Changes in extracellular glutamate and pressor response during muscle contraction following AMPA-receptor blockade in the RVLM and CVLM

We examined whether modulation of cardiovascular responses by administering 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, an AMPA-receptor antagonist) into the rostral (RVLM) or caudal (CVLM) ventrolateral medulla are mediated via changes in extracellular levels of glutamate. Microdialysis probes were inserted bilaterally into the RVLM or the CVLM. For the RVLM experiments (n=8), muscle contraction for 2 min increased mean arterial pressure (MAP) and heart rate (HR) by 18+/-3 mmHg and 24+/-5 bpm, respectively. Extracellular glutamate concentrations increased from 1.5+/-0.3 to 4.3+/-0.9 ng/5 microl during the contraction. Microdialysis of CNQX (1.0 microM) for 30 min into the RVLM attenuated the increases in MAP, HR, and glutamate concentration in response to a muscle contraction (8+/-2 mmHg, 11+/-3 bpm, and 2.2+/-0.7 ng/5 microl, respectively). Developed tensions did not change during contractions before and after CNQX. Microdialysis of CNQX into the CVLM (n=8) potentiated the contraction-evoked responses in MAP (19+/-3 vs. 34+/-3 mmHg) and HR (25+/-4 vs. 49+/-5 bpm) without a change in developed tension. Following CNQX perfusion into the CVLM, the levels of extracellular glutamate in the CVLM were also augmented during the contraction. Results suggests that AMPA-receptors within the RVLM and CVLM differentially modulate cardiovascular responses during static muscle contraction via increasing and decreasing, respectively, extracellular glutamate concentrations.

[An analysis of the psychophysiological components in subjects with temporomandibular disorders. Myographic tension and the management of aggressiveness]

BACKGROUND

The stomatognathic literature doesn't sufficiently stress the role of aggressiveness as a modulator of muscular tensions. Our study focused on the hypothesis that 1) original psychological problems related to the modulation of aggressivity could produce 2) chronic muscular tension of the oral district 3) they can become the basis of the malocclusive phenomenon. The investigation was conducted in the laboratory of Clinical Psychophysiology of the University of Rome "La Sapienza".

METHODS

We have examined the myographic activity of the temporal and masseter muscles of both sides in 20 women with temporomandibular dysfunction and in the control group comparable by age. The myographic tension was examined in three "stimulus situations": a) closed lips without any teeth contact; b) with light teeth contact; c) with compression of the dental arcade. Moreover, we have examined the style of aggressiveness modulation through Rosenzweig's PFS test. Features of the experimental group were. 1) age between 20 and 30 yrs; 2) presence of condylomeniscal uncoordination; 3) deviation of the median line of incisors; 4) lateral deviation in the opening and/or closing mandible.

RESULTS

The experimental group showed a higher score of myographic amplitude for the above-mentioned muscles of both sides in three "stimulus situations". Moreover, it presented at the Rosenzweig's test more elevated scores for the Dominance of Obstacle (O-D); b) less elevated scores for Ego Defence (E-D).

CONCLUSIONS

Results are commented on the basis of an integrated psychophysiological model.

Measurement of upper esophageal sphincter tone and relaxation during swallowing in premature infants

Upper esophageal sphincter (UES) motor function has not been previously evaluated in premature infants. The motor patterns associated with tonic activity and swallow-related relaxation of the UES were recorded for 1 h after completion of gavage feeding in 11 healthy preterm neonates (postmenstrual age 33-37 wk) with a micromanometric assembly, which included a sleeve sensor specifically adapted for UES recordings. A clearly defined UES high-pressure zone was observed in all premature infants studied. Resting UES pressure ranged from 2.3 to 26.2 mmHg and was higher during periods of irritability and apparent discomfort. During dry swallows, UES pressure relaxed from a resting pressure of 28.2 +/- 4.0 mmHg to a nadir of 1.1 +/- 3.3 mmHg. The mean UES relaxation interval (the time from relaxation onset to relaxation offset) was 0. 31 +/- 0.11 s. We conclude that in premature infants >/=33 wk postmenstrual age the motor mechanisms regulating UES resting pressure and the onset of UES relaxation are well developed.

[Respiratory muscle force and resistance in patients with SAHS. The effect of using nighttime CPAP]

During nighttime episodes of obstructive apnea in patients with sleep apnea-hypopnea syndrome (SAHS), repeated and progressive inspiratory efforts are made. Such intense nighttime activity can have a deleterious effect on daytime function of respiratory muscles.

OBJECTIVE

The objective of this study was to evaluate daytime respiratory muscle function in a group of SAHS patients before and after two months of treatment with nighttime continuous positive airway pressure (CPAP).

