Low-Frequency Repetitive Transcranial Magnetic Stimulation for Chronic Tension-Type Headache: A Randomized Controlled Study.

BACKGROUND: Nearly 1-3% of the population is affected by chronic tension-type headaches (CTTH). However, it is still difficult to treat owing to the lack of knowledge of the disease's pathophysiology. Available literature suggests a role for pericranial muscle activity and abnormal modulation of central pain. Repetitive transcranial magnetic stimulation (rTMS) therapy done at the dorsolateral prefrontal cortex (DLPFC) can help modulate pericranial muscle overactivity and central pain modulation in subjects with CTTH. AIM: This randomized controlled study aimed to assess the effect of rTMS used in the low-frequency dorsolateral prefrontal cortex on pain and muscle activity in subjects with a chronic tension-type headache. MATERIALS AND METHODS: The present randomized controlled clinical study was commenced in a health care center on 20 subjects with chronic tension-type headaches who were given either sham or low-frequency repetitive transcranial magnetic stimulation at the right dorsolateral prefrontal cortex. The therapy effect was evaluated statistically using Welch's corrected t-test. RESULTS: The study results depicted that daily use of rTMS therapy for two weeks led to a considerable reduction in the intensity of the pain, the activity of pericranial muscles, and headache impact, along with an increase in the nociceptive excitability thresholds in subjects with CTTH, with p=0.001 compared to the sham group. CONCLUSION: Considering its limitations, the present study depicts that rTMS is an efficacious management tool for reducing pain associated with CTTH and can serve as the cornerstone for additional investigations.

Electromagnetic Field Stimulation Attenuates Phasic Nociception after Complete Spinal Cord Injury in Rats.

Traumatic spinal cord injury (SCI) is one of the most incapacitating pathologies, leading to huge rehabilitation challenges besides a social-economic burden on SCI patients and their families. There is no complete curative treatment available so far. Non-invasive and patient-friendly use of extremely low-frequency electromagnetic field stimulation (EMF) has emerged as a therapeutic and rehabilitation option. In this study, we tested whole-body EMF stimulation on thoracic complete SCI-induced nociception including sensorimotor deficits in rats. The EMF application significantly attenuated hyperalgesia and allodynia to thermal, electrical, and chemical stimuli from 6 weeks onwards as well as restoration of spinal reflexes, viz., H-reflex and nociceptive flexion reflex at the study endpoint (week 8). Besides, massively increased glutamate at the SCI injury site was observed in SCI rats with no treatment, which was also attenuated significantly by EMF stimulation. Spinal cord histology of the injury area showed a decrease in lesion volume and glial population in the EMF-stimulated rats. These findings indicate the beneficial role of EMF stimulation after thoracic complete SCI in adult male rats and, thereby, a beneficial patient-friendly rehabilitation tool.

Lithium acts to modulate abnormalities at behavioral, cellular, and molecular levels in sleep deprivation-induced mania-like behavior.

BACKGROUND: Ample amount of data suggests role of rapid eye movement (REM) sleep deprivation as the cause and effect of mania. Studies have also suggested disrupted circadian rhythms contributing to the pathophysiology of mood disorders, including bipolar disorder. However, studies pertaining to circadian genes and effect of lithium treatment on clock genes are scant. Thus, we wanted to determine the effects of REM sleep deprivation on expression of core clock genes and determine whether epigenetics is involved. Next, we wanted to explore ultrastructural abnormalities in the hippocampus. Moreover, we were interested to determine oxidative stress, tumor necrosis factor-α (TNF-α), and brain-derived neurotrophic factor levels in the central and peripheral systems. METHODS: Rats were sleep deprived by the flower pot method and were then analyzed for various behaviors and biochemical tests. Lithium was supplemented in diet. RESULTS: We found that REM sleep deprivation resulted in hyperactivity, reduction in anxiety-like behavior, and abnormal dyadic social interaction. Some of these behaviors were sensitive to lithium. REM sleep deprivation also altered circadian gene expression and caused significant imbalance between histone acetyl transferase/histone deacetylase (HAT/HDAC) activity. Ultrastructural analysis revealed various cellular abnormalities. Lipid peroxidation and increased TNF-α levels suggested oxidative stress and ongoing inflammation. Circadian clock genes were differentially modulated with lithium treatment and HAT/HDAC imbalance was partially prevented. Moreover, lithium treatment prevented myelin fragmentation, disrupted vasculature, necrosis, inflammation, and lipid peroxidation, and partially prevented mitochondrial damage and apoptosis. CONCLUSIONS: Taken together, these results suggest plethora of abnormalities in the brain following REM sleep deprivation, many of these changes in the brain may be target of lithium's mechanism of action.

