Behavioural Brain Research 144 (2003) 1–9
Effects of magnetic ﬁeld exposure on open ﬁeld behaviour
and nociceptive responses in mice
Cristina Del Seppia
, Lorena Mezzasalma
, Elena Choleris
, Sergio Ghione
Institute of Clinical Physiology, CNR, via Moruzzi 1, 56124 Pisa, Italy
Department of Psychology, University of Guelph, Guelph, Ont., Canada
Department of Ethology, Ecology, Evolution, University of Pisa, Pisa, Italy
Received 22 October 2002; received in revised form 29 January 2003; accepted 29 January 2003
Results of previous studies have shown that nociceptive sensitivity in male C57 mice is enhanced by exposure to a regular 37 Hz or an
irregularly varying (<1 Hz) electromagnetic ﬁeld. In order to test whether these ﬁelds affect more generally mouse behaviour, we placed
Swiss CD-1 mice in a novel environment (open ﬁeld test) and exposed them for 2 h to these two different magnetic ﬁeld conditions. Hence,
we analysed how duration and time course of various behavioural patterns (i.e. exploration, rear, edge chew, self-groom, sit, walk and
sleep) and nociceptive sensitivity had been affected by such exposure.
Nociceptive sensitivity was signiﬁcantly greater in magnetically treated mice than in controls. The overall time spent in exploratory
activities was signiﬁcantly shorter in both magnetically treated groups (<1 Hz, 33% and 37 Hz, 29% of total time), than in controls (42%).
Conversely, the time spent in sleeping was markedly longer in the treated groups (both 27% of total time) than in controls (11%). These
results suggest that exposure to altered magnetic ﬁelds induce a more rapid habituation to a novel environment.
© 2003 Elsevier Science B.V. All rights reserved.
Keywords: Magnetic ﬁelds; Mouse; Behaviour; Open ﬁeld test; Nociceptive response; Hot plate test
Alterations in nociceptive or pain responses are among the
best documented effects of magnetic ﬁelds. Various types of
magnetic ﬁeld exposures have repeatedly and independently
been shown to affect nociceptive sensitivity in a variety of
species, including that of humans (see ). These studies
showed that acute exposures to magnetic ﬁelds suppressed
stress-induced decrease in pain sensitivity (stress-induced
analgesia) in a manner similar to that seen after treatment
with the prototypic opiate antagonist, naloxone . This
fact led to the proposal that magnetic ﬁelds may, in part,
exert their effects through modiﬁcations in the activity of
endogenous opioid systems .
Since opioid systems are part of a phylogenetically con-
served mechanism involved in regulating the organism’s
response to both physical and psychological stress ,
Corresponding author. Tel.: +39-50-3153345; fax: +39-50-3152650.
E-mail address: firstname.lastname@example.org (C. Del Seppia).
one could expect that exposure to electromagnetic ﬁeld
treatments may also affect other behavioural responses to
In this study, we addressed this question by performing a
behavioural analysis of exploratory activity (open ﬁeld test)
in outbred Swiss CD-1 mice exposed to magnetic ﬁelds.
The open ﬁeld test consists in observing the behaviours
elicited by placing mice in a novel environment (typically
an arena) from which it is impossible to escape . This
novel situation is considered to be a stressful condition
for rodents  and the ﬁrst behaviour observed usually
consists in moving around the arena. This motor activity is
thought to be compounded of pure locomotor behaviour to-
gether with an exploratory component. These two elements
can be modiﬁed by manipulating the environmental situ-
ation . In general, the rodents’ behaviour in the open
ﬁeld test is considered to represent the result of a motiva-
tional conﬂict between a tendency to explore (motivated
by curiosity) and that (induced by fear) of staying in close
contact with the walls and thus in a more protected area
. The open ﬁeld test is commonly used to investigate
0166-4328/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved.