- Email: [email protected]
Attenuation of morphine-induced analgesia in mice by exposure to magnetic resonance imaging: Separate effects of the static, radiofrequency and time-varying magnetic fields
Mognerrc Resonance Printed in the USA.
Imaging, Vol. 5, PP. 9-14, All rights reserved.
1987
Copyright
0
0730-725X187 $3.00 + .OO 1987 Pergamon Journals Ltd.
l Original Contribution
ATTENUATION OF MORPHINE-INDUCED ANALGESIA IN MICE BY EXPOSURE TO MAGNETIC RESONANCE IMAGING: SEPARATE EFFECTS OF THE STATIC, RADIOFREQUENCY AND TIME-VARYING MAGNETIC FIELDS FRANKS . PRATO, * KLAUS-PETER EDMUND
SESTINI~
OSSENKOPP,
AND G.
t MARTIN
CAMPBELL
KAVALIERS, $
TESKEY~
*Department of Nuclear Medicine, St. Joseph’s Health Centre of London, Ontario, Canada; thychology IDivision of Oral Biology, Faculty of Dentistry, University of Western Ontario, London, Ontario,
Department, Canada
Exposure of adult male mice to a magnetic resonance imaging (MRI) procedure has been shown to abolish the nocturnal analgesic responses observed following treatment with morphine. The field component(s) responsible for this inhibitory effect were examined by exposing mice to either the static, time-varying or rf magnetic field components associated with an MRI procedure. In the middle of the night portion of their day-night cycle, mice were exposed for 23.2 min to one of the above field components, intraperitoneally injected with morphine sulphate (10 mg/kg) and then exposed to the field conditions for another 23.2 min, after which analgesic responses were determined. Analgesia was quantitated by determining the length of time mice were content to be on a hot surface (50°C) before they showed discomfort by licking their paws. It was observed that the time-varying magnetic field completely abolished, the rf field significantly reduced, while the static field component (0.15 T) had no evident effect on morphine-induced analgesia. These results indicate that the time-varying, and to a lesser extent the rf, fields associated with the MRI procedure inhibit morphine-induced analgesia in mice. These data also raise the possibility that exposure in humans to some of the magnetic field components associated with MRI may have clinically relevant effects on the actions of narcotic drugs such as morphine. Keywords:
MRI safety, Biomagnetic
effects, Analgesia
attenuation.
ma)s 1,13,21,25-27,30,36,39.42,43 no adverse
INTRODUCTION
imaging have been found Magnetic resonance imaging (MRI) is a powerful noninvasive diagnostic procedure that is receiving increased clinical application. This procedure is useful not only for advanced medical imaging,10~12~23 but also for providing information about the chemical and physiological status of the biological system of interest without the use of damaging ionising radiation.5S6215The imaging procedure is based on measurement of proton responses to a known rf stimulus in the presence of a magnetic field.12,23 This entails the concurrent exposure of subjects to a static field, an rf field and time-varying magnetic field. While exposure to magnetic stimuli has been shown to have significant biobehavioural effects in a variety of ani-
ture 8,14,32,44 sister-chromatid
of MR
on chromosome
struc-
exchanges,8,46,47
and
DNA synthesis or mutation rates.8*46Results of other studies have also shown that MRI procedures have no detrimental
effects
on
early
stages
of amphibian
development33 or cardiac function in rabbits,14 rats and guinea pigs. 44 However, the possible physiological and behavioural consequences of an MRI procedure have received minimal consideration. Among the more dramatic effects of magnetic stimuli is the suppression tory effects of morphine.
of the analgesic and locomoExposure of mice to earth-
strength, O-l.5 G, 60-Hz magnetic fields results in a reversible, dose-dependent inhibition of the nocturnal peak in the day-night rhythm of morphine-induced
RECEIVED3/26/86; ACCEPTED 7/25/86 AcknowledgementsWe would like to thank John Parr for
his assistance research was and Research Services Inc.
cffccts
ences and Engineering Research Council of Canada, Grant Nos. UOl51 (to K-P.O.) and S22A9 (to M.K.). Address correspondence and reprint requests to Frank S. Prato, Ph.D., Department of Nuclear Medicine, St. Joseph’s Health Centre, London, Ontario, Canada N6A 4v2.
in the preparation of this manuscript. This supported by a grant from National Health Development and a grant from the Physicians’ to F.S.P., and grants from the Natural Sci9
Magnetic Resonance Imaging 0 Volume 5, Number 1, 1987
10
analgesia. ” Natural geomagnetic disturbances arising from intense solar activity also reduce peak nighttime morphine-induced analgesia.2s Furthermore, relatively weak rotating magnetic fields can reduce both the daytime and nighttime analgesic and locomotory effects of morphine in mice. l8 Recently, it was shown that exposure to MRI also suppressed the daytime and nighttime analgesic responses of mice receiving morphine injections. 2g,34Since MR imaging involves concurrent exposure to several magnetic field components, it is of practical importance to establish which of the magnetic parameters exerts these inhibitory actions. In the present study, we describe the effects of the static, time-varying and rf components of MR imaging on morphine-induced analgesia in mice. MATERIALS AND METHODS
Animals Male CF-1 mice (Charles River, Quebec) l-2 months of age and 25-30 gm in weight were held in groups of 5 or 6 in polyethylene cages with stainless steel wire tops. The animals were housed in a colony room kept on a 12-h light/l2-h dark cycle (lights on 0600-1800 h with daytime light levels approximately 85 pW/cm2 and nighttime levels less than 0.005 pW/cm2). The mice were maintained at 21 f 1°C with food and water freely available. Every 4-5 days the animals were removed from their cages in the daytime for routine maintenance. MRI Conditions The MRI machine was a Teslacon 0.15 T resistive system (Technicare Corporation, Cleveland, Ohio).
