Vagal afferents are necessary for the establishment but not the maintenance of kainic acid-induced hyperalgesia in mice

Cardiovascular autonomic nervous system function and hip fracture risk: the Cardiovascular Health Study

Among 1299 older adults with 24-h Holter monitoring data at baseline, followed for approximately 15 years, 190 incident hip fractures occurred. Increased heart rate variability was independently associated with reduced risk of hip fracture among female participants.

PURPOSE

Autonomic nervous system function modulates bone remodeling in rodent osteoporosis models. We tested whether cardiovascular autonomic function is associated with hip fracture risk in humans.

METHODS

Participants were 1299 subjects from the Cardiovascular Health Study (mean age 72.8 years). Eight heart rate variability (HRV) measures (time and frequency domains, detrended fluctuation analysis variables, and heart rate turbulence) were derived from 24-h Holter monitor scans in sinus rhythm. Median follow-up for incident hip fracture was 14.7 years [IQR 9.1, 20.2]. Cox proportional hazards models were used to calculate hazard ratios (95% confidence intervals, CI).

RESULTS

There were 144 hip fractures among 714 women (1.31 [1.06, 1.61] per 100-person years) and 46 among 585 men (0.62 [0.43, 0.90] per 100 person-years). From among HRV variables examined, a one standard deviation (SD) higher variation between normal heart beats over 24 h (the SD of NN intervals [SDNN]) was associated with a multivariable-adjusted lower hip fracture risk (HR [Formula: see text] 0.80; 95% CI 0.65-0.99; p = 0.04) in women. The adjusted association between very low frequency power, and hip fracture was borderline statistically significant in women (HR [Formula: see text] 0.82; 95% CI, 0.66-1.00; p = 0.06). When the 8 HRV variables were considered conjointly and adjusted for each other's association with hip fracture risk, a 1 SD higher SDNN value was significantly associated with reduced hip fracture risk in women (HR 0.74; 95% CI, 0.50-0.99; p = 0.05). No HRV variables were associated with hip fracture in men.

CONCLUSIONS

In older women, increased heart rate variation is associated with hip fracture risk.

The Central Nervous System and Bone Metabolism: An Evolving Story

Our understanding of the control of skeletal metabolism has undergone a dynamic shift in the last two decades, primarily driven by our understanding of energy metabolism. Evidence demonstrating that leptin not only influences bone cells directly, but that it also plays a pivotal role in controlling bone mass centrally, opened up an investigative process that has changed the way in which skeletal metabolism is now perceived. Other central regulators of bone metabolism have since been identified including neuropeptide Y (NPY), serotonin, endocannabinoids, cocaine- and amphetamine-regulated transcript (CART), adiponectin, melatonin and neuromedin U, controlling osteoblast and osteoclast differentiation, proliferation and function. The sympathetic nervous system was originally identified as the predominant efferent pathway mediating central signalling to control skeleton metabolism, in part regulated through circadian genes. More recent evidence points to a role of the parasympathetic nervous system in the control of skeletal metabolism either through muscarinic influence of sympathetic nerves in the brain or directly via nicotinic receptors on osteoclasts, thus providing evidence for broader autonomic skeletal regulation. Sensory innervation of bone has also received focus again widening our understanding of the complex neuronal regulation of bone mass. Whilst scientific advance in this field of bone metabolism has been rapid, progress is still required to understand how these model systems work in relation to the multiple confounders influencing skeletal metabolism, and the relative balance in these neuronal systems required for skeletal growth and development in childhood and maintaining skeletal integrity in adulthood.

Skeletal parasympathetic innervation communicates central IL-1 signals regulating bone mass accrual

Bone mass accrual is a major determinant of skeletal mass, governed by bone remodeling, which consists of bone resorption by osteoclasts and bone formation by osteoblasts. Bone mass accrual is inhibited by sympathetic signaling centrally regulated through activation of receptors for serotonin, leptin, and ACh. However, skeletal activity of the parasympathetic nervous system (PSNS) has not been reported at the bone level. Here we report skeletal immune-positive fibers for the PSNS marker vesicular ACh transporter (VAChT). Pseudorabies virus inoculated into the distal femoral metaphysis is identifiable in the sacral intermediolateral cell column and central autonomic nucleus, demonstrating PSNS femoral innervation originating in the spinal cord. The PSNS neurotransmitter ACh targets nicotinic (nAChRs), but not muscarinic receptors in bone cells, affecting mainly osteoclasts. nAChR agonists up-regulate osteoclast apoptosis and restrain bone resorption. Mice deficient of the α(2)nAChR subunit have increased bone resorption and low bone mass. Silencing of the IL-1 receptor signaling in the central nervous system by brain-specific overexpression of the human IL-1 receptor antagonist (hIL1ra(Ast)(+/+) mice) leads to very low skeletal VAChT expression and ACh levels. These mice also exhibit increased bone resorption and low bone mass. In WT but not in hIL1ra(Ast)(+/+) mice, the cholinergic ACh esterase inhibitor pyridostigmine increases ACh levels and bone mass apparently by inhibiting bone resorption. Taken together, these results identify a previously unexplored key central IL-1-parasympathetic-bone axis that antagonizes the skeletal sympathetic tone, thus potently favoring bone mass accrual.

