The STING-IRF3 pathway is involved in lipotoxic injury of pancreatic ß cells in type 2 diabetes.

Lipotoxic injury of pancreatic ß cells is an important pathological feature in type 2 diabetes mellitus (T2DM). Stimulator of interferon genes (STING) can recognize its own DNA leaked into the cytoplasm from damaged mitochondria or nuclei of the host cell, thus activating its downstream factor interferon regulatory factor 3 (IRF3), causing inflammation and apoptosis. The STING-IRF3 signaling pathway is closely related to glycolipid metabolism, but its relationship with the lipotoxicity of pancreatic ß cells has rarely been reported. Here, we investigated the role of the STING-IRF3 signaling pathway in lipotoxicity-induced inflammation, apoptosis, and dysfunction of pancreatic ß cells. We examined the activation of STING and IRF3 in islets of db/db mice and identified the role of the STING-IRF3 signaling pathway in palmitic acid (PA)-induced lipotoxic injury of INS-1, a rat insulinoma cell line. STING and phosphorylated IRF3 including downstream interferon-ß were upregulated in islets of db/db mice and PA-induced INS-1 cells. Gene silencing of STING or IRF3 ameliorated PA-induced INS-1 cell inflammation and apoptosis, and reversed impaired insulin synthesis. Additionally, PA induced downregulation of the phosphoinositide 3-kinase-AKT signaling pathway, and impaired high glucose-stimulated insulin secretion was reversed after knockdown of STING or IRF3. Our results suggest that activation of the STING-IRF3 pathway triggers inflammation and apoptosis of pancreatic ß cells, leading to ß-cell damage and dysfunction. Hence, inhibition of this signaling pathway may represent a novel approach for ß-cell protection in T2DM.

Activation of the STING-IRF3 pathway promotes hepatocyte inflammation, apoptosis and induces metabolic disorders in nonalcoholic fatty liver disease.

BACKGROUND: Nonalcoholic fatty liver disease (NAFLD) is a common result of obesity and metabolic syndrome. Hepatocyte injury and metabolic disorders are hallmarks of NAFLD. Stimulator of interferon genes (STING) and its downstream factor interferon regulatory factor 3 (IRF3) trigger inflammatory reaction in response to the presence of cytosolic DNA. STING has recently been shown to play an important role in early alcoholic liver disease. However, little is known about the role of STING-IRF3 pathway in hepatocyte injury. Here, we aimed to examine the effect of STING-IRF3 pathway on hepatocyte metabolism, inflammation and apoptosis. METHODS: We examined the activation of the STING-IRF3 pathway, a high-fat diet (HFD)-induced obese mouse model, and determined the role of this pathway in a free fatty acid (FFA)-induced hepatocyte inflammatory response, injury, and dysfunction in L-O2 human liver cells. RESULTS: STING and IRF3 were upregulated in livers of HFD-fed mice and in FFA-induced L-O2 cells. Knocking down either STING or IRF3 led to a significant reduction in FFA-induced hepatic inflammation and apoptosis, as evidenced by modulation of the nuclear factor κB (NF-κB) signaling pathway, inflammatory cytokines, and apoptotic signaling. Additionally, STING/IRF3 knockdown enhanced glycogen storage and alleviated lipid accumulation, which were found to be associated with increased expression of hepatic enzymes in glycolysis and lipid catabolism, and attenuated expression of hepatic enzymes in gluconeogenesis and lipid synthesis. CONCLUSIONS: Our results suggest that the STING-IRF3 pathway promotes hepatocyte injury and dysfunction by inducing inflammation and apoptosis and by disturbing glucose and lipid metabolism. This pathway may be a novel therapeutic target for preventing NAFLD development and progression.

Functional circuitry of a unique cerebellar specialization: the valvula cerebelli of a mormyrid fish.