PULSE Gz
r
SEOUENCE
FOR:
TR = JOJO.
I
TE = 30;
The mice were exposed to the MRI procedure in groups in their home cages. The wire cage tops were replaced with Plexiglas tops during exposure and a foam-rubber pad was placed between the machine and the animals’ cage to minimise mechanical vibrations. Four different exposure conditions were used: (1) a sham exposure condition consisting of placing the animals inside the MRI machine with the machine not turned on; MRI conditions consisting of exposure to either the (2) static field, (3) rf field or (4) timevarying field. The field conditions are described in Fig. 1 and Table 1. For the sham exposure, there were residual static magnetic fields between 2 and 4 G around the MRI machine when it was turned off which were in the delivery path of the animals to the exposure area. The centre of the mouse cage was offset 32 cm from the magnetic centre of the imager along the bore of the magnet (along the z axis). This was done to ensure
Table 1. Mouse exposure conditions magnetic field gradients dB/dt (T.sec-‘)
from
Maximum
Average
Maximum Amplitude (mT)
0.4 0.4 0.6
0.2 0.2 0.3
0.4 0.4 0.9
Gx* GY* GZ
Rise Times (msec) 2 2 3
*These are approximate exposure conditions since both Gx and Gy varied slightly within the mouse cage and the mice were free to move around within their cages.
SLICES
= 22
1
**-SLICE SELECTION
Fig. 1. Imaging pulse sequence used in mouse exposure (TR = 1030, TE = 30, 22 slices, 0.75cm thick). For the time-varying field, the position encoding gradients Gx, Gy and Gz were left on but the rf transmitter was turned off and the power to the main electromagnet left off. For the rf field exposure, the 90” and 180” excitations were slice selecting pulses with Gaussian amplitude modulation, the gradient values were set to zero (Gx = Gy = Gz = 0) and the rf transmitter was left on while the power to the main electromagnet was turned off. In this schematic, the rise and fall times of the gradients are shown to be infinitely steep, however, rise and fall times did take approximately 3 msec for the 2 gradient and 2 msec for the X and Y gradients.
Attenuation of morphine-induced
analgesia in mice 0
adequate exposure of the mice to the time-varying fields associated with positional encoding. This was necessary since the mice were free to move about within their cages during the exposure. The imaging procedure was a 23.2-min multislice transverse spinecho sequence and is schematically shown in Fig. 1. This 22-slice, 0.75cm-thick imaging sequence with a repetition time (TR) of 1030 msec and an echo time (TE) of 30 msec employed a 2 gradient (Gz) of approximately 0.19 G cm-‘, and a Y gradient and X gradient (Gy and Gx, respectively) of approximately 0.14 G cm-‘. To measure the magnitude of the timevarying field associated with the rise and fall times of Gx, Gy and Gz, a 13-turn, &cm-radius coil of thin transformer wire was placed at the geometric location corresponding to where the mice were exposed. The effect of each gradient was measured separately by placing the plane of this pickup coil normal to the gradient being measured. For example, to measure the time-varying fields associated with Gz, the flat surface of the pickup coil was placed in the x-y plane. The static magnetic field was turned off so that the output of the pickup coil could be connected by a 2-m cable to an oscillosocpe. This allowed for a direct readout of induced electromotive force (emf) in units of volts (I’) with minimum attenuation of the signal along the cable. Faraday’s law of induction relates the induced emf in volts to the number of turns in the coil (N) and the area of the coil (A) normal to the timevarying field (dB/dt) by the following equation: V=-N*A*dB/dt
.
This relationship was then solved for the three field conditions and is reported in Table 1. The rf pulses corresponded to Gaussian modulated (slice-selective) pulses with nominal widths of 4 msec (90”) and 2 msec (180”). MRI Exposure
and Drug Injection Procedures
At the mid dark period, one group of mice was transported inside a light-tight wooden box from the animal colony room to the MRI room and placed inside the MRI machine under a dim red light (co.005 pW/cm’). Animals (n = 15 in all cases except n = 14 for static field and n = 16 for rf field) were exposed to either the static, time-varying, rf magnetic fields or sham exposure condition for 23.2 min. They were then briefly removed from the machine and injected intraperitoneally (i.p.) with either morphine sulphate (10 mg/kg; B.D.H., Toronto) dissolved in isotonic saline or the saline vehicle (10 ml/kg). The animals were then put back in the MRI machine and exposed to the same preinjection experimental condition for
FRANK S. PRATO ET AL.