METHODS

We enrolled 12 patients with SAHS and 10 normal subjects (control group). To evaluate respiratory muscle strength we measured maximum esophageal pressure (Pesmax), transdiaphragmatic pressure (Pdimax) and inspiratory pressure in the mouth (PM). Respiratory muscle resistance was assessed using peak pressure in the mouth (PMPeak), time of tolerance (Tlim) and maximum inspiratory pressure-time index (PTimax). We also analyzed the nighttime function of respiratory muscles during apneic episodes in 10 of the 12 SAHS patients. We propose and define an index of nighttime respiratory muscle activity (RMian) as the product of the tension-time index for the diaphragm observed at the end of nighttime apneic episodes (TTdiapnea) and the apnea-hypopnea index (AHI).

RESULTS

Respiratory muscle strength was similar in the two groups and no changes were observed in SAHS patients after treatment with nighttime CPAP. However, tolerance was lower in SAHS patients (PMpeak--30%, Tlim--31% and PTimax--49%). Two months of nighttime CPAP normalized all three variables in these patients. MRian was related to percent improvement in PMpeak after treatment with nighttime CPAP in SAHS patients (r = 0.66, p < 0.04).

CONCLUSION

SAHS has an adverse effect on the daytime endurance of respiratory muscles that is proportional to the increase of nighttime mechanical muscle activity. The application of nighttime CPAP is restorative, probably because it allows respiratory muscles to rest.

A proposed psychosomatic etiologic model for rheumatoid arthritis

This model attributes rheumatoid arthritis to reduction or loss of muscle tone. It is hypothesized that tone is maintained via a neurological feedback loop consisting of a spontaneous (fusimotor) signal from the central nervous system (CNS), a return signal from the sensors and a toning signal from the CNS to the muscles. Frequency of return and toning signals are thought to be identical. Arthritis patients believed to react to psychological stress with increased fusimotor frequency (i.e. muscle tension) which over-stretches the sensing tissue. Because of this damage, the lower fusimotor frequency following the stress episode cannot elicit an adequate frequency response from the sensors and this leads to a matching decline in toning pulse frequency and hence muscle tone. Reduced vascular/cardiac tone lowers blood pressure triggering a compensatory hypervolemia. The resulting hypoxia increases vascular leakage causing tissue/lymph edema and pleural/pericardial/joint effusions. Regular ingestion of ephedrine is thought to increase fusimotor frequency and this reactivates the sensors re-establishing muscle tone.

Leptin-induced increase in sympathetic nervous and cardiovascular tone is mediated by proopiomelanocortin (POMC) products

The mechanism underlying the leptin-induced increased sympathetic nerve activity and cardiovascular tone was investigated in normal rats. The melanocortin (MC) peptides and other fragments derived from proopiomelancortin (POMC) have a diverse array of biological activities and have been implicated in mediating the feeding behavioral responses to leptin. In this study we evaluated the possible involvement of two major products of POMC, alpha-melanocyte stimulating hormone (alpha-MSH) and beta-endorphin, in mediating the effects of leptin on sympathetic activity and mean arterial pressure (MAP) in normal rats. Intraventricular (i.c.v.) cannulas were implanted in normal rats and allowed to recover. On the day of the study the animals were anesthetized with urethane alpha-chloralose and instrumented for the recording of MAP, lumbar sympathetic nerve activity (LSNA), and heart rate (HR). To determine the correlation between the leptin response and the POMC products, alpha-MSH and beta-endorphins were also injected into the lateral ventricle. alpha-MSH acted to increase MAP and LSNA while beta-endorphin decreased these parameters. Leptin administration by i.c.v. cannula increased the MAP and LSNA in normal rats. The i.c.v. administration of agouti protein, an alpha-MSH receptor antagonist, prior to leptin infusion blocked this response. Likewise, pretreatment with naloxone a beta-endorphin receptor antagonist also blocked the response to leptin. From these studies we conclude that the acute increased LSNA and MAP in response to i.c.v. leptin may be mediated by increased POMC and its subsequent production of breakdown product alpha-MSH and/or beta-endorphin and it is the subsequent action of alpha-MSH that increases MAP and LSNA by activation of the MC4 receptor. The naloxone antagonism of the leptin response is likely due to the blockade of presynaptic opioid inhibition of the MC4 receptor-mediated pressor response.