The valvula cerebelli of the mormyrid electric fish is a useful site for the study of cerebellar function. The valvula forms a part of the electrosensory-electromotor system of this fish, a system that offers many possibilities for the study of sensory-motor integration. The valvula also has a number of histological features not present in mammals which facilitate investigation of cerebellar circuitry and its plasticity. This initial study characterizes the basic physiology and pharmacology of cells in the valvula using an in vitro slice preparation. Intrinsic properties and synaptic responses of Purkinje cells and other cell types were examined. We found that Purkinje cells fire a small narrow Na(+) spike and a large broad Ca(2+) spike, generated in the axon initial segment and dendritic-soma region, respectively. Purkinje cells respond to parallel fiber inputs with graded excitatory postsynaptic potentials (EPSPs) and to climbing fiber inputs with all-or-none EPSPs. Efferent cells, Golgi cells, and deep stellate cells all fire a single type of large narrow spike and respond only to parallel fiber inputs. Both parallel fiber and climbing fiber responses in Purkinje cells appear to be entirely mediated by AMPA-type glutamate receptors, whereas parallel fiber responses in efferent cells and stellate cells include AMPA and NMDA components. In addition, a strong synaptic inhibition was uncovered in both Purkinje cells and efferent cells in response to the focal stimulation of parallel fibers. Dual cell recordings indicate that deep stellate cells contribute at least partially to this inhibition. We conclude that despite its unique histology, the local functional circuitry of the mormyrid valvula cerebelli is largely similar to that of the mammalian cerebellum. Thus, what is learned concerning the functioning of the mormyrid valvula cerebelli may be expected to be informative about cerebellar function in general.

Interleukin 1beta facilitates bone cancer pain in rats by enhancing NMDA receptor NR-1 subunit phosphorylation.

It has been shown that interleukin-1beta (IL-1beta) facilitates nociception during neuropathic and inflammatory pain, but its involvement in bone cancer pain and its mechanisms have not previously been established. This study is an investigation of IL-1beta spinal expression and the N-methyl-D-aspartate (NMDA) receptor (NMDAR) NR1 subunit phosphorylation during cancer pain, co-localization of IL-1 receptor type I (IL-1RI) and NMDAR in the spinal cord, and the effects of IL-1 receptor antagonist (IL-1ra) on NMDAR1 (NR1) phosphorylation and hyperalgesia in a rat model of bone cancer pain. Cancer was induced by injecting AT-3.1 prostate cancer cells into the tibia of the male Copenhagen rat. Phosphorylation of NR1, an essential subunit of the NMDAR, is known to modulate NMDAR activity and facilitate pain. Mechanical hyperalgesia, established by a decrease in paw withdrawal pressure threshold (PWPT), was measured at baseline and 2 h after IL-1ra treatment. IL-1ra was given (i.t.) daily for 7 days between days 13 and 19 after the cancer cell inoculation. Spinal cords were removed for Western blot to measure IL-1beta and NR1 phosphorylation and for double immunostaining of IL-1RI and NR1. The data showed that 1) spinal IL-1beta was up-regulated and NR1 phosphorylation was increased, 2) IL-1ra at 0.1 mg/rat significantly (P<0.05) inhibited mechanical hyperalgesia, increasing PWPT on day 14 from 71.1+/-3.1-85.3+/-4.6 g and on day 19 from 73.5.0+/-3.5-87.1+/-3.7 g, and inhibited NR1 phosphorylation compared with saline control, and 3) IL-1RI is localized in NR1-immunoreactive neurons within the spinal cord. The results suggest that spinal IL-1beta enhances NR1 phosphorylation to facilitate bone cancer pain.

Amyloid beta-protein fragment 31-35 forms ion channels in membrane patches excised from rat hippocampal neurons.

