The ß-lactam clavulanic acid mediates glutamate transport-sensitive pain relief in a rat model of neuropathic pain.

BACKGROUND: Following nerve injury, down-regulation of astroglial glutamate transporters (GluTs) with subsequent extracellular glutamate accumulation is a key factor contributing to hyperexcitability within the spinal dorsal horn. Some ß-lactam antibiotics can up-regulate GluTs, one of which, ceftriaxone, displays analgesic effects in rodent chronic pain models. METHODS: Here, the antinociceptive actions of another ß-lactam clavulanic acid, which possesses negligible antibiotic activity, were compared with ceftriaxone in rats with chronic constriction injury (CCI)-induced neuropathic pain. In addition, the protein expression of glutamate transporter-1 (GLT1), its splice variant GLT1b and glutamate-aspartate transporter (GLAST) was measured in the spinal cord of CCI rats. Finally, protein expression of the same GluTs was evaluated in cultured astrocytes obtained from rodents and humans. RESULTS: Repeated injection of ceftriaxone or clavulanic acid over 10 days alleviated CCI-induced mechanical hypersensitivity, whilst clavulanic acid was additionally able to affect the thermal hypersensitivity. In addition, clavulanic acid up-regulated expression of GLT1b within the spinal cord of CCI rats, whereas ceftriaxone failed to modulate expression of any GluTs in this model. However, both clavulanic acid and ceftriaxone up-regulated GLT1 expression in rat cortical and human spinal astrocyte cultures. Furthermore, clavulanic acid increased expression of GLT1b and GLAST in rat astrocytes in a dose-dependent manner. CONCLUSIONS: Thus, clavulanic acid up-regulates GluTs in cultured rodent- and human astroglia and alleviates CCI-induced hypersensitivity, most likely through up-regulation of GLT1b in spinal dorsal horn. SIGNIFICANCE: Chronic dosing of clavulanic acid alleviates neuropathic pain in rats and up-regulates glutamate transporters both in vitro and in vivo. Crucially, a similar up-regulation of glutamate transporters in human spinal astrocytes by clavulanic acid supports the development of novel ß-lactam-based analgesics, devoid of antibacterial activity, for the clinical treatment of chronic pain.

Vendor-derived differences in injury-induced pain phenotype and pharmacology of Sprague-Dawley rats: Does it matter?

BACKGROUND: Outbred Sprague-Dawley (SD) rats are a commonly used strain in preclinical pain research. Here, we established empirically how SD rats obtained from different vendors might vary in sensitivity to injury and pharmacotherapy. METHODS: Chronic Constriction Injury (CCI) or complete Freund's adjuvant (CFA) hindpaw inflammation was induced in male SD rats sourced from three to four different vendors, respectively. Neuropathic hypersensitivity was evaluated over 58 days using von Frey filaments, pinprick stimulation and the hot plate test. Pharmacological sensitivity was evaluated by treatment with gabapentin (100 mg/kg, p.o.) or morphine (3 mg/kg, s.c.). CFA-induced hyperalgesia and sensitivity to morphine (0.3-6 mg/kg, s.c.) was measured using a digital Randall-Selitto device. In addition, paw weight gain was used as an index of peripheral oedema. RESULTS: Significant differences between the vendor-supplied SD rats in relation to onset, magnitude and resolution of hypersensitivity after CCI were observed. Although all sub-strains eventually developed a robust and reversible neuropathic hypersensitivity to mechanical stimulation, the thermal hypersensitivity varied. Whereas pharmacological response to gabapentin varied enormously, the response to morphine was both robust and much more consistent between sub-strains. Despite a similar degree of CFA-induced hypersensitivity, the paw oedema level differed between sub-strains. Here, morphine dose-dependently alleviated the CFA-induced hypersensitivity, with only a subtle difference in sensitivity between sub-strains observed. CONCLUSIONS: Our data reveal that the source of vendor used to obtain SD rats may be one key factor responsible for 'between laboratory variation' in reproducing sensitivity to some drugs targeting various pathophysiological mechanisms in specific animal pain models. SIGNIFICANCE: The choice of vendor used to source the same strain of rat for use in preclinical pain research can profoundly affect the level of nociceptive hypersensitivity and response to reference analgesics in neuropathic versus inflammatory models.

