Characterization of striatal phenotypes in heterozygous Disc1 mutant mice, a model of haploinsufficiency.

Disrupted-in-Schizophrenia 1 (DISC1) is a susceptibility gene for several psychiatric illnesses. To study the pathogenesis of these disorders, we generated Disc1 mutant mice by introducing the 129S6/SvEv 25-bp deletion Disc1 variants into the C57BL/6J strain. In this study, we used heterozygous Disc1 mutant (Het) mice to evaluate the DISC1 haploinsufficiency model of schizophrenia. No changes in locomotor behaviors were observed in Het mice; however, after amphetamine injection, greater locomotor activity was observed in Het mice compared with wild-type (WT) mice. Moreover, amphetamine-induced elevations of c-Fos expression and dopamine level in the striatum were greater in Het mice than in WT controls, suggesting an altered dopaminergic regulation in the striatum of Het mice. Compared with those in WTs, the striatal protein levels of dopamine transporter and D2 dopamine receptor were increased in Het mice, while D1 dopamine receptor level was decreased. DISC1 interacting proteins, GSK3α and GSK3ß, were downregulated in Het mice, whereas the levels of PDE4B and CREB were not altered. Morphologically, the complexities of striatal median spiny neurons (MSNs), parvalbumin-positive interneurons and Iba1-positive microglia were all decreased in Het mice. The density and head diameter of dendritic spines in the MSNs of Het mice were also reduced. Our results indicate that mice lacking one WT Disc1 allele are more sensitive to psychostimulant amphetamine challenge, which might be attributed to the altered structure and function of the striatal dopaminergic system. Here, we demonstrated striatal phenotypes in heterozygous Disc1 mutant mice, which could be a promising model of DISC1 haploinsufficiency.

Apigenin, a natural flavonoid, inhibits glutamate release in the rat hippocampus.

The purpose of this study was to examine the effect and mechanism of apigenin, a natural flavonoid, on glutamate release in the rat hippocampus. In rat hippocampal nerve terminals (synaptosomes), apigenin inhibited glutamate release and the elevation of the cytosolic free Ca(2+) concentration evoked by 4-aminopyridine, whereas it had no effect on 4-aminopyridine-mediated depolarization and Na(+) influx. The apigenin-mediated inhibition of evoked glutamate release was prevented by chelating the extracellular Ca(2+) ions and blocking Cav2.2 (N-type) and Cav2.1 (P/Q-type) channel activity. Furthermore, we determined that gamma-aminobutyric acid type A (GABAA) receptors are present in the hippocampal nerve terminals because they are colocalized with the presynaptic marker synaptophysin. However, the effect of apigenin on 4-aminopyridine-evoked glutamate release from synaptosomes was unaffected by the GABAA receptor antagonists SR95531 and bicuculline. Furthermore, in slice preparations, whole-cell patch-clamp experiments showed that apigenin reduced the frequency of spontaneous excitatory postsynaptic currents without affecting their amplitude, suggesting a presynaptic mechanism. On the basis of these results, we suggested that apigenin exerts its presynaptic inhibition probably by reducing Ca(2+) entry mediated by the Cav2.2 (N-type) and Cav2.1 (P/Q-type) channels, thereby inhibiting glutamate release from the rat hippocampal nerve terminals.

Cyclooxygenase 2 inhibitor celecoxib inhibits glutamate release by attenuating the PGE2/EP2 pathway in rat cerebral cortex endings.

