Gabapentin suppresses spasticity in the spinal cord-injured rat

Spasticity poses a major detrimental impact on the quality of life in a significant number of people with spinal cord injury (SCI). Recent observations in our laboratory suggest that spinal transection at the sacral S(2) level induces a significant increase in glutamatergic input to sacrocaudal motoneurons during the time spasticity is present in the tail muscles. The present study examined the efficacy of gabapentin, an agent that has been shown to reduce glutamate release, in managing spasticity within the tail musculature. METHOD: In this blinded, crossover study adult Sprague-Dawley rats with S(2) spinal transections were tested behaviorally for the progression of spasticity in the tail musculature using our established system. When the animals demonstrated a significant level of spastic behavior (e.g. increased response to quick stretch, noxious and non-noxious cutaneous stimuli), they received either saline or the antiepileptic agent gabapentin (GBP; 50 mg/kg i.p.) and were assessed behaviorally and electrophysiologically at 1, 3, 6, 12 and 24 h post-injection. RESULTS: Both spastic behavior and electromyography (EMG) activity were significantly decreased at 1 and 3 h post-GBP injection when compared with the activity level following administration of saline. Spastic behavior and EMG activity gradually increased over time and returned to baseline activity by 24 h post-injection. CONCLUSION: Gabapentin diminishes both the behavioral and electrophysiological manifestation of SCI-induced spasticity, in the tail musculature, in a time dependent manner.     

Glutamate receptor blockade in the rostral ventromedial medulla reduces the force of multisegmental motor responses to supramaximal noxious stimuli

The rostral ventromedial medulla (RVM) has been established as part of a descending pain-modulatory pathway. While the RVM has been shown to modulate homosegmental nociceptive reflexes such as tail flick or hindpaw withdrawal, it is not known what role the RVM plays in modulating the magnitude of multisegmental, organized motor responses elicited by noxious stimuli. Using local blockade of glutamate receptors with the non-specific glutamate receptor antagonist kynurenate (known to selectively block nociceptive facilitatory ON-cells), we tested the hypothesis that the RVM facilitates the magnitude of multi-limb movements elicited by intense noxious stimuli. In male Sprague–Dawley rats, we determined the minimum alveolar concentration (MAC) of isoflurane necessary to block multi-limb motor responses to noxious tail clamp. MAC was determined so that all animals were anesthetized at an equipotent isoflurane concentration (0.7 MAC). Supramaximal mechanical stimulation of the hindpaw or electrical stimulation of the tail elicited synchronous, repetitive movements in all four limbs that ceased upon, or shortly after (<5 s) termination of the stimulus. Kynurenate microinjection (2 nmol) into the RVM significantly attenuated, by 40–60%, the peak and integrated limb forces elicited by noxious mechanical stimulation of the hindpaw (p < 0.001; two-way ANOVA; n = 8) or electrical stimulation of the tail (peak force: p < 0.011, two-way ANOVA; n = 8), with significant recovery 40–60 min following injection. The results suggest that glutamatergic excitation of RVM neurons, presumably ON-cells, facilitates organized, multi-limb escape responses to intense noxious stimuli.     

Morphine, but not atropine, blocks nociceptor-driven activity in rat dorsal hippocampal neurones

Neurones in the CA1 region of the dorsal hippocampus of urethane-anaesthetized rats were recorded extracellularly with microelectrodes, and tested for their response to non-noxious and noxious peripheral stimuli. None of the cells responded to non-noxious stimuli but 91 of 216 cells were excited by noxious stimuli. Morphine (5.0 mg/kg i.v.) increased the background firing rate in 7 of 10 cells tested and blocked the response to noxious heating of the tail in all cases. Naloxone (0.5 mg/kg i.v.) reversed these effects of morphine. Atropine (0.1 plus 0.2 mg/kg i.v.), in another group of animals, produced only transient changes of an inconsistent nature in 7 cells tested.     