11
another 23.2 min. At the end of the second exposure period, the mice were removed from the exposure area and transported inside the light-tight box to a test room where their latency to react to a thermal stimulus (hotplate, Technilab, New Jersey) was recorded. There is extensive literature on the use of the hot-plate antinociceptive test in rodents and it has become a common test procedure in psychopharmacology.2S1’P22,31 Thirty minutes after injection, mice were placed individually on a warmed surface (50 f O.S’C) and the latency to paw-lick was recorded (a maximum score of 150 set was used as an upper limit after which the animal was immediately removed from the hot plate). (This animal protocol was approved by the Council on Animal Care, University of Western Ontario, London, Ontario, Canada.) Additional determinations were made of the effects of morphine in control mice (n = 15 in all cases) that received handling procedures (transport and injection) without any accompanying sham or magnetic field exposures. The behavioural tests were administered by an experienced observer who was blind to the experimental designation of the mice. Data analysis consisted of analysis of variance procedures and the post hoc comparisons were orthogonal tests. The minimum significance level used for hypothesis testing was the 0.05 level. RESULTS
The mean response latencies to the thermal stimulus for each of the groups of mice injected with morphine on the test nights are presented in Fig. 2. In all cases, morphine had an analgesic effect in the control mice, significantly (p < 0.001) elevating their response latencies above those of the saline treated animals. The response latencies of the saline treated groups (sham and various magnetic field condition exposures) which are not illustrated in Fig. 2 were statistically equivalent and ranged from 18 to 22 sec. The response latencies and degree of analgesia induced in the morphine-treated sham exposed groups was comparable to that of the control groups. Mice given morphine and exposed to the static field displayed a slight, nonsignificant decrease in response latencies relative to sham-exposed or control mice. Mice exposed to the rf fields demonstrated a significant (p < 0.01) decrease in their response latencies as compared to the response times of either the sham-exposed or control individuals. However, the morphine injected mice exposed to the rf fields were still analgesic, their response latenties being significantly (p < 0.01) greater than those of the saline treated mice. Mice treated with morphine and exposed to the time-varying fields displayed a marked attenuation (p < 0.001) of their response
Magnetic Resonance Imaging 0 Volume 5, Number 1, 1987
12
T
140 r
T
120 -
;
$
loo-
z :
60-
2 2
x
60-
g
40-
:
2
rl 20-
S STATIC FIELD
i F
S RADIO
FREQUENCY FIELD
F
F TIME VARYING FIELD
Fig. 2. Analgesic response of mice to a fixed dose of morphine sulphate (10 mg/kg) and exposure to the static field (0.15 T), the rf field or the time-varying field associated with an MR imaging procedure. Error bars correspond to one standard error of the mean. For each of the three exposure conditions, three experiments were performed: mice exposed (F), mice sham exposed (S), and mice treated identically neither exposed nor sham exposed (C). The two stars indicate
a statistically significant (p < 0.01) depression in morphineinduced analgesia for both rf and time-varying magnetic field exposure conditions.
latencies. The response times of the morphine-injected mice exposed to the time-varying fields were reduced to the same level as that of the saline injected animals. DISCUSSION
The present results demonstrate a significant interaction between MRI procedures and a drug-induced response. They show (i) the time-varying magnetic fields associated with MRI abolish nocturnal morphine-induced analgesia in mice, (ii) the rf field component of MRI attenuates analgesic responses and (iii) the static field (0.15 T) component of the MRI has little effect on morphine-induced analgesia. These results confirm and extend previous observations of significant daytime and nighttime inhibitions of morphine-induced analgesia in CF-1 mice by an MRI procedure.z9 Exposure to either the complete MR imaging procedure consisting of static, rf and time-varying magnetic fields, or just the time-varying field resulted in a complete abolition of nocturnal morphine-induced analgesia. This suggests that the
inhibitory effects of MRI on morphine-induced analgesia primarily arise from and/or involve fluctuations in magnetic field strength. However, as previously reported for magnetophosphenes,’ this effect seems to be related to the waveform (frequency and amplitude) of these time-varying fields. This is supported by the observation that exposure to the lower amplitude but higher frequency rf field has a less pronounced inhibitory effect on morphine-induced analgesia than does the time-varying field. This does not, however, preclude the possibility of either synergistic effects of the magnetic field components of the MR imaging procedure and/or more potent effects of the static and rf fields on other biological systems. The present findings are also consistent with our previous reports showing that various types of fluctuating magnetic stimuli can reduce the daytime and nighttime analgesic responses to morphine.” It was observed that relatively weak (1.5-90 G) 0.5 Hz rotating magnetic fields, as well as earth-strength (O-l .5 G) 60-Hz fields attenuated morphine-induced analgesia. The latter observations provide further support for the suggestion that it is the fluctuations or timedependent variations in magnetic field intensity rather than absolute (static) field strength that affect the actions of morphine. However, the mechanisms whereby these effects are exerted are not well understood. Magnetic fields have been shown to influence the release and levels of a number of neurotransmitters and their metabolites,1~9~35with these actions being proposed to involve alterations in neuronal calcium levels (and possibly other divalent ions) and in the stability of calcium binding to neuronal membranes.1,3,4,19~24~37 However, as pointed out in a recent review, not all authors agree with this point of view.24 Results of recent investigations using a calcium chelator and ionophore have shown that at least some of the inhibitory effects of magnetic fields on morphine-induced analgesia and activity are compatible with actions on calcium and other divalent ions.” Moreover, these findings are consistent with available data on adverse relations between calcium, as well as that of other divalent ions and the effects of exogenous opiates such as morphine.‘6*38 The reduction of nighttime morphine-induced analgesia after exposure to the time-varying and rf components of the MRI procedure may also reflect in part a modulatory effect of the pineal gland on this response. It has been shown that noninvasive inhibition of the nocturnal pineal gland activity reversibly abolishes nocturnal morphine-induced analgesia.” Semm and his colleagues have further shown that artificial low-intensity time-varying magnetic fields can alter the electrical activity of certain cells in the pineal glands of pigeons,
Attenuation of morphine-induced
analgesia in mice0 FRANKS. PRATO ETAL.
guinea pigs and rats, as well as decrease the levels of the pineal gland hormonal product, melatonin.36T‘k-43 These findings lend some credence to the suggestion that the pineal gland may be one key link in mediating at least some of the effects of fluctuating and time-varying magnetic fields on biological processes. However, it is also clear that other nonpineal mechanisms are involved since daytime levels of morphineinduced analgesia were attenuated by exposure to the MRI procedure,29 a part of the daily cycle in which pineal gland activity is at a minimum. Researchers using MRI procedures to study biological mechanisms should be aware of the possible interactions between the measurement procedure and the experimental manipulation. Moreover, investigators should recognise that various magnetic field components of the MR imaging procedure may have differential effects on biological systems, with it being probable that the time-varying and rf components have the most significant effects. Thus, evaluation of the actions of a single field component, and in particular the static field,45 may not give a complete indication of the possible biological effects of exposure to an MR imaging procedure. However, it should be noted that although the rf and time-varying magnetic field components of the MRI procedure produced a significant biological effect in mice, the observed consequences of this procedure during the nighttime were comparable to those produced by a high-intensity light stimulus. ” Further investigations of the possible interactions between exposure to the components of the MRI procedure and other drug-induced responses in both humans and laboratory animals are essential.