Surface height effects on postural control: a hypothesis for a stiffness strategy for stance

One possible factor influencing the control of upright stance is the perceived threat to one's personal safety, i.e. balance confidence. We explored this factor by examining the control of stationary stance when standing on an elevated platform under various conditions of reduced visual and vestibular inputs. Twenty-eight adults (14 male and 14 female, mean age = 23.5 years) participated in the experiment. Postural control was examined by recording the amplitude variability (RMS) and mean power frequency (MPF) of center of pressure excursions (COP) over a 2-minute interval while participants stood in a normal stance on a low (0.19 m) and a high (0.81 m) platform with toes positioned either at or away from the edge of the platform. Vision was manipulated through eyes open and eyes closed trials. Vestibular input was reduced by tilting the head into extension [1]. Anterior-posterior RMS and MPF of COP were significantly influenced by an interaction between surface height and vision. When vision was available, a significant decrease in RMS was observed during quiet standing on a high surface compared to a low surface independent of step restriction. When vision was available MPF increased when subjects were raised from a low to a high surface. The mean position of the COP was significantly influenced by an interaction between height and step restriction. Differences in RMS and MPF responses to height manipulation were observed between genders in eyes closed conditions. Vestibular input influenced postural control at both low and high levels with significant increases in RMS when vestibular input was reduced. The reciprocal changes observed in RMS and MPF suggest modifications to postural control through changes in ankle stiffness. Vision appears to play a role in increasing ankle stiffness when balance confidence is compromised.

Group I secreted PLA2 and arachidonic acid metabolites in the maintenance of cat LES tone

Spontaneous tone of in vitro lower esophageal sphincter (LES) circular muscle is associated with elevated levels of arachidonic acid (AA), PGF(2alpha), and increased [35S]guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) binding to Gq-, Gi3-, and G(i1/i2)-like G proteins. Tone and AA levels were reduced by inhibitors of a pancreatic-like (group I) secreted phospholipase A2 (sPLA2), by the cyclooxygenase inhibitor indomethacin, and by the thromboxane A2 antagonist SQ-29548. In addition, pertussis toxin (PTX) reduced LES tone, confirming a role of PTX-sensitive G proteins in maintenance of LES tone. PGF(2alpha) contracted LES smooth muscle (strips and cells) and increased [35S]GTPgammaS binding to Gq and Gi3 in solubilized LES circular muscle membranes. PGF(2alpha)-induced contraction of LES permeable muscle cells was inhibited by Gq and Gi3 but not by G(i1/i2) and Go antibodies. The thromboxane A2 analog U-46619 contracted LES smooth muscle and increased Gq binding. U-46619-induced contraction was inhibited by Gq but not by Gi3, G(i1/i2), and Go antibodies. LES tone and [(35)S]GTPgammaS binding were significantly reduced by indomethacin. We conclude that group I sPLA2 may mediate "spontaneous" LES tone by producing AA, which is metabolized to PGF(2alpha) and thromboxane A2. These AA metabolites activate receptors linked to Gi3 and Gq to maintain LES contraction.

Reliability of the Tone Assessment Scale and the modified Ashworth scale as clinical tools for assessing poststroke spasticity

OBJECTIVES

To establish reliability of the Tone Assessment Scale and modified Ashworth scale in acute stroke patients.

SETTING

A North Liverpool university hospital.

PATIENTS

Eighteen men and 14 women admitted with acute stroke and still in hospital at the study start date (median age, 74 yrs; median Barthel score, 8).

MAIN OUTCOME MEASURES

The modified Ashworth scale and the Tone Assessment Scale.

STUDY DESIGN

The 32 patients were examined with both scales on the same occasion by two raters (interrater comparison) and on two occasions by one rater (intrarater comparison).

RESULTS

The reliability of the modified Ashworth scale was very good (kappa = .84 for interrater and .83 for intrarater comparisons). The reliability of the Tone Assessment Scale was not as strong as the modified Ashworth scale, with marked variability in the assessment of posture (kappa = .22 to .50 for interrater and .29 to .55 for intrarater comparisons) and associated reaction (kappa/kappaW = -.05 to .79 for interrater and .19 to .83 for intrarater comparisons). However, those aspects of the Tone Assessment Scale that addressed response to passive movement and that are scored similarly to the modified Ashworth scale showed good to very good interrater reliability (kappaW = .79 to .92) and good to very good intrarater reliability (kappaW = .72 to .86), except for the question related to movement at the ankle where agreement was only moderate (kappaW = .59).

CONCLUSIONS

The modified Ashworth scale is reliable. The section of the Tone Assessment Scale relating to response to passive movement is reliable at various joints, except the ankle. It may assist in studies on the prevalence of spasticity after stroke and the relationship between tone and function. Further development of a measure of spasticity at the ankle is required. The Tone Assessment Scale is not reliable for measuring posture and associated reactions.