Role of 5-HT(1A) and 5-HT(1B) receptors in the antidepressant-like effect of piperine in the forced swim test

Our previous studies have showed that treating mice with piperine significantly decreased the immobility time of the animals in the forced swim test and tail suspension test, which was related to up-regulation of serotonin (5-HT) level in the brain. The purpose of this study is to explore the contribution of 5-HT receptors in the antidepressant-like effect of piperine. The results showed that pre-treating mice with methiothepin (a non-selective 5-HT receptor antagonist, 0.1 mg/kg, intraperitoneally), 4-(2′-methoxy-phenyl)-1-[2′-(n-2″-pyridinyl)-p-iodobenzamino-]ethyl-piperazine (a selective 5-HT_1A receptor antagonist, 1 mg/kg, subcutaneously) or 1-(2-(1-pyrrolyl)-phenoxy)-3-isopropylamino-2-propanol (a 5-HT_1B receptor antagonist, 2.5 mg/kg, intraperitoneally) was found to abolish the anti-immobility effect of piperine (10 mg/kg, intraperitoneally) in the forced swim test. On the other hand, a sub-effective dose of piperine (1 mg/kg, intraperitoneally) produced a synergistic antidepressant-like effect with (+)-8-hydroxy-2-(di-n-propylamino)tetralin (a 5-HT_1A receptor agonist, 1 mg/kg, intraperitoneally) or anpirtoline (a 5-HT_1B receptor agonist, 0.25 mg/kg, intraperitoneally). Taken together, these results suggest that the antidepressant-like effect of piperine in the mouse forced swim test may be mediated, at least in part, by the activation of 5-HT_1A and 5-HT_1B receptors.     

Evidence for the involvement of the spinoparabrachial pathway,but not the spinothalamic tract or post-synaptic dorsal column,in acute bone nociception

We have previously reported that acute noxious mechanical stimulation of bone activates neurons throughout the dorsal horn of the lumbar spinal cord, and argued that the spinal mechanisms that mediate bone nociception are different to those that mediate cutaneous and visceral nociception. In the present study, we provide evidence that the ascending spinal pathways that mediate acute bone nociception also differ to those that mediate acute cutaneous and visceral nociception. Injections of a retrograde tracer (Fluorogold) were made into the thalamus, gracile nucleus or lateral parabrachial nucleus to identify spinothalamic, post-synaptic dorsal column or spinoparabrachial projection neurons respectively (n = 4 in each group). Spinal dorsal horn neurons activated by acute noxious mechanical stimulation of bone (bone drilling) were identified in these animals using Fos immunohistochemistry. Fluorogold and Fos-like immunoreactivity was not colocalized in any dorsal horn neurons projecting to the thalamus or gracile nucleus. In contrast, a total of 12.2 ± 1.1% (mean ± S.E.M.) of the spinoparabrachial projection neurons contained Fos-like immunoreactive nuclei following bone drilling and this was significantly greater than the percentage (3.4 ± 0.5%) in animals of a sham surgery group (n = 4) that were not exposed to bone drilling (Mann–Whitney; p < 0.05). These data provide evidence for the involvement of the spinoparabrachial pathway, but not the spinothalamic or post-synaptic dorsal column pathways, in the relay of information regarding acute noxious mechanical stimuli applied to bone, and suggest that spinal pathways that mediate acute bone nociception may be different to those that mediate acute nociception of cutaneous and visceral origin.     

Nitric oxide mechanism in protective effect of imipramine and venlafaxine against acute immobilization stress-induced behavioral and biochemical alteration in mice

