Stimulation-Produced Analgesia From the Occipital or Retrosplenial Cortex of Rats Involves Serotonergic and Opioid Mechanisms in the Anterior Pretectal Nucleus

The electrical stimulation of the occipital (OC) or retrosplenial (RSC) cortex produces antinociception in the rat tail-flick test. These cortices send inputs to the anterior pretectal nucleus (APtN) which is implicated in antinociception and nociception. At least muscarinic cholinergic, opioid, and serotonergic mechanisms in the APtN are involved in stimulation-produced antinociception (SPA) from the nucleus. In this study, the injection of 2% lidocaine (.25 mu L) or methysergide (40 and 80 ng/.25 mu L) into the APtN reduced the duration but did not change the intensity of SPA from the OC, whereas both duration and intensity of SPA from the RSC were significantly reduced in rats treated with lidocaine or naloxone (10 and 50 ng/.25 mu L), injected into the ANN. Naloxone or methysegide injected into the APtN was ineffective against SPA from the OC or RSC, respectively. Atropine (100 ng/.25 mu L) injected into the ANN was ineffective against SPA from either the OC or RSC. We conclude that the APtN acts as an intermediary for separate descending pain inhibitory pathways activated from the OC and RSC, utilizing at least serotonin and endogenous opioid as mediators in the nucleus. Perspective: Stimulation-induced antinociception from the retrosplenial or occipital cortex in the rat tail-flick test depends on the activation of separate descending pain inhibitory pathways that utilize the APtN as a relay station. (C) 2011 by the American Pain Society

Hypoalgesia induced by elbow manipulation in lateral epicondylalgia does not exhibit tolerance

Previous studies have demonstrated that the initial hypoalgesic effect of spinal manipulative therapy was not antagonized by naloxone and did not exhibit tolerance with repeated applications. The implication is that endogenous opioid mechanisms of pain relief are probably not at play in spinal manipulative therapy. The role of endogenous opioid peptides in manipulation of the peripheral joints has not been investigated. The aim of this study was to evaluate whether the initial hypoalgesic effect of a peripheral manipulative technique (mobilization-with-movement treatment for the elbow) demonstrated a tolerance to repeated applications (ie, reduction in magnitude of effect over repeated applications). Twenty-four participants with unilateral chronic lateral epicondylalgia participated in the study. A repeated measures study was conducted to examine the effect of repeated applications of the mobilization-with-movement treatment for the elbow on 6 separate treatment occasions at least 2 days apart. Pain-free grip strength and pressure pain threshold were chosen as the pain-related outcome measures. Changes in the percent maximum possible effect scores of measures of hypoalgesia were evaluated across the 6 treatment sessions by using linear trend analysis. The results showed no significant difference for the hypoalgesic effect of the treatment technique between sessions (P >.05). This peripheral manipulative therapy treatment technique appeared to have a similar effect profile to previously studied spinal manipulative therapy techniques, thereby contributing to the body of knowledge that indicates that manipulative therapy most likely induces a predominant non-opioid form of analgesia.

Endogenous opioid peptide-mediated neurotransmission in central and pericentral nuclei of the inferior colliculus recruits mu(1)-opioid receptor to modulate post-ictal antinociception

Background: The aim of the present work was to investigate the involvement of the mu(1)-endogenous opioid peptide receptor-mediated system in post-ictal antinociception. Methods: Antinociceptive responses were determined by the tail-flick test after pre-treatment with the selective mu(1)-opioid receptor antagonist naloxonazine, peripherally or centrally administered at different doses. Results: Peripheral subchronic (24 h) pre-treatment with naloxonazine antagonised the antinociception elicited by tonic-clonic seizures. Acute (10 min) pre-treatment, however, did not have the same effect. In addition, microinjections of naloxonazine into the central, dorsal cortical and external cortical nuclei of the inferior colliculus antagonised tonic-clonic seizure-induced antinociception. Neither acute (10-min) peripheral pre-treatment with naloxonazine nor subchronic intramesencephalic blockade of mu(1)-opioid receptors resulted in consistent statistically significant differences in the severity of tonic-clonic seizures shown by Racine's index (1972), although the intracollicular specific antagonism of mu(1)-opioid receptor decreased the duration of seizures. Conclusion: mu(1)-Opioid receptors and the inferior colliculus have been implicated in several endogenous opioid peptide-mediated responses such as antinociception and convulsion. The present findings suggest the involvement of mu(1)-opiate receptors of central and pericentral nuclei of the inferior colliculus in the modulation of tonic-clonic seizures and in the organisation of post-ictal antinociception. (C) 2011 Elsevier Ltd. All rights reserved.

