Provided by the author(s) and NUI Galway in accordance with publisher policies. Please cite the published version when available. Effects of direct periaqueductal grey administration of a Title cannabinoid receptor agonist on nociceptive and aversive responses in rats Finn, David P.; Jhaveri, M.D.; Jhaveri, Maulik D.; Beckett, Author(s) Simon Richard Graham; Roe, Clare H.; Kendall, David A.; Marsden, Charles Alexander; Chapman, Victoria Publication Date 2003-07-31 Finn, D. P., Jhaveri, M. D., Beckett, S. R. G., Roe, C. H., Kendall, D. A., Marsden, C. A., & Chapman, V. (2003). Publication Effects of direct periaqueductal grey administration of a Information cannabinoid receptor agonist on nociceptive and aversive responses in rats. Neuropharmacology, 45(5), 594-604. doi:https://doi.org/10.1016/S0028-3908(03)00235-1 Publisher Elsevier Link to publisher's https://doi.org/10.1016/S0028-3908(03)00235-1 version Item record http://hdl.handle.net/10379/16252 DOI http://dx.doi.org/10.1016/S0028-3908(03)00235-1 Downloaded 2021-09-25T11:27:31Z Some rights reserved. For more information, please see the item record link above. Neuropharmacology 45 (2003) 594–604 www.elsevier.com/locate/neuropharm Effects of direct periaqueductal grey administration of a cannabinoid receptor agonist on nociceptive and aversive responses in rats D.P. Finn ∗,1, M.D. Jhaveri 1, S.R.G. Beckett, C.H. Roe, D.A. Kendall, C.A. Marsden, V. Chapman Institute of Neuroscience, School of Biomedical Sciences, University of Nottingham, Queen’s Medical Centre, Nottingham NG7 2UH, UK Received 23 April 2003; accepted 23 May 2003 Abstract The analgesic potential of cannabinoids may be hampered by their ability to produce aversive emotion when administered sys- temically. We investigated the hypothesis that the midbrain periaqueductal grey (PAG) is a common substrate mediating the anti- nociceptive and potential aversive effects of cannabinoids. The rat formalin test was used to model nociceptive behaviour. Intra- PAG microinjection of the excitatory amino acid d,l-homocysteic acid (DLH) was used to induce an aversive, panic-like reaction characteristic of the defensive “fight or flight” response. Administration of the cannabinoid receptor agonist HU210 (5 µg/rat) into the dorsal PAG significantly reduced the second phase of formalin-evoked nociceptive behaviour, an effect which was blocked by µ co-administration of the CB1 receptor antagonist SR141716A (50 g/rat). This anti-nociceptive effect was accompanied by an HU210-induced attenuation of the formalin-evoked increase in Fos protein expression in the caudal lateral PAG. Intra-dorsal PAG administration of HU210 (0.1, 1 or 5 µg/rat) significantly reduced the aversive DLH-induced explosive locomotor response. The anti-nociceptive effect of HU210 is likely to result from activation of the descending inhibitory pain pathway. Mechanisms mediating the anti-aversive effects of cannabinoids in the PAG remain to be elucidated. These data implicate a role for the PAG in both cannabinoid-mediated anti-nociceptive and anti-aversive responses. 2003 Elsevier Ltd. All rights reserved. Keywords: Cannabinoid receptor; Pain; Periaqueductal grey; Aversion; Formalin test; Panic; c-Fos 1. Introduction (Jaggar et al., 1998). The finding that the anti-nocicep- tive effects of systemically administered cannabinoids The analgesic potential of cannabis and cannabinoids are reduced following disruption of the descending has long been recognised (Pertwee, 2001). However, inhibitory control pathway (Hohmann et al., 1999b) sup- cannabinoids induce aversive emotion and precipitate ports studies demonstrating that supraspinal sites of anxiety or panic attacks in about 22% of individuals action play a crucial role in the analgesia mediated by (Thomas, 1996). A greater understanding of the mech- systemically administered cannabinoids (Lichtman and anisms underlying cannabinoid-induced analgesia and Martin, 1991). aversion is needed if analgesic drugs without this Cannabinoid agonists are aversive in conditioned adverse side-effect profile are to be developed. place preference, taste avoidance and defensive with- Systemic administration of cannabinoids is anti- drawal paradigms (Parker and Gillies, 1995; McGregor nociceptive in the tail-flick test (Lichtman and Martin, et al., 1996a; De Fonseca et al., 1996; Sanudo-Pena et 1991) and in the formalin model of tonic, persistent pain al., 1997; Hutcheson et al., 1998; Cheer et al., 2000a). However, there is also some evidence for anti-aversive effects of cannabinoids in rat pup ultrasonic vocalisation ∗ Corresponding author. Tel.: +44-115-9709462; fax: +44-115- 9709259. (McGregor et al., 1996b) and light–dark box (Berrendero E-mail address: david.fi[email protected] (D.P. Finn). and Maldonado, 2002) paradigms. 