Frequent and persistent stressful events caused depressive illness. Stress is an aversive stimulus which disturbs physiological homeostasis and reflects a variety of biological systems. The present study was designed to investigate the nitric oxide mechanism in the protective effect of imipramine and venlafaxine against acute immobilization stress-induced behavioral and biochemical alterations in mice. Mice were immobilized for 6 h. Imipramine (10 and 20 mg/kg) and venlafaxine (5 and 10 mg/kg) were administered 30 min before subjecting the animals to acute stress. Behavioral tests (mirror chamber, actophotometer, tail flick test) and biochemical analysis (malondialdehyde level, nitrite, glutathione and catalase enzyme) were performed subsequently. Acute immobilization stress caused anxiety like behavior, analgesia, impaired locomotor activity and oxidative stress as compared to naive. Pretreatment with imipramine (10 and 20 mg/kg) and venlafaxine (5 and 10 mg/kg) significantly reversed immobilized stress-induced behavioral and biochemical alterations. l-arginine (100 mg/kg) pretreatment with imipramine (10 mg/kg) and venlafaxine (5 mg/kg) significantly attenuated the protective effect of imipramine and venlafaxine. However, l-NAME (10 mg/kg) and/or methylene blue (10 mg/kg) pretreatment with lower dose of imipramine and venlafaxine significantly potentiated their protective effects which were significant as compared to their effect per se respectively. Present study highlights the involvement of nitric oxide mechanism in the protective effect of imipramine and venlafaxine against acute immobilization-induced behavioral and biochemical alterations in mice.     

Repeated Baclofen treatment ameliorates motor dysfunction,suppresses reflex activity and decreases the expression of signaling proteins in reticular nuclei and lumbar motoneurons after spinal trauma in rats

The interruption of supraspinal input to the spinal cord leads to motor dysfunction and the development of spasticity. Clinical studies have shown that Baclofen (a GABA_B agonist), while effective in modulating spasticity is associated with side-effects and the development of tolerance. The aim of the present study was to assess if discontinued Baclofen treatment and its repeated application leads antispasticity effects, and whether such changes affect neuronal nitric oxide synthase (nNOS) in the brainstem, nNOS and parvalbumin (PV) in lumbar α-motoneurons and glial fibrillary acidic protein in the ventral horn of the spinal cord. Adult male Wistar rats were exposed to Th9 spinal cord transection. Baclofen (30 mg/b.w.) diluted in drinking water, was administered for 6 days, starting at week 1 after injury and then repeated till week 4 after injury. The behavior of the animals was tested (tail-flick test, BBB locomotor score) from 1 to 8 weeks. Our results clearly indicate the role of nitric oxide, produced by nNOS in the initiation and the maintenance of spasticity states 1, 6 and 8 weeks after spinal trauma. A considerable decrease of nNOS staining after Baclofen treatment correlates with improvement of motor dysfunction. The findings also show that parvalbumin and astrocytes participate in the regulation of ion concentrations in the sub-acute phase after the injury.     

Atorvastatin prevents early apoptosis after thoracic spinal cord contusion injury and promotes locomotion recovery

The systemic administration of atorvastatin has been shown to be neuroprotective after spinal cord injury (SCI), by decreasing the inflammatory response at the lesion site and by reducing neuronal and oligodendrocyte apoptosis. The latter effect spares white matter at the injury site and improves locomotion. The aim of this study was to confirm the neuroprotective efficacy of atorvastatin as well as its early action in limiting apoptosis with its administration post-SCI. Female Sprague-Dawley rats received an intra peritoneal injection of: (1) statin/saline (5 mg/kg) at 2 h after the contusion injury; (2) physiological saline at 2 h post-SCI; or (3) physiological saline without injury. Statin-treated rats showed significant (p < 0.05) improvement in locomotion at week 4 post-SCI compared to vehicle-treated animals. Explaining this outcome, caspase-3 activity decreased by 50% (p < 0.05), and the histological TUNEL method revealed a decrease of approximately 20% in apoptotic cells at the injury site (p < 0.01) at 4 h post-SCI in atorvastatin-treated rats in comparison to vehicle-treated controls. These data demonstrate that atorvastatin is effective after experimental spinal cord contusion injury in preventing early apoptosis at the injury site within 2 h post-administration.     