Inside-out membrane patches excised from rat hippocampal neurons were used to test if ion channels could be formed by fragment 31-35 of amyloid beta-protein. The results showed: (1) after application of fragment 31-35 of amyloid beta-protein (5 microM) to either the inner or outer side of the patches, spontaneous currents could be recorded from those patches that had previously been 'silent'; (2) the fragment 31-35-induced conductance was cation-selective with a permeability ratio of P(Cs)/P(Cl)=23; (3) different levels of conductance, ranging from 25 to 500 pS, could be recorded in different patches, and in some cases, different conductances and spontaneous transitions among them could be recorded in a single patch; and (4) application of ZnCl(2) (1 mM) to the inner side of the patches reversibly blocked the newly formed channel activity; a similar effect was observed after application of CdCl(2) (1 mM). These results show that fragment 31-35 of amyloid beta-protein can insert into membrane patches from both sides and form cation-selective, Zn(2+)- and Cd(2+)-sensitive ion channels. It is proposed that fragment 31-35 in amyloid beta-protein might be the shortest active sequence known to date to form ion channels across neuronal membranes.

Opiate-like substances mediate norepinephrine-induced but not serotonin-induced antinociception at spinal level: reevaluation by an electrophysiological model of formalin test in rats.

After subcutaneous injection of formalin (5%, 50 microl) into a hindpaw of rats, biphasic excitatory nociceptive discharges were recorded extracellularly in thalamic parafascicular neurons. Intrathecal (i.t.) administration of either norepinephrine (NE. 6 nmol, 10 microl) or serotonin (5-HT, 120 nmol, 10 microl) prior to the second phase significantly inhibited the second phase of the formalin-induced parafascicular nociceptive discharges. Intrathecal naloxone (Nal, 50 nmol, 10 microl) did not show any effect on the parafascicular nociceptive discharges. However, when i.t. Nal was given 5 min before NE, Nal prevented the NE antinociceptive effect. Pre-administration of Nal before 5-HT did not affect the antinociceptive effects of 5-HT on the second phase of nociceptive discharges. These results indicate that opiate-like substances are involved in the mediation of NE-induced antinociception. It is suggested that endogenous NE and 5-HT released from brainstem descending terminals at the spinal level carry out their antinociceptive actions differently.

Long-term potentiation in hippocampus of rats is enhanced by endogenous acetylcholine in a way that is independent of N-methyl-D-aspartate receptors.

By using extracellular recordings of field potential, the exact pathway by which the endogenous ACh influencing the induction of long-term potentiation (LTP) in CA1 area was analysed in slices of rat hippocampus. The results showed that: (1) the application of (-) huperzine A, an AChE inhibitor extracted from Chinese herb Qian Ceng Ta (Huperzia Serrata), could enhance the induction of LTP, while this drug showed little effect on the second components of multiple population spikes that were recorded in Mg(2+)-free medium and had proven to be N-methyl-D-aspartate (NMDA) receptor-mediated response; and (2) scopolamine, a muscarinic receptor antagonist, could significantly suppressed the induction of LTP, while most of the suppressive effect of scopolamine was blocked when slices were pretreated by bicuculline, a gamma-aminobutyric acid (GABA(A)) receptor antagonist. These results suggest that endogenous ACh potentiates the induction of LTP through the inhibition of GABAergic interneurons that modulate pyramidal neurons, but not through the activation of NMDA receptors located on pyramidal neurons.

Suppression of large conductance Ca2+-activated K+ channels by amyloid beta-protein fragment 31-35 in membrane patches excised from hippocampal neurons.

To clarify the shortest essential active sequence in amyloid beta-protein (AbetaP) responsible for affecting neuronal electrophysiological properties, the effects of fragments 31-35 and 25-35 of AbetaP on the large conductance Ca(2+)-activated potassium (BK) channels were investigated in the "inside-out" membrane patches excised from hippocampal neurons of rats. After application of AbetaP 3l-35 (5 micromol/L, n=10), the mean P(o) and open frequency of BK channels decreased by 85.8+/-l3.5 percent;percent; (P<0.01) and 72.1+/-22.8 percent; (P<0.01), respectively, and the mean open time decreased by 41.l+/-l8.5 percent; (P<0.0l), while the mean current amplitude was not significantly affected (P>0.05). Application of AbetaP 25-35 (5 micromol/L) also induced a decrease of 85.5+/-22.l percent; (P<0.0l) in mean P(o) and of 5l.4+/-18.3 percent; (P<0.05) in mean open time within l~3 min after application. These results suggest that the functional alteration in BK channels elicited by AbetaP fragments may play an important role in the mechanisms underlying AbetaP neurotoxicity, and AbetaP 31-35 may be the shortest active sequence in AbetaP responsible for affecting the electrophysiological properties of neurons.