REFERENCES 1. Adey, W.R. Tissue interactions with nonionising electromagnetic fields. Physiol. Rev. 61:435-513; 1981. 2. Bardo, M.T.; Wellman, P.J.; Hughes, R.A. The role of hot-plate and general environmental stimuli in morphine analgesic tolerance. Pharmacol. Biochem. Behav. 14:757-760; 1981. 3. Bawin, S.M.; Adey, W.R. Sensitivity of calcium binding in cerebral tissue to weak environmental electrical fields oscillating at low frequency. Proc. Nat. Acad. Sci. 73: 1999-2003; 1976. 4. Bawin, S.M.; Adey, W.R.; Sabbot, I.M. Ionic factors in the release of 45Ca2+ from chicken cerebral tissue by electromagnetic fields. Proc. Nat. Acad. Sci. 75: 6314-6318; 1978. 5. Bottomley, P.A. ; Hart, H.R.; Edelstein, W .E.; Schenck, J.F.; Smith, L.S.; Leue, W.M.; Mueller, O.M.; Redington, T.R. Anatomy and metabolism of the normal brain studied by magnetic resonance at 1.5 T. Radiology 150:441-446; 1984. 6. Brownell, G.L.; Budinger, T.F.; Lauterbur, P.C.; McGeer, P.L. Positron tomography and nuclear magnetic resonance imaging. Science 215:619-626; 1982.
13
7. Budinger, T.F. Thresholds for physiological effects due to rf and magnetic fields used in NMR imaging. IEEE Trans. Nucl. Sci. NS-2632821-2825; 1979. 8. Crooke, P.; Morris, P.G. The effects of NMR exposure on living organisms. II. A genetic study of human lymphocytes. Br. J. Radiol. 54:622-625; 1981. release poten9. Dixey, R.; Rein, Cl. 3H-noradrenaline tiated in a clonal cell line by low-intensity pulsed magnetic fields. Nature 206:253-256; 1982. 10. Doyle, F.H.; Gore, J.C.; Pennock, J.M.; Bydder, G.M.; Orr, J.S.; Steiner, R.E.; Young, I.R.; Burl, M.; Clow, H.; Gilderdale, D. J.; Bailes, D.R.; Walters, P.E. Imaging of the brain by nuclear magnetic resonance. Lancet 2:53-57;1981. D. Synthetic analgesics II. 11. Eddy, N.B.; Liemback, Dithienylbutenyl and Dithienylbutamines. J. Pharmacol. Exp. Ther. 107:385-389; 1943. G.D. Basic concepts for nuclear magnetic 12. Fullerton, Magnetic Resonance Imaging resonance imaging. 1:39-53; 1982. 13. Golding, G.P.; Newboult, L.; Rees, J.M.H.; Varlow, B.R. The effects of 50 Hz magnetic fields on opioid peptide mediated inhibition of guinea pig ileum. Neuropeptides 5:357-358; 1985. 14. Gore, J.C.; McDonnell, M.J.; Pennock, J.M.; Stanbrook, H.S. An assessment of the safety of rapidly changing magnetic fields in the rabbit: Implications for NMR imaging. Magnetic Resonance Zmaging 1: 19 1- 195, 1982. 15. Gunby, P. The new wave in medicine: Nuclear magnetic resonance. J. Am. Med. Assoc. 247:151-155, 159; 1982. 16. Harris, R.A.; Loh, H.H.; Way, E.L. Effect of divalent cations; cation chelators and ionophore on morphine analgesia and tolerance. J. Pharmacol. Exp. Ther. 153:134-141; 1975. 17. Kavaliers, M.; Hirst, M.; Teskey, G.C. Ageing, opioid analgesia and the pineal gland. Life Sci. 32:2279-2287; 1983. 18. Kavaliers, M.; Ossenkopp, K-P. Exposure to rotating magnetic fields alters morphine-induced behavioural responses in two strains of mice. Neuropharmacology 24:337-340; 1985. 19. Kavaliers, M.; Ossenkopp, K-P. Magnetic field inhibition of morphine-induced analgesia and behavioural activity in mice: Evidence for involvement of calcium ions. Brain Res. 376:30-38; 1986. 20. Kavaliers, M.; Ossenkopp, K-P; Hirst, M: Magnetic fields abolish the enhanced nocturnal analgesic response to morphine in mice. Physiol. Behav. 32:261-264; 1984. 21. Keeton, W.R. Avian orientation and navigation. Ann. Res. Physiol. 41:353-366; 1979. 22. Kitchen, I.; Crowder, M. Assessment of the hot-plate antinociceptive test in mice: A new method for the statistical treatment of graded data. J. Pharmacol. Meth. 13:1-7; 1985. 23. Mansfield, P.; Morris, P.G. NMR imaging in biomedicine. J. Waugh ed. Advances in Magnetic Resonance Supplement No. 2. New York: Academic; 1982: 174-187. 24. Meyers, R.D.; Ross, D.H. Radiation and brain calcium: A review and critique. Neurosci. Biobehav. Rev. 5:503-543; 1981. 25. Ossenkopp, K-P.; Barbeito, R. Bird orientation and the geomagnetic field: A review. Neurosci. Biobehav. Rev. 21255-279: 1978.