Brain Plasticity and Neurophysiological Correlates of Meditation in Long-Term Meditators: A 18Fluorodeoxyglucose Positron Emission Tomography Study Based on an Innovative Methodology.

Objective: Previous studies evaluating neurophysiological correlates of long-term meditation are constrained by some methodological limitations. The objective of this study was to measure changes in the regional cerebral glucose metabolism during meditation using a novel methodological approach. Design: The present study was a part of a larger, nonrandomized, single-center open-label study. Setting/location: The study was conducted at the Department of Physiology and Department of Nuclear Medicine and Positron Emission Tomography. A dedicated place was set up as a yoga room, away from the positron emission tomography (PET) scanning room in the Department of Nuclear Medicine and Positron Emission Tomography, where meditators performed meditation in a peaceful environment in a sitting posture with eyes closed. The electroencephalography (EEG) was recorded to affirm the meditation objectively. Subjects: Twenty-four sets of PET scans were obtained at 2 different occasions (baseline and postmeditation within 40 min of 18FDG [18fluorodeoxyglucose] injection) from 12 apparently healthy, male, right-handed long-term meditators practicing Preksha meditation (since >5 years, at least 5 days a week) who were recruited from a well-established meditation center in Delhi. Outcome measures: Changes in the regional cerebral glucose metabolism during meditation versus baseline. Results: Regional cluster analysis showed significantly activated well-defined areas of fronto-parieto-temporal regions of the right versus left hemisphere during meditation. Interestingly, right homolog of Broca's area and right lentiform nucleus were hyperactive during meditation in all the meditators. Conclusions: Long-term meditation might potentially enhance the explicit functions of specific parts of the right hemisphere, possibly due to neuroplastic changes in the brain. Importantly, results of the current study are encouraging and show a novel methodological approach to acquire 18FDG PET/CT (computed tomography) images. The study was registered at Clinical Trial Registry India (CTRI), CTRI/2009/091/000727.

Neuroregenerative Effects of Electromagnetic Field and Magnetic Nanoparticles on Spinal Cord Injury in Rats.

The present study aimed to evaluate the effect of iron oxide nanoparticles (IONPs) along with electromagnetic fields (MF) exposure on spontaneous and induced axonal sprouting after spinal cord injury (SCI). Adult male Wistar rats were subjected to spinal cord transection at the T13 segment. The IONP (25 µg/mL) embedded in 3% agarose gel was implanted at the injury site and subsequently exposed to MF (50 Hz, 17.96 µT, 2 hours/day for 5 weeks). Histological analysis of spinal cord tissue showed a significant increase in the expression of the growth-associated protein GAP-43 and it was found to be co-localized with neuronal nuclei marker and neurofilaments. The results show sprouting from mature neurons and axons, significantly less demyelination and more myelinated fibers were evident at the lesion site. However, no motor or somatosensory evoked potential response was observed, suggesting lack of long-distance functional connectivity. These findings highlight the therapeutic potential of IONPs along with MF exposure in promoting neuroregeneration after SCI.

Extremely low frequency magnetic field protects injured spinal cord from the microglia- and iron-induced tissue damage.