The excitotoxicity caused by excessive glutamate is a critical element in the neuropathology of acute and chronic brain disorders. Therefore, inhibition of glutamate release is a potentially valuable therapeutic strategy for treating these diseases. In this study, we investigated the effect of celecoxib, a selective cyclooxygenase-2 (COX-2) inhibitor that reduces the level of prostaglandin E2 (PGE2), on endogenous glutamate release in rat cerebral cortex nerve terminals (synaptosomes). Celecoxib substantially inhibited the release of glutamate induced by the K(+) channel blocker 4-aminopyridine (4-AP), and this phenomenon was prevented by chelating the extracellular Ca(2+) ions and by the vesicular transporter inhibitor bafilomycin A1. Celecoxib inhibited a 4-AP-induced increase in cytosolic-free Ca(2+) concentration, and the celecoxib-mediated inhibition of glutamate release was prevented by the Cav2.2 (N-type) and Cav2.1 (P/Q-type) channel blocker ω-conotoxin MVIIC. However, celecoxib did not alter 4-AP-mediated depolarization and Na(+) influx. In addition, this glutamate release-inhibiting effect of celecoxib was mediated through the PGE2 subtype 2 receptor (EP2) because it was not observed in the presence of butaprost (an EP2 agonist) or PF04418948 [1-(4-fluorobenzoyl)-3-[[6-methoxy-2-naphthalenyl)methyl]-3-azetidinecarboxylic acid; an EP2 antagonist]. The celecoxib effect on 4-AP-induced glutamate release was prevented by the inhibition or activation of protein kinase A (PKA), and celecoxib decreased the 4-AP-induced phosphorylation of PKA. We also determined that COX-2 and the EP2 receptor are present in presynaptic terminals because they are colocalized with synaptophysin, a presynaptic marker. These results collectively indicate that celecoxib inhibits glutamate release from nerve terminals by reducing voltage-dependent Ca(2+) entry through a signaling cascade involving EP2 and PKA.

Dissociating effects of spatial learning from locomotor activity for ouabain-induced bipolar disorder-like rats.

Whether ouabain, a Na+ - and K+-activated adenosine triphosphatase inhibitor, mimics cognitive impairments that can be dissociated from motor effects in the bipolar disorder-like animal model remains unclear. Ouabain and the vehicle aCSF were microinjected into the left lateral ventricle immediately, after 4h, and after 24h. The results showed that (a) locomotion responses of the Immediate group were significantly decreased compared to those of the aCSF group, particularly the first five minutes. (b) The ouabain-treated rats have longer latency and total distance traveled in the water maze task; however, the velocity was not affected for the ouabain group. (c) The analysis of covariance showed that the latency time (but not the total distance traveled and velocity) of the ouabain group was more impaired than that of the aCSF group, regardless of omitting total distance traveled and cross movement in the open field test. The latency might be more sensitive than the distance traveled and the velocity for assessing spatial learning. Dissociating the spatial learning from the movement may allow testing drug treatments of cognitive deficits independent of locomotor effects associated with bipolar disorder.

Upregulation of presynaptic proteins and protein kinases associated with enhanced glutamate release from axonal terminals (synaptosomes) of the medial prefrontal cortex in rats with neuropathic pain.

Although nerve injury-induced long-term postsynaptic changes have been investigated, less is known regarding the molecular mechanisms within presynaptic axonal terminals. We investigated the molecular changes in presynaptic nerve terminals underlying chronic pain-induced plastic changes in the medial prefrontal cortex (mPFC). After neuropathic pain was induced by spared nerve injury (SNI) in rats, we assessed the release of the excitatory neurotransmitter glutamate by using in vitro synaptosomal preparations from the mPFC. We also measured the levels of synaptic proteins and protein kinases in synaptosomes using Western blotting. The results showed that unilateral long-term SNI augmented depolarization-evoked glutamate release from synaptosomes of the bilateral mPFC. This result was confirmed by a rapid destaining rate of FM1-43 dye in SNI-operated rats. Unilateral long-term nerve injury also significantly increased synaptic proteins (including synaptophysin, synaptotagmin, synaptobrevin, syntaxin, and 25-kDa synaptosome-associated protein) in synaptosomal fractions from the bilateral mPFC, and ultrastructure images demonstrated increased synaptic vesicular profiles in synaptosomes from SNI animals. Chronic pain upregulated the phosphorylation of endogenous protein kinases, including extracellular signal-regulated kinases 1 and 2 (ERK1/2) and Ca(2+)/calmodulin-dependent kinase II (CaMKII), and synapsin I, the primary presynaptic target of ERK1/2 and CaMKII. Both presynaptic proteins and protein kinases were upregulated after SNI in a time-dependent manner. These results indicate that the long-term neuropathic pain-induced enhancement of glutamate release in the mPFC is linked to increased synaptic vesicle proteins and the activation of the ERK1/2- and CaMKII-synapsin signaling cascade in presynaptic axonal terminals.