Norepinephrine modulates single hypothalamic arcuate neurons via alpha(1)and beta adrenergic receptors.

The effects of norepinephrine (NE) on the electrophysiological activities of single hypothalamic arcuate neurons were studied using extracellular recording of 385 neurons from 169 brain slices in rats. The results showed that: (1) of 236 neurons selected randomly and tested with NE application, 137 (58.0%) were excited, 67 (28.4%) were inhibited, and 32 (13.6%) failed to respond; (2) substitution of low Ca(2+)-high Mg(2+) artificial cerebrospinal fluid (ACSF) for normal ACSF abolished the NE-induced inhibitory effect but failed to abolish the excitatory effect; (3) both the NE-induced excitatory and inhibitory effects were antagonized partly by phentolamine, prazosin, and propranolol but not by yohimbine; (4) naloxone and glibenclamide, a blocker of adenosine triphosphate-sensitive (K(ATP)) channels, blocked the NE-induced inhibitory effect; and (5) neurons that were inhibited by NE were also inhibited by morphine and cromakalim, an agonist of K(ATP) channels, and moreover, the morphine-induced inhibitory effect could be blocked by glibenclamide, while the cromakalim-induced inhibitory effect was not blocked by naloxone. These results imply that: (a) NE excites arcuate neurons through a mechanism that is insensitive to lowering the extracellular Ca(2+) suggesting a direct postsynaptic response through alpha(1)- and beta-adrenergic receptors, while NE inhibits cells through at least an inhibitory interneuron in arcuate and so is dependent on a Ca(2+)-sensitive presynaptic release mechanism; and (b) the inhibitory interneuron may be opioidergic, being excited first through alpha(1)- and beta-adrenergic receptors, after which the released opioids inhibit the neurons being recorded with an involvement of activation of K(ATP) channels. This possibility needs to be substantiated in much more detail.

Neurokinin A, calcitonin gene-related peptide, and dynorphin A (1-8) in spinal dorsal horn contribute to descending inhibition evoked by nociceptive afferent pathways: an immunocytochemical study.

Immunocytochemical technique was used to compare the contents of neurokinin A (NKA), calcitonin gene-related peptide (CGRP), and dynorphin A (1-8) (DynA) on two sides of the lumbar dorsal horn of rats in which the unilateral thoracic dorsalateral funiculus (DLF) was transected while formalin (0.2 ml, 0.5%) was injected equally into two hindpaws. The results showed that all the NKA-like, CGRP-like, and DynA (1-8)-like immunoreactivities were significantly lower in the superficial laminae of the dorsal horn on the side ipsilateral to the lesioned DLF than that on the side with intact DLF. This implies that peripheral noxious inputs activate the supraspinal descending inhibitory systems which in turn modulate the transmission of noxious message at the spinal level by changing the release of related neuropeptides.

Suppressive action produced by beta-amyloid peptide fragment 31-35 on long-term potentiation in rat hippocampus is N-methyl-D-aspartate receptor-independent: it's offset by (-)huperzine A.

