Hypokinetic stress-induced modifications of the pain sensitivity in rats

We examined the modifying effect of hypokinetic stress on the duration of behavioral phenomena in rats under conditions of experimentally induced tonic somatic, visceral, acute thermal, and electrostimulation-evoked pain. Stress of the above type (hypokinetic) was found to modify the pain sensitivity in rats related to all tested types of pain stresses of different etiology. Changes in the pain sensitivity of the animals under conditions of experimental pain tests depended on the duration of mobility restriction and could demonstrate opposite directions. Neirofiziologiya/Neurophysiology, Vol. 39, No. 2, pp. 174–183, March–April, 2007.     

Coupling of c-fos expression in the spinal cord and amygdala induced by dorsal neck muscles fatigue

c-fos gene expression in the cervical spinal cord and amygdala was examined in anaesthetized rats following muscle fatigue caused by intermittent high-rate (100 s⁻¹) electrical stimulation of the dorsal neck muscles (m. trapezius and m. splenius). Fatigue-related increases in c-fos expression were observed on the stimulated muscle side in the cervical C2–C4 (layers 1, 3–5, 7 and 10) spinal segments, bilaterally in the lumbar L4–L6 (layer 1) segments and in contralateral central (Ce), medial (Me), and basomedial (BM) amygdaloid nuclei. A scarce number of staining cells were found within lateral and basolateral nuclei. The rostro-caudal extent of c-fos expression in the spinal cord supports functional coupling of the cervical and lumbar regions during the neck muscle fatigue development. The distinct c-fos expression in the Ce and Me amygdaloid nuclei suggests that they may contribute to mediating the neck muscle fatigue-related nociception, autonomic and behavioural responses.     

Infantile stage of rat development in behavioral parameters of depression-like state and pain response

In the 7–8- and the 10–11-day old male rat pups born to dams exposed to an immobilization stress for the last week of pregnancy and to the dams exposed to no stress (control), behavioral parameters were studied: the level of depression in the test of forced swimming (the Porsolt’s test) and 24 h after a long pain response during inflammation (the formalin test—a subcutaneous injection of 2.5% formalin into the hind leg plantar pad). In control pups, significant age-related changes in the forced swimming were revealed: the immobility time was longer in animals of the older age group, whereas no age differences were found in parameters of the persistent inflammatory pain and in flexing + shaking behavior. The prenatal stress produced an increase in the immobility time and the flexing + shaking behavior in the 7–8-day old, but not in the 10–11-day old rat pups. This resulted in elimination of the age differences in the immobility time in the prenatally stressed animals. Thus, use of different methodic approaches has allowed revealing peculiarities in the parameters of the degree of depression and duration of the pain response at inflammation in the 7–8- and 10–11-day old rat pups, which indicates heterogeneity of the infantile development stage that, according to literature data, includes in rats the period from the 5th to the 10th postnatal days.     

Behavioral responses to phasic nociceptive stimulation occurring on the background of a tonic pain focus in ontogeny of the rabbit

The effect of a focus of tonic pain (a subcutaneous injection of formalin into the dorsal field of the shin) on the thresholds of a defense reaction, an attempt to jump out of the chamber in response to a nociceptive electrocutaneous stimulation of the hindpaw1, was studied in the 20– 25-day-old and adult rabbits. The tonic pain produces a biphasic reduction of the defense reaction threshold. At the first phase, hyperalgesia is more pronounced than in the second one, but its duration is shorter. Changes in pain sensitivity in the rabbits proceed in the same direction in both age groups and coincide in time with increase of specific behavioral responses to the formalin injection (licking and shaking the paw). In the 20–25-day-old rabbits the reduction of the threshold of the defense reaction and duration of hyperalgesia phases are more pronounced than in adult animals. Deceased.     