Bupropion attenuates kainic acid-induced seizures and neuronal cell death in rat hippocampus.

Excessive release of glutamate is believed to be a major component of cell damage following excitotoxicity associated with epilepsy. Bupropion, an atypical antidepressant, has been shown to inhibit glutamate release from rat cerebrocortical nerve terminals. The present study was undertaken to investigate whether bupropion has anti-seizure and anti-excitotoxic effects by using a kainic acid (KA) rat seizure model, an animal model for temporal lobe epilepsy and excitotoxic neurodegeneration. Our results show that bupropion (10 or 50mg/kg), administrated intraperitoneally to the rats 30 min before the KA (15 mg/kg) intraperitoneal injection, increased the seizure latency and decreased the seizure score. Bupropion pretreatment attenuated KA-induced neuronal cell death and microglia activation in the CA3 region of the hippocampus. Furthermore, KA-induced c-Fos expression and extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation in the hippocampus were also reduced by bupropion pretreatment. These results suggest that bupropion has therapeutic potential in the treatment of seizure and other neurological diseases associated with excitotoxicity.

Effects of lithium and carbamazepine on spatial learning and depressive behavior in a rat model of bipolar disorder induced by ouabain.

Lithium (LiCl) and carbamazepine (CBZ), the common mood stabilizers, are thought to be effective treatments for bipolar disorder. The aim of the present study was to investigate whether LiCl as well as CBZ has similar effects on the bipolar disorder-associated cognitive dysfunctions in rats, particularly the spatial learning and depressive responses. Adult male Wistar rats were administered intracerebroventricularly with 5µl of 10(-3)M ouabain on session 1, and then received an intraperitoneal injection of LiCl or CBZ for 4 sessions (1 session/2days). For the behavioral tests, all rats were subjected to the water maze 15min for spatial learning and the forced swimming test 5min for depression on each session. The present results showed that ouabain resulted in increased latency and longer distance traveled to reach the hidden platform in the water maze, indicating that ouabain impaired the spatial learning. However, ouabain did not affect swimming velocity in the water maze and depressive responses in the forced swimming test. LiCl treatment decreased the ouabain-enhanced latency and the total distance, but not the velocity, swam to reach the hidden platform in the water maze task. Additionally, LiCl did not result in changes of any depressive indices, such as struggling behavior, swimming behavior, and floating behavior. Likewise, CBZ did not affect any behavioral indices of spatial learning and depression. A linear regression analysis suggested that LiCl, but not CBZ, could predict the decreased latency and total distance traveled except the velocity of swimming in the water maze and depressive behaviors. In summary, the present results suggested that lithium provided a better therapeutic effect than CBZ for ouabain-caused dysfunctions of spatial learning in a rat model of bipolar disorder.

Neural substrates of amphetamine-induced behavioral sensitization: unconditioned (zero context) and conditioned (switch versus same context) components in c-fos overexpression.

The neural substrates of the unconditioned and conditioned components of amphetamine (AMPH)-induced behavioral sensitization remain unknown. The present study examines the brain activation of rats in response to an AMPH challenge with augmented locomotion in groups receiving chronic AMPH under chloral hydrate anesthetization (i.e., the 'zero context') or when tested in the 'same context' as a chronic treatment, or when tested in a 'different context'. The neural activations of the three groups reveal fairly consistent patterns: (a) The substantia nigra is activated in the same context condition and the pure AMPH effect (i.e., the zero context with the unconditioned component), but not in the switch context condition. (b) The ventral pallidum showed Fos expression in the switch context and the same context, but not in the zero context condition. (c) The other nuclei, including the medial prefrontal cortex, nucleus accumbens, caudate putamen, medial thalamus, hippocampus, amygdala, and ventral tegmental area, are activated in all contextual conditions and the pure AMPH effect (the zero context). The context exerts definable effects on the mesocorticolimbic dopamine system on AMPH-induced behavioral sensitization. (d) The ventral pallidum and the substantia nigra activations dissociate the unconditioned component from the conditioned component in behavioral sensitization. Further studies are needed to determine how these two nuclei mediate the effect in terms of primary and conditioned rewards.