Spinal cord injury (SCI) is insult to the spinal cord, which results in loss of sensory and motor function below the level of injury. SCI results in both immediate mechanical damage and secondary tissue degeneration. Following traumatic insult, activated microglia release proinflammatory cytokines and excess iron due to hemorrhage, initiating oxidative stress that contributes to secondary degeneration. Literature suggests that benefits are visible with the reduction in concentration of iron and activated microglia in SCI. Magnetic field attenuates oxidative stress and promotes axonal regeneration in vitro and in vivo. The present study demonstrates the potential of extremely low frequency magnetic field to attenuate microglia- and iron-induced secondary injury in SCI rats. Complete transection of the spinal cord (T13 level) was performed in male Wistar rats and subsequently exposed to magnetic field (50 Hz,17.96 µT) for 2 h daily for 8 weeks. At the end of the study period, spinal cords were dissected to quantify microglia, macrophage, iron content and study the architecture of lesion site. A significant improvement in locomotion was observed in rats of the SCI + MF group as compared to those in the SCI group. Histology, immunohistochemistry and flow cytometry revealed significant reduction in lesion volume, microglia, macrophage, collagen tissue and iron content, whereas, a significantly higher vascular endothelial growth factor expression around the epicenter of the lesion in SCI + MF group as compared to SCI group. These novel findings suggest that exposure to ELF-MF reduces lesion volume, inflammation and iron content in addition to facilitation of angiogenesis following SCI.

BDNF mediated activity dependent maturation of visual Wulst following prenatal repetitive auditory stimulation at a critical developmental period in domestic chicks (Gallus domesticus).

The developing visual circuitry attains its mature adult pattern through the process of activity-dependent refinement in which photic stimulation plays the major role. However, auditory stimulation can also facilitate the developing visual Wulst synaptic plasticity and postnatal perceptual behavior, though the underlying mechanism is unclear. We exposed the fertilized eggs of white Leghorn chickens during incubation to either species-specific calls or no sound for varying time periods depending on the functional development of the auditory and/or visual systems. The visual evoked potential (VEP) from the Wulst was recorded at embryonic days (E) 19, 20 and posthatch days (PH) 1-3, to assess functional maturation. A significant attenuation in latencies and higher amplitudes at PH1-3 in the stimulated groups that received exposure during visual system maturation, suggest beneficial effect of auditory inputs only during critical periods. Concomitant with this, there was a significant increase in the expression of BDNF and levels of neurotransmitters GABA, glutamate, norepinephrine and serotonin from E18 only in both hemispheres of the visual Wulst. A significant inter-hemispheric difference in expression was also found in all groups. These results suggest the role of BDNF in activity driven structural and functional maturation of the visual system following prenatal repetitive auditory stimulation.

Prenatal music stimulation facilitates the postnatal functional development of the auditory as well as visual system in chicks (Gallus domesticus).

Rhythmic sound or music is known to improve cognition in animals and humans. We wanted to evaluate the effects of prenatal repetitive music stimulation on the remodelling of the auditory cortex and visual Wulst in chicks. Fertilized eggs (0 day) of white leghorn chicken (Gallus domesticus) during incubation were exposed either to music or no sound from embryonic day 10 until hatching. Auditory and visual perceptual learning and synaptic plasticity, as evident by synaptophysin and PSD-95 expression, were done at posthatch days (PH) 1, 2 and 3. The number of responders was significantly higher in the music stimulated group as compared to controls at PH1 in both auditory and visual preference tests. The stimulated chicks took significantly lesser time to enter and spent more time in the maternal area in both preference tests. A significantly higher expression of synaptophysin and PSD-95 was observed in the stimulated group in comparison to control at PH1-3 both in the auditory cortex and visual Wulst. A significant inter-hemispheric and gender-based difference in expression was also found in all groups. These results suggest facilitation of postnatal perceptual behaviour and synaptic plasticity in both auditory and visual systems following prenatal stimulation with complex rhythmic music.

Iron oxide nanoparticles and magnetic field exposure promote functional recovery by attenuating free radical-induced damage in rats with spinal cord transection.

BACKGROUND: Iron oxide nanoparticles (IONPs) can attenuate oxidative stress in a neutral pH environment in vitro. In combination with an external electromagnetic field, they can also facilitate axon regeneration. The present study demonstrates the in vivo potential of IONPs to recover functional deficits in rats with complete spinal cord injury. METHODS: The spinal cord was completely transected at the T11 vertebra in male albino Wistar rats. Iron oxide nanoparticle solution (25 µg/mL) embedded in 3% agarose gel was implanted at the site of transection, which was subsequently exposed to an electromagnetic field (50 Hz, 17.96 µT for two hours daily for five weeks). RESULTS: Locomotor and sensorimotor assessment as well as histological analysis demonstrated significant functional recovery and a reduction in lesion volume in rats with IONP implantation and exposure to an electromagnetic field. No collagenous scar was observed and IONPs were localized intracellularly in the immediate vicinity of the lesion. Further, in vitro experiments to explore the cytotoxic effects of IONPs showed no effect on cell survival. However, a significant decrease in H2O2-mediated oxidative stress was evident in the medium containing IONPs, indicating their free radical scavenging properties. CONCLUSION: These novel findings indicate a therapeutic role for IONPs in spinal cord injury and other neurodegenerative disorders mediated by reactive oxygen species.