The first reported outbreak of equine herpesvirus myeloencephalopathy in New Zealand.

CASE HISTORY AND CLINICAL FINDINGS: On 9 January 2014 (Day 0) a mare from a stud farm in the Waikato region presented with urinary incontinence without pyrexia. Over the following 33 days 15 mares were clinically affected with neurological signs. All but one mare had a foal at foot. The most commonly observed clinical signs were hind limb paresis and ataxia. In some cases recumbency occurred very early in the course of disease and seven mares were subject to euthanasia for humane reasons. LABORATORY FINDINGS: Equid herpesvirus (EHV) type 1 was detected using PCR in various tissues collected post mortem from two mares with neurological signs. DNA sequencing data from the DNA polymerase gene of the virus showed a nucleotide transition at position 2254, a mutation encoding amino acid D752 that is highly associated with the neuropathogenic genotype of EHV-1. In total 12/15 mares were confirmed positive for EHV-1 on PCR. Results from a virus neutralisation test and ELISA on paired serum samples, and PCR on whole blood and nasal swabs, indicated that of four paddocks in a high-risk area where a cluster of cases had occurred, 20/21 (95%) horses were likely to have been exposed or were confirmed infected with EHV-1. Subsequent to the outbreak two mares aborted, one at 9 months and one at 10 months of gestation. The cause of abortion was confirmed as EHV-1 with the same genotype as that involved in the outbreak. DIAGNOSIS: Equine herpesvirus myeloencephalopathy. CLINICAL RELEVANCE: The outbreak described shows the considerable impact that can occur in outbreaks of equine herpesvirus myeloencephalopathy in New Zealand. Early biosecurity controls not only reduced the effect on the farm but mitigated the potential for the virus to spread to other horse enterprises.

GABAA α5 subunit-containing receptors do not contribute to reversal of inflammatory-induced spinal sensitization as indicated by the unique selectivity profile of the GABAA receptor allosteric modulator NS16085.

GABAA receptor positive allosteric modulators (PAMs) mediate robust analgesia in animal models of pathological pain. Restoration of diminished spinal GABAA-α2 and -α3 subunit-containing receptor function is a principal contributor to this analgesia, albeit involvement of GABAA-α5-receptors has not been excluded. Thus, we compared NS11394 and TPA023 (PAMs with selectivity/efficacy at GABAA-α2/α3/α5 receptors) with TP003 (a reportedly GABAA-α3 selective PAM) against spinal sensitization. However, in-house electrophysiology studies designed to confirm the selectivity of TPA023 and TP003 for human GABAA receptors did not corroborate published data, with TP003 displaying considerable GABAA-α5 receptor efficacy. Therefore, we identified a novel PAM, NS16085, which possesses negligible efficacy at GABAA-α5 receptors, but with GABAA-α2/α3 efficacy equivalent to NS11394. At the GABAA-α1 receptor the compound gives low level of negative modulation further separating it from the other compounds. Rat pups with carrageenan-induced hindpaw inflammatory hyperalgesia were used to make ex vivo spinal dorsal root-evoked ventral root recordings. Some spontaneous activity and large numbers of spikes to repetitive stimulation of dorsal roots at C-fibre intensity, indicative of wind-up and sensitization were observed. Equimolar concentrations of NS11394, TP003 and NS16085 all attenuated wind-up to a similar degree; TPA023 was clearly less effective. In adult rats, NS16085 (3-30 mg/kg, p.o.) dose-dependently reduced formalin-induced hindpaw flinching with efficacy comparable to NS11394. Thus, potentiation of GABAA-α2 and-α3 receptors is sufficient to depress spinal sensitization and mediate analgesia after inflammatory injury. Positive modulation at GABAA-α5-receptors is apparently dispensable for this process, an important consideration given the role of this receptor subtype in cognitive function.

Antinociceptive activity of the new triple reuptake inhibitor NS18283 in a mouse model of chemotherapy-induced neuropathic pain.