Cognitive dysfunction and glutamate reuptake: effect of EAAT2 polymorphism in schizophrenia

Spinal noradrenaline is thought to play an important role in descending pain inhibitory pathways and the modulation of nociceptive information at the spinal level. Tapentadol is a μ-opioid receptor (MOR) agonist and noradrenaline reuptake inhibitor (NRI). We showed previously that tapentadol, in contrast to morphine, elevates levels of noradrenaline, but not serotonin, in the ventral hippocampus of rats. The aim of this study was to examine the effects of tapentadol, morphine and venlafaxine on spinal monoamine levels.Rats were implanted with spinal microdialysis probes. Drugs were administered intraperitoneally, and samples were collected for 3 h in isoflurane-anesthetized animals and analysed for monoamine content using HPLC-MS/MS.In terms of area-under-curve (AUC, 0-180 min), tapentadol (4.64-21.5 mg/kg) produced a dose-dependent, significant increase in extracellular spinal noradrenaline levels (9275 ± 4346 min % at the highest dose versus −1047 ± 889 min % for vehicle). A maximum increase of 182 ± 32% of baseline was reached 60 min after administration of 10 mg/kg tapentadol. Venlafaxine (10 mg/kg) produced an effect of similar magnitude. In contrast, tapentadol decreased extracellular spinal serotonin levels (non-significantly compared to vehicle), while venlafaxine increased spinal serotonin to 267 ± 74% of baseline.In contrast to tapentadol and venlafaxine, morphine slightly decreased levels of noradrenaline and serotonin.This study demonstrates that analgesic doses of tapentadol (and venlafaxine), but not morphine, increase spinal noradrenaline levels and that tapentadol is devoid of a relevant serotonergic effect. It supports the suggestion that the NRI component of tapentadol is functionally relevant and contributes to its mechanism of action.     

The endocannabinoid transport inhibitor AM404 modulates nociception in cholestasis

Cholestasis is associated with increased activity of the endogenous opioid system that results in analgesia. Endocannabinoid system can reduce pain sensitivity. Considering the interaction that has been shown between the endogenous opioid and endocannabinoid systems in nociception processing, we studied the effect of AM404, an endocannabinoid transport inhibitor, on modulation of nociception in cholestasis, a model of elevated endogenous opioid tone. Cholestasis was induced by ligation of the main bile duct using two ligatures and transection of the duct at the midpoint between them. A significant increase (P < 0.01) in TF was observed in cholestatic rats compared to unoperated and sham rats. AM404 (10 mg/kg, i.p.) significantly increased TFL at 5, 30 min but not 60 min after injection in cholestatic animals compared to the vehicle treated cholestatic group (P < 0.05, P < 0.001, respectively). AM404 injection to unoperated and sham rats did not alter baseline TFL. The effect of AM404 in cholestatic rats was blocked by co-administration of a CB₁ receptor antagonist, AM251 (1 mg/kg, i.p.) but not by the CB2 receptor antagonist, SR144528 (1 mg/kg, i.p.). Naloxone injection blocked the antinociception induced by cholestasis in bile duct ligated group. Antinociception produced by injection of AM404 in cholestatics was also attenuated by co-administration of naloxone. These data show that AM404 potentiates antinociception induced by cholestasis and indicate that there are possible interactions between opioid and cannabinoid systems in this experimental model of elevated endogenous opioid tone. The inhibitory effects of AM404 in this model are mediated by cannabinoid CB₁ and not CB₂ receptors.     

Tail muscles become slow but fatigable in chronic sacral spinal rats with spasticity