Hispidulin inhibits the release of glutamate in rat cerebrocortical nerve terminals.

Hispidulin, a naturally occurring flavone, has been reported to have an antiepileptic profile. An excessive release of glutamate is considered to be related to neuropathology of epilepsy. We investigated whether hispidulin affected endogenous glutamate release in rat cerebral cortex nerve terminals (synaptosomes) and explored the possible mechanism. Hispidulin inhibited the release of glutamate evoked by the K⁺ channel blocker 4-aminopyridine (4-AP). The effects of hispidulin on the evoked glutamate release were prevented by the chelation of extracellular Ca²âº ions and the vesicular transporter inhibitor bafilomycin A1. However, the glutamate transporter inhibitor dl-threo-beta-benzyl-oxyaspartate did not have any effect on hispidulin action. Hispidulin reduced the depolarization-induced increase in cytosolic free Ca²âº concentration ([Ca²âº](C)), but did not alter 4-AP-mediated depolarization. Furthermore, the effect of hispidulin on evoked glutamate release was abolished by blocking the Ca(v)2.2 (N-type) and Ca(v)2.1 (P/Q-type) channels, but not by blocking ryanodine receptors or mitochondrial Na⁺/Ca²âº exchange. Mitogen-activated protein kinase kinase (MEK) inhibition also prevented the inhibitory effect of hispidulin on evoked glutamate release. Western blot analyses showed that hispidulin decreased the 4-AP-induced phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2) and synaptic vesicle-associated protein synapsin I, a major presynaptic substrate for ERK; this decrease was also blocked by the MEK inhibitor. Moreover, the inhibition of glutamate release by hispidulin was strongly attenuated in mice without synapsin I. These results show that hispidulin inhibits glutamate release from cortical synaptosomes in rats through the suppression of presynaptic voltage-dependent Ca²âº entry and ERK/synapsin I signaling pathway.

σ-1 Receptor agonist SKF10047 inhibits glutamate release in rat cerebral cortex nerve endings.

σ-1 Receptors are expressed in the brain, and their activation has been shown to prevent neuronal death associated with glutamate toxicity. This study investigates the possible mechanism and effect of [2S-(2α,6α,11R*]-1,2,3,4,5,6-hexahydro-6,11-dimethyl-3-(2-propenyl)-2,6-methano-3-benzazocin-8-ol (SKF10047), a σ-1 receptor agonist, on endogenous glutamate release in the nerve terminals of rat cerebral cortex. Results show that SKF10047 inhibited the release of glutamate evoked by the K⁺ channel blocker 4-aminopyridine (4-AP), and the σ-1 receptor antagonist N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine (BD1047) blocked this phenomenon. The effects of SKF10047 on the evoked glutamate release were prevented by the chelating extracellular Ca²âºions and the vesicular transporter inhibitor bafilomycin A1. However, the glutamate transporter inhibitor DL-threo-ß-benzyl-oxyaspartate did not have any effect on the action of SKF10047. SKF10047 decreased the depolarization-induced increase in the cytosolic free Ca²âº concentration ([Ca²âº](C)), but did not alter 4-AP-mediated depolarization. Furthermore, the effects of SKF10047 on evoked glutamate release were prevented by blocking the Ca(v)2.2 (N-type) and Ca(v)2.1 (P/Q-type) channels, but not by blocking the ryanodine receptors or the mitochondrial Na⁺/Ca²âº exchange. In addition, conventional protein kinase C (PKC) inhibitors abolished the SKF10047 effect on 4-AP-evoked glutamate release. Western blot analyses showed that SKF10047 decreased the 4-AP-induced phosphorylation of PKC and PKCα. These results show that σ-1 receptor activation inhibits glutamate release from rat cortical nerve terminals. This effect is linked to a decrease in [Ca²âº](C) caused by Ca²âº entry through presynaptic voltage-dependent Ca²âº channels and the suppression of the PKC signaling cascade.