Duodenal lipid-induced symptom generation in gastroesophageal reflux disease: role of apolipoprotein A-IV and cholecystokinin

BACKGROUND

  Duodenal lipid intensifies the perception of esophageal acid perfusion. Recently, we showed that genes implicated in lipid absorption were upregulated in the duodenum of fasting gastro-esophageal reflux disease (GERD) patients. This suggests that chylomicron production and secretion may be enhanced and, consequently, the release of apolipoprotein A-IV (apoA-IV), a chylomicron-derived signaling protein. ApoA-IV may stimulate release of cholecystokinin (CCK), an activator of vagal afferents. This study evaluated putative involvement of abnormal apoA-IV and CCK responses to lipid in GERD.

METHODS

  Ten GERD patients and 10 healthy volunteers (HV) underwent duodenal perfusion with Intralipid 20%, 2 kcal min(-1) , for 60 min. Symptoms were scored, blood samples collected every 15 min during lipid perfusion and 15 min after discontinuation when duodenal biopsies were taken. Plasma and mucosal concentrations of apoA-IV and CCK and transcript levels of 21 genes implicated in lipid absorption, differentially expressed under fasting conditions, were quantified.

KEY RESULTS

  Heartburn (P = 0.003), abdominal discomfort (P = 0.037) and nausea (P = 0.008) only increased significantly during lipid infusion in GERD patients. Following lipid infusion mean mucosal apoA-IV concentration was lower in GERD patients compared with HV (P = 0.023), whereas plasma concentration tended to be elevated (P = 0.068). Mean mucosal CCK concentration was also lower in GERD patients (P = 0.009). Two genes, HIBADH and JTB, were upregulated in GERD patients (P = 0.008 and P = 0.038, respectively).

CONCLUSIONS & INFERENCES

  Our results suggest excessive duodenal lipid-induced release of apoA-IV and CCK in GERD. We postulate that the resulting heightened activation of duodenal vagal afferents may underlie central sensitization, thereby increasing the perception of reflux events.

Chemical lesioning and glutamate administration reveal a major role for the nucleus tractus solitarius in the cardiac-somatic reflex in rats

Many patients suffer from secondary muscle hyperalgesia after experiencing angina pectoris. In this study, we examined the role of the nucleus tractus solitarius (NTS) and glutamate receptors in modulating cardiac-evoked muscle hyperalgesia induced by pericardial capsaicin, which was monitored by recording electromyogram (EMG) activity from the spinotrapezius muscle in the anesthetized rat. Unilateral chemical lesioning of the commissural NTS with the neurotoxin ibotenic acid significantly depressed the cardiac-somatic reflex; the EMG responses decreased to 56.4 ± 6.9% of that of the controls (5 of 5). Microinjection of the excitatory amino acid glutamate, at 10, 20, and 50 nmol, into the commissural NTS increased the EMG response, in a dose-dependent manner, to 116.9 ± 4.9%, 143.9 ± 10.2%, and 214.2 ± 15.8% (n=8), respectively, of that of the controls. In contrast, microinjection of the N-methyl-D-aspartate (NMDA) receptor antagonist (+)-5-methyl-10, 11-dihydro-5H-dibenzo [a, d]-cyclohepten-5,10-imine maleate (MK-801) at 4 and 6 nmol, decreased the EMG response to 45.2 ± 10.6% and 36.8 ± 14.3%, respectively, of that of the controls (n=8 for each dose). Similarly, the metabotropic glutamate receptor (mGluR) antagonist (RS)-a-methyl-4-carboxyphenylglycine (MCPG), at 2.5 and 5 nmol, decreased the EMG response to 65.2 ± 16.3% and 57.0 ± 4.2%, respectively, of that of the controls. When a combination of MK-801 and MCPG was administrated, the EMG response further decreased to 22.5 ± 13.2% (n=6) of that of the controls. However, administration of a non-NMDA receptor antagonist 6, 7-dinitroquinoxaline-2, 3-dione (DNQX), at 2 and 5 nmol, had no effect on the EMG response. These results suggest that the NTS is involved in the facilitation of the cardiac-somatic reflex, and that the NMDA receptor and mGluRs play an important role in mediating this effect.