Magnetic Resonance Imaging 0 Volume 5, Number
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26. Ossenkopp, K-P.; Cain, D.P.; Smith, S. Low-intensity 60-Hz magnetic fields and epilepsy: Reduced incidence of lethal pentylenetetrazol induced seizures in rats preexposed to magnetic fields. Sot. Neurosci. Abstr. 11:1280; 1985. 27. Ossenkopp, K-P.;
Kolteck, W.T.; Persinger, M.A. Prenatal exposure to an extremely low-frequency-lowintensity rotating magnetic field and increases in thyroid and testicle weight in rats. Dev. Psychobiol. 5:275-285;
1972. 28. Ossenkopp,
K-P.; Kavaliers, M.; Hirst, M. Reduced nocturnal morphine analgesia in mice following a geomagnetic disturbance. Neurosci. Lett. 40:321-325; 1983. 29. Ossenkopp, K-P.; Kavaliers, M.; Prato, F.S.; Teskey, G.C.; Sestini, E.A.; Hirst, M. Exposure to nuclear magnetic resonance imaging procedure attenuates morphine-induced analgesia in mice. Life Sci. 37: 15071514; 1985. 30. Ossenkopp, K-P.; Ossenkopp, M.D. Geophysical variables and behaviour. XI Open-field behaviour in young rats exposed to an ELF rotating magnetic field. Psychol. Rep. 52:343-350; 1983. 31. Pleury, B.J.; Tobias, M.A. Comparison of the antinociceptive activities of physostignine; oxotremorine and morphine in the mouse. Br. J. Pharmacol. 43:706-714; 1971. 32. Prasad,
N.; Bushong, R.N.; Hazlewood, C.F.; magnetic resonance on marrow cells. Magnetic
S.C.; Thornby, J.I.; Bryan, Harrell, J.E. Effects of nuclear chromosomes of mouse bone Resonance Imaging 2:37-39;
1984. 33. Prasad,
N.; Wright, D.A.; Forster, J.D. Effect of nuclear magnetic resonance on early stages of amphibian development. Magnetic Resonance Imaging 1:3537; 1982. 34. Prato, F.S.; Ossenkopp, K-P.; Kavaliers, M.; Sestini, E.A. Magnetic resonance imaging and morphine-induced analgesia: Some temporal effects of the timevarying magnetic field. Sot. Neurosci. Abstr. 2:1280; 1985. 35. Raybourn,
M.S. The effects of direct-current magnetic fields on turtle retina in vitro. Science 220:715-717; 1983. 36. Reuss, S.T.; Semm, P.; Vollrath, L. Different types of
1, 1987
magnetically sensitive cells in the rat pineal gland. Neu1983. 37. Ross, D.H.; Medina, M.A.; Cardenas, H.L. Morphine and ethanol: Selective depletion of regional brain calcium. Science 186:63-65; 1974. 38. Sadee, W.; Pfeiffer, A.; Herz, A. Opiate receptor: Multiple effects of metal ions. J. Neurochem. 39:659-667; rosci. Lett. 40:23-26;
1982. 39. Seegal, R.F. Exposure to 60-Hz electric and magnetic
fields alters biogenic murine metabolite concentrations in nonhuman primate cerebrospinal fluid. Sot. Neurosci. Abstr. 11:443; 1985. 40. Semm, P. Electrophysiology of the mammalian pineal gland: Evidence for rhythmical and nonrhythmical elements and for magnetic influence on electrical activity. J. Aschoff, S. Daan, G. Groos eds. Vertebrate Circadian Systems. Berlin: Springer-Verlag; 1982: 147-157. 41. Semm, P.; Schneider, T.; Vollrath, L.; Wiltschko, W. Magnetic sensitive pineal cells in pigeons. F. Papi, H.G. Walraff eds. Avian Navigation. Berlin: Springer-Verlag; 1982: 329-337. 42. Smith, R.F.; Jasteson, D.R. Effects of a 60-Hz magnetic field on activity levels of mice. Radiol. Sci. 12:279-285; 1977. 43. Welker, H.A.; Semm, P.; Willig, R.P.;
Commentz, J.C.; Wiltschko, W.; Vollrath, L. Effects of an artificial magnetic field on serotonin N-acetyltransferase activity and melatonin content of the rat pineal gland.
Exp. Brain Res. 50:426-432; 1983. 44. Willis, R.J.; Brooks, W.M. Potential hazards of NMR
imaging: No evidence of the possible effects of static and changing magnetic fields on cardiac function of the rat and guinea pig. Magnetic Resonance Imaging 2:89-95; 1985. 45. Withers, H.R.; Mason, K.A.; Davis, C.A. MR effects on murine spermatogenesis. Radiology 156:741-742; 1985. 46. Wolff, S.; Crooks, L.E.; Brown, P.; Howard, R.;
Painter, R.B. Tests for DNA and chromosomal damage induced by nuclear magnetic resonance imaging. Radiology 136:707-710; 1980. 47. Wolff, S.; James, T.L.; Young, G.B.; Margulis, A.R.;
Bodycote, J.; Afzal, V. Magnetic resonance imaging: Absence of in vitro cytogenetic damage. Radiology 155:163-165;
1985.
Imaging, Vol. 5, PP. 9-14, All rights reserved.