Extracellular recordings of field potential from CA1 region of rat hippocampal slices were used to observe the effects of a shorter synthetic fragment of beta-amyloid peptide (A beta31-35) on the induction of long-term potentiation (LTP) and the action of (-)huperzine A, a potent acetylcholinesterase (AChE) inhibitor on these processes was also observed. The results showed that: (1) 0.1 microM A beta31-35 suppressed the induction of LTP in a similar mode as the longer fragment A beta25-35, did, while they did not change the amplitude of the baseline population spike (PS); (2) when PSs were recorded separately in Mg2+-free medium, which unveils the N-methyl-D-aspartate (NMDA)-mediated responses, both A beta31-35 and A beta25-35 showed little effect on the components of multiple PSs; (3) two concentrations of 0.1 microM or 1.0 microM (-)huperzine A showed no effects on the PS amplitude while the latter could enhance the LTP and (4) co-administration of (-)huperzine A with 0.1 microM concentration could block most of the suppressive action induced by A beta31-35 or A beta25-35 upon the LTP. The results suggest that the shorter fragment A beta31-35, is long enough to suppress the induction of LTP and these two fragments might suppress the induction of LTP through a NMDA receptor-independent pathway that involves cholinergic terminals in hippocampus.

Peripheral nitric oxide contributes to both formalin- and NMDA-induced activation of nociceptors: An immunocytochemical study in rats.

Nociceptive c-fos expressions in the dorsal horn following intraplantar injection of two kinds of algogenic agents combined with different doses of nitric oxide (NO) synthase inhibitor (N(omega)-nitro-L-arginine methyl ester (L-NAME)) or of NO donor (L-arginine) were used to explore if NO was involved in the activation of peripheral nociceptors. The results showed that: 1) combined injections of L-NAME with formalin into the plantar aspect of one hindpaw of normal rats elicited a dose-dependent suppression of c-fos expression as compared to that induced by formalin alone; 2) combined injections of L-arginine with formalin elicited considerable enhancement of c-fos expression when the dosages of L-arginine were less than 20 micromol, while it elicited marked suppression of c-fos expression when the dosages were in the range from 50 to 100 micromol; and 3) combined injection of L-NAME with NMDA, a selective agonist for NMDA receptors, into the hindpaw could also inhibit the NMDA-induced c-fos expression in the spinal dorsal horn. These results suggest that endogenously generated concentrations of nitric oxide may enhance the initiation of nociceptive inputs of peripheral nociceptors following local injection of formalin or NMDA.

Endogenous adenosine involved in the mediation of spinal antinociception produced by stimulating locus coeruleus.

The focus of this study was to investigate whether spinal adenosine is involved in mediating descending nociceptive modulation by the locus coeruleus (LC). Nociceptive evoked responses in parafascicular (PF) neurons were studied before and after electrical stimulation of the LC as well as before and after intrathecal (i.t.) administration of phentolamine (Ph) or aminophylline (Aph), an adenosine receptor antagonist, and 5'ethylcarboxamidoadenosine (NECA), an adenosine agonist. The main results were as follows: (1) the nociceptive evoked responses recorded in PF neurons were suppressed by LC stimulation; (2) pretreatment with i.t., Ph (40 nmol) reversed the LC effects, i.e., the suppressive effect of LC stimulation on the PF nociceptive evoked responses was reversed in the presence of Ph; (3) smaller doses of i.t. Aph (120 nmol) blocked only the suppressive effect produced by LC stimulation, while larger doses (240 nmol) reversed the LC stimulation, i.e., the LC stimulation exerted a facilatatory effect; and (4) i.t. application of NECA, an adenosine agonist, suppressed the nociceptive discharges in PF neurons. The results suggest that spinal adenosine may be involved in the mediation of the spinal antinociceptive effect produced by LC stimulation.

Beta-amyloid peptide fragment 31-35 induces apoptosis in cultured cortical neurons.

A synthetic fragment 31-35 of beta-amyloid peptide was used in cultured cortical neurons to examine whether this smaller sequence could trigger apoptotic degeneration in vitro by using morphological, biochemical and flow-cytometric examinations. The results showed that: (i) neurons treated with fragment 31-35 of beta-amyloid peptide exhibited membrane blebbing, compaction of nuclear chromatin, nuclear shrinkage and nuclear fragmentation; (ii) a typical DNA ladder was revealed by agarose gel electrophoresis following fragment 31-35 of beta-amyloid peptide exposure; (iii) the internucleosome DNA fragmentation was also detected by flow-cytometric examination following fragment 31-35 of beta-amyloid peptide exposure; and (iv) the DNA fragmentation induced by fragment 31-35 of beta-amyloid peptide in the above two examinations could be blocked by co-treatment with aurintricarboxylic acid or actinomycin D. It is suggested that fragment 31-35 of the beta-amyloid peptide may be a shorter sequence of beta-amyloid peptide responsible for triggering an apoptotic process in cultured neurons.