Exposure to extremely low-frequency magnetic field restores spinal cord injury-induced tonic pain and its related neurotransmitter concentration in the brain.

Spinal cord injury (SCI) is unequivocally reported to produce hyperalgesia to phasic stimuli, while both hyper- and hypoalgesia to tonic stimuli. The former is spinally mediated and the latter centrally. Besides, its management is unsatisfactory. We report the effect of magnetic field (MF; 17.96 µT, 50 Hz) on tonic pain behavior and related neurotransmitters in the brain of complete thoracic (T13) SCI rats at week 8. Adult male Wistar rats were divided into Sham, SCI and SCI+MF groups. Formalin-pain behavior was compared utilizing 5 min block pain rating (PR), 60 min session-PR, time spent in various categories of increasing pain (T0-T3) and flinch incidences. Serotonin (5-HT), dopamine (DA), norepinepherine (NE), gamma-aminobutyric acid (GABA), glutamate and glycine were estimated in brain tissue by liquid chromatography-mass spectrometry. Session-PR, block-PR and number of flinches were significantly lower, while time spent in categories 0-1 was higher in the SCI versus Sham group. These parameters were comparable in the SCI+MF versus Sham group. 5-HT concentration in cortex, remaining forebrain areas and brain stem (BS), was lower while GABA and NE were higher in BS of SCI, which were comparable with Sham in the SCI+MF group. The concentration of DA, glutamate and glycine was comparable amongst the groups. The data indicate significant hypoalgesia in formalin pain while increased in GABA, NE and decreased in 5-HT post-SCI, which were restored in the SCI+MF group. We suggest beneficial effect of chronic (2 h/day × 8 weeks) exposure to MF (50 Hz, 17.96 µT) on tonic pain that is mediated by 5-HT, GABA and NE in complete SCI rats.

Repetitive auditory stimulation at a critical prenatal period modulates the postnatal functional development of the auditory as well as visual system in chicks (Gallus domesticus).

The extrinsic sensory stimulation plays a crucial role in the formation and integration of sensory modalities during development. Postnatal behavior is thereby influenced by the type and timing of presentation of prenatal sensory stimuli. In this study, fertilized eggs of white Leghorn chickens during incubation were exposed to either species-specific calls or no sound. To find the prenatal critical period when auditory stimulation can modulate visual system development, the former group was divided into three subgroups: in subgroup A (SGA), the stimulus was provided during embryonic day (E)10 to E16, in SGB E17- hatching, and in SGC E10-hatching. The auditory and visual perceptual learning was recorded at posthatch day (PH) 1-3, whereas synaptic plasticity (evident from synaptophysin and PSD-95 expression), was observed at E19, E20, and PH 1-3. An increased number of responders were observed in both auditory and visual preference tests at PH 1 following stimulation. Although a decrease in latency of entry and an increase in total time spent were observed in all stimulated groups, it was most significant in SGC in auditory preference and in SGB and SGC in visual preference test. The auditory cortex of SGC and visual Wulst of SGB and SGC revealed higher expression of synaptic proteins, compared to control and SGA. A significant inter-hemispheric and gender-based difference in expression was also found in all groups. These results indicate facilitation of postnatal behaviour and synaptogenesis in both auditory and visual systems following prenatal repetitive auditory stimulation, only when given during prenatal critical period of development.

Effect of extremely low frequency magnetic field in prevention of spinal cord injury-induced osteoporosis.