Paralyzed skeletal muscle sometimes becomes faster and more fatigable after spinal cord injury (SCI) because of reduced activity. However, in some cases, pronounced muscle activity in the form of spasticity (hyperreflexia and hypertonus) occurs after long-term SCI. We hypothesized that this spastic activity may be associated with a reversal back to a slower, less fatigable muscle. In adult rats, a sacral (S2) spinal cord transection was performed, affecting only tail musculature and resulting in chronic tail spasticity beginning 2 wk later and lasting indefinitely. At 8 mo after injury, we examined the contractile properties of the segmental tail muscle in anesthetized spastic rats and in age-matched normal rats. The segmental tail muscle has only a few motor units (<12), which were easily detected with graded nerve stimulation, revealing two clear motor unit twitch durations. The dominant faster unit twitches peaked at 15 ms and ended within 50 ms, whereas the slower unit twitches only peaked at 30-50 ms. With chronic injury, this slow twitch component increased, resulting in a large overall increase (>150%) in the fraction of the peak muscle twitch force remaining at 50 ms. With injury, the peak muscle twitch (evoked with supramaximal stimulation) also increased in its time to peak (+48.9%) and half-rise time (+150.0%), and decreased in its maximum rise (-35.0%) and decay rates (-40.1%). Likewise, after a tetanic stimulation, the tetanus half-fall time increased by 53.8%. Therefore the slow portion of the muscle was enhanced in spastic muscles. Consistent with slowing, posttetanic potentiation was 9.2% lower and the stimulation frequency required to produce half-maximal tetanus decreased 39.0% in chronic spinals. Interestingly, in spastic muscles compared with normal, whole muscle twitch force was 81.1% higher, whereas tetanic force production was 38.1% lower. Hence the twitch-to-tetanus ratio increased 104.0%. Inconsistent with overall slowing, whole spastic muscles were 61.5% more fatigable than normal muscles. Thus contrary to the classical slow-to-fast conversion that is seen after SCI without spasticity, SCI with spasticity is associated with a mixed effect, including a preservation/enhancement of slow properties, but a loss of fatigue resistance.     

Modulation of noxious and non-noxious spinal mechanical transmission from the rostral medial medulla in the rat

Modulatory influences on spinal mechanical transmission from the rostral medial medulla (RMM) were studied. Noxious stimulation, produced by von Frey-like monofilaments, and non-noxious stimulation, produced by a soft brush, was applied to the glabrous skin of the hind foot. At 28 sites in RMM, electrical stimulation facilitated responses to noxious mechanical stimulation at low intensities (5-25 microA) and inhibited responses of the same neurons at greater intensities (50-100 microA) of stimulation. At 24 and 9 other sites in RMM, stimulation at all intensities only inhibited or only facilitated, respectively, responses to noxious mechanical stimulation of the hind foot. Stimulus-response functions to mechanical stimulation were shifted leftward by low intensities and decreased by high intensities of stimulation. Inhibitory influences were found to descend in the dorsolateral funiculi; facilitatory effects were contained in the ventral spinal cord. Descending modulation of non-noxious brush stimulation revealed biphasic facilitatory-inhibitory effects (9 sites in RMM), only inhibitory effects (14 sites) and only facilitatory effects (8 sites). The effects of electrical stimulation were replicated by intra-RMM administration of glutamate; a low concentration (0.25 nmol) facilitated and a greater concentration (2.5 nmol) inhibited spinal mechanical transmission, providing evidence that cells in RMM are sufficient to engage descending influences. Descending modulatory effects were specific for the site of stimulation, not for the spinal neuron, because modulation of the same neuron was different from different sites in RMM. These results show that spinal mechanical transmission, both noxious and non-noxious, is subject to descending influences, including facilitatory influences that may contribute to exaggerated responses to peripheral stimuli in some chronic pain states.     

Group II metabotropic glutamate receptors in the striatum of non-human primates: Dysregulation following chronic cocaine self-administration

A growing body of evidence has demonstrated a role for group II metabotropic glutamate receptors (mGluRs) in the reinforcing effects of cocaine. These receptors are important given their location in limbic-related areas, and their ability to control the release of glutamate and other neurotransmitters. They are also potential targets for novel pharmacotherapies for cocaine addiction. The present study investigated the impact of chronic cocaine self-administration (9.0 mg/kg/session for 100 sessions, 900 mg/kg total intake) on the densities of group II mGluRs, as assessed with in vitro receptor autoradiography, in the striatum of adult male rhesus monkeys. Binding of [³H]LY341495 to group II mGluRs in control animals was heterogeneous, with a medial to lateral gradient in binding density. Significant elevations in the density of group II mGluRs following chronic cocaine self-administration were measured in the dorsal, central and ventral portions of the caudate nucleus (P < 0.05), compared to controls. No differences in receptor density were observed between the groups in either the putamen or nucleus accumbens. These data demonstrate that group II mGluRs in the dorsal striatum are more sensitive to the effects of chronic cocaine exposure than those in the ventral striatum. Cocaine-induced dysregulation of the glutamate system, and its consequent impact on plasticity and synaptic remodeling, will likely be an important consideration in the development of novel pharmacotherapies for cocaine addiction.     