Combination of nerve blockade and intravenous alfentanil is better than single treatment in relieving postoperative pain.

BACKGROUND/PURPOSE: Multimodal analgesia can improve perioperative analgesia but knowledge of combination protocols is still incomplete. This study was designed to evaluate whether the combination of sciatic nerve blockade (SNB) and intravenous alfentanil (IVA) is more effective than either single treatment in relieving postoperative pain in rats. METHODS: In a plantar incision model, withdrawal thresholds were evaluated by von Frey test before incision as baselines and for 7 days after incision. The animals were randomly allocated into various groups to receive SNB with 1% or 2% lidocaine, IVA of 50 or 150 µg/kg, or combined treatments (SNB 1% + 50 µg/kg IVA or SNB 2% + 150 µg/kg IVA) before incision. The results were compared with those of sham procedures--i.e., injections of peri-sciatic or intravenous saline, or a combination of both. RESULTS: Plantar incision caused postoperative allodynia for 3 days. SNB with 2% lidocaine reduced allodynia at 1 hour, 3 hours, day 1, and day 2, but not at postoperative 5 hours or days 3-7, whereas 150 µg/kg IVA produced short analgesia for only 3 hours after surgery. Neither low-dose SNB nor low-dose IVA had a significant effect. When high-dose SNB and high-dose IVA were combined, a strong antiallodynic effect was shown in an additive manner. No synergism was evidently displayed by the combination. CONCLUSION: Our results indicated that in an incisional pain model, multimodal analgesia is superior to single or no pretreatment; however, the combination of multimodal analgesic treatments should be individually discerned depending on nociceptive types and analgesic mechanisms.

Spinal microglia initiate and maintain hyperalgesia in a rat model of chronic pancreatitis.

BACKGROUND & AIMS: The chronic, persistent pain associated with chronic pancreatitis (CP) has many characteristics of neuropathic pain, initiated and maintained by the activation of spinal microglia. We investigated whether activated microglia in the thoracic spinal cord contribute to chronic pain in a rat model of CP. METHODS: CP was induced in Sprague-Dawley rats by an intraductal injection of 2% trinitrobenzene sulfonic acid. Hyperalgesia was assessed by the measurement of mechanical sensitivity of the abdomen and nocifensive behavior to electrical stimulation of the pancreas. Three weeks after induction of CP, spinal samples were analyzed by immunostaining and immunoblot analyses for levels of CD11 (a marker of microglia, determined with the antibody OX42) and phosphorylated p38 (P-p38, a marker of activation of p38 mitogen-activated protein kinase signaling). We examined the effects of minocycline (inhibitor of microglia) and fractalkine (microglia-activating factor) on visceral hyperalgesia in rats with CP. RESULTS: Rats with CP had increased sensitivity and nociceptive behaviors to mechanical probing of the abdomen and electrical stimulation of the pancreas. The dorsal horn of the thoracic spinal cords of rats with CP contained activated microglia (based on increased staining with OX42), with an ameboid appearance. Levels of P-p38 increased in rats with CP and colocalized with OX42-positive cells. Intrathecal injection of minocycline reversed and prevented the increase of nocifensive behaviors and levels of P-p38 in rats with CP. Fractalkine induced hyperalgesia in rats without CP, which was blocked by minocycline. CONCLUSIONS: Activated spinal microglia have important roles in maintaining and initiating chronic pain in a rat model of CP. Microglia might be a target for treatment of hyperalgesia caused by pancreatic inflammation.

Curcumin inhibits glutamate release in nerve terminals from rat prefrontal cortex: possible relevance to its antidepressant mechanism.