The present study was designed to investigate the effect of extremely low frequency (ELF) magnetic field (MF) on spinal cord injury (SCI)-induced osteoporosis in rats. Adult male Wistar rats (n = 24) were equally divided into sham, SCI, and SCI+MF groups. Complete transection of spinal cord (thoracic 11 vertebra) was surgically performed under anesthesia, whereas in the sham group only laminectomy was done. Post-SCI day 1, rats were either exposed (2 h/d × 8 wk) to ELF-MF (17.96 micro-Tesla, 50 Hz; SCI+MF group) or sham exposed (SCI group). Basso, Beattie, and Bresnahan (BBB) score was recorded weekly. All the rats were sacrificed 8 wk post-SCI; tibia and femur bones were isolated for the analysis of bone mineral content (BMC; total calcium [Ca], phosphorus [P], carbon [C]), bone mineral density (BMD), and biochemical status (osteocalcin, collagen I, alkaline phosphatase). The BBB score decreased post-SCI, which partially recovered after ELF-MF. In SCI rats, there was a statistically significant decrease in BMC, Ca, P, C, BMD, and biochemical level in both the bones as compared with the sham group, which was attenuated in SCI+MF rats except the C content. Electron microscopic study revealed the enhancement of microstructural composition and compactness in cortical and trabecular parts of treated bones. The results suggest that the chronic (2 h/d × 8 wk) ELF-MF exposure (17.96 micro-Tesla, 50 Hz) to SCI rats is effective in attenuating SCI-induced osteoporosis.

Exposure to ELF- magnetic field promotes restoration of sensori-motor functions in adult rats with hemisection of thoracic spinal cord.

Clinically effective modalities of treatment for spinal cord injury (SCI) still remain unsatisfactory and are largely invasive in nature. There are reports of accelerated regeneration in injured peripheral nerves by extremely low-frequency pulsed electromagnetic field (ELF-EMF) in the rat. In the present study, the effect of (50 Hz), low-intensity (17.96 µT) magnetic field (MF) exposure of rats after-hemisection of T13 spinal cord (hSCI) was investigated on sensori-motor and locomotor functions. Rats were divided into hSCI (sham-exposed) and hSCI+MF (MF: 2 h/d X 6 weeks) groups. Besides their general conditions, locomotor function by Basso, Beattie, and Brenahan (BBB) score; motor responses to noxious stimuli by threshold of tail flick (TTF), simple vocalization (TSV), tail flick latency (TFL), and neuronal excitability by H-reflex were noted. It is found that, in the hSCI+MF group, a statistically significant improvement over the hSCI control group was noted in BBB score from post-SCI wk2 and TFL and TTF by post-hSCI wk1 and wk3, respectively. Correspondingly, TSV gradually restored by post-hSCI wk5.The threshold of H-reflex was reduced on ipsilateral side vs. contralateral side in hSCI and hSCI+MF group. A complete bladder control was dramatically restored on post-hSCI day4 (vs. day7 of hSCI group) and the survival rate was 100% in the hSCI+MF group (vs. 90% of hSCI group). The results of our study suggest that extremely low-frequency (50 Hz), low-intensity (17.96 µT) MF exposure for 2 h/d x 6wks promotes recovery of sensori-motor behavior including locomotion and bladder control both in terms of temporal pattern and magnitude in hemisection injury of (T13) spinal cord rats.

Progressive impairment in motor skill learning at 12 and 20 weeks post 6-OHDA- SNc lesion in rats.

Deficiency in skilled motor activity is primarily attributed to the loss of dopaminergic neurons in the pars compacta of substantia nigra (SNc), which can be detected by performance of the rotarod test. Previous reports have demonstrated impaired skilled motor behavior in rats during the pre-motor stage of Parkinson's disease (PD) (3-8 weeks post 6-OHDA lesion of striatum). We studied skilled motor learning in 6-hydroxydopamine (6-OHDA) SNc lesion rats at 12 and 20 weeks by rotarod task after providing sufficient training to give allowance for ageing (3 sessions/day for 14 consecutive days). On each day, the stay duration on rotarod was noted and compared between the groups (Group 1 = Control, Group 2 = Post lesion (PL) week 12, Group 3 = PL week 20). In Group 2 rats, the duration of stay on rotarod gradually increased from day 1 through 7 {day 7 = 193.1 (81.8-247.4) vs. control group day 7 = 202.1 (87.7-279.8), p = 0.771} and declined thereafter. While, the stay duration in Group 3 rats remained lower {day 7 = 32.5 (20.4-52.1), p = 0.011} than that of the control rats throughout the study period. The results of our study suggest a slower brief learning of skilled motor tasks at post lesion week 12 whereas no learning at all at post-lesion week 20.

