without producing nociceptive or antinociceptive actions. A
wide body of evidence indicates that diazepam produces
anxiolysis in humans and anxiolytic-like responses in most
animal models by stimulating the benzodiazepine receptor
coupled to the GABA complex (for review, see Ashton
1994; Smith 2001; Treit 1985). Buspirone, by contrast, is a
serotonergic agonist that stimulates primarily the 1A re-
ceptor subtype. This drug, after chronic treatment, reduces
anxiety in humans and, interestingly after its acute ad-
ministration, produces anxiolytic-like actions in some an-
*imal models (for review, see Tunnicliff 1991). Since the
interaction between nociception and anxiety was inves-
tigated and some drugs share antinociceptive and anxio-
lytic properties [for example, morphine (Shin et al. 2003;
*Hernandez-Delgadillo et al. 2003; Deciga-Campos et al.
*2003) or gabapentin (Singh et al. 1996)], acetylsalicylic
acid was selected as an antinociceptive compound that lacks
anxiety-related actions (LaBuda and Fuchs 2000).
The general purpose of the present study was to ana-
lyse the influence of nociception on basal levels of an anx-
iety-like behaviour and on the action of anxiolytic drugs.
Nociception was induced by an intra-articular injection of
low doses of uric acid (UA) and was measured by using
the pain-induced functional impairment model in the rat
(PIFIR model), which has been described in detail else-
where (López-Muñoz et al. 1993). To determine the levels
of experimental anxiety, we used the burying behaviour
and the elevated plus maze tests, which may reflect both
physiological- and pharmacological-induced modifications
(Fernandez-Guasti et al. 2001; Fernández-Guasti and Picazo
1992; Lee and Rodgers 1990; Treit et al. 1981; Treit 1985,
1990). Diazepam and buspirone were the anxiolytic drugs
selected for the present study. Acetylsalicylic acid was
used to test whether the changes in burying behaviour or
exploration in the plus maze, produced by the intra-ar-
ticular injection of UA, were specifically related to noci-
ception. Finally, to determine if the changes in burying
behaviour particularly reflect anxiety-related behaviours,
a spontaneous locomotor activity test was included. It
must be emphasised that the principal advantage of using
the anxiety tests and the intra-articular nociception is that
under these conditions it is possible to assess anxiety-like
responses and nociception simultaneously, rather than
sequentially, as has been the case for other studies relating
experimental anxiety and nociception.