There is abundant evidence suggesting the relevance of glutamate to depression and antidepressant mechanisms. Curcumin, a major active compound of Curcuma longa, has been reported to have the biological function of antidepressant. The aim of the present study was to investigate the effect of curcumin on endogenous glutamate release in nerve terminals of rat prefrontal cortex and the underlying mechanisms. The results showed that curcumin inhibited the release of glutamate that was evoked by exposing synaptosomes to the K(+) channel blocker 4-aminopyridine (4-AP). This phenomenon was blocked by the chelating the extracellular Ca(2+) ions, and by the vesicular transporter inhibitor bafilomycin A1, but was insensitive to the glutamate transporter inhibitor DL-threo-ß-benzyl-oxyaspartate (DL-TBOA). Further experiments demonstrated that curcumin decreased depolarization-induced increase in [Ca(2+)](C), whereas it did not alter the resting membrane potential or 4-AP-mediated depolarization. Furthermore, the inhibitory effect of curcumin on evoked glutamate release was prevented by blocking the Ca(v)2.2 (N-type) and Ca(v)2.1 (P/Q-type) channels, but not by blocking intracellular Ca(2+) release or Na(+)/Ca(2+) exchange. These results suggest that curcumin inhibits evoked glutamate release from rat prefrontocortical synaptosomes by the suppression of presynaptic Ca(v)2.2 and Ca(v)2.1 channels. Additionally, we also found that the inhibitory effect of curcumin on 4-AP-evoked glutamate release was completely abolished by the clinically effective antidepressant fluoxetine. This suggests that curcumin and fluoxetine use a common intracellular mechanism to inhibit glutamate release from rat prefrontal cortex nerve terminals.

Changes in dietary folate intake differentially affect oxidised lipid and mitochondrial DNA damage in various brain regions of rats in the absence/presence of intracerebroventricularly injected amyloid ß-peptide challenge.

Accumulating evidence suggests that changes in dietary folate intake may modulate the risks of Alzheimer's disease (AD) through as yet unknown mechanisms. The aims of the present study were to investigate how dietary folate affects the brain folate distribution, levels of oxidised lipid and DNA damage in the absence/presence of ß-amyloid(25-35) (Aß) peptide challenge, a pathogenic hallmark of AD. Male Wistar rats were assigned to diets with folic acid at 0 (folate deprivation; FD), 8 (moderate folate; MF) and 8 mg folic acid/kg diet+0·003 % in drinking-water (folate supplementation; FS) for 4 weeks. A single injection of Aß peptide (1 mg/ml) or the vehicle solution was intracerebroventricularly (icv) administrated to rats a week before killing. Brain folate, a marker of oxidative injury, and neuronal death were assayed. In the absence of an Aß injection, FD rats showed reduced folate levels, and increased 2-thiobarbituric acid-reactive substances and a mitochondrial (mt)DNA 4834 bp large deletion (mtDNA4834 deletion) in the hippocampus compared with the counterpart brains of control rats (P < 0·05). A single icv injection of Aß peptide potentiated lipid peroxidation in the medulla of FD rats, which was ameliorated by feeding FD rats with the MF and FS diets (P < 0·05). Feeding the FS diet to Aß-injected rats enriched brain folate levels and reduced mtDNA4834 deletion in the hippocampal and medullary regions compared with corresponding tissues of Aß+FD rats (P < 0·05). Aß+FS rats had reduced rates of neuronal death in the frontal cortex compared with Aß+FD rats (P < 0·05). Taken together, our data revealed that folate deprivation differentially depleted brain folate levels, and increased lipid peroxidation and mtDNA4834 deletions, particularly, in the hippocampus. Upon Aß challenge, the FS diet may protect various brain regions against lipid peroxidation, mitochondrial genotoxicity and neural death associated with folate deprivation.

Characterized polysaccharides from black soybean induce granulocyte colony-stimulated factor gene expression in a phosphoinositide 3-kinase-dependent manner.