[Mechanogenic regulation of the tonus and reactivity of blood vessels]

In acute experiments on cats and rats, as well as on isolated segments of the rat mesenteric and tail arteries, the parameters of myogenic and endothelium-dependent regulation of the blood vessels were studied. An important role of mechanical stimulation of the endothelium in development of vasodilatation in the skeletal muscles along with the increase of the pressure pulse amplitude, was revealed. A diminution of endothelium-dependent vasodilatation was shown in spontaneously hypertensive rats in an increase of the pulse pressure.

Inducible expression of the kinin B1 receptor in the endotoxemic heart: mechanisms of des-Arg9bradykinin-induced coronary vasodilation

1 We have investigated the role of kinin B1 receptor induction in the endotoxemic rat heart and elucidated the mechanisms underlying B1 receptor-mediated coronary vasodilation. We also investigated the role of these receptors in endotoxin-induced hypotension. 2 Endotoxin treatment induced cardiac B1 receptor mRNA expression and promoted a coronary vasodilation response to des-Arg9bradykinin (DABK; ED50 = 149.4 pmol, n = 9) ex vivo peaking at 6 h. The B1 receptor antagonist des-Arg9-[Leu8]-BK (DALBK, 30 nM) significantly (P<0.05) inhibited the DABK-induced response (pA2 = 8.4, n = 5) whilst HOE140 (B2 receptor antagonist, 10 nM) was inactive (n = 4). 3 Removal of the endothelium or infusion with indomethacin (5 microM), but not L-NAME (300 microM) or ODQ (1 microM), inhibited (>85%, P<0.05, n = 5) the DABK-induced response. DABK caused a dose-dependent release of the prostacyclin metabolite, 6-keto-PGF1a (Emax = 0.3 ng ml-1, n = 6). 4 In vitro perfusion of hearts with endotoxin (1 microg ml-1, n = 6) or interleukin-1beta (5 ng ml-1, n = 6) induced B1 receptor mRNA expression and promoted a time-dependent vasodilation response to DABK. 5 Endotoxin treatment (6 h) in vivo promoted a hypotensive response to DABK (ED50 = 29.7 nmol kg-1, n = 10) which was antagonised by DALBK (3-6 nmol kg-1 min-1, P<0.05, n = 7). DALBK (3 nmol kg-1 min-1) and des-Arg10HOE140 (B1 receptor antagonist, 30 nmol kg-1 min-1) produced a 5.3% (n = 6, P<0.05) and 8.8% (n = 5, P<0.05) reversal, respectively, of endotoxin-induced hypotension. 6 In summary, we have shown that in endotoxemia activation of B1 receptors causes coronary vasodilation via endothelial prostacyclin release. Additionally, B1 receptor antagonists partially reversed endotoxin-induced hypotension. Therefore activation of B1 receptors may have a role to play in the vascular changes associated with endotoxemia.

Heterogeneity of endothelium-dependent vasodilation in pressurized cerebral and small mesenteric resistance arteries of the rat

We compared endothelial responses to calcium-mobilizing agents in mesenteric and cerebral resistance arteries of the rat. Middle cerebral and small mesenteric arteries were mounted in a pressure myograph, and myogenic responses were recorded. The effects of acetylcholine (ACh), bradykinin, substance P, histamine, A23187, cyclopiazonic acid (CPA), and sodium nitroprusside were investigated in both arteries with myogenic tone in the absence and presence of nitric oxide synthase and cyclooxygenase inhibitors. The effects of raised potassium, K(+) channel blockers, and arachidonic metabolism inhibition were examined on the nitric oxide (NO) synthase/cyclooxygenase inhibitor-resistant dilation induced by ACh and CPA. Cerebral arteries display a high level of myogenic reactivity compared with mesenteric arteries. In cerebral arteries, only bradykinin and substance P induced endothelium-dependent dilation. The observed dilation was solely related to the activation of the NO pathway. However, in mesenteric arteries, all of the vasoactive agents induced endothelium-dependent dilation. A combination of NO, cyclooxygenase-derived prostanoids, and a factor with endothelium-derived hyperpolarizing factor-like properties was responsible for the observed vasodilation. NO and cyclooxygenase derivatives were able to compensate for each other in the CPA-induced endothelium-dependent vasodilation when one of the two pathways was blocked. Moreover, small Ca(2+)-activated K(+) channels and a combination of both large and small Ca(2+)-activated K(+) channels were implicated in the endothelium-derived hyperpolarizing factor-like component of dilation to ACh and CPA, respectively. Finally, the results suggest that the pathway by which agonists raise intracellular calcium concentration may determine the nature of the endothelial secretory product.