BACKGROUND: Chronic neuropathic pain can lead to anxiety and depression. Drugs that block reuptake of serotonin, norepinephrine and/or dopamine are widely used to treat depression, and have emerged as useful drugs in the treatment of neuropathic pain. This study compared the acute antinociceptive effects of NS18283, a novel triple monoamine reuptake inhibitor (MRI) with indatraline, venlafaxine and escitalopram in a mouse model of neuropathic pain. METHOD: Neuropathic pain-like behaviours were induced in mice by repeated injections of oxaliplatin (OXA), and assessed using the von Frey hair test, the cold plate test and the thermal preference plate test. Anxio/depressive phenotype and antidepressant-like properties of compounds were assessed by the novelty suppressed feeding test and the tail suspension test, respectively. RESULTS: In vivo microdialysis experiments showed that each MRI increased extracellular serotonin, norepinephrine and/or dopamine levels in the cingulate cortex, in agreement with their in vitro reuptake inhibitory properties. Indatraline (3 mg/kg) reversed the full repertoire of OXA-induced neuropathic hypersensitivity. NS18283 (10 mg/kg) reversed OXA-induced mechano-hypersensitivity and cold allodynia. Venlafaxine (16 mg/kg) and escitalopram (4 mg/kg) only reversed cold allodynia and mechano-hypersensitivity, respectively. All MRIs produced antidepressant-like activity in anxio/depressive phenotype of OXA mice. CONCLUSIONS: Acute administration of drugs that enhance the activity of serotonin, norepinephrine and dopamine neurotransmission within nociceptive pathways may provide a broader spectrum of antinociception than dual or selective reuptake inhibitors in animal models of neuropathic pain. Whether similar observations would occur after repeated administration of such compounds in an attempt to simulate dosing in humans, or be compromised by dopaminergic-mediated adverse effects warrants further investigation.

Positive allosteric modulation of α4ß2 nAChR agonist induced behaviour.

Neuronal cholinergic transmission is a prerequisite for proper CNS function. Consequently, disturbance of this system is associated with a number of pathophysiological conditions such as Parkinson's disease, Alzheimer's disease, schizophrenia and ADHD. Consequently, drug discovery efforts have spurred considerable research endeavours into identifying specific compounds for this system. Nicotinic acetylcholine receptors (nAChR) are ligand gated ion channels involved in cholinergic transmission. nAChRs are homo- or heteromeric pentamers with α4ß2 receptors being the most abundant heteromer. The stoichiometry of α4ß2 receptors can be either (α4)(3)(ß2)(2) or (α4)(2)(ß2)(3) representing channels with low (LS) or high (HS) sensitivity, respectively, to endogenous ligands. In the present study we applied the partial nAChR α4ß2 LS and HS agonist NS3956 and the LS selective positive allosteric modulator NS9283 to investigate the role of α4ß2 in Parkinson and pain models. In 6-OHDA lesioned rats, NS3956 increased rotational behaviour when rats were co-treated with nomifensine. This effect was absent in the presence of mecamylamine. In contrast, co-treatment with NS3956 and NS9283 reduced rotational behaviour in the animals. In a rat formalin pain model NS3956 induced an analgesic response that was strongly potentiated by NS9283. Finally in vitro experiments were applied to determine dopamine release from striatal minces. NS3956 induced a concentration dependent release while NS9283 was unable to potentiate agonist induced release. Together these results emphasize involvement of α4ß2 nAChR in rotational and analgesic responses and confirm striatal α4ß2 receptors to be of the HS form.

The α7 nicotinic ACh receptor agonist compound B and positive allosteric modulator PNU-120596 both alleviate inflammatory hyperalgesia and cytokine release in the rat.