Black soybean (Glycine max L. merr.) is an edible Chinese medicine for nourishment spleen. In the present study, effects of characterized polysaccharides from black soybean (PGM) on granulocyte colony-stimulated factor (G-CSF) production in human peripheral blood mononuclear cells (PBMC) were determined and their action mechanisms were examined. The results indicated that PGM concentration-dependently enhanced G-CSF production in PBMC through modulation of mRNA expression. Data from Western blotting showed that PGM significantly induced the extracellular signal-regulated protein kinase (ERK) activation in PBMC. The nuclear factor (NF)-κB activation in PBMC was increased with PGM by modulation of IκB degradation and PKC θ activation. The levels of G-CSF mRNA in PGM-treated PBMC could be reduced by ERK inhibitor U0126 and NF-κB inhibitor pyrrolidine dithiocarbamate, respectively. Furthermore, the data showed that PGM stimulated phosphoinositide 3-kinase (PI3K)-regulated Akt phosphorylation. The PI3K inhibitor, Ly294002, blocked ERK, NF-κB, and PKC θ activation and G-CSF mRNA expression in PBMC induced by PGM. Thus, we first proved that the enhancement mechanisms of PGM on G-CSF production, appeared to be mediated, at least in part, through activation of PI3K, ERK, PKC θ, and NF-κB signaling pathways in PBMC. We suggest that PGM from black soybean is a potential G-CSF stimulator.

Effects of single and group housing conditions and alterations in social and physical contexts on amphetamine-induced behavioral sensitization in rats.

Repeated administration of amphetamine (AMPH) can produce behavioral sensitization. However, whether contextual elements and housing conditions influence AMPH-induced behavioral sensitization remains uncertain. This study was designed to examine the effects of housing conditions (single- vs. group-housed) and different contextual changes, including social (with two other co-drug partners) and physical (novel box) context changes, on AMPH-induced behavioral sensitization. During the training phase, all rats were exposed for 7 days to AMPH (1mg/kg, intraperitoneally) in a Locometer chamber, with the exception of animals tested for the effects of physical context changes trained in a novel box. Following a 7-day withdrawal phase, all rats received an AMPH (0.5mg/kg) challenge, and locomotor activity in a Locometer box was recorded before and after AMPH injection during the testing phase. Under group housing conditions, animals exposed to a different physical environment between the training and testing phases or accompanying co-drug partners during the training phase exhibited decreased AMPH-induced locomotor sensitization. In contrast, single housing conditions did not have an inhibitory effect on AMPH-induced behavioral sensitization after manipulations of the physical and social contexts. These results suggest that under group housing conditions, both physical and social context changes can attenuate AMPH-induced behavioral sensitization. The possible neural mechanisms underlying the involvement of different housing conditions in AMPH-induced behavioral sensitization are discussed.

DNIC-mediated analgesia produced by a supramaximal electrical or a high-dose formalin conditioning stimulus: roles of opioid and alpha2-adrenergic receptors.

BACKGROUND: Diffuse noxious inhibitory controls (DNIC) can be produced by different types of conditioning stimuli, but the analgesic properties and underlying mechanisms remain unclear. The aim of this study was to differentiate the induction of DNIC analgesia between noxious electrical and inflammatory conditioning stimuli. METHODS: First, rats subjected to either a supramaximal electrical stimulation or an injection of high-dose formalin in the hind limb were identified to have pain responses with behavioral evidence and spinal Fos-immunoreactive profiles. Second, suppression of tail-flick latencies by the two noxious stimuli was assessed to confirm the presence of DNIC. Third, an opioid receptor antagonist (naloxone) and an alpha2-adrenoreceptor antagonist (yohimbine) were injected, intraperitoneally and intrathecally respectively, before conditioning noxious stimuli to test the involvement of descending inhibitory pathways in DNIC-mediated analgesia. RESULTS: An intramuscular injection of 100 microl of 5% formalin produced noxious behaviors with cumulative pain scores similar to those of 50 microl of 2% formalin in the paw. Both electrical and chemical stimulation significantly increased Fos expression in the superficial dorsal horns, but possessed characteristic distribution patterns individually. Both conditioning stimuli prolonged the tail-flick latencies indicating a DNIC response. However, the electrical stimulation-induced DNIC was reversed by yohimbine, but not by naloxone; whereas noxious formalin-induced analgesia was both naloxone- and yohimbine-reversible. CONCLUSIONS: It is demonstrated that DNIC produced by different types of conditioning stimuli can be mediated by different descending inhibitory controls, indicating the organization within the central nervous circuit is complex and possibly exhibits particular clinical manifestations.