Effect of magnetic field on food and water intake and body weight of spinal cord injured rats.

Chronic (2 h/d x 8 weeks) exposure to magnetic field (MF; 50 Hz, 17.9 microT) in complete spinal cord (T13) transected rats restored food intake (FI), water intake (WI) and body weight (BW) which were decreased in the spinal cord injured rats. The results suggest a significant beneficial effect of chronic exposure to magnetic field of paraplegic rats.

Effect of low level capacitive-coupled pulsed electric field stimulation on mineral profile of weight-bearing bones in ovariectomized rats.

Mineral content, mineral composition, and crystalline pattern of bone in osteoporosis are different from those of normal individuals. Present management of bone mineral loss is rather unsatisfactory primarily because of socioeconomic factors and untoward effects of the treatment drugs. We report the efficacy of capacitive-coupled pulsed electric field (CCPEF) to prevent bone loss in an ovariectomized rat model of osteoporosis. One month postsurgery either leg was stimulated with CCPEF, whereas the other leg did not receive any stimulation (sham exposed). The treatment was given in 60 sessions each of 2 h/d (5 days a week). The control group of rats was sham operated. At the end of the observation period, femur and tibia bones were removed. Their bone mineral content (BMC), calcium, phosphorus, and carbon contents were analyzed and bone mineral density (BMD) was calculated. The BMC data were supported by X-ray diffraction (XRD) method. In sham-exposed bones, a statistically significant decrease in BMC, BMD, calcium, and phosphorus contents were obtained as compared to the control. Although in CCPEF bones, there was an attenuation of decrement in the noted parameters except phosphorus. XRD pattern supported these observations. The results suggest that chronic, 60 sessions of 2 h/d, 5 d/wk CCPEF (14 MHz with 16 Hz modulation 16 Hz and 10 V peak to peak) is effective in attenuating the ovariectomy-induced bone mineral loss in rats.

Effect of procainization of ventromedial nucleus of hypothalamus on the feeding behavior of rats.

Bilateral lesions in the Ventromedial nucleus of hypothalamus (VMH) cause hyperphagia and a preference for high lipid, high carbohydrate diet. Reversible lesion by procaine microinfusion produces a decrease in serum glucose and immunoreactive insulin levels. In the present study the effect of procaine microinfusion on feeding behavior and taste preference was observed. 5 h and 24 h food intake, water intake and weekly body weight of the rats was measured. Three bottle preference test was used to study the diet preferences. The 24 h food intake was found to be significantly more on 1(st), 2(nd) and 3(rd) day (41 +/- 6.03, 38.83 +/- 6.17 and 33.66 +/- 5.88 g/day, respectively) of procaine injection. There was also a significant increase in food intake at 0.25 h (4.166 +/- 2.04 g) and 1 h (5 +/- 0 g) as compared to saline group (0 +/- 0 g at 0.25 h and 0.83 +/- 2.04 g at 1 h). Post procaine water intake and body weight for seven days was not statistically significantly when compared to pre-lesion values. In the three bottles preference test, after procaine microinfusion there was a significantly increased preference for 20% sucrose and 0.15% saccharin than quinine and citric acid. The results suggest that bilateral procainization of VMH produces a transient increase in food intake and enhance preference for sweet tasting substances.

Threshold of pain in chronic magnetic field- (50 Hz, 17.9 microT) exposed rats: effect of sucrose ingestion.