BACKGROUND AND PURPOSE: Agonists selective for the α7 nicotinic acetylcholine (nACh) receptor produce anti-hyperalgesic effects in rodent models of inflammatory pain, via direct actions on spinal pain circuits and possibly via attenuated release of peripheral pro-inflammatory mediators. Increasingly, allosteric modulation of ligand-gated receptors is recognized as a potential strategy to obtain desired efficacy in the absence of the putative adverse effects associated with agonist activation. EXPERIMENTAL APPROACH: We compared the anti-hyperalgesic and anti-inflammatory effects of the α7 nACh receptor agonist compound B with the positive allosteric modulator (PAM) PNU-120596 and the standard non-steroidal anti-inflammatory drug (NSAID), diclofenac, in rats with hind paw inflammation induced by either formalin, carrageenan or complete Freund's adjuvant (CFA). KEY RESULTS: When administered before carrageenan, both diclofenac (30 mg·kg(-1) ) and PNU-120596 (30 mg·kg(-1) ) significantly reduced mechanical hyperalgesia and weight-bearing deficits for up to 4 h. Compound B (30 mg·kg(-1) ) also attenuated both measures of pain-like behaviour, albeit less robustly. Whereas compound B and PNU-120596 attenuated the carrageenan-induced increase in levels of TNF-α and IL-6 within the hind paw oedema, diclofenac only attenuated IL-6 levels. Established mechanical hyperalgesia induced by carrageenan or CFA was also partially reversed by compound B and PNU-120596. However, diclofenac was considerably more efficacious. Formalin-induced nocifensive behaviours were only reversed by compound B, albeit at doses which disrupted motor performance. CONCLUSIONS AND IMPLICATIONS: α7 nACh receptor PAMs could prove to be useful in the treatment of inflammatory pain conditions, which respond poorly to NSAIDs or in situations where NSAIDs are contra-indicated.

Comparison of malleable stylet and reusable and disposable bougies by paramedics in a simulated difficult intubation.

In a randomised crossover study, 60 ambulance paramedics attempted tracheal intubation of a manikin model of a Cormack and Lehane grade 3/4 view using a Portex stylet, Portex and Frova single-use bougies, and a Portex reusable bougie. Tracheal intubation within 30 s was achieved by 34/60 (57%) using the stylet, 18/60 (30%) using a Portex single-use bougie, 16/60 (27%) using a Frova single-use bougie and 5/60 (8%) using a Portex reusable bougie. The proportion intubating within 30 s was significantly higher with the stylet compared with any bougie (p < 0.001), but significantly lower with a Portex reusable bougie than any other device (p < 0.004). Participants rated the Portex reusable bougie as significantly more difficult to use than the other devices (p < 0.001). There was no evidence of a relationship between previous experience and success rate for any device.

Comparison of the novel subtype-selective GABAA receptor-positive allosteric modulator NS11394 [3'-[5-(1-hydroxy-1-methyl-ethyl)-benzoimidazol-1-yl]-biphenyl-2-carbonitrile] with diazepam, zolpidem, bretazenil, and gaboxadol in rat models of inflammatory and neuropathic pain.

Spinal administration of GABA(A) receptor modulators, such as the benzodiazepine drug diazepam, partially alleviates neuropathic hypersensitivity that manifests as spontaneous pain, allodynia, and hyperalgesia. However, benzodiazepines are hindered by sedative impairments and other side effect issues occurring mainly as a consequence of binding to GABA(A) receptors containing the alpha(1) subunit. Here, we report on the novel subtype-selective GABA(A) receptor-positive modulator NS11394 [3'-[5-(1-hydroxy-1-methyl-ethyl)-benzoimidazol-1-yl]-biphenyl-2-carbonitrile], which possesses a functional efficacy selectivity profile of alpha(5) > alpha(3) > alpha(2) > alpha(1) at GABA(A) alpha subunit-containing receptors. Oral administration of NS11394 (1-30 mg/kg) to rats attenuated spontaneous nociceptive behaviors in response to hindpaw injection of formalin and capsaicin, effects that were blocked by the benzodiazepine site antagonist flumazenil. Ongoing inflammatory nociception, observed as hindpaw weight-bearing deficits after Freund's adjuvant injection, was also completely reversed by NS11394. Likewise, hindpaw mechanical allodynia was fully reversed by NS11394 in two rat models of peripheral neuropathic pain. Importantly, NS11394-mediated antinociception occurred at doses 20 to 40-fold lower than those inducing minor sedative or ataxic impairments. In contrast, putative antinociception associated with administration of either diazepam, zolpidem, or gaboxadol only occurred at doses producing intolerable side effects, whereas bretazenil was completely inactive despite minor influences on motoric function. In electrophysiological studies, NS11394 selectively attenuated spinal nociceptive reflexes and C-fiber-mediated wind-up in vitro pointing to involvement of a spinal site of action. The robust therapeutic window seen with NS11394 in animals suggests that compounds with this in vitro selectivity profile could have potential benefit in clinical treatment of pain in humans.