Local and cellular Ca2+ transients in smooth muscle of pressurized rat resistance arteries during myogenic and agonist stimulation

1. Confocal laser scanning microscopy was used to visualize Ca2+ transients in the vascular smooth muscle cells (VSMC) of intact, pressurized rat mesenteric resistance arteries loaded with fluorescent calcium indicators. Vasoconstriction was assessed by measuring inner arterial diameter. All arteries were studied at 70 mmHg intralumenal pressure and 37 C. 2. In the control condition of myogenic tone the arteries were constricted to 62 % (n = 10) of their passive diameter (p.d.). The [Ca2+]i in most VSMC of these arteries was constant over time. In a small percentage (< 10 %) of cells in each artery, [Ca2+]i oscillated regularly. Local calcium transients (Ca2+ sparks) were observed in five arteries studied with confocal linescan imaging. 3. Activation of alpha-adrenoceptors by phenylephrine (PE, 1.0 microM) induced further vasoconstriction of pressurized arteries (to 27 % of p.d.). In this condition, [Ca2+]i oscillations were prominent in a large percentage (83 %) of the VSMC. The Ca2+ oscillations ranged in frequency from 4 to 22 min-1, and were usually asynchronous between cells. 4. High [KCl]o (65 mM) induced nearly comparable vasoconstriction to PE (37 % of p.d.) but [Ca2+]i oscillated in only about 13 % of cells in each artery. 5. Block of L-type Ca2+ channels (with nifedipine) in arteries activated by PE caused nearly full vasodilatation, but did not abolish the Ca2+ oscillations. Subsequent block of the sarcoplasmic reticulum Ca2+ pump (with cyclopiazonic acid) abolished Ca2+ oscillations in all cells. 6. We conclude that Ca2+ entering VSMC via L-type Ca2+ channels has an obligatory role in force development, both in myogenic tone and during alpha1-adrenoceptor activation. The oscillatory pattern of [Ca2+]i that persists in the absence of Ca2+ entry via L-type Ca2+ channels is ineffective in activating contraction.

Control of vascular tone in isolated mesenteric arterial segments from hypertensive patients

1. Experimental hypertension is associated with several functional alterations of vascular endothelium and smooth muscle, but relatively few studies have examined the control of arterial tone in isolated vascular preparations from patients with essential hypertension. Therefore, we compared functional characteristics in vitro of distal ring segments of the mesenteric artery from 17 hypertensive and 22 normotensive humans. 2. Arterial constrictor responses induced by cumulative addition of Ca(2+) in the presence of noradrenaline (NA) were more effectively inhibited by the Ca(2+) entry blocker nifedipine (0.5 nM) in hypertensive than normotensive subjects (by 55.4+/-4.9, n=17 and 35.0+/(-5.2%), n=22, respectively). Also the contractions elicited by high concentrations of KCl were more effectively inhibited by nifedipine in arterial rings from hypertensive than normotensive patients (by 38.9+/(-3.7), n=17 and 20. 2+/(-4.6%), n=22, respectively). However, the concentration-response curves of contractions to NA, serotonin and KCl in the absence of nifedipine were similar between the study groups. 3. The concentration-response curves of endothelium-dependent relaxations to acetylcholine and Ca(2+) ionophore A23187, as well as of endothelium-independent relaxations to the nitric oxide donor nitroprusside, beta-adrenoceptor agonist isoprenaline and K+ channel opener cromakalim did not show any differences between the groups. Moreover, the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (0.1 mM) almost abolished the relaxations to acetylcholine and Ca(2+) ionophore in both groups, indicating that these responses were largely mediated by nitric oxide. The function of arterial sodium pump was evaluated by relaxations elicited by the return of K+ upon contractions induced by K+-free solution. The rate of K+-relaxation was similar in hypertensive and normotensive arteries (for all these responses n=20 - 22 in the normotensive and 15 - 17 in the hypertensive group). 4. These results suggest abnormal function of voltage-dependent Ca(2+) channels in arterial smooth muscle of hypertensive patients, whereas vascular responses to endothelium-dependent and -independent vasodilators and classical contractile agents were similar between hypertensive and normotensive subjects. The present findings support the view that blockade of voltage-dependent Ca(2+) channels is an effective means of reducing arterial tone in essential hypertension.