Both magnetic field (MF) exposure and sucrose ingestion produce opioid mediated analgesia, independently. This article addresses the query whether or not sucrose ingestion potentiates the analgesia of MF exposure. The pain threshold, as reflected by withdrawal of tail (thresholds of tail flick, TF), vocalization during stimulus (VD), and vocalization after stimulus (VA) were determined in 7 sessions at 0, 5, 10, 15, 30, 45, and 60 min, respectively (control rats). After an interval of 24 h the rats were provided with sucrose solution and were allowed to ingest it for 10 min. The pain thresholds were determined (Control sucrose-fed rats). The rats then received exposure to magnetic field (50 Hz, 17.9 microT) for 7 d (8 h/d) (MF-exposed rats) and the effect of sucrose ingestion was repeated (MF-Sucrose-fed rats). The basal threshold of pain did not vary in between the control and MF-exposed rats. Pain threshold during sessions II-VII did not vary in control rats but it increased in MF rats. Moreover, the pain thresholds were elevated in MF rats as compared to control rats. Sucrose-ingestion elevated the threshold of TF in controls but not in MF-exposed rats; while the thresholds of VA and VD were elevated more in control than MF rats. The results suggest that the MF exposure (50 Hz, 17.9 microT, 8 h/d) for 7 d did not affect the basal thresholds of pain, increased stress induced analgesia, and attenuated the sucrose ingestion-induced analgesia.

Effect of chronic intermittent exposure to AM radiofrequency field on responses to various types of noxious stimuli in growing rats.

There are several reports of altered pain sensation after exposure (from a few minutes to hours in single or repeated doses for 2-3 weeks) to electromagnetic fields (EMF) in adults. The commonly utilized noxious stimulus is radiant heat. The nociceptive responses are known to be influenced by characteristics of stimulus, organism, and environment. We studied the pattern of nociceptive responses to various noxious stimuli in growing rats exposed to radiofrequency field (73.5 MHz amplitude modulated, 16 Hz power density 1.33 mw/cm(2), SAR = 0.4 w/kg) for 45 d (2 h/d). Threshold current for stimulation of nociceptive afferents to mediate motor response of tail (TF), vocalization during stimulus (VD), and vocalization after discharge (VA); the withdrawal latency of tail (TFL) and hind paw (HPL) to thermal noxious stimulus and tonic pain responses were recorded in every rat. The TFL was not affected, HPL was decreased (p < 0.01), and the thresholds of TF and VD were not affected, while, that of VA was significantly decreased. The tonic pain rating was decreased (p < 0.01). A decrease in the threshold of VA (p < 0.01) is indicative of an increase in the emotional component of the response to the phasic pain, whereas a decrease in the pain rating indicates analgesia in response to the tonic pain. The results of our study suggest that chronic (45 d), intermittent (2 h/d) amplitude modulated RF field exposure to the peripubertal rat increases the emotional component of phasic pain over a basal eaualgesic state, while late response to tonic pain is decreased. The data suggest that amplitude modulated RF field differentially affects the mechanisms involved in the processing of various noxious stimuli.

Gender specificity of sucrose induced analgesia in human adults.

Sweet, palatable substances such as sucrose are reported to calm infants undergoing routine investigative procedures. The analgesic effect persists in pre pubertal children and adults with a hint of gender dependent variation in the analgesic response. The present study was therefore designed to explore gender specificity of sucrose induced analgesia in adult volunteers utilizing the nociceptive flexion reflex, an objective tool for pain assessment. Nociceptive flexion reflex was recorded, both before and after (up to 15 min) ingestion of 100 ml of 25% sucrose solution in 6 male and 6 female volunteers. In the male volunteers the maximum amplitude of the response was 20.8 +/- 7.7 microV before sucrose ingestion and 22.6 +/- 9.1 microV, 6.6 +/- 0.7 microV, 6.2 +/- 1.1 microV, 7.5 +/- 0.9 microV at 0, 5, 10 and 15 minutes post sucrose ingestion respectively. In female volunteers, the maximum amplitude of the response was 33.7 +/- 17.7 microV before sucrose ingestion and 43.6 +/- 17.2 microV, 7.1 +/- 1.2 microV, 25.9 +/- 16.1 microV, 50.6 +/- 16.3 microV at the same time intervals post sucrose ingestion. The maximum amplitude values were significantly lower in the males at 10 and 15 minutes after sucrose ingestion (P < 0.05). This is the first objective report of gender specificity in sucrose induced analgesia in adult humans. The gender dependent variation in sucrose induced analgesia is prolonged in male (15 min) and short lived in female (5 min) volunteers. This knowledge may have important implications in pain management.