Effect of stimulus pre-exposure on inhibitory avoidance retrieval-associated changes in the phosphorylated form of the extracellular signal-regulated kinase-1 and -2 (pERK1/2).

One goal of the present study was to determine how pre-exposure to a set of contextual cues affected subsequent reinforced inhibitory avoidance task performance using those cues (latent inhibition model). In addition, immunohistochemical assessment of the phosphorylated (activated) form of the extracellular signal-regulated kinase-1 and -2 (pERK1/2) was examined. Adult, male Long Evans rats were randomly assigned into either pre-exposure (PE) or different pre-exposure (DPE) groups. All rats received 3days of contextual pre-exposure (same or different context as that used for reinforced training) and were trained, 24h later, on an inhibitory avoidance task (with or without shock). Rats were euthanized 24h after training; half with a retention test and half without. Behaviorally, the PE group showed reduced latencies to enter the dark/shock compartment during the retention test compared to the DPE group showing the latent inhibition phenomenon. Compared to the shocked and tested DPE group, the shocked and tested PE group showed fewer pERK1/2-ir neurons in the secondary motor cortex, the anterior cingulate, the pre- and infra-limbic cortices, and the central nucleus of the amygdala. These regions showed similar numbers of pERK1/2-labeled neurons when comparing the shocked and tested PE group with the nonshocked and tested PE group. This suggests the possibility that brain regions showing decreased pERK1/2 levels in association with attenuated inhibitory avoidance performance may be involved in different aspects of the memory retrieval process.

Roles of corticosterone in formalin-induced conditioned place aversion in rats.

Glucocorticoid hormones have been shown to contribute to many cognitive functions, such as depressions, learning and memory, and abnormal glucocorticoid secretion results in functional changes in prefrontal cortex and amygdala. In the present study, we used the conditioned place aversion (CPA) paradigm to investigate the role of corticosterone (CORT) in the negative affective component of chemical somatic pain induced by intraplantar injection of formalin into male adult Long-Evan rats. Five percent of formalin produced acute biphasic nociceptive behaviors, including flinching and licking of hindpaw, and CPA. Intraplantar formalin induced CPA was abolished by bilateral adrenalectomy and the impairment of CPA can be restored by the CORT treatment. However, the adrenalectomy failed to affect the formalin-produced acute nociceptive behaviors. Therefore, data from the present study suggest that CORT secretion by the adrenal cortex may play a role in chemical somatic noxious stimuli-induced avoidance learning and aversive memory, but not sensory discrimination of noxious stimulation.

Modulation of presynaptic glucocorticoid receptors on glutamate release from rat hippocampal nerve terminals.

In this study, we have examined the role of corticosterone (CORT) in the regulation of neuronal glutamate release using nerve terminals (synaptosomes) isolated from the rat hippocampus. Adult male Sprague-Dawley rats received either a chronic systemic administration of CORT (daily 25 mg/kg in sesame oil, subcutaneously) or long-term bilateral adrenalectomy (ADX) (3-4 weeks), and then the release of 4-aminopyridine (4AP)-evoked endogenous glutamate and the levels of glucocorticoid receptor (GR) expression from hippocampal nerve terminals were studied. Chronic administration of CORT resulted in a significant increase of 4AP-evoked glutamate release from hippocampal nerve terminals, whereas ADX reduced 4AP-evoked glutamate release. In addition, chronic administration of CORT and ADX induced a significant reduction and increase in GR expression in hippocampal synaptosomes, respectively, as detected by Western blots. Furthermore, acute treatment of CORT or dexamethasone facilitated 4AP-evoked glutamate release from synaptosomes freshly isolated from naïve rat hippocampus and this effect can be significantly prevented by pretreatment of GR antagonist mifepristone, but not by mineralocorticoid receptor (MR) antagonist RU28318. Together, our results strongly support the presence of GRs on presynaptic nerve terminals in the rat hippocampus acting to facilitate the release of neuronal glutamate.