Bronchodilation by pituitary adenylate cyclase-activating peptide and related peptides

Pituitary adenylate cyclase-activating peptide (PACAP) is present in nerves in the vicinity of bronchial and vascular smooth muscle in the airways. At least one endogenous form of PACAP, PACAP 1-27, has high affinity binding sites in the lung, probably including cholinergic nerve terminals, bronchial smooth muscle, epithelial and mononuclear inflammatory cells. The mechanism of action for PACAP 1-27 and 1-38 in vivo involves endogenous catecholamines, peptidases and nitric oxide, depending on tissue type. Intracellularly, cyclic adenosine monophosphate (cAMP) as well as calcium and sodium mobilization is probably involved. PACAP 1-27 and 1-38 inhibit airway smooth muscle tone in vitro and in vivo. The inhibitory effect of PACAP 1-38 is more sustained than that of PACAP 1-27, in vitro as well as in vivo. PACAP 1-38 also causes more sustained inhibition of bronchoconstriction after inhalation in vivo, than does vasoactive intestinal peptide (VIP). PACAP 1-27 given intravenously virtually abolishes allergen-induced bronchoconstriction in vivo. Novel synthetic analogues of PACAP 1-27 cause more sustained inhibition of airway smooth muscle tone in vitro and in vivo than do PACAP 1-27 or 1-38. Both PACAP 1-27 and 1-38 inhibit arterial smooth muscle tone but, administration of PACAP 1-27, 1-38 or a structural analogue of PACAP 1-27 in the airways, induces no cardiovascular side effects at doses inhibiting bronchoconstriction. PACAP 1-38 enhances phagocytosis in macrophages and inhibits the release of the pro-inflammatory cytokine interleukin-2 in lymphocytes, suggesting antiinflammatory effects. It is concluded that pituitary adenylate cyclase-activating peptide 1-27 and 1-38, or structurally related molecules, may be useful as bronchodilators but their effect on human bronchial smooth muscle and on human inflammatory cells is in need of evaluation.

Estrous variations in behavioral responses to vaginal and uterine distention in the rat

Response properties of peripheral afferent fibers supplying the vagina and uterus of the rat vary with estrous stage (Robbins A, Berkley KJ, Sato Y. Estrous cycle variation of afferent fibers supplying reproductive organs in the female rat. Brain Res 1992,596:353-356), suggesting that behavioral sensitivity to vaginal and uterine stimulation might similarly vary. To test this hypothesis, detection and escape responses of 12 rats to different volumes of distention of the vaginal canal or uterine horn (six rats each) were compared during each of the four estrous stages, proestrus (P), estrus (E), metestrus (M), and diestrus (D), using previously-published behavioral techniques (Berkley KJ, Wood E, Scofield SL, Little M. Behavioral responses to uterine or vaginal distention in the rat. Pain 1995;61:121-131). Estrous variations in vaginal or uterine tone (pressure-volume functions) were also measured in the same rats. Vaginal canal: escape response percentages increased significantly as vaginal distention volume increased, but neither escape nor detection responses varied with estrous stage. Vaginal tone, however, was greater in P and E than in M and D, with the greatest tone in E and the least in D. When escape responses to different pressures were analyzed, it was found that escape response percentages to the same vaginal pressure were lower during P and E than during M and D. One outcome of these estrous influences would be that a vaginal stimulus of a given volume (such as an erect penis) would exert higher pressures during P and E (i.e. the penis would be held within the vaginal canal more firmly) than during M and D, but would be less likely during P and E to provoke escape responses. This modification of nociceptive sensitivity has obvious reproductive advantages, because P and E constitute the rat's fertile period. Uterine horn: escape response percentages increased significantly as uterine distention volume increased only during M and D, with no differences between them. Detection responses also occurred only during M and D. Similarly, uterine tone was significantly greater in M and D than in P and E, with the greatest tone occurring during M and the least during P. Although these changes in uterine tone were opposite to those of the vaginal canal, escape response percentages to the same uterine pressures were, in a manner similar to vaginal pressures, lower during P and E than during M and D. The functional significance of these variations for the uterus is unclear, but does suggest that, under pathophysiological conditions, stimulation of the uterine horn, as well as the vaginal canal, would be more likely to provoke escape behaviors in M and D than in P and E. A similar increased sensitivity in rats during M and D to noxious stimulation of other pelvic organs has been observed by others. This situation resembles that in women, for whom many visceral pain conditions are exacerbated during a comparable part of their ovarian cycle, i.e. perimenstrually.

The effect of muscle-tone-reducing procedures in athetotic head movements: partial nerve block by lidocaine and surgical release of the neck muscles

OBJECTIVE

To investigate the effect of muscle-tone-reducing procedures (MTRPs), i.e. partial nerve block by lidocaine (PNB) and surgical release of muscle attachment to bone (SRMAB), on incessant involuntary head movements in athetotic patients.

METHODS

Pre/post-MTRP changes in neck-muscle activities, glabella movement and maximum isometric forces of the head were measured in six athetotic patients with severe spondylotic myelopathy resulting from incessant involuntary head movements.

