-dimethy~t~ptam!~: s#nal cord and brainstem ,aediation of e~ei~atory eff~ts on acoustic startle, Psychopharmacology, 79 (1980) !23-130. e~p.

1'4-79.

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9 Davis, M., Astrachan, D.L and Kass, E., Excitatory and inhibitory effects of serotor~n on, sen~,~rimotor reactivity measured with,afoust:ic st_ert~,~Sciellce,209 0980)~2~$2~ ~ : :~ .... ~...... 10 Durc~n, D.A. and Phillips, S.R.. Kinetic measurements of the turnov~rates of pheny~ethylamhne and t ~ II ~-Kellr~, Ph~e

12 Larson, A.A., Chaagesin~n-reflexes!fter intr~th~admim'strati~a: 0 ~ t r ~ i ~

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13 Larson, A.A., Hyperatgesia producedby;t~intratheceladministrati0n of t r y p t ~ n e tolrats~,Brain Res., in press. .:~ 14 Larson, A.A. and Armstrong, M.J., Mbrphine analgesia after intrathecal a ~ t r a t i 6 n / d f / ~ ~ cotic agonist, chloroxymorphamine and antagonist, chlornaltrexamine, Eurov. 'J: I/lmr.;iacSl~.',:68 (1980) 25-31. 15 Martin, W.R., Sloan, LW., Buchwald, W,F. and Clemew,s, T.H., Neurocliemical evidencefoftryptaminergi~ ascending and descending pathwaysin tliespinal cord of the dog' Ps~cl~o~ha,~acblogia, 43 (1975) 131-134. ~ 16 Martin, W.R., Sloan, J.W., Christian, S.T. and Clements, T.H., B~ain levels of tryptamine, Psychopnarmacologia, 24 0_972) 331-346. 17 Martin, W.R., Thompson, J.A. andNozaki, M., Physiologicevidence for descendingt~ptanfinergie pathways in the spinal cord,:Life ~ i . , ] 9 (1976)t383-1386. • ~i ~ • ' 18 Mes~'ng~ R.B. and Lyric, L.G., Serotonin-contalning neurons: theiz possible role Ln pain and analgesia, Pain, 4 0977) 1-21, 19 Saavedra, J.M. and Axelrod, J., A specific and sensitive enzymatic assay for tryptamine in tissues, .L Pharmacol. exp. Ther., 182 (1972) 363-~69. 20 ~;aavedra, J.M. and Axelrod, J., Effect of drugs on the trypmmine content of rat tissues, L PharLnacol. exp. Ther., 185 (1973) 523-529. 21 Sloan, J.W., Martin, W.R., Clements, T.H,, Buchwald, W.F. and Bridges, S.R., Factors influencing brain and t.issuelevels of tryptamine: species, drugs and lesions, J. Ncurochem., 24 (1975~ 523-632. 22 Snodgrass, S.R. and Horn, A.S., An assay procedure for tryptamine inbrain and spinal cord using its (3H)dansyl derivative, J. Neurochem., 21 (1973) 687-696. 23 Wu, P.H. and Boulton, A.A., Distribution and metabolism of tryptamine in ra~ brain, Canad. J. Biochem., 51 (1973) 1104-1112. 24 Yaksh, T.L. and Rudy, T.A., Chronic catheterization of the spinal subarachnoid space, Physiol. Bchav., t7 (1976) 1031-1036~ 25 Yaksh, T.L. and Wilson, P.R., Spinal serotonin ~erminal system mediates antinociccption, J. Pharmacol, exp. Ther., 208 (1979) 446-453. -

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