1987
Copyright
0
0730-725X187 $3.00 + .OO 1987 Pergamon Journals Ltd.
l Original Contribution
ATTENUATION OF MORPHINE-INDUCED ANALGESIA IN MICE BY EXPOSURE TO MAGNETIC RESONANCE IMAGING: SEPARATE EFFECTS OF THE STATIC, RADIOFREQUENCY AND TIME-VARYING MAGNETIC FIELDS FRANKS . PRATO, * KLAUS-PETER EDMUND
SESTINI~
OSSENKOPP,
AND G.
t MARTIN
CAMPBELL
KAVALIERS, $
TESKEY~
*Department of Nuclear Medicine, St. Joseph’s Health Centre of London, Ontario, Canada; thychology IDivision of Oral Biology, Faculty of Dentistry, University of Western Ontario, London, Ontario,
Department, Canada
Exposure of adult male mice to a magnetic resonance imaging (MRI) procedure has been shown to abolish the nocturnal analgesic responses observed following treatment with morphine. The field component(s) responsible for this inhibitory effect were examined by exposing mice to either the static, time-varying or rf magnetic field components associated with an MRI procedure. In the middle of the night portion of their day-night cycle, mice were exposed for 23.2 min to one of the above field components, intraperitoneally injected with morphine sulphate (10 mg/kg) and then exposed to the field conditions for another 23.2 min, after which analgesic responses were determined. Analgesia was quantitated by determining the length of time mice were content to be on a hot surface (50°C) before they showed discomfort by licking their paws. It was observed that the time-varying magnetic field completely abolished, the rf field significantly reduced, while the static field component (0.15 T) had no evident effect on morphine-induced analgesia. These results indicate that the time-varying, and to a lesser extent the rf, fields associated with the MRI procedure inhibit morphine-induced analgesia in mice. These data also raise the possibility that exposure in humans to some of the magnetic field components associated with MRI may have clinically relevant effects on the actions of narcotic drugs such as morphine. Keywords:
MRI safety, Biomagnetic
effects, Analgesia
attenuation.
ma)s 1,13,21,25-27,30,36,39.42,43 no adverse
INTRODUCTION
imaging have been found Magnetic resonance imaging (MRI) is a powerful noninvasive diagnostic procedure that is receiving increased clinical application. This procedure is useful not only for advanced medical imaging,10~12~23 but also for providing information about the chemical and physiological status of the biological system of interest without the use of damaging ionising radiation.5S6215The imaging procedure is based on measurement of proton responses to a known rf stimulus in the presence of a magnetic field.12,23 This entails the concurrent exposure of subjects to a static field, an rf field and time-varying magnetic field. While exposure to magnetic stimuli has been shown to have significant biobehavioural effects in a variety of ani-
ture 8,14,32,44 sister-chromatid
of MR
on chromosome
struc-
exchanges,8,46,47
and
DNA synthesis or mutation rates.8*46Results of other studies have also shown that MRI procedures have no detrimental
effects
on
early
stages
of amphibian
development33 or cardiac function in rabbits,14 rats and guinea pigs. 44 However, the possible physiological and behavioural consequences of an MRI procedure have received minimal consideration. Among the more dramatic effects of magnetic stimuli is the suppression tory effects of morphine.
of the analgesic and locomoExposure of mice to earth-
strength, O-l.5 G, 60-Hz magnetic fields results in a reversible, dose-dependent inhibition of the nocturnal peak in the day-night rhythm of morphine-induced
RECEIVED3/26/86; ACCEPTED 7/25/86 AcknowledgementsWe would like to thank John Parr for
his assistance research was and Research Services Inc.
cffccts
ences and Engineering Research Council of Canada, Grant Nos. UOl51 (to K-P.O.) and S22A9 (to M.K.). Address correspondence and reprint requests to Frank S. Prato, Ph.D., Department of Nuclear Medicine, St. Joseph’s Health Centre, London, Ontario, Canada N6A 4v2.
in the preparation of this manuscript. This supported by a grant from National Health Development and a grant from the Physicians’ to F.S.P., and grants from the Natural Sci9
Magnetic Resonance Imaging 0 Volume 5, Number 1, 1987
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analgesia. ” Natural geomagnetic disturbances arising from intense solar activity also reduce peak nighttime morphine-induced analgesia.2s Furthermore, relatively weak rotating magnetic fields can reduce both the daytime and nighttime analgesic and locomotory effects of morphine in mice. l8 Recently, it was shown that exposure to MRI also suppressed the daytime and nighttime analgesic responses of mice receiving morphine injections. 2g,34Since MR imaging involves concurrent exposure to several magnetic field components, it is of practical importance to establish which of the magnetic parameters exerts these inhibitory actions. In the present study, we describe the effects of the static, time-varying and rf components of MR imaging on morphine-induced analgesia in mice. MATERIALS AND METHODS
Animals Male CF-1 mice (Charles River, Quebec) l-2 months of age and 25-30 gm in weight were held in groups of 5 or 6 in polyethylene cages with stainless steel wire tops. The animals were housed in a colony room kept on a 12-h light/l2-h dark cycle (lights on 0600-1800 h with daytime light levels approximately 85 pW/cm2 and nighttime levels less than 0.005 pW/cm2). The mice were maintained at 21 f 1°C with food and water freely available. Every 4-5 days the animals were removed from their cages in the daytime for routine maintenance. MRI Conditions The MRI machine was a Teslacon 0.15 T resistive system (Technicare Corporation, Cleveland, Ohio).
PULSE Gz
r
SEOUENCE
FOR:
TR = JOJO.