RESULTS

Pre/post-MTRP changes in neck-muscle activities resembled those after gamma-block. In four patients, PNB reduced the maximum isometric force by no more than 40% of pre-PNB force, while decreasing the amount of involuntary head movements to 37-65% of the pre-PNB value in the frontal plane. MRSAB reduced the force by less than 40% of pre-SRMAB force in 4 MRSAB tested patients, while decreasing the amount of involuntary head movements to 12-45% of the pre-SRMAB value in all 6 patients.

CONCLUSION

MTRPs reduced involuntary head movements significantly while preserving voluntary muscle forces relatively well. PNB and SRMAB procedures have in common the effect of reducing gain in the myotatic reflex pathway by decreasing the excitatory inflows to alpha-motoneurons via muscle spindle Ia-afferents, which resulted from blocking mainly gamma-efferent conduction by PNB, and reducing background tension in muscle spindles by SRMAB.

Alteration of microtubule polymerization modulates arteriolar vasomotor tone

Microtubules are important cytoskeletal elements that have been shown to play a major role in many cellular processes because of their mechanical properties and/or their participation in various cell signaling pathways. We tested the hypothesis that depolymerization of microtubules would alter vascular smooth muscle (VSM) tone and hence contractile function. In our studies, isolated cremaster arterioles exhibited significant vasoconstriction that developed over a 20- to 40-min period when they were treated with microtubule depolymerizing drugs colchicine (10 microM), nocodazole (10 microM), or demecolcine (10 microM). Immunofluorescent labeling of microtubules in cultured rat VSM revealed that both colchicine and nocodazole caused microtubule depolymerization over a similar time course. The vasoconstriction was maintained over a wide range of intraluminal pressures (30-170 cmH(2)O). The increased tone was not affected by endothelial denudation, suggesting that it was due to an effect on VSM. Microtubule depolymerization with demecolcine or colchicine had no effect on VSM intracellular Ca(2+) concentration ([Ca(2+)](i)). These data indicate that microtubules significantly interact with processes leading to the expression of vasomotor tone. The mechanism responsible for the effect of microtubules on vasomotor tone appears to be independent of both the endothelium and an increase in VSM [Ca(2+)](i).

Role of K+ channels and sodium pump in the vasodilation induced by acetylcholine, nitric oxide, and cyclic GMP in the rabbit aorta

The endothelium-dependent relaxation caused by acetylcholine (ACh) in rabbit aorta segments was reduced by the nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine methyl ester and by blockade of: Na+ pump with ouabain, large-conductance Ca2+-activated K+ (BK(Ca)) channels with charybdotoxin (ChTx), or voltage-dependent K+ (Kv) channels with 4-aminopyridine (4-AP). ACh relaxation was unaltered by glibenclamide, apamin, and Ba2+, blockers of ATP-sensitive K+ channels, small-conductance Ca2+-activated K+ channels, and inward rectifier K+ channels, respectively. The relaxation induced by exogenous NO and 8-bromocyclic GMP (8-BrcGMP) was similar in intact and endothelium-denuded segments, and it was reduced or unaltered by the same drugs used in the case of ACh. However, a 4-AP concentration 20-fold higher was necessary to reduce exogenous NO relaxation. These data suggest a resemblance in the mechanisms implicated in the relaxation elicited by ACh, exogenous NO, and 8-BrcGMP. Therefore, the relaxation caused by ACh is mainly mediated by endothelial NO, which in turn, enhances cGMP levels; this messenger appears to be the major one responsible for the smooth muscle cell hyperpolarization in the relaxation elicited by ACh, which is mediated by activation of the Na+ pump and ChTx- and 4-AP-sensitive K+ channels, likely BK(Ca) and Kv channels.

Effect of ceramide on KCa channel activity and vascular tone in coronary arteries

A sphingomyelin metabolite, ceramide, serves as a second messenger in a variety of mammalian cells. Little is known regarding the production and actions of this novel intracellular signaling lipid molecule in the vasculature. The present study was designed to test the hypothesis that a ceramide-mediated signaling pathway is present in coronary arterial smooth muscle and that ceramide serves as an inhibitor of the large-conductance Ca2+-activated potassium (KCa) channels and mediates vasoconstriction in coronary circulation. We found that C2-ceramide produced a concentration-dependent decrease in KCa channel activity in vascular smooth muscle cells from small bovine coronary arteries. The average channel activity of the KCa channels in cell-attached patches decreased from 0.046+/-0.01 to 0. 008+/-0.001 at a C2-ceramide concentration of 10 micromol/L. In inside-out patches, C2-ceramide (1 micromol/L) reduced the average channel activity of the KCa channels from 0.06+/-0.007 to 0.016+/-0. 004. Dithiothreitol, an inhibitor of acidic sphingomyelinase (1 mmol/L), increased the average channel activity of the KCa channels in cell-attached patches from 0.05+/-0.02 of control to 0.26+/-0.04, a 5-fold increase that was reversed by addition of 1 micromol/L ceramide. Glutathione, an inhibitor of neutral sphingomyelinase, was without effect. C2-ceramide significantly reduced the diameter of isolated perfused small coronary arteries in a concentration-dependent manner. Addition of 1 micromol/L C2-ceramide decreased average arterial diameter by 28%. When 14C-sphingomyelin was incubated with coronary arterial homogenates at pH 7.4 and pH 5. 0, 14C-choline phosphate and ceramide were produced. The conversion rates of 14C-sphingomyelin into 14C-choline phosphate and ceramide were 65.1+/-1.0 fmol/min per milligram protein at pH 7.4 and 114. 6+/-8.3 fmol/min per milligram protein at pH 5.0. We conclude that both acidic and neutral sphingomyelinases are present in the bovine coronary arteries and that ceramide inactivates the KCa channel in arterial smooth muscle cells and hence exerts a tonic vasoconstrictor action in coronary microcirculation.

