Effect of methergoline on body temperature in mice

Neuroscience Letters, 4 (1977) 225--229 © Elsevier/North-HoUand Scientific Publishers Ltd.

EFFECT OF ME ~HERGOLINE ON BODY TEMPERATURE

225

IN MICE

C. CARDANO, P. STROCCHI, D. GONNI, M. WALSH and L.F. AGNATI*

Institute of Pharmacoiogy, University of Bologna, Bologna (Italy) (Received November 1st, 1976) (Accepted November 12th, 1976)

SUMMARY

Serotonin (5-HT) involvement in body temperature regulation has been studied in mice by means of a 5-HT-selective blocking agent (methergoline). This drug causes an effect on body temperature which is dependent on environmental temperature. At environmental temperatures of 25°(: and 11°C methergolhle has a hypothermic effect, while at 36°C environmental tempe,ature, methergoline has a hyperthermic effect. At 25°C environmental temperature, the hypothermic effect induced by 125 gg/kg i.p. of methergoline could be antagonized by low doses of LAE-32 (80 gg/kg s.c. ), while there was not such an antagonism using higher dose~ of LAE-32 (100 and 300 ug/kg s.c.). This has been explained using Jalfre's hypothesis of the existence of 5-HT inhibitory and excitatory receptors.

Previous work [4] on serotonin {5.HT), dopamixle (DA) and noradrenaline (NA) turnover has demonstrated methergoline'~ selective blockade of 5-HT receptors in rat brain. Methergoline does influence 5-HT levels, but only at high doses; for doses less than 1 mg/kg no reduction of 5-HT level~ has been observed. It has been further noticed that the LSD-induced reduction of 5-HT turnover can be selectively antagonized by methergoline. Methergoline's blockade of the 5-HT receptors seems to be selective since experimentation has failed to demonstrate changes in DA and NA turnover induced by this compound. This can be further demonstrated by the fact that methergoline fails to alter amphetamine-induced rotational b~ haviour (DAmediated) or modify the flexor reflex in acute spinal rats (NA-rnediated). However, methergoline selective::~y antagonizes the LSD-induced increase of the extensor reflex (5-HT-mediat~d) in acute spinal rats in a do~-dependent manner. *Present address: Institute of Physiology, University of Bologna, Bologna, Italy.

226 Since experi_me_ntal observations demonstrate that 5-HT is involved in thermoregulation, more precisely as a mediator of hypo~hermia in the mouse [3,5], it was decided to study the effects of methergol~e on mouse thermoregulation at an environmental temperature (Te) of 25°C and during thermal loads (at Te oi 11°C and 36°C). The ~uteraction between methergoline and LAE-32 (lysergic acid ethylamide) on rectal temperature in mouse at Te of 25°C has also been studied. Swiss albino male adult mice weighin~ 20--25 g were used. The mice were randomly chosen from mice which were u J a l r . ~ e d in cages of 10 animals each with free access to water (tap water) and food (Nossan pellets). Ambient temperature was kept at 22 ± 2°C at a relative humidity of 80% with continuous ventilation and artificial illumination from 0 7 . 0 0 - 1 9 . 0 0 h with darkness for the remaining hours of the day. LAE-32 was used to act on 5-HT receptors. In fact, it has been reported tha~ this substance has the same peripheral antiserotonin effect as LSD, although quantitatively the effect is about one.eighth that of LSD [6]; furthermore, LAE-32 induces the same behavioural modifications as LSD both in man (psychological changes, [6] ) and in mice (head-twitches [8] ). LAE.32 was injected in 250/~1 of solvent (Ringer's lactate solution) while methergoline was dissolved in 250/~1 of ascorbic acid solution (pH = 4). Temperature was measured by a thermistor introduced at a depth of about I cm into the rectum. Acute exposure of animals occurred at three different environmental temperatures (Te): at 25°C (room temperature), at l l ° C (1°C above the lower limit of the critical interval [ 1 ] ) and at 36°C (1°C below the upper limit of the critical intereal [ 1 ] ). The Te was maintained within ~ 1°C of the desired value. Animals were put in plastic containers which had been previously placed in the thermally controlled environment in order to bring them to the desired temperature. LAE-32 administration at doses of 80, 100 or 300/~g/kg s.c. followed methergoline administration (125 pg/kg i.p.) by 30 rain. Data on rectal temperature were collected every 12 rain for 72 rain from the time of LAE-32 administration. Methergoline was injected 30 rain before ~he administration of LAE.32 since it has been found in previous unpublished experiments that the effect of methergoline (at the doses used) on mice rectal temperature lasts longer than 2 h and that the peak effect usually occurs between 30 and 60 rain. As regards the treatment with methergoline alone, it was assessed whether [ (Tr) t -- (Tr) c ] was greater or less than zero (Tr = rectal temperature; t = time = 30, 4 2 , 5 4 , . . . . , 1 0 2 rain; (Tr)t = value after treatment observed at time t; (Tr)c = control value observed before any treatment). The overall effect of the treatment wa~ considered as hyperthermic if ~ [ (Tr) t -- (Tr) c ] >0, or as hypothermic if T. [ (Tr)t -- (Tr)c ] < 0. The most positive value (peak effect of (Tr)t) quantified as PETr = (Tr)t - (Tr) c was considered in the case of hyperthermia, while the