Role of spinal metabotropic glutamate receptors in regulation of lower urinary tract function in the decerebrate unanesthetized rat

The role of spinal metabotropic glutamate receptors (mGluRs) in control of lower urinary tract functions was evaluated in rats using an mGluR antagonist administered via the intrathecal route. Cystometrograms in combination with external urethral sphincter (EUS) EMG recordings were performed on 13 decerebrate unanesthetized Sprague–Dawley female rats (n = 6 for spinal cord intact rats; n = 7 for spinal cord transected rats). In spinal cord intact rats, a group I/II mGluR antagonist, (±)-alpha-methyl-4-carboxyphenylglycine (MCPG), at doses of 3–30 μg, changed neither bladder nor EUS EMG activity, whereas a larger dose (100 μg) produced a significant facilitation of EUS EMG activity (41% increase in the peak activity) with little effect on bladder contractions. In chronically spinal cord transected rats, MCPG (3–100 μg) had no effect on bladder and EUS EMG activity. The results suggest that group I/II mGluRs are likely to be involved in inhibition of the excitatory pathway to the EUS but not involved in the control of the bladder. The lack of effect of MCPG on the EUS EMG activity in chronic spinal cord transected rats indicates that mGluR-mediated inhibitory control of the EUS was eliminated after spinal cord injury.     

Long-term normalization of blood pressure in SHR and 1-kidney 1-clip rats by synthetic precursor of stable PAF analogue without systemic effects in normotensive rats

This study characterized the actions of the newly synthesized PAF precursor 1-hexadecyl-2-alkylcarbamoyl-glycerol (HAG) on blood pressure (BP) in male spontaneously hypertensive rats (SHR), SHR-stroke prone (SHRSP) and Wistar rats with 1-kidney 1-clip (1K1C) renovascular hypertension used as experimental models of human primary and secondary hypertension. Systolic blood pressure (SBP) in the tail artery and mean arterial pressure (MAP) in the abdominal aorta were measured by tail plethysmography and invasive pressure transducer, respectively. Intravenous treatment with 1 mg/kg HAG in SHR resulted in a rapid decline of MAP from 151 ± 4 to 127 ± 4 mm Hg in 50 min (p < 0.001) that was maintained for 24 h after injection (128 ± 5 mm Hg, p < 0.01). We also observed a profound hypotensive effect of HAG in SHRSP but not in normotensive Wistar rats. In 1K1C rats, the magnitude of the BP decline evoked by HAG was correlated with MAP measured before drug administration (R = 0.74, p < 0.005). In 1K1C rats with SBP > 140 mm Hg, 5 mg/kg/48 h HAG, given orally for 14 days, decreased SBP by 20-30 mm Hg without an increase in the death rate and other adverse effects. Thus, our results show that intravenous and oral administration of HAG led to a long-lasting reduction of BP in experimental models of primary and secondary hypertension. In contrast to PAF and its derivatives, the hypotensive action of HAG was preserved for 24 h after a single administration, was absent in normotensive animals, and was not accompanied by visible side-effects, at least during 2 weeks of treatment.     

Involvement of monoaminergic systems in the antidepressant-like effect of nobiletin