Roles of different neurochemical systems in mechanisms underlying the antinociceptive effect of extrahigh-frequency electromagnetic radiation

We studied the effect of low-intensity extrahigh-frequency (EHF) electromagnetic radiation (EMR) on the duration of a pain behavioral reaction in rats under conditions of experimental induction of tonic pain (formalin test). The antinociceptive effect of EHF irradiation was modulated by suppression of the activity of a few neurochemical systems resulting from the blockade of receptors of opioid peptides, α-and β-adrenoreceptors, receptors of dopamine and melatonin, as well as from inhibition of serotonin synthesis. We demonstrated that all the respective neurochemical systems are to a certain extent involved in the mechanisms underlying the analgesic action of EHF EMR. Within an early phase of pain stress, functioning of the opioidergic and noradrenergic systems and the effects of melatonin play leading roles, while the activity of the serotonergic system plays such a role within the second (tonic) phase. Neirofiziologiya/Neurophysiology, Vol. 39, No. 2, pp. 165–173, March–April, 2007.     

Antinociceptive effects of low-intensity extrahigh-frequency electromagnetic radiation

We studied the effect of low-intensity extrahigh-frequency (EHF) electromagnetic radiation (EMR) on changes of behavior phenomena in rats observed under conditions of experimentally induced tonic somatic, visceral, and acute thermal pain. Preliminary irradiation of the animals with EHF EMR was found to exert clear antinociceptive effects. Decreases in the intensity of pain reactions were observed under conditions of both single and repeated irradiation sessions. Neirofiziologiya/Neurophysiology, Vol. 38, No. 4, pp. 331–341, July–August, 2006.     

Nociceptive reaction-related state of glial intermediate filaments in the brain of rats with hyperfunction of the thyroid gland: An ontogenetic aspect

In experiments on Wistar rats of two age groups (5 weeks old and mature, 5 months old), we studied the content and polypeptide composition of glial fibrillary acidic protein (GFAP) in the cerebral cortex, hippocampus, thalamus, and brainstem under conditions of experimentally induced hyperfunction of the thyroid gland, as well as of combination of hyperthyroidism with the pain model (consequences of laparotomy). The hyperthyroid state was created by administration of L-thyroxine (initial dose, 10 μg/day) with food for 2 weeks; the dose was increased daily by 10 μg. At the end of experiment, we measured the level of thyroxine in the blood serum using an immunoenzymatic technique. We found that in the hyperthyroid state 5-week-old rats showed a significant increase in the content of filamentous GFAP fraction in the hippocampus, while when this influence was combined with the postoperation pain syndrome, an increase was observed in the brainstem (by 18 to 27%). Results of immunoblotting demonstrated that degraded polypeptides with a molecular mass of 47 to 45 kdalton were manifested under these conditions, which is indicative of intensification of cytoskeletal rearrangement of astroglia. In mature rats under the same conditions, we observed a drop in the level of insoluble polypeptides of intermediate filaments in astrocytes in the thalamus, hippocampus, and cerebral cortex. Neirofiziologiya/Neurophysiology, Vol. 38, No. 4, pp. 280–286, July–August, 2006.     

Gut retention of metals in rats

In sucklings, a high fraction of orally administered metals and radionuclides is retained in the gut. The location of elements in the gut is of interest because of their potential local health effect. The purpose of this work was to evaluate the influence of chelation therapy on gut retention and location of cadmium, mercury, and cerium in-suckling rats. Radionuclides^115mCd,²⁰³Hg, and¹⁴¹Ce were administered orally to 6-d-old rats. Chelating agent Zn-DTPA (3.64 mmol/kg) was administered to animals that received^115m Cd or¹⁴¹Ce and Na-DMPS (375 μmol/kg) to those that received²⁰³Hg, immediately and 24 h or 24 and 48 h after radionuclide administration. Radio-activity was determined in the whole body and gastrointestinal tract 6 d later. Both early and delayed chelation treatment very effectively reduced whole body retention, and this was mainly owing to reduced gut retention. Although chelation therapy reduced gut retention of administered radionuclides 3–30 times, the site of metal accumulation and retention in the intestine remained unchanged. For all 3 radionuclides, both after early and delayed therapy, the site of metal accumulation was always the lower part of small intestine—ileum.     