Hemodynamic responses to aortic depressor nerve stimulation in conscious L-NAME-induced hypertensive rats

Durand MT, Castania JA, Fazan R Jr, Salgado MC, Salgado HC. Hemodynamic responses to aortic depressor nerve stimulation in conscious L-NAME-induced hypertensive rats. Am J Physiol Regul Integr Comp Physiol 300: R418-R427, 2011. First published November 24, 2010; doi: 10.1152/ajpregu.00463.2010.-The present study investigated whether baroreflex control of autonomic function is impaired when there is a deficiency in NO production and the role of adrenergic and cholinergic mechanisms in mediating reflex responses. Electrical stimulation of the aortic depressor nerve in conscious normotensive and nitro-L-arginine methyl ester (L-NAME)-induced hypertensive rats was applied before and after administration of methylatropine, atenolol, and prazosin alone or in combination. The hypotensive response to progressive electrical stimulation (5 to 90 Hz) was greater in hypertensive (-27 +/- 2 to -64 +/- 3 mmHg) than in normotensive rats (-17 +/- 1 to -46 +/- 2 mmHg), whereas the bradycardic response was similar in both groups (-34 +/- 5 to -92 +/- 9 and -21 +/- 2 to -79 +/- 7 beats/min, respectively). Methylatropine and atenolol showed no effect in the hypotensive response in either group. Methylatropine blunted the bradycardic response in both groups, whereas atenolol attenuated only in hypertensive rats. Prazosin blunted the hypotensive response in both normotensive (43%) and hypertensive rats (53%) but did not affect the bradycardic response in either group. Prazosin plus angiotensin II, used to restore basal arterial pressure, provided hemodynamic responses similar to those of prazosin alone. The triple pharmacological blockade abolished the bradycardic response in both groups but displayed similar residual hypotensive response in hypertensive (-13 +/- 2 to -27 +/- 2 mmHg) and normotensive rats (-10 +/- 1 to -25 +/- 3 mmHg). In conclusion, electrical stimulation produced a well-preserved baroreflex-mediated decrease in arterial pressure and heart rate in conscious L-NAME-induced hypertensive rats. Moreover, withdrawal of the sympathetic drive played a role in the reflex bradycardia only in hypertensive rats. The residual fall in pressure after the triple pharmacological blockade suggests the involvement of a vasodilatory mechanism unrelated to NO or deactivation of alpha(1)-adrenergic receptor.

Sucrose ingestion causes opioid analgesia

The intake of saccharin solutions for relatively long periods of time causes analgesia in rats, as measured in the hot-plate test, an experimental procedure involving supraspinal components. In order to investigate the effects of sweet substance intake on pain modulation using a different model, male albino Wistar rats weighing 180-200 g received either tap water or sucrose solutions (250 g/l) for 1 day or 14 days as their only source of liquid. Each rat consumed an average of 15.6 g sucrose/day. Their tail withdrawal latencies in the tail-flick test (probably a spinal reflex) were measured immediately before and after this treatment. An analgesia index was calculated from the withdrawal latencies before and after treatment. The indexes (mean ± SEM, N = 12) for the groups receiving tap water for 1 day or 14 days, and sucrose solution for 1 day or 14 days were 0.09 ± 0.04, 0.10 ± 0.05, 0.15 ± 0.08 and 0.49 ± 0.07, respectively. One-way ANOVA indicated a significant difference (F(3,47) = 9.521, P<0.001) and the Tukey multiple comparison test (P<0.05) showed that the analgesia index of the 14-day sucrose-treated animals differed from all other groups. Naloxone-treated rats (N = 7) receiving sucrose exhibited an analgesia index of 0.20 ± 0.10 while rats receiving only sucrose (N = 7) had an index of 0.68 ± 0.11 (t = 0.254, 10 degrees of freedom, P<0.03). This result indicates that the analgesic effect of sucrose depends on the time during which the solution is consumed and extends the analgesic effects of sweet substance intake, such as saccharin, to a model other than the hot-plate test, with similar results. Endogenous opioids may be involved in the central regulation of the sweet substance-produced analgesia.