Relations between biased tonicity of the body and vertical judgement in poststroke hemiplegic persons

The influence of muscular tension upon visual vertical judgement in a standing posture was investigated in 16 hemiplegic persons and 12 normal elderly persons. The normal elderly group showed that their judgements of verticality were accurate and stable. In hemiplegic persons, judgements were displaced opposite to the side in which there was high tension in the body. Differences between groups in body tension and the side to which judgement was displaced were significant. The peculiar judgement errors made by hemiplegic persons are thus an overcorrection for tonicity. It was related to one's own body perception.

Development of REM sleep atonia

OBJECTIVES

To study the functional development of neuronal systems that suppress muscle activity, we quantified the chronological change of atonia in rapid-eye-movement sleep (REMS).

METHODS

REMS atonia was quantified by the tonic and phasic inhibition indices (TII and PII). TII indicates the shortness of chin muscle activity, whereas PII standardizes the simultaneous occurrence of chin muscle activity and bursts of rapid eye movements. TII and PII were calculated in REMS of 135 polysomnographical recordings obtained in healthy humans from premature babies to a 77-year-old man.

RESULTS

TII increased significantly with age, while PII decreased significantly. TII reached an adult level at preadolescence, while PII at early infancy.

CONCLUSION

Human nervous systems involved in both tonic and phasic inhibition in REMS raise their activities with age. Since TII and PII reach adult levels at different ages, suppression of muscle activity is hypothesized to be mediated through at least 2 independent systems in humans.

Partial midline fusion of the cerebellar hemispheres with vertical folia: a new cerebellar malformation?

MR imaging depicted vertically oriented folia instead of the normal horizontal folial pattern, hypoplastic cerebellar vermis, fusion of the inferior posterior cerebellum, and probable polymicrogyria in the superior cerebellar hemispheres in a child with hypotonia, nystagmus, ataxia, and psychomotor retardation. We propose that this newly discovered cerebellar malformation be added to the list of malformations associated with aplasia or hypoplasia of the cerebellar vermis, such as Dandy-Walker malformation, Joubert syndrome, tectocerebellar dysraphia, and rhombencephalosynapsis.

Involvement of platelet-activating factor in the modulation of vascular tone in the isolated perfused rabbit kidney

The hypothesis that platelet-activating factor (PAF) plays a role in the modulation of the vasomotor tone and blood pressure was put forward by our group in previous in vivo studies in anaesthetised rabbits. The present study was undertaken to investigate the putative role of this lipid mediator in the vascular reactivity of the renal circulation, using the experimental model of the isolated perfused rabbit kidney. Dose-response curves to noradrenaline-induced vasoconstriction were performed before and after continuous infusions of two different PAF-receptor antagonists (WEB 2086 and yangambin) and of the phospholipase A2 inhibitor mepacrine. The increases in renal perfusion pressure elicited by noradrenaline were potentiated by all the above-mentioned treatments in a dose-dependent manner. Moreover, prostaglandin F2alpha-induced vasoconstriction was also potentiated by the administration of the PAF receptor antagonists and mepacrine. Furthermore, the administration of PAF into the renal circulation induced dose-related and long-lasting vasodilator responses, which were blocked by the PAF receptor antagonists. Nevertheless, PAF-induced renal vasodilation was also abolished by a pretreatment with mepacrine or with the cyclooxygenase inhibitor indomethacin, suggesting that it enhances the secondary formation of vasodilator arachidonic acid metabolites. The data indicate that PAF is involved in the modulation of the vasomotor tone in the renal circulation, through the release of cyclooxygenase products, constituting an additional mechanism of modulation of smooth muscle cell contractility to the ones exerted by well-known vasoactive substances of endothelial origin such as nitric oxide.