NS11394 [3'-[5-(1-hydroxy-1-methyl-ethyl)-benzoimidazol-1-yl]-biphenyl-2-carbonitrile], a unique subtype-selective GABAA receptor positive allosteric modulator: in vitro actions, pharmacokinetic properties and in vivo anxiolytic efficacy.

The novel positive allosteric modulator NS11394 [3'-[5-(1-hydroxy-1-methyl-ethyl)-benzoimidazol-1-yl]-biphenyl-2-carbonitrile] possesses a functional selectivity profile at GABA(A) receptors of alpha(5) > alpha(3) > alpha(2) > alpha(1) based on oocyte electrophysiology with human GABA(A) receptors. Compared with other subtype-selective ligands, NS11394 is unique in having superior efficacy at GABA(A)-alpha(3) receptors while maintaining low efficacy at GABA(A)-alpha(1) receptors. NS11394 has an excellent pharmacokinetic profile, which correlates with pharmacodynamic endpoints (CNS receptor occupancy), yielding a high level of confidence in deriving in vivo conclusions anchored to an in vitro selectivity profile and allowing for translation to higher species. Specifically, we show that NS11394 is potent and highly effective in rodent anxiety models. The anxiolytic efficacy of NS11394 is most probably mediated through its high efficacy at GABA(A)-alpha(3) receptors, although a contributory role of GABA(A)-alpha(2) receptors cannot be excluded. Compared with benzodiazepines, NS11394 has a significantly reduced side effect profile in rat (sedation, ataxia, and ethanol interaction) and mouse (sedation), even at full CNS receptor occupancy. We attribute this benign side effect profile to very low efficacy of NS11394 at GABA(A)-alpha(1) receptors and an overall partial agonist profile across receptor subtypes. However, NS11394 impairs memory in both rats and mice, which is possibly attributable to its efficacy at GABA(A)-alpha(5) receptors, albeit activity at this receptor might be relevant to its antinociceptive effects (J Pharmacol Exp Ther 327:doi;10.1124/jpet.108.144, 2008). In conclusion, NS11394 has a unique subtype-selective GABA(A) receptor profile and represents an excellent pharmacological tool to further our understanding on the relative contributions of GABA(A) receptor subtypes in various therapeutic areas.

Stability of a receptor-binding active human immunodeficiency virus type 1 recombinant gp140 trimer conferred by intermonomer disulfide bonding of the V3 loop: differential effects of protein disulfide isomerase on CD4 and coreceptor binding.

Stable trimeric forms of human immunodeficiency virus recombinant gp140 (rgp140) are important templates for determining the structure of the glycoprotein to assist in our understanding of HIV infection and host immune response. Such information will aid the design of therapeutic drugs and vaccines. Here, we report the production of a highly stable and trimeric rgp140 derived from a HIV type 1 (HIV-1) subtype D isolate that may be suitable for structural studies. The rgp140 is functional in terms of binding to CD4 and three human monoclonal antibodies (17b, b12, and 2G12) that have broad neutralizing activities against a range of HIV-1 isolates from different subtypes. Treatment of rgp140 with protein disulfide isomerase (PDI) severely restricted 17b binding capabilities. The stable nature of the rgp140 was due to the lack of processing at the gp120/41 boundary and the presence of an intermonomer disulfide bond formed by the cysteines of the V3 loop. Further characterization showed the intermonomer disulfide bond to be a target for PDI processing. The relevance of these findings to the roles of the V3 domain and the timing of PDI action during the HIV infection process are discussed.

Activation of p38 and p42/44 MAP kinase in neuropathic pain: involvement of VPAC2 and NK2 receptors and mediation by spinal glia.

Activation of intracellular signaling pathways involving p38 and p42/44 MAP kinases may contribute importantly to synaptic plasticity underlying spinal neuronal sensitization. Inhibitors of p38 or p42/44 pathways moderately attenuated responses of dorsal horn neurons evoked by mustard oil but not brush and alleviated the behavioral reflex sensitization seen following nerve injury. Activation of p38 and p42/44 MAP kinases in spinal cord ipsilateral to constriction injury was reduced by antagonists of NMDA, VPAC2 and NK2 (but not related) receptors, the glial inhibitor propentofylline and inhibitors of TNF-alpha. A VPAC2 receptor agonist enhanced p38 phosphorylation and caused behavioral reflex sensitization in naïve animals that could be blocked by co-administration of p38 inhibitor. Conversely, an NK2 receptor agonist activated p42/44 and caused behavioral sensitization that could be prevented by co-administration of p42/44 inhibitor. Thus, spinal p38 and p42/44 MAP kinases are activated in neuropathic pain states by mechanisms involving VPAC2, NK2, NMDA receptors and glial cytokine production.