I
TE = 30;
The mice were exposed to the MRI procedure in groups in their home cages. The wire cage tops were replaced with Plexiglas tops during exposure and a foam-rubber pad was placed between the machine and the animals’ cage to minimise mechanical vibrations. Four different exposure conditions were used: (1) a sham exposure condition consisting of placing the animals inside the MRI machine with the machine not turned on; MRI conditions consisting of exposure to either the (2) static field, (3) rf field or (4) timevarying field. The field conditions are described in Fig. 1 and Table 1. For the sham exposure, there were residual static magnetic fields between 2 and 4 G around the MRI machine when it was turned off which were in the delivery path of the animals to the exposure area. The centre of the mouse cage was offset 32 cm from the magnetic centre of the imager along the bore of the magnet (along the z axis). This was done to ensure
Table 1. Mouse exposure conditions magnetic field gradients dB/dt (T.sec-‘)
from
Maximum
Average
Maximum Amplitude (mT)
0.4 0.4 0.6
0.2 0.2 0.3
0.4 0.4 0.9
Gx* GY* GZ
Rise Times (msec) 2 2 3
*These are approximate exposure conditions since both Gx and Gy varied slightly within the mouse cage and the mice were free to move around within their cages.
SLICES
= 22
1
**-SLICE SELECTION
Fig. 1. Imaging pulse sequence used in mouse exposure (TR = 1030, TE = 30, 22 slices, 0.75cm thick). For the time-varying field, the position encoding gradients Gx, Gy and Gz were left on but the rf transmitter was turned off and the power to the main electromagnet left off. For the rf field exposure, the 90” and 180” excitations were slice selecting pulses with Gaussian amplitude modulation, the gradient values were set to zero (Gx = Gy = Gz = 0) and the rf transmitter was left on while the power to the main electromagnet was turned off. In this schematic, the rise and fall times of the gradients are shown to be infinitely steep, however, rise and fall times did take approximately 3 msec for the 2 gradient and 2 msec for the X and Y gradients.
Attenuation of morphine-induced
analgesia in mice 0
adequate exposure of the mice to the time-varying fields associated with positional encoding. This was necessary since the mice were free to move about within their cages during the exposure. The imaging procedure was a 23.2-min multislice transverse spinecho sequence and is schematically shown in Fig. 1. This 22-slice, 0.75cm-thick imaging sequence with a repetition time (TR) of 1030 msec and an echo time (TE) of 30 msec employed a 2 gradient (Gz) of approximately 0.19 G cm-‘, and a Y gradient and X gradient (Gy and Gx, respectively) of approximately 0.14 G cm-‘. To measure the magnitude of the timevarying field associated with the rise and fall times of Gx, Gy and Gz, a 13-turn, &cm-radius coil of thin transformer wire was placed at the geometric location corresponding to where the mice were exposed. The effect of each gradient was measured separately by placing the plane of this pickup coil normal to the gradient being measured. For example, to measure the time-varying fields associated with Gz, the flat surface of the pickup coil was placed in the x-y plane. The static magnetic field was turned off so that the output of the pickup coil could be connected by a 2-m cable to an oscillosocpe. This allowed for a direct readout of induced electromotive force (emf) in units of volts (I’) with minimum attenuation of the signal along the cable. Faraday’s law of induction relates the induced emf in volts to the number of turns in the coil (N) and the area of the coil (A) normal to the timevarying field (dB/dt) by the following equation: V=-N*A*dB/dt
.
This relationship was then solved for the three field conditions and is reported in Table 1. The rf pulses corresponded to Gaussian modulated (slice-selective) pulses with nominal widths of 4 msec (90”) and 2 msec (180”). MRI Exposure
and Drug Injection Procedures
At the mid dark period, one group of mice was transported inside a light-tight wooden box from the animal colony room to the MRI room and placed inside the MRI machine under a dim red light (co.005 pW/cm’). Animals (n = 15 in all cases except n = 14 for static field and n = 16 for rf field) were exposed to either the static, time-varying, rf magnetic fields or sham exposure condition for 23.2 min. They were then briefly removed from the machine and injected intraperitoneally (i.p.) with either morphine sulphate (10 mg/kg; B.D.H., Toronto) dissolved in isotonic saline or the saline vehicle (10 ml/kg). The animals were then put back in the MRI machine and exposed to the same preinjection experimental condition for
FRANK S. PRATO ET AL.
11
another 23.2 min. At the end of the second exposure period, the mice were removed from the exposure area and transported inside the light-tight box to a test room where their latency to react to a thermal stimulus (hotplate, Technilab, New Jersey) was recorded. There is extensive literature on the use of the hot-plate antinociceptive test in rodents and it has become a common test procedure in psychopharmacology.2S1’P22,31 Thirty minutes after injection, mice were placed individually on a warmed surface (50 f O.S’C) and the latency to paw-lick was recorded (a maximum score of 150 set was used as an upper limit after which the animal was immediately removed from the hot plate). (This animal protocol was approved by the Council on Animal Care, University of Western Ontario, London, Ontario, Canada.) Additional determinations were made of the effects of morphine in control mice (n = 15 in all cases) that received handling procedures (transport and injection) without any accompanying sham or magnetic field exposures. The behavioural tests were administered by an experienced observer who was blind to the experimental designation of the mice. Data analysis consisted of analysis of variance procedures and the post hoc comparisons were orthogonal tests. The minimum significance level used for hypothesis testing was the 0.05 level. RESULTS
The mean response latencies to the thermal stimulus for each of the groups of mice injected with morphine on the test nights are presented in Fig. 2. In all cases, morphine had an analgesic effect in the control mice, significantly (p < 0.001) elevating their response latencies above those of the saline treated animals. The response latencies of the saline treated groups (sham and various magnetic field condition exposures) which are not illustrated in Fig. 2 were statistically equivalent and ranged from 18 to 22 sec. The response latencies and degree of analgesia induced in the morphine-treated sham exposed groups was comparable to that of the control groups. Mice given morphine and exposed to the static field displayed a slight, nonsignificant decrease in response latencies relative to sham-exposed or control mice. Mice exposed to the rf fields demonstrated a significant (p < 0.01) decrease in their response latencies as compared to the response times of either the sham-exposed or control individuals. However, the morphine injected mice exposed to the rf fields were still analgesic, their response latenties being significantly (p < 0.01) greater than those of the saline treated mice. Mice treated with morphine and exposed to the time-varying fields displayed a marked attenuation (p < 0.001) of their response
Magnetic Resonance Imaging 0 Volume 5, Number 1, 1987
12
T
140 r
T
120 -
;
$
loo-
z :
60-
2 2
x
60-
g
40-
:
2
rl 20-
S STATIC FIELD
i F
S RADIO
FREQUENCY FIELD
F
F TIME VARYING FIELD
Fig. 2. Analgesic response of mice to a fixed dose of morphine sulphate (10 mg/kg) and exposure to the static field (0.15 T), the rf field or the time-varying field associated with an MR imaging procedure. Error bars correspond to one standard error of the mean. For each of the three exposure conditions, three experiments were performed: mice exposed (F), mice sham exposed (S), and mice treated identically neither exposed nor sham exposed (C). The two stars indicate
a statistically significant (p < 0.01) depression in morphineinduced analgesia for both rf and time-varying magnetic field exposure conditions.