Nobiletin isolated from citrus peels up-regulates synaptic transmission and improves memory impairment in rodents. This study investigated the antidepressant-like effect of nobiletin in the forced swimming test (FST) and tail suspension test (TST) in mice. Additionally, the monoaminergic mechanisms involved in the antidepressant-like effect of nobiletin in mice were also assessed. Nobiletin (25, 50 and 100 mg/kg, p.o.) decreased the immobility time in both the FST and TST without locomotor alterations in the open-field test (OFT). The anti-immobility effect of nobiletin (50 mg/kg, p.o.) was completely prevented by the pretreatment of mice with WAY 100635 (0.1 mg/kg, s.c., a serotonin 5-HT_1A receptor antagonist), cyproheptadine (3 mg/kg, i.p., a serotonin 5-HT₂ receptor antagonist), prazosin (62.5 μg/kg, i.p., an α₁-adrenoceptor antagonist), SCH23390 (0.05 mg/kg, s.c., a dopamine D₁ receptor antagonist) or sulpiride (50 mg/kg, i.p., a dopamine D₂ receptor antagonist). On the other hand, the pretreatment of mice with yohimbine (1 mg/kg, i.p., an α₂-adrenoceptor antagonist) or propranolol (5 mg/kg, i.p., a β-adrenoceptor antagonist) did not block the antidepressant-like effect of nobiletin in the TST. Taken together, the data demonstrated that nobiletin produced an antidepressant-like effect that seems to be dependent on its interaction with the serotonergic, noradrenergic and dopaminergic systems. Thus, the present study suggests the therapeutic potential of this dietary flavonoid for the treatment of depression.     

Electrophysiological characteristics of identified kidney-related neurons in adult rat spinal cord slices

Whole-cell patch-clamp recordings were made from kidney-related neurons in the intermediolateral cell column (IML) in horizontal slices of thoracolumbar spinal cord from adult rats. Kidney-related neurons were identified in vitro subsequent to inoculation of the kidney with a fluorescent, retrograde, transynaptic pseudorabies viral label (i.e., PRV-152). Kidney-related neurons detected in the IML expressed choline acetyltransferase, characteristic of spinal preganglionic motor neurons. Their mean resting potential was −51 ± 4 mV and input resistance was 448 ± 39 MΩ. Both spontaneous inhibitory and excitatory post-synaptic currents (i.e., sIPSCs and sEPSCs) were observed in all neurons. The mean frequency for sEPSCs (3.1 ± 1 Hz) was approximately 2.5 times that for sIPSCs (1.4 ± 0.3 Hz). Application of the glycine and GABA_A receptor-linked Cl⁻ channel blocker, picrotoxin (100 μM) blocked sIPSCs, while the ionotropic glutamate receptor antagonist, kynurenic acid (1 mM) blocked all sEPSCs, indicating they were mediated by GABA/glycine and glutamate receptors, respectively. Thus, using PRV-152 labeling allowed whole-cell patch-clamp recording of neurons in the adult spinal cord, which were kidney-related. Excitatory glutamatergic input dominated synaptic responses in these cells, the membrane characteristics of which resembled those of immature IML neurons. Combined PRV-152 pre-labeling and whole-cell patch-clamp recordings may allow more effective analysis of synaptic plasticity seen in adult models of injury or chronic disease.     

The impact of prenatal stress on basal nociception and evoked responses to tail-docking and inflammatory challenge in juvenile pigs

The consequences of tail-docking (at 2-4 days) and prenatal stress (maternal social stress during the 2nd third of pregnancy) on baseline nociceptive thresholds and responses to acute inflammatory challenge were investigated in juvenile pigs in two studies. Nociceptive thresholds were assessed on the tail root and on the hind foot using noxious mechanical and cold stimulation before and after acute inflammatory challenge by intradermal injection of 30 μg capsaicin (study 1) or 3% carrageenan (study 2) into the tail root. Four groups of 8 (study 1, n = 14-16 pigs/treatment) or 5 (study 2, n = 6 pigs/treatment/sex) week-old pigs were exposed to the main factors: maternal stress and treatment (docked vs. intact tails). In study 1, tail docking did not significantly alter thresholds to noxious mechanical stimulation, whilst prenatally stressed pigs had significantly higher baseline thresholds to noxious mechanical stimulation on the tail root and on the hind foot than unstressed pigs, whether tail-docked or intact. Capsaicin injection induced localised mechanical allodynia around the tail root in all treatment groups, but had no effect on noxious plantar mechanical responses; however prenatally stressed offspring exhibited significantly attenuated response thresholds to capsaicin compared to controls. In study 2 tail docking did not alter thresholds to either mechanical or noxious cold stimulation. Baseline response durations to noxious cold stimulation of the tail root were significantly shorter in both sexes of prenatally stressed pigs, whilst male but not female prenatally stressed pigs exhibited significantly higher baseline thresholds to mechanical stimulation than controls, although results in female pigs tended towards significance. Carrageenan injection into the tail root induced localised mechanical and cold allodynia in all treatment groups, effects that were attenuated in prenatally stressed pigs. Collectively, these findings indicate that prenatal stress can induce long-term alterations in nociceptive responses, manifest as a reduced sensitivity to noxious mechanical and cold stimulation and evoked inflammatory allodynia. Neonatal tail-docking does not lead to long-term alterations in nociception in pigs.     