Antinociception induced by stimulating amygdaloid nuclei in rats: changes produced by systemically administered antagonists

The antinociceptive effects of stimulating the medial (ME) and central (CE) nuclei of the amygdala in rats were evaluated by the changes in the latency for the tail withdrawal reflex to noxious heating of the skin. A 30-s period of sine-wave stimulation of the ME or CE produced a significant and short increase in the duration of tail flick latency. A 15-s period of stimulation was ineffective. Repeated stimulation of these nuclei at 48-h intervals produced progressively smaller effects. The antinociception evoked from the ME was significantly reduced by the previous systemic administration of naloxone, methysergide, atropine, phenoxybenzamine, and propranolol, but not by mecamylamine, all given at the dose of 1.0 mg/kg. Previous systemic administration of naloxone, atropine, and propranolol, but not methysergide, phenoxybenzamine, or mecamylamine, was effective against the effects of stimulating the CE. We conclude that the antinociceptive effects of stimulating the ME involve at least opioid, serotonergic, adrenergic, and muscarinic cholinergic descending mechanisms. The effects of stimulating the CE involve at least opioid, ß-adrenergic, and muscarinic cholinergic descending mechanisms.

Time course of the hemodynamic responses to aortic depressor nerve stimulation in conscious spontaneously hypertensive rats

The time to reach the maximum response of arterial pressure, heart rate and vascular resistance (hindquarter and mesenteric) was measured in conscious male spontaneously hypertensive (SHR) and normotensive control rats (NCR; Wistar; 18-22 weeks) subjected to electrical stimulation of the aortic depressor nerve (ADN) under thiopental anesthesia. The parameters of stimulation were 1 mA intensity and 2 ms pulse length applied for 5 s, using frequencies of 10, 30, and 90 Hz. The time to reach the hemodynamic responses at different frequencies of ADN stimulation was similar for SHR (N = 15) and NCR (N = 14); hypotension = NCR (4194 ± 336 to 3695 ± 463 ms) vs SHR (3475 ± 354 to 4494 ± 300 ms); bradycardia = NCR (1618 ± 152 to 1358 ± 185 ms) vs SHR (1911 ± 323 to 1852 ± 431 ms), and the fall in hindquarter vascular resistance = NCR (6054 ± 486 to 6550 ± 847 ms) vs SHR (4849 ± 918 to 4926 ± 646 ms); mesenteric = NCR (5574 ± 790 to 5752 ± 539 ms) vs SHR (5638 ± 648 to 6777 ± 624 ms). In addition, ADN stimulation produced baroreflex responses characterized by a faster cardiac effect followed by a vascular effect, which together contributed to the decrease in arterial pressure. Therefore, the results indicate that there is no alteration in the conduction of the electrical impulse after the site of baroreceptor mechanical transduction in the baroreflex pathway (central and/or efferent) in conscious SHR compared to NCR.

mu(1)- and 5-HT1-dependent mechanisms in the anterior pretectal nucleus mediate the antinociceptive effects of retrosplenial cortex stimulation in rats