227

m o s t negative value (peak e f f e c t o f (Tr) t) q u a n t i f i e d as PETr = (Tr)t -- (Tr)c was considered in the case o f h y p o t h e r m i a . C o n t r o l studies were also p e r f o r m e d on mice t r e a t e d with solvent alone and t h e n e x p o s e d to thermal load (acute e x p o s u r e at 11 ± 1°C and 36 ± 1°C). Regarding the interaction b e t w e e n m e t h e r g o l i n e and LAE-32, the mean value o f t h e differences b e t w e e n (Tr)t and (Tr) c was considered as an index of the e f f e c t o f t r e a t m e n t on the Tr o f the mice. This mean value will be referred t o a s / , T r . Statistical analysis was p e r f o r m e d using S t u d e n t ' s t-test. The m e a n (-+ S.E.M.) o f the (Tr) c values was 39.13 + 0.07. Methetgoline m a r k e d l y influences Tr at a n y given Te. In particular, it is interesting to note a h y p o t h e r m i c effect at Te = 11°C or Te = 25°C and a h y p e r t h e r m i c effect at Te = 36°C (see Fig. 1). F o r every group, the (Tr) t peak values were significant. ly d i f f e r e n t from the respective (Tr) c values (statistical analysis according to S t u d e n t paired t test; P < 0.01). C o n t r o l studies on mice treated with solvent alone and u n d e r identical thermal load conditions as above, gave T r values around zero (at 36°C the P--ETr was 0.05 +- 0.09 while at 11°C it w a s - - 0 . 2 9 +- 0.07; mean ± S.E.M., sample size n = 5). LAE-32 at low doses (80 pg/kg s.c.) antagonizes the h y p o t h e r m i c effect of methergoline ( 1 2 5 / J g / k g i.p.) at Te = 25°C while higher doses of LAE-32 do n o t e x e r t such an e f f e c t (significances according to S t u d e n t ' s t test; see Fig. 2). DOSE~-.EFFECT CURVE OF METERGOLINE ON RECTAL TEMPERATURE IN MICE

I~,1,,

~

~ ~3Bt3

metergoll~n~. (mg/kg)

T,,=25 C 6

Fig 1. Dose-effect curve of rnethergoline on recta| temperature in rnice.__On the x axis (log scale) methergoline d ~ (mg/kg i.p.) are gi,:en. On the y axis ~.he PE Tr value~ (means of 4 data ~ S.E.M.) are repor'~ed (for further details see texQ. Three ~e have been taken into account: ll°C, 25~C and 36~C (see text).