Interrelations of opioids with monoamines in descending inhibition of nociceptive transmission at the spinal level: an immunocytochemical study.

This study was designed to reexamine a previous proposal of whether the opioid-like substances (OLS) being acting mainly as an intrinsic spinal mediator in the descending inhibition of nociception of the bulbospinally projecting NE-ergic, and/or 5-HT-ergic terminals in the dorsal horn by using an immunocytochemical method. The effects of intrathecal (i.t.) phentolamine (Ph), cyproheptadine (Cyp), and naloxone (Nal), administered separately or coadministered by two of them, on the expression of Fos-like-immunoreactive (FLI) neurons were observed on both sides of the lumbar dorsal horn of rats, in which equal volumes of formalin were injected into two hindpaws and the ipsilateral dorsolateral funiculus (DLF) was transected at the thoracic level antecedently. The results showed: (1) when rats were pretreated with i.t. saline, the number of nociceptive FLI neurons was significantly lowered 44% (p<0.01) on the side of the lumbar dorsal horn with intact DLF compared to the opposite side with sectioned DLF; (2) when rats were separately pretreated with i.t. Ph, Cyp and Nal, the reduction of FLI neurons on the DLF-intact side were decreased by 27% (p<0.01), 21% (p<0.01), and 25% (p<0.01), respectively; (3) when rats were pretreated with combined i.t. Ph+Cyp, the reduction on the intact side was eliminated almost completely (4%); (4) when rats were pretreated with combined i.t. Ph+Nal, the reduction on the intact side was 21% (p<0.01); and (5) when rats were pretreated with i.t. Cyp+Nal, the reduction on the intact side was 9.1%. These results suggest that: (1) nearly all the suppressive action exerted by the DLF-descending fibers are produced by the release of either NE or 5-HT as neurotransmitters at the spinal level; (2) most of the opioid-like substances act as an intrinsic spinal mediator mainly for the descending NE-ergic, but in a lesser extent for the 5-HT-ergic terminals in the dorsal horn circuitry; and (3) some OLS-ergic interneurons may only be activated by local nociceptive input.

Involvement of endogenous opioids and ATP-sensitive potassium channels in the mediation of apomorphine-induced antinociception at the spinal level: a study using EMG planimetry of flexor reflex in rats.

The effects of intrathecally (i.t.) administered naloxone or glibenclamide, a blocker of adenosine triphosphate-sensitive potassium (KATP) channels, on the antinociception produced by i.t. apomorphine were observed by an integrated electromyogram measurement of hindlimb flexor reflex in lightly pentobarbital-anesthetized rats. The results showed that i.t. apomorphine produced a significant and dose-dependent antinociception and that the antinociception produced by i.t. apomorphine could be blocked dose dependently by i.t. naloxone or glibenclamide. The results suggest that endogenous opioids and ATP-sensitive potassium channels might be sequentially involved in the mediation of apomorphine-induced antinociception at the spinal level.

Decreased expression of N-methyl-D-aspartate (NMDA) receptors in rat dorsal root ganglion following complete Freund's adjuvant-induced inflammation: an immunocytochemical study for NMDA NR1 subunit.