Aim: This study examines if injection of cobalt chloride (CoCl2) or antagonists of muscarinic cholinergic (atropine), mu(1)-opioid (naloxonazine) or 5-HT1 serotonergic (methiothepin) receptors into the dorsal or ventral portions of the anterior pretectal nucleus (APtN) alters the antinociceptive effects of stimulating the retrosplenial cortex (RSC) in rats. Main method: Changes in the nociceptive threshold were evaluated using the tail flick or incision pain tests in rats that were electrically stimulated at the RSC after the injection of saline, CoCl2 (1 mM, 0.10 mu L) or antagonists into the dorsal or ventral APtN. Key findings: The injection of CoCl2, naloxonazine (5 mu g/0.10 mu L) or methiothepin (3 mu g/0.10 mu L) into the dorsal APtN reduced the stimulation-produced antinociception from the RSC in the rat tail flick test. Reduction of incision pain was observed following stimulation of the RSC after the injection of the same substances into the ventral APtN. The injection of atropine (10 ng/0.10 mu L) or ketanserine (5 mu g/0.10 mu L) into the dorsal or ventral APtN was ineffective against the antinociception resulting from RSC stimulation. Significance: mu(1)-opioid- and 5-HT1-expressing neurons and cell processes in dorsal and ventral APtN are both implicated in the mediation of stimulation-produced antinociception from the RSC in the rat tail flick and incision pain tests, respectively. (c) 2012 Elsevier Inc. All rights reserved.

Time course of the hemodynamic responses to aortic depressor nerve stimulation in conscious spontaneously hypertensive rats

The time to reach the maximum response of arterial pressure, heart rate and vascular resistance (hindquarter and mesenteric) was measured in conscious male spontaneously hypertensive (SHR) and normotensive control rats (NCR; Wistar; 18-22 weeks) subjected to electrical stimulation of the aortic depressor nerve (ADN) under thiopental anesthesia. The parameters of stimulation were 1 mA intensity and 2 ms pulse length applied for 5 s, using frequencies of 10, 30, and 90 Hz. The time to reach the hemodynamic responses at different frequencies of ADN stimulation was similar for SHR (N = 15) and NCR (N = 14); hypotension = NCR (4194 +/- 336 to 3695 +/- 463 ms) vs SHR ( 3475 +/- 354 to 4494 +/- 300 ms); bradycardia = NCR (1618 +/- 152 to 1358 +/- 185 ms) vs SHR (1911 +/- 323 to 1852 +/- 431 ms), and the fall in hindquarter vascular resistance = NCR (6054 +/- 486 to 6550 +/- 847 ms) vs SHR (4849 +/- 918 to 4926 +/- 646 ms); mesenteric = NCR (5574 +/- 790 to 5752 +/- 539 ms) vs SHR (5638 +/- 648 to 6777 +/- 624 ms). In addition, ADN stimulation produced baroreflex responses characterized by a faster cardiac effect followed by a vascular effect, which together contributed to the decrease in arterial pressure. Therefore, the results indicate that there is no alteration in the conduction of the electrical impulse after the site of baroreceptor mechanical transduction in the baroreflex pathway (central and/or efferent) in conscious SHR compared to NCR.

The antinociceptive effect of electroacupuncture at different depths of acupoints and under the needling surface

Background The stimulation of acupoints along the meridians, but not the non-acupoints outside of the meridians, produces analgesia. Although the acupoint is defined at the body surface, the exact location of the acupoints is not known. This study aims to examine whether the intensity and duration of the analgesic effect of electroacupuncture (EA) at the Zusanli (ST36) and Sanynjiao acupoints (SP6) change according to the depth of the stimulation. Methods Ninety-six male Wistar rats classified as responders were arbitrarily allocated into 16 groups of six rats each. Six groups received EA with uninsulated acupuncture needles (type I) or needles that were immersed in varnish and had the varnish circularly peeled 0.2 mm from the tip (type II), 0.2 mm at 3 mm (type III) or 5 mm (type IV) from the tip, or 0.2 mm at 5 and 1 mm from the tip (type V), or EA sham for 20 min. Five groups received injection of formalin into the acupoint bilaterally at 5 mm or 1 mm deep into ST36, 5 mm below ST36 but inserting the needle at 45° to the skin surface, or 5 mm deep into non-acupoints. The remaining groups received intraplantar injection of saline, 1% or 2.5% formalin. The analgesic effects were measured by the rat tail-flick test. Results The bilateral stimulation of ST36 and SP6 by uninsulated or insulated needles produced analgesia in the rat tail-flick test. The stronger and longer lasting effects occurred after EA with the types I and V needles, or injection of formalin 5 mm deep into ST36. The remaining needles produced weaker and shorter lasting effects. Slow analgesic effect also occurred after formalin injection at 1 mm or 5 mm below ST36 by inserting the needle at 45° to the skin surface. Conclusion The experimental results suggest that the efficacy of the EA stimulation depends on the spatial distribution of the current density under the needling surface rather than only the acupoint or the depth of needling.