MICE RECTAL TErPERATURE" INTERACTION BETWEEN METERGOLINE AND LAE +0.5

-1 ~r nl

Fig. 2. Mice rectal temperature: interaction between methergoline and LAE-32. Methergoline (125 .g/kg) was given i.p. 30 rain before LAE-32(0, 80, 100, 300 .g/kg). On the x axis the different treatments are given. Ov the y axis the ~ T r values (for further detaib, see text) during the 72 rain of recording ar~; given. Mean values (n = 4) ~ S.E.M. are plotted. Comparisons have been performed between methergoline plus LAE-32 treated groups with the respective methergoiine-afone treated groups. Statistical analysis according to Student's 't' test; ** P < 0,01; ns ~ not sigr~ifica.t. For the sake of comparison, treatment with LAE-32 alone is reposed,

Since methergoline has a t~lective action on serotoninergic receptors, it has been shown to be an int~resting instrument for the study of some serotonin-mediated CNS effects. Particularly, in this study it was used in an attempt to clarify the role of the serotoninergic pathway in thermoregulation. It was observed that methergoline, like rzany other substances, has an effect on the Tr which is dependent on the Te [2 ]. Furthermore, it has a notable hypothermic effect at Te = 25°C which does not seem to be doserelated. Antagonism between LAE-32 and methergoline in thermoregulation presents characteristics worth comparing. In fact, it remains to be explained why LAE-32 is effective only at small doses (80/~g/kg s.c.) in antagonizing the methergoline-induced hypothermia (125 ~g/kg i.p.). Regarding this point, it should be mentioned that microiontophoretic studies in the brain indicate the presence of 5-HT inhibitory and excitatory receptors [7 ]. One could speculate on the basis of the present findings that LAE-32 at low doses stimulates mainly inhibitory receptors causing a slight hyperthermia while at higher doses LAE-32 could act preferentially on 5-HT excitatory receptors causing hypothermia. The acute hypotherrnic effect of

229 m e t h e r g o l i n e c o u l d be e x p l a i n e d o n t h e basis o f a b l o c k a d e o f 5 - H T i n h i b i t o r y receptors. H e n c e , L A E - 3 2 a t l o w doses m a y a n t a g o n i z e t h e b l o c k a d e of 5-HT i n h i b i t o r y r e c e p t o r s c a u s e d b y m e t h e r g o l i n e a n d , t h e r e f o r e , t h e methergo!inei n d u c e d h y p o t h e r m i a , while h i g h e r doses o f L A E - 3 2 a c t i n g o n 5 - H T e x c i t a t o r y r e c e p t o r s , c o u l d even cause a t r e n d f o r p o t e n t i a t i o n o f t h e m e t h e r g o l i n e - i n d u c e d h y p o t h e r m i a (see Fig. 2). REFERFJ4CES 1 Altman, P.L. and Dittmer, D.S., Environmental Biology, Fed. Amer. Soc. for Exp. Bioi., Bethesda, Md., 1966, pp. 1--694. 2 Baumann, I.R. and Bligh, J., The influence of ambient temperature on drug-induced disturbances of body temperature. In P. Lomax, E. Schonbaum and J. Jacob (Eds.), P~oc. Symp. on Temperature Regulation and Drug Action, Paris, April 1974, Karger, Basel, 1975, pp. 241--251. 3 Brittain, R.T. and Handley, S.L., Temperature changes produced by the injection of catccholamines and 5-hydroxytryptamine into the cerebral ventricles of the conscious mouse, J. PhysioL (Lond.), 192 (1967) 805--813. 4 Fuxe, K., Agnati, L. and Everitt, B., Effects of methergeline on central monoamine neurones. Evidence for a selective blockade of central 5-HT receptors, Neuroscience Letters, 1 (1975)283--290. 5 Grabowska, M., Michaluk, J. and Antkiewicz, L., Possible involvement of brain serotonin in apomorphine-induced hypothermia, Europ. J. Pharnaacol., 23 (1973) 82--89. 6 Hoffer, A. and Osmond, I4., d-Lysergic acid diethylamide. In A. Hoffer and H. Osmond (Eds.), The Hallucinogens, Academic Press, New York, 1967, pp. 83--265. 7 Jalfre, M., Ruch-Monachon, M.A. and Haefely, W., Methods for assessing the interaction of agents with 5-HT neotons and receptors in the brain. In G.L. Costa and M. Sandier (Eds.), Advanc. Biocbem. Psychophar,nacol., Vol. 10, i~aven Press, New York, 1974, pp. 12i--134. 8 Strocchi, P., Walsh, M. and Agnati, L.F., The inhibitory effect of methergoline on LAE-32 induced head-twitches in mice, Neuroscience Letters, 4 (1977) 221 - 224