Antiepileptics and the treatment of neuropathic pain: evidence from animal models.

Neuropathic pain is characterised by both positive (hyperalgesia and allodynia) and negative (sensory deficits) symptoms and remains intractable to many commonly used analgesics. Antiepileptics are increasingly utilised in the treatment of neuropathic pain. This class of drugs works via three major mechanisms of action in order to dampen neuronal hyperexcitability within the central nervous system: potentiation of GABA transmission, reduction of glutamate-mediated excitatory transmission, and block of voltage-activated ion channels. The latter mechanism of action in particular, is exemplified by the success of the newer generation of antiepileptics such as lamotrigine and gabapentin in the clinical treatment of neuropathic pain symptoms. In the current review article, we will examine in detail, the antinociceptive effects of a diverse range of antiepileptics as tested in animal models of nerve injury. Where appropriate, we will compare these findings with their analgesic efficacy in the clinical treatment of neuropathic pain.

Retigabine: chemical synthesis to clinical application.

Retigabine [D23129; N-(2-amino-4-(4-fluorobenzylamino)-phenyl)carbamic acid ethyl ester] is an antiepileptic drug with a recently described novel mechanism of action that involves opening of neuronal K(V)7.2-7.5 (formerly KCNQ2-5) voltage-activated K(+) channels. These channels (primarily K(V)7.2/7.3) enable generation of the M-current, a subthreshold K(+) current that serves to stabilize the membrane potential and control neuronal excitability. In this regard, retigabine has been shown to have a broad-spectrum of activity in animal models of electrically-induced (amygdala-kindling, maximal electroshock) and chemically-induced (pentylenetetrazole, picrotoxin, NMDA) epileptic seizures. These encouraging results suggest that retigabine may also prove useful in the treatment of other diseases associated with neuronal hyperexcitability. Neuropathic pain conditions are characterized by pathological changes in sensory pathways, which favor action potential generation and enhanced pain transmission. Although sometimes difficult to treat with conventional analgesics, antiepileptics can relieve some symptoms of neuropathic pain. A number of recent studies have reported that retigabine can relieve pain-like behaviors (hyperalgesia and allodynia) in animal models of neuropathic pain. Neuronal activation within several key structures within the CNS can also be observed in various animal models of anxiety. Moreover, amygdala-kindled rats, which have a lowered threshold for neuronal activation, also display enhanced anxiety-like responses. Retigabine dose-dependently reduces unconditioned anxiety-like behaviors when assessed in the mouse marble burying test and zero maze. Early clinical studies have indicated that retigabine is rapidly absorbed and distributed, and is resistant to first pass metabolism. Tolerability is good in humans when titrated up to its therapeutic dose range (600-1200 mg/day). No tolerance, dependence or withdrawal potential has been reported, although adverse effects can include mild dizziness, headache, nausea and somnolence. Thus, retigabine may prove to be useful in the treatment of a diverse range of disease states in which neuronal hyperexcitability is a common underlying factor.

Prediction of alcohol-related harm from controlled drinking strategies and alcohol consumption trajectories.

AIMS: To establish predictors of age 21 alcohol-related harm from prior drinking patterns, current levels of alcohol consumption and use of controlled drinking strategies. PARTICIPANTS: One thousand, five hundred and ninety-six students recruited from an initial sample of 3300 during their final year of high school in 1993. DESIGN: Longitudinal follow-up across five waves of data collection. SETTING: Post high school in Victoria, Australia. MEASUREMENTS: Self-administered surveys examining a range of health behaviours, including alcohol consumption patterns and related behaviour. FINDINGS: Drinking behaviours at age 21 were found to be strongly predicted by drinking trajectories established through the transition from high school. Multivariate regression analysis revealed that alcohol-related harms at age 21 were reduced where current levels of alcohol use fell within limits recommended in Australian national guidelines. After controlling for this effect it was found that the range of strategies employed by participants to control alcohol use maintained a small protective influence. Post-high-school drinking trajectories continued to demonstrate a significant effect after controlling for current behaviours. FINDINGS: revealed that over one quarter of males and females drank alcohol, but on a less-than-weekly basis. This pattern of alcohol use demonstrated considerable stability through the post-school transition and was associated with a low level of subsequent harm at age 21. CONCLUSIONS: Future research should investigate whether encouraging more Australian adolescents to drink alcohol on a less-than-weekly basis may be a practical intervention target for reducing alcohol-related harms.