The Impairment of Liver DNA Conformation and Liver Apoptosis of Mice Caused by CeCl3

Cerium (Ce) was shown to cause various toxic effects both in rats and mice; however, the molecular mechanism by which Ce exert theirs toxicity is still understood. In this report, the impairment of liver DNA conformation and liver apoptosis of mice caused by CeCl₃ was studied in vivo using inductively coupled plasma–mass spectrometry, various spectral methods, gel electrophoresis, and transmission electron micrograph. We found that the coefficients of liver to body weight of the mice treated with CeCl₃ were significantly increased. Ce³⁺ could be significantly accumulated in the liver, and it insert itself into DNA base pairs and/or bind to DNA nucleotide, and alter the conformation of DNA. Furthermore, the evaluation by gel electrophoresis and transmission electron micrograph showed that higher dose of Ce³⁺ could cause DNA cleavage and hepatocyte apoptosis in mice. Therefore, our study aroused the attention of Ce application and exposure effects especially on human liver for long-term and low-dose treatment.     

Lateral spinal nucleus of the rat: NADPH-diaphorase activity and Fos expression after noxious peripheral stimulation

Results of electrophysiological studies suggest a significant role of the lateral spinal nucleus (LSpN) in the transmission of nociceptive signals. In our study, the presence of Fos immunoreactivity and NADPH-diaphorase positivity was observed in the rat LSpN following noxious peripheral subcutaneous stimulation. Formalin-induced unilateral hindpaw stimulation in the rat caused bilateral NADPH-d reactivity and ipsilateral Fos expression in this nucleus. In the LSpN of the L3–L5 segments of stimulated rats, on average, 4.1 ± 1.2 NADPH-d-positive, NADPH-d(+), 5.1+1.8 Fos-immunoreactive, Fos(+), and 3.0 ± 1.1 double-labeled neurons per 25-μm-thick section were found unilaterally. A close anatomical relationship between NADPH-d(+) processes and Fos(+) cell nuclei in the LSpN was also observed following noxious peripheral stimulation. These neuroanatomical findings support the hypothesis that the LSpN is involved in pain processing and suggest an important role of nitric oxide-mediated signal transduction in this nucleus. Neirofiziologiya/Neurophysiology, Vol. 40, No. 1, pp. 38–42, January–February, 2008.     

Effect of Adaptation to Graduated Physical Exercises on the Function of the Rat Myocardium

On isolated hearts obtained from control rats and rats subjected to regular physical exercises (forced swimming) during 6 weeks, we studied the contractile activity of the heart, resistance of the myocardium to ischemia/reperfusion-induced injuries, as well as the dependence of the developed and end-diastolic pressures in the aortic ventricle (AV) on the strain of the myocardium (by means of a dosed increase in the volume of a polyethylene reservoir inserted into the ventricle). It was demonstrated that adaptation to regular graduated physical exercises exerts a positive effect on the functional state of the AV myocardium and its contractile function. This was manifested in intensification of the contractile activity of the myocardium, a decrease in its oxygen “job cost,” and an increase in the resistance to injuries induced by ischemia-reperfusion. In addition, regular physical trainings led to an increase in the resistance of the AV myocardium to the strain. In trained rats, the plateau of the Frank–Starling plot was significantly greater than that in control animals, while the rigidity of the AV myocardium was significantly lower. Neirofiziologiya/Neurophysiology, Vol. 41, No. 1, pp. 41–47, January–February, 2009.     

Cutaneous Magnetic Stimulation Reduces Rat Chronic Pain via Activation of the Supra-Spinal Descending Pathway

Recent studies have demonstrated that magnetic stimulation (MS) can induce cellular responses such as Ca²⁺ influx into the cultured neurons and glia, leading to increased intracellular phosphorylation. We have demonstrated previously that MS reduces rat neuropathic pain associated with the prevention of neuronal degeneration. Thus, we aimed to elucidate the actions of MS in relation to modulation of spinal neuron–glia and the descending inhibitory system in chronic pain. The male SD rats intrathecally implanted with catheters were subjected to sciatic nerve ligation (CCI). MS is a low power apparatus characterized by two different frequencies, 2 KHz and 83 MHz. Rats were given MS to the skin (injured sciatic nerve) for 10 min from the seventh day after CCI. The paw withdrawal latency (PWL) evoked by thermal stimuli was measured for 14 days after CCI. Immunohistochemistry for Iba-1 or GFAP was performed after 4% paraformaldehyde fixation (microscopic analysis). We employed microdialysis for measuring CSF 5-HIAA as a reflection of 5-HT release by MS stimulation. Following CCI, rats showed a decrease in PWL after CCI, and the decrease continued until the 14th day. With MS treatment, the decrease in PWL was reduced during the 10–14 day after CCI. Injection of JNK-1 inhibitors on the 14th day antagonized the analgesic effect of MS. MS also eliminated the CCI-induced decrease in GFAP immunoreactivity. Moreover, MS evoked spinal 5-HT release reflected by increase in spinal 5-HIAA level. Thus, we demonstrate that a novel magnetic stimulator used cutaneously can ameliorate chronic pain by not only preventing abnormal spinal neuron–glia interaction, but also through the activation of the supra-spinal descending inhibitory system.     