Induction of a physiological memory in the cerebral cortex by stimulation of the nucleus basalis.

Auditory cortical receptive field plasticity produced during behavioral learning may be considered to constitute "physiological memory" because it has major characteristics of behavioral memory: associativity, specificity, rapid acquisition, and long-term retention. To investigate basal forebrain mechanisms in receptive field plasticity, we paired a tone with stimulation of the nucleus basalis, the main subcortical source of cortical acetylcholine, in the adult guinea pig. Nucleus basalis stimulation produced electroencephalogram desynchronization that was blocked by systemic and cortical atropine. Paired tone/nucleus basalis stimulation, but not unpaired stimulation, induced receptive field plasticity similar to that produced by behavioral learning. Thus paired activation of the nucleus basalis is sufficient to induce receptive field plasticity, possibly via cholinergic actions in the cortex.

Effect of a tumour-produced lipid-mobilizing factor on protein synthesis and degradation

Treatment of murine myoblasts, myotubes and tumour cells with a tumour-produced lipid mobilizing factor (LMF), caused a concentration-dependent stimulation of protein synthesis, within a 24 h period. There was no effect on cell number or [3H] thymidine incorporation, but a similar concentration-dependent stimulation of 2-deoxyglucose uptake. LMF produced an increase in intracellular cyclic AMP levels, which was linearly (r2 = 0.973) related to the increase in protein synthesis. The effect of LMF was attenuated by the adenylate cyclase inhibitor MDL12330A, and was additive with the stimulation produced by forskolin. Both propranolol (10 μM) and the specific β3-adrenergic receptor antagonist SR 59230A (10-5M), significantly reduced the stimulation of protein synthesis induced by LMF. Protein synthesis was also increased by 69% (P = 0.006) in soleus muscles of mice administered LMF, while there was a 26% decrease in protein degradation (P = 0.03). While LMF had no effect on the lysosomal enzymes, cathepsins B and L, there was a decrease in proteasome activity, as determined both by the 'chymotrypsin-like' enzyme activity, as well as expression of proteasome α-type subunits, determined by Western blotting. These results show that in addition to its lipid-mobilizing activity LMF also increases protein accumulation in skeletal muscle both by an increase in protein synthesis and a decrease in protein catabolism. © 2001 Cancer Research Campaign.

GABA(A) receptor blockade in dorsomedial and ventromedial nuclei of the hypothalamus evokes panic-like elaborated defensive behaviour followed by innate fear-induced antinociception