The differential effect of morphine and beta-endorphin administered intracerebroventricularly on pERK and pCaMK-II expression induced by various nociceptive stimuli in mice brains

The present study was performed to characterize the differential molecular mechanisms of morphine and beta-endorphin which are injected intracerebroventiricularly in mice. In the immunoblot assay, the increases of phosphorylated extracellular signal-regulated protein kinase (pERK) as well as phosphorylated calcium/calmodulin-dependent protein kinase IIalpha (pCaMK-IIalpha) expression induced by noxious stimuli were attenuated by intracerebroventricular (i.c.v.) beta-endorphin pretreatment in the hypothalamus, but not by i.c.v. morphine pretreatment. In addition to these immunoblot results, immunohistochemical study also showed that the attenuation of pERK or pCaMK-IIalpha immunoreactivity elicited by i.c.v. pretreatment of beta-endorphin mainly occurred in the paraventricular nucleus of the hypothalamus (PVN). We also investigated the effect of morphine and beta-endorphin on pERK and pCaMK-IIalpha expression in the locus coeruleus (LC). I.c.v. injection of morphine significantly increased pERK as well as pCaMK-IIalpha expression in the locus coeruleus, while beta-endorphin increased only pCaMK-IIalpha in the LC. In addition, beta-endorphin significantly attenuated pERK expression induced by SP i.t. injection. These results suggest that the antinociceptive effects of supraspinally administered morphine and beta-endorphin are involved with differentially intracellular signal transduction molecules-pERK, pCaMK-IIalpha in the PVN and the LC.

Involvement of phosphorylated Ca2+/calmodulin-dependent protein kinase II and phosphorylated extracellular signal-regulated protein in the mouse formalin pain model

In the present study, we investigated the role of phosphorylated calcium/calmodulin-dependent protein kinase II (pCaMK-II) and phosphorylated extracellular signal-regulated protein kinase (pERK) in nociceptive processing at the spinal and supraspinal levels in the formalin subcutaneous induced mouse pain model. In the immunoblot assay, subcutaneous (s.c.) injection with formalin increased the pERK and pCaMK-IIalpha level in the spinal cord, and an immunohistochemical study showed that the increase of pERK and pCaMK-IIalpha immunoreactivity mainly occurred in the laminae I and II areas of the spinal dorsal horn. At the supraspinal level, although pERK was not changed in the hippocampus induced by formalin s.c. injection, pCaMK-IIalpha was increased in the hippocampus and hypothalamus by s.c. formalin injection, and an increase of pCaMK-IIalpha immunoreactivity mainly occurred in the pyramidal cells and the stratum lucidum/radiatum layer of the CA3 region of hippocampus and paraventricular nucleus of the hypothalamus. Moreover, pERK immunoreactivity in the hypothalamic paraventricular nucleus was also increased. The second phase of nociceptive behavior induced by formalin administered either i.t. or intracerebroventricularly (i.c.v.) was attenuated by PD98059 (ERK inhibitor) as well as KN-93(a CaMK-II inhibitor). On the other hand, the first phase of nociceptive behavior induced by formalin s.c. injection was not affected by i.t. KN-93. Our results suggest that pERK and pCaMK-II located at both the spinal cord and supraspinal levels are an important regulator during the nociceptive processes induced by formalin administered s.c. respectively.

Involvement of phosphorylated extracellular signal-regulated kinase in the mouse substance P pain model

In the present study, we investigated the role of pERK in nociceptive processing at the spinal and supraspinal levels in the substance P (SP)-induced mouse pain model. In the immunoblot assay, intrathecal (it) injection with SP increased pERK level at the spinal cord and an immunohistochemical study showed that increase of pERK immunoreactivity mainly occurred in the lamina I and II areas of the spinal dorsal horn. At the supraspinal level, pERK was increased in hippocampus and hypothalamus by i.t. SP injection, and an increase of pERK immunoreactivity mainly occurred in the dentate gyrus and CA3 region of hippocampus and paraventricular nucleus on hypothalamus. The nociceptive behavior induced by Sub P administered either i.t. or intracerebroventricularly (i.c.v.) was attenuated by PD98059 (a MEK 1/2 inhibitor) in a dose-dependent manner. Our results suggest that pERK located at both spinal cord and supraspinal levels plays as an important regulator during the nociceptive process activated by SP administered it.