Auditory brainstem responses to airborne sounds in the aquatic frog Xenopus laevis: correlation with middle ear characteristics

In this study we recorded auditory brainstem responses to airborne sounds to determine the hearing sensitivity of Xenopus laevis frogs and correlated their hearing profiles with middle ear characteristics. In newly metamorphosed frogs (body mass 0.5–0.76 gm, snout-vent length 17–20 mm) best hearing sensitivities were measured in the 2.4–2.8 kHz range, whereas optimal hearing sensitivity of older adults (body mass 18–90 gm; snout-vent length 57–100 mm) ranged from 1.0 to 1.2 kHz. Middle ear volumes reconstructed from serial sections showed approximate volume of 0.002 cc and 0.04–0.07 cc in newly metamorphosed and older frogs, respectively. This inverse frequency–volume relationship is consistent with the properties of an acoustic resonator indicating that differences in best hearing sensitivity are at least in part correlated to variation in middle ear volumes for airborne sounds. These results are consistent with peak frequency vibrational velocity profiles of Xenopus tympanic disk that have been shown to be dependent on underlying middle ear volumes and corroborate the occurrence of peak amplitudes of otoacoustic emissions in the 1.0–1.2 kHz region in adult Xenopus frogs.     

Nasal administration of arthritis-related T cell epitopes of heat shock protein 60 as a promising way for immunotherapy in chronic arthritis

Adjuvant Arthritis (AA) can be induced in Lewis rats by immunisation with mycobacterial antigens. The disease can be passively transferred with T cell clone A2b, which recognises the 180–188 amino acid sequence in mycobacterial heat shock protein 60 (hsp60) and which crossreacts with crude cartilage proteoglycans. We succeeded to induce peripheral tolerance to this AA-associated T cell epitope following nasal administration of a peptide containing this epitope (mycobacterial hsp60 176–190). In rats treated nasally with 176–190 and immunised with mycobacterial hsp60, proliferative responses to 176–190 were reduced. AA was inhibited nasally with 176–190 treated rats and not in rats nasally treated with a control mycobacterial hsp60 peptide (211–225). Moreover, nasal 176–190 led to similar arthritis protective effects in a non-microbially induced experimental arthritis (avridine induced arthritis). In a subsequent study we tried to prevent and to treat AA through nasal administration of mycobacterial hsp60 peptide 180–188 and a peptide analogue of 180–188, 180–188_L183->A (Alanine 183), which has been shown to have an increased MHC-binding affinity for rat RT1 B¹ and an increased capacity to inhibit the proliferative A2b responsein vitro. We found that nasal administration of 180–188 had a moderate arthritis suppressive effect in AA, whereas its analogue peptide Alanine 183, had a strong suppressive effect. This strong arthritis suppressive effect was only partly due to the higher MHC-binding affinity for rat RT1 B¹. Furthermore, it was possible to passively transfer nasal Alanine 183 induced disease protection. The present findings may in our view offer novel prospects for immunotherapy through nasal administration of (analogue) peptides, with a mimicry relationship with joint specific cartilage proteoglycan epitopes.     