Dysfunction in the hypothalamic GABAergic system has been implicated in panic syndrome in humans. Furthermore, several studies have implicated the hypothalamus in the elaboration of pain modulation. Panic-prone states are able to be experimentally induced in laboratory animals to study this phenomenon. The aim of the present work was to investigate the involvement of medial hypothalamic nuclei in the organization of panic-like behaviour and the innate fear-induced oscillations of nociceptive thresholds. The blockade of GABA(A) receptors in the neuronal substrates of the ventromedial. or dorsomedial hypothalamus was followed by elaborated defensive panic-like reactions. Moreover, innate fear-induced antinociception was consistently elicited after the escape behaviour. The escape responses organized by the dorsomedial and ventromedial hypothalamic nuclei were characteristically more elaborated, and a remarkable exploratory behaviour was recorded during GABA(A) receptor blockade in the medial hypothalamus. The motor characteristic of the elaborated defensive escape behaviour and the patterns of defensive alertness and defensive immobility induced by microinjection of the bicuculline either into the dorsomedial. or into the ventromedial hypothalamus were very similar. This was followed by the same pattern of innate fear-induced antinociceptive response that lasted approximately 40 min after the elaborated defensive escape reaction in both cases. These findings suggest that dysfunction of the GABA-mediated neuronal system in the medial hypothalamus causes panic-like responses in laboratory animals, and that the elaborated escape behaviour organized in both dorsomedial and ventromedial hypothalamic nuclei are followed by significant innate-fear-induced antinociception. Our findings indicate that the GABA(A) receptor of dorsomedial and ventromedial hypothalamic nuclei are critically involved in the modulation of panic-like behaviour. (C) 2009 Elsevier B.V. All rights reserved.

Ventilatory effects of neurophysiological facilitation and passive movement in patients with neurological injury

Thirteen intubated, high dependency patients with neurological injuries were studied in order to investigate the short term respiratory effects of neurophysiological facilitation and passive movement on tidal volume (V-T), minute ventilation (V-E), respiratory rate (V-R) and oxygen saturation (SpO(2)). The subjects were studied under four conditions: no intervention (control) and during periods of neurophysiological facilitation, passive movement and sensory stimulation. All periods were standardised to three minutes duration and all parameters were recorded before and after each intervention. Neurophysiological facilitation produced significant increases (p < 0.01) in V-E and SpO(2) (p < 0.05) when compared with control values, with an overall mean increase in V-E of 14.6%. Similarly, passive movement increased V-E (p < 0.01) by an average of 9.8% and also increased SpO(2) (p < 0.01). In contrast, sensory stimulation produced significant increases (p < 0.01) in SpO(2) with control levels, with no significant change in V-T or V-E. There was no significant difference in V-R with all treatments. This study provides preliminary evidence of improved short term ventilatory function following neurophysiological facilitation, independent of generalised sensory stimulation, which has not been previously examined in the literature, supporting its use in the management of high dependency neurological patients.

Oxidants positively or negatively regulate nuclear factor kappaB in a context-dependent manner.

Redox-based mechanisms play critical roles in the regulation of multiple cellular functions. NF-kappaB, a master regulator of inflammation, is an inducible transcription factor generally considered to be redox-sensitive, but the modes of interactions between oxidant stress and NF-kappaB are incompletely defined. Here, we show that oxidants can either amplify or suppress NF-kappaB activation in vitro by interfering both with positive and negative signals in the NF-kappaB pathway. NF-kappaB activation was evaluated in lung A549 epithelial cells stimulated with tumor necrosis factor alpha (TNFalpha), either alone or in combination with various oxidant species, including hydrogen peroxide or peroxynitrite. Exposure to oxidants after TNFalpha stimulation produced a robust and long lasting hyperactivation of NF-kappaB by preventing resynthesis of the NF-kappaB inhibitor IkappaB, thereby abrogating the major negative feedback loop of NF-kappaB. This effect was related to continuous activation of inhibitor of kappaB kinase (IKK), due to persistent IKK phosphorylation consecutive to oxidant-mediated inactivation of protein phosphatase 2A. In contrast, exposure to oxidants before TNFalpha stimulation impaired IKK phosphorylation and activation, leading to complete prevention of NF-kappaB activation. Comparable effects were obtained when interleukin-1beta was used instead of TNFalpha as the NF-kappaB activator. This study demonstrates that the influence of oxidants on NF-kappaB is entirely context-dependent, and that the final outcome (activation versus inhibition) depends on a balanced inhibition of protein phosphatase 2A and IKK by oxidant species. Our findings provide a new conceptual framework to understand the role of oxidant stress during inflammatory processes.