latencies. The response times of the morphine-injected mice exposed to the time-varying fields were reduced to the same level as that of the saline injected animals. DISCUSSION
The present results demonstrate a significant interaction between MRI procedures and a drug-induced response. They show (i) the time-varying magnetic fields associated with MRI abolish nocturnal morphine-induced analgesia in mice, (ii) the rf field component of MRI attenuates analgesic responses and (iii) the static field (0.15 T) component of the MRI has little effect on morphine-induced analgesia. These results confirm and extend previous observations of significant daytime and nighttime inhibitions of morphine-induced analgesia in CF-1 mice by an MRI procedure.z9 Exposure to either the complete MR imaging procedure consisting of static, rf and time-varying magnetic fields, or just the time-varying field resulted in a complete abolition of nocturnal morphine-induced analgesia. This suggests that the
inhibitory effects of MRI on morphine-induced analgesia primarily arise from and/or involve fluctuations in magnetic field strength. However, as previously reported for magnetophosphenes,’ this effect seems to be related to the waveform (frequency and amplitude) of these time-varying fields. This is supported by the observation that exposure to the lower amplitude but higher frequency rf field has a less pronounced inhibitory effect on morphine-induced analgesia than does the time-varying field. This does not, however, preclude the possibility of either synergistic effects of the magnetic field components of the MR imaging procedure and/or more potent effects of the static and rf fields on other biological systems. The present findings are also consistent with our previous reports showing that various types of fluctuating magnetic stimuli can reduce the daytime and nighttime analgesic responses to morphine.” It was observed that relatively weak (1.5-90 G) 0.5 Hz rotating magnetic fields, as well as earth-strength (O-l .5 G) 60-Hz fields attenuated morphine-induced analgesia. The latter observations provide further support for the suggestion that it is the fluctuations or timedependent variations in magnetic field intensity rather than absolute (static) field strength that affect the actions of morphine. However, the mechanisms whereby these effects are exerted are not well understood. Magnetic fields have been shown to influence the release and levels of a number of neurotransmitters and their metabolites,1~9~35with these actions being proposed to involve alterations in neuronal calcium levels (and possibly other divalent ions) and in the stability of calcium binding to neuronal membranes.1,3,4,19~24~37 However, as pointed out in a recent review, not all authors agree with this point of view.24 Results of recent investigations using a calcium chelator and ionophore have shown that at least some of the inhibitory effects of magnetic fields on morphine-induced analgesia and activity are compatible with actions on calcium and other divalent ions.” Moreover, these findings are consistent with available data on adverse relations between calcium, as well as that of other divalent ions and the effects of exogenous opiates such as morphine.‘6*38 The reduction of nighttime morphine-induced analgesia after exposure to the time-varying and rf components of the MRI procedure may also reflect in part a modulatory effect of the pineal gland on this response. It has been shown that noninvasive inhibition of the nocturnal pineal gland activity reversibly abolishes nocturnal morphine-induced analgesia.” Semm and his colleagues have further shown that artificial low-intensity time-varying magnetic fields can alter the electrical activity of certain cells in the pineal glands of pigeons,
Attenuation of morphine-induced
analgesia in mice0 FRANKS. PRATO ETAL.
guinea pigs and rats, as well as decrease the levels of the pineal gland hormonal product, melatonin.36T‘k-43 These findings lend some credence to the suggestion that the pineal gland may be one key link in mediating at least some of the effects of fluctuating and time-varying magnetic fields on biological processes. However, it is also clear that other nonpineal mechanisms are involved since daytime levels of morphineinduced analgesia were attenuated by exposure to the MRI procedure,29 a part of the daily cycle in which pineal gland activity is at a minimum. Researchers using MRI procedures to study biological mechanisms should be aware of the possible interactions between the measurement procedure and the experimental manipulation. Moreover, investigators should recognise that various magnetic field components of the MR imaging procedure may have differential effects on biological systems, with it being probable that the time-varying and rf components have the most significant effects. Thus, evaluation of the actions of a single field component, and in particular the static field,45 may not give a complete indication of the possible biological effects of exposure to an MR imaging procedure. However, it should be noted that although the rf and time-varying magnetic field components of the MRI procedure produced a significant biological effect in mice, the observed consequences of this procedure during the nighttime were comparable to those produced by a high-intensity light stimulus. ” Further investigations of the possible interactions between exposure to the components of the MRI procedure and other drug-induced responses in both humans and laboratory animals are essential.
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