Novel 8-(furan-2-yl)-3-benzyl thiazolo [5,4-e][1,2,4] triazolo [1,5-c] pyrimidine-2(3H)-thione as selective adenosine A2A receptor antagonist

Adenosine A_2A receptor (A_2AR) antagonists have emerged as potential drug candidates to alleviate progression and symptoms of Parkinson's disease (PD), and reduce the dopaminergic side effects. The synthesis of novel compound 8-(furan-2-yl)-3-benzyl thiazolo [5,4-e][1,2,4] triazolo [1,5-c] pyrimidine-2-(3H)-thione (BTTP) was carried out to evaluate the potential of BTTP as A_2AR antagonist using SCH58261, a standard A_2AR antagonist. The strong interaction of BTTP with A_2AR (ΔG = −12.46 kcal/mol and K_i = 0.6 nM) in silico analysis was confirmed by radioligand receptor binding studies showing high affinity (K_i = 0.004 nM) and selectivity with A_2AR (A_2A/A₁ = 1155-fold). The effect of CGS21680 (selective A_2AR agonist) induced cAMP concentration (0.1 pmol/ml) in HEK293 cells was antagonized with BTTP (0.065 pmol/ml) and SCH58261 (0.075 pmol/ml). Furthermore, BTTP pre-treated (5, 10 and 20 mg/kg) haloperidol-induced mice demonstrated significant attenuation in catalepsy and akinesia. BTTP induced elevation in the striatal dopamine concentration (2.90 μM/mg of tissue) was comparable to SCH58261 (2.92 μM/mg of tissue) at the dose of 10 mg/kg. The results firmly articulate that BTTP possesses potential A_2AR antagonist activity and can be further explored for the treatment of PD.     

Riluzole effect on occipital cortex: A structural and spectroscopy pilot study

Background

To investigate the mechanism underlying the anxiolytic properties of riluzole, a glutamate-modulating agent, we previously studied the effect of this drug on hippocampal N-acetylaspartate (NAA) and volume in patients with generalized anxiety disorder (GAD). In the same cohort, we now extend our investigation to the occipital cortex, a brain region that was recently implicated in the antidepressant effect of riluzole.

Methods

Fourteen medication-free adult patients with GAD received 8-week of open-label riluzole. Ten healthy subjects served as a comparison group. The healthy group did not receive riluzole treatment. Both groups underwent magnetic resonance imaging and spectroscopy at baseline and at the end of Week 8. Hamilton Anxiety Rating Scale (HAM-A) and Penn State Worry Questionnaire (PSWQ) were used as the primary and secondary outcome measures, respectively.

Results

At baseline, we found clusters of increased cortical thickness in the occipital region in GAD compared to healthy subjects. In the right hemisphere, 8 weeks of treatment reduced occipital cortical thickness in the GAD group (t = 3.67, p = 0.004). In addition, the improvement in HAM-A scores was negatively correlated with post-treatment right occipital NAA (r = −0.68, p = 0.008), and with changes in NAA levels (r = −0.53, p = 0.051). In the left hemisphere, we found positive associations between changes in occipital cortical thickness and improvement in HAM-A (r = 0.60, p = 0.04) and PSWQ (r = 0.62, p = 0.03).

Conclusion

These pilot findings implicate the occipital cortex as a brain region associated with pathology and clinical improvement in GAD. In addition, the region specific effect of riluzole implies a distinct pathophysiology in the occipital cortex – compared to other, previously studied, frontolimbic brain structures.