Differential effects of aging on EEG after baclofen administration

Baclofen is a selective gamma-aminobutyric acid (GABA) type B agonist that may have important medicinal uses, such as in analgesics and drug addiction treatment. In addition, evidence is accumulating that suggests GABAergic-mediated neurotransmission is altered during aging. This study investigated whether baclofen administration (5 mg kg⁻¹) induces differential effects on cortical electrical activity with age. Electroencephalograms (EEGs) were recorded from young (3–4 months) and aged (15–17 months) rats, and both the absolute and relative powers in five frequency bands (delta: 2–4 Hz; theta: 4–8 Hz; alpha: 8–12 Hz; beta: 12–20 Hz; gamma: 20–100 Hz) were analyzed. Before administration of baclofen, we found that the EEG relative power in the beta band was higher in the aged than that in the young rats. After administration of baclofen, there was a slower increase in the relative power in the delta band in the aged than that in the young rats. Moreover, there was no significant difference between the two age groups in absolute power in any frequency band. These findings indicate that baclofen treatment appears to differentially modify cortical EEG activity as a function of age. Our data further elucidate the relationship between GABA_B receptor-mediated neurotransmission and aging.     

Characterization of beam patterns of bottlenose dolphin in the transverse plane

The characteristics of absolute auditory sensitivity of the bottlenose dolphin (Tursiops truncatus) in the transverse plane have been measured using short broadband stimuli simulating dolphin clicks (with energy maximum at frequencies 8, 16, 30, 50 and 100 kHz). Experiments were performed using the method of conditioned reflexes with food reinforcement. It is shown that, in the frequency range of 8–30 kHz, the absolute sensitivity of dolphin hearing in any ventral and lateral directions of the transverse plane is only 2–8 dB worse than in the rostral direction. Moreover, it is 25–30 dB better than at 50–100 kHz. At 8–30 kHz, pronounced dorsoventral asymmetry has been observed. In this frequency range, it reaches 15–18 dB whereas at 50–100 kHz this asymmetry decreases to 2–3 dB. In the dorsal direction, the auditory sensitivity is 18 dB worse than in the rostral one at ∼8 kHz, and the difference rises smoothly to 33 dB at ∼100 kHz. At 50–100 kHz, the acoustical thresholds in the transverse plane relative to those for the with rostral direction get worse almost uniformly in all directions by 25–33 dB. As a result, in the transverse plane the beam patterns are nearly circular, unlike those at 8–30 kHz. The results are discussed in terms of the model of sound perception through the left and right mental foramens. The biological relevance of such asymmetry is emphasized.     

Consequences of the prenatal depletion of serotonin and stress on nociceptive sensitivity in rats

The long-term effects of serotonin (5-HT) synthesis alteration and of restraint stress experienced by pregnant Wistar rats on pain sensitivity (evaluated by the indices of the biphasic behavioral response in the formalin test) were studied in their 90-day-old offspring. Prenatal 5-HT depletion decreased pain sensitivity in one third of the rats and failed to change it in the rest of the rast. In these later, however, an obvious tendency for an increase of interphase duration in females and its decrease in males were revealed that indicates changing of the activity of the descending serotoninergic system modulating nociceptive signals at the level of the spinal dorsal horns. Prenatal stress decreased pain sensitivity in 50% of the rats with prenatal deficiency of 5-HT but increased it in the rest of the animals. Increase of pain sensitivity also occurred in the control rats but to a lesser extent (significantly in flexing + shaking behavior during the second phase) compared to the animals with prenatal 5-HT depletion. In the latter, sex differences were found in effects of prenatal stress on pain sensitivity. The present data point an important role of 5-HT in: 1) embryonic development of tonic nociceptive system which is modulated in the CNS by mechanisms differing from those of acute pain; 2) mediation of the prenatal stress influence on pain sensitivity in the formalin test in adult rats.     