The changes in expression of NMDA NR1, an essential functional subunit of N-methyl-D-aspartate (NMDA) receptors, were examined in the rat lumbar dorsal root ganglion (DRG) by immunocytochemical technique following injection of complete Freund's adjuvant (CFA) into the unilateral hindpaw. The results showed that there appeared a significant and several days-lasting down-regulation in expression of NMDA NR1 in the lumbar DRG following CFA injection, and especially, this change mainly appeared in the small and medium sized DRG neurons. It is suggested that a long-lasting flow of nociceptive inputs in nociceptors will elicit a decreased expression of NMDA receptors on primary afferent neurons and this plastic change would act as a factor leading towards the hyposensitization for nociception at the nociceptor level.

[A quantitative study on the synaptic ultrastructural alterations in visual cortex in the maintenance of LTP].

The ultrastructure of synapses three hours after formation of long-term potentiation (LTP) was examined in the local microslices of visual cortical brain slices of 18-20 d rats. Slices without potentiating stimulation which were similarly incubated served as controls. The following structural changes were examined using a graph analyzer: (1) synaptic cleft width; (2) thickness of the postsynaptic densities(PSD); (3) length of the active zones; and (4) curvature of the synaptic interface. The number of synapses of different types in layer II/III of visual cortex was quantified by double-blind scoring procedures. The various counts were converted to the number of synapses per unit volume using stereological quantitation method. Analysis of variance was used for statistical evaluation. Our results suggest that field potentials reached their peak values at about one and a half hours after tetanus and could be maintained as long as three hours without decay. In comparison with the control groups, synaptic cleft width, thickness of PSD, surface density per unit volume(Sv) of the active zones, curvature of the synaptic interface, numeric density per unit volume (Nv) of all synapses, spine synapses and the Nv of perforated synapses were all increased significantly. These data suggest that the increase of Sv of active zones and the increase of the curvature of synaptic interface may be the morphological feature characterizing the maintenance of LTP, in addition to the formation of perforated synapses.

Nociceptive c-fos expression in supraspinal areas in avoidance of descending suppression at the spinal relay station.

The number and distribution of Fos-like-immunoreactive neurons in different supraspinal brain areas induced by formalin injection into one hindpaw was estimated in rats with transected dorsal half of the spinal cord at the thoracic level in an attempt to avoid most of the descending modulatory actions. The results showed that: (i) after spinal lesion, the peripheral noxious inputs, going up mainly through the ventral spinal cord, elicited a more widespread and densely located Fos-like-immunoreactive neurons in subcortical areas, many of them showed no Fos expression when noxious stimulation was given in rats with intact spinal cord; (ii) at the same time, a small number of subcortical areas, such as the lateral ventroposterior thalamic nucleus and dorsal raphe nucleus, exhibited no significant increase of nociceptive Fos-like immunoreactive neurons after spinal lesion as compared to that with intact spinal cord; and (iii) there appeared a prominent expansion of cortical areas with densely located Fos-like-immunoreactive neurons in spinal-lesioned rats as compared with the limited labelled areas in the control group with intact spinal cord. These results indicate that: (i) in avoiding the spinally descending modulatory mechanisms, more widespread supraspinal and cortical neurons will be recruited and activated in response to the noxious stimulation; and (ii) the descending systems exert differential actions on the spinal targets which project nociceptive signals to different supraspinal regions. The implication of these facts is discussed.

Endogenous opioids and ATP-sensitive potassium channels are involved in the mediation of apomorphine-induced antinociception at the spinal level: a behavioral study in rats.

The effects of intrathecally (i.t.) administered glibenclamide, a blocker of adenosine triphosphate-sensitive potassium (K(ATP)) channels, or naloxone on the antinociception produced by i.t. apomorphine or morphine were observed and analyzed in rats by tail-flick (TF) test. The results showed that: (1) i.t. apomorphine produced a significant and dose-dependent antinociception, (2) the antinociception produced by i.t. apomorphine could be blocked dose-dependently by i.t. glibenclamide or naloxone, (3) the antinociception produced by i.t. morphine could also be blocked dose-dependently by i.t. glibenclamide. The results suggest that endogenous opioids and ATP-sensitive potassium channels might be involved in the mediation of apomorphine-induced antinociception at the spinal level.