Chronic pain, chronic stress and depression: coincidence or consequence?

Chronic pain and depressive illness are debilitating disease states that are variably resistant to currently available therapeutic agents. Animal models of chronic pain are associated with activation of the hypothalamo-pituitary-adrenal (HPA) axis, upon which chronic pain acts as an inescapable stressor. Inescapable stress is also associated with 'depressive-like' symptoms in experimental animals. Based on reports of the comorbidity between chronic pain and depressive illness in human patients, it is possible that these disease states are linked, via chronic stress-induced HPA dysfunction. Here, we discuss the possible involvement of the HPA axis in the aetiology of both chronic pain and clinical depression, and suggest a strategy for the development of novel pharmacotherapies.

Non-opioid actions of lamotrigine within the rat dorsal horn after inflammation and neuropathic nerve damage.

Some opioid-resistant pain conditions can be alleviated by voltage-dependent Na(+) channel blockers such as lamotrigine. The mu-opioid-receptor agonist morphine can modulate cation entry into cells to affect overall cellular excitability, an effect which can in turn be endogenously antagonised by the neuropeptide cholecystokinin (CCK). However, lamotrigine may also modulate cellular excitability by non-specifically blocking voltage-dependent ion channels. We have looked for interactions of lamotrigine with the opioid/CCK pathway within the spinal dorsal horn, to rule out the possibility that lamotrigine may attenuate nociceptive responses via actions on this pathway. Both lamotrigine and the mu-opioid agonist DAMGO inhibited mustard oil-evoked cell firing by approximately 50% compared with control levels. Co-application of CCK8S reversed DAMGO-, but not lamotrigine-induced inhibition of cell firing and this reversal was prevented with the selective CCK(B) receptor antagonist PD 135158. Although lamotrigine inhibited both brush- and cold-evoked cell firing in neuropathic animals, lamotrigine inhibition of mustard oil-evoked cell firing in the same animals was not significantly greater than that observed in controls. These results suggest that the antinociceptive properties of lamotrigine within the spinal dorsal horn are unlikely to be mediated via interactions with the opioid/CCK pathway.

Verapamil prevents withdrawal excitation of oxytocin neurones in morphine-dependent rats.

We investigated whether the full expression of morphine withdrawal excitation by supraoptic nucleus (SON) oxytocin neurones is a property of the neurones themselves or a partial function of their afferent inputs, by interrupting synaptic input activity via central administration of the L-type Ca(2+) channel blocker verapamil. In morphine-dependent rats, withdrawal-induced release of oxytocin from the posterior pituitary was suppressed by prior administration of intracerebroventricular (i.c.v.) verapamil (160 microg), as was release of oxytocin within the SON measured by microdialysis. During morphine withdrawal the increased electrical activity of SON neurones was also reduced both by i.c.v. verapamil and microdialysis application of verapamil or nifedipine into the SON. Oxytocin secretion evoked by electrical stimulation of the pituitary stalk was unaffected by i.c.v. verapamil suggesting a central site of action. To determine whether the inhibitory actions of verapamil were specific to morphine withdrawal, we also investigated the effects of verapamil on other oxytocin-secreting stimuli. I.C.V. verapamil given to morphine-naïve rats abolished pituitary oxytocin release in response to activation of brainstem or rostral excitatory inputs by cholecystokinin (20 microg kg(-1), i.v.) and 1.5 M saline (4 ml kg(-1), i.p.) respectively, whilst in lactating rats, i.c.v. verapamil reduced suckling-induced release of oxytocin within the SON. These results suggest that verapamil has a central site of action on stimulated oxytocin release (including an action within the SON) and that both pre and post-synaptic L-type Ca(2+) channels are required for the full expression of morphine withdrawal in SON oxytocin neurones.