Metrifonate and dichlorvos: Effects of a single oral administration on cholinesterase activity in rat brain and blood

Cholinesterase activities in rat forebrain, erythrocytes, and plasma were assessed after a single oral administration of metrifonate or dichlorvos. In 3-month-old rats, the dichlorvos (10 mg/kg p.o.)-induced inhibition of cholinesterase reached its peak in brain after 15–45 min and after 10–30 min in erythrocytes and plasma. Cholinesterase activity recovered rapidly after the peak of inhibition, but did not reach control values in brain and erythrocytes within 24 h after drug administration. The recovery of plasma cholinesterase activity, in contrast, was already complete 12 h after dichlorvos treatment. Metrifonate (100 mg/kg p.o.) had qualitatively similar inhibition kinetics as dichlorvos, albeit with a slightly delayed onset. Peak values were attained 45–60 min (brain) and 20–45 min (blood), after drug administration. Apparently complete recovery of cholinesterase activity was noted in both tissues 24 h after treatment. The dose-dependence of drug-induced inhibition of cholinesterase in rat blood and brain was determined at the time of maximal inhibition, i.e., 30 min after dichlorvos treatment and 45 min after metrifonate treatment. The oral ED₅₀ values obtained for dichlorvos were 8 mg/kg for brain and 6 mg/kg for both erythrocyte and plasma cholinesterase. The corresponding oral ED₅₀ values for metrifonate were 10 to 15 times higher, i.e., 90 mg/kg in brain and 80 mg/kg in erythrocytes and plasma. In rats deprived of food for 18 h before drug treatment, the corresponding ED₅₀ values for metrifonate were 60 and 45 mg/kg, respectively, indicating an about two-fold higher sensitivity of fasted rats to metrifonate-induced cholinesterase inhibition compared to non-fasted rats. Compared to 3-month-old rats, 19-month-old rats showed a higher sensitivity towards metrifonate and dichlorvos. At the time of maximal inhibition, there was a strong correlation between the degree of cholinesterase inhibition in brain and blood. These results demonstrate that single oral administration of metrifonate and dichlorvos induces an inhibition of blood and brain cholinesterase in the conscious rat in a dose-dependent and apparently fully reversible manner. While the efficiency of a given dose of inhibitor may vary with the satiety status or age of the animal, the extent of brain ChE inhibition can be estimated from the level of blood ChE activity.     

Modifications of NMDA-induced convulsive reactions in diazepam-tolerant rats

In acute experiments on rats, the mean ED₅₀ values of intraventricularly injected NMDA for evoking clonic seizures and tonic extension of the forelimbs were 0.69 and 11.36 μg per animal, respectively. When these indices were measured under conditions of the development of tolerance to diazepam (2 weeks from the abolition of a 3-week-long diazepam treatment, 0.5 mg/kg, i.p.), the dropped to 0.30 and 2.66 μg per animal, respectively. The results show that in diazepam-tolerant rats the sensitivity to the epileptogenic influence of NMDA increases, and such an increase is more significant with respect to tonic seizure manifestations. Neirofiziologiya/Neurophysiology, Vol. 32, No. 2, pp. 95–97, March–April, 2000.     

Thyroid hormones increase Na+–Pi co-transport activity in intestinal brush border membrane: Role of membrane lipid composition and fluidity

In the present study, we documented the promising role of thyroid hormones status in animals in modulation of Na⁺–P_i transport activity in intestinal brush border membrane vesicles (BBMV) which was accompanied with alterations in BBM lipid composition and fluidity. Augmentation of net P_i balance in hyperthyroid (Hyper-T) rats was fraternized with accretion of P_i transport across BBMV isolated from intestine of Hyper-T rats as compared to hypothyroid (Hypo-T) and euthyroid (Eu-T) rats while Na⁺–P_i transport across BBMV was decreased in Hypo-T rats relative to Eu-T rats. Increment in Na⁺–P_i transport in intestinal BBMV isolated from Hyper-T rats was manifested as an increase in the maximal velocity (V_max) of Na⁺–P_i transport system. Furthermore, BBMV lipid composition profile in intestinal BBM from Hyper-T was altered to that of Hypo-T rats and Eu-T rats. The molar ratio of cholesterol/phospholipids was higher in intestinal BBM from Hypo-T rats. Fluorescence anistropy of diphenyl hexatriene (rDPH) and microviscosity were significantly decreased in the intestinal BBM of Hyper-T rats and decreased in Hypo-T rats as compared to Eu-T rats which corroborated with the alteration in membrane fluidity in response to thyroid hormone status of animals. Therefore, thyroid hormone mediated change in membrane fluidity might play an important role in modulating Na⁺–P_i transport activity of intestinal BBM. (Mol Cell Biochem 