1 Both authors contributed equally to this study. The midbrain periaqueductal grey (PAG) mediates 0028-3908/$ - see front matter 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0028-3908(03)00235-1 D.P. Finn et al. / Neuropharmacology 45 (2003) 594–604 595 behavioural responses to both aversive and nociceptive tal sinus, under isoflurane (1.5–2%) in nitrous oxide (1.5 stimuli (for review, see Bandler and Keay, 1996). The l/min)–oxygen (0.5 l/min) anaesthetic gas mixture. A PAG is an important component of the descending stylet made from stainless steel tubing (18 mm, 31 G) inhibitory pain control pathway (Wall and Melzack, was inserted into the guide cannula to prevent blockage 1999). PAG stimulation results in profound analgesia by debris. A non-steroidal anti-inflammatory agent, car- (Levine et al., 1991) which may occur with or without profen (4.5 mg kgϪ1, s.c., Rimadyl, Pfizer, UK), was aversive side-effects (Hosobuchi, 1983). Indeed Besson administered before the surgery for post-operative anal- et al. (1991) have suggested that anti-nociception gesia. Following cannula implantation, the rats were mediated by the dorsal PAG may be a consequence of housed singly. At least 6 days were allowed for recovery aversion. The defensive “fight or flight” response can be post-surgery. During this recovery period, the rats were induced in animals following chemical stimulation of the handled and their body weight and general health moni- PAG with excitatory amino acids such as d,l-homocys- tored once daily. teic acid (DLH) (Bandler, 1982; Beckett et al., 1992). CB1 receptors are present in moderate density and dis- 2.3. Microinjections tributed heterogeneously in the PAG (Herkenham et al., 1991; Tsou et al., 1998). Intra-PAG microinjection of Drugs or vehicle were microinjected manually into the cannabinoid agonists is anti-nociceptive in the rat tail- dorsal PAG (as defined by Bandler and Keay, 1996)in flick test (Lichtman et al., 1996). To date, the role of a volume of 250 nl or 500 nl over 60 s using an injector cannabinoid receptors in the PAG in modulation of and Hamilton syringe. These injection volumes were tonic, persistent pain behaviour or aversion has not selected on the basis of a large number of studies which been reported. have investigated the effects of direct microinjection of The aim of this study was to investigate the effect cannabinoids into discrete brain regions in models of of intra-dorsal PAG administration of the potent non- nociception including the tail-flick and formalin tests selective cannabinoid agonist HU210 on formalin- (Martin et al., 1998, 1999; Lichtman et al., 1996; Licht- evoked nociceptive behaviour, PAG Fos protein man and Martin, 1997; Monhemius et al., 2001). The expression and DLH-induced aversive behaviour in rats. injector comprised a stainless steel tube (31 G) with a We demonstrate for the first time that the PAG is a com- collar (23 G) sizing it to 20 mm (2 mm longer than the mon anatomical substrate mediating both cannabinoid- guide cannula) and an attached 1 m long polystyrene induced anti-nociceptive and anti-aversive responses. tube (0.75 mm OD, 0.28 mm ID) to allow injection of Some of this work has been published in abstract form the drug when the rat was placed in the arena. (Finn et al., 2001, 2002). 2.4. Effect of HU210 on formalin-induced nociceptive behaviour 2. Methods Each rat received HU210 (0.1, 1, 5 µg/250 nl) or 2.1. Animals dimethyl sulphoxide (DMSO, 60%) microinjection into the dorsal PAG followed 10 min later by formalin (50 Adult male Sprague-Dawley rats (250–300 g, Charles µl, 2.5% formaldehyde in 0.9% NaCl) or saline (0.9%) River, UK) were used for these experiments. One group injection into the sub-plantar region of the right hind of rats was used for the study of formalin-evoked behav- paw. Intra-plantar injections were carried out under brief iour and Fos expression, another group was used for isoflurane anaesthesia to minimise stress to the animals. determination of CB1 receptor involvement in the effects Behaviour was tracked for 10 min post-drug and 60 min observed and a separate group was used for the DLH- post-formalin in a transparent perspex box (30 × 30 × induced aversion study. Rats were group housed in cages 30 cm) and scored using Ethovision software by a of five prior to surgery. Food and water were available trained experimenter, blind to the treatments. The ad libitum and rats were housed on a 12 h light–dark maximum time taken to recover from anaesthesia, as cycle. All experiments were carried out in the light per- judged by regain of the righting reflex, was 2.5 min, and iod according to the UK Home Office Animals this initial period of the formalin trial was removed from (Scientific Procedures) Act 1986. the analysis. The video image was obtained from a cam- era positioned under the perspex box enabling clear 2.2. Cannula implantation examination of paw-directed behaviour throughout the experiment. In addition to rearing, grooming and dis- A stainless steel guide cannula (18 mm, 23 G) was tance moved, pain behaviours were scored according to stereotaxically implanted above the midbrain dorsal the weighted composite pain scoring technique (CPS- Ϫ + Ϫ PAG (AP 6.7, ML 1.7, DV 3.6, Paxinos and Wat- WST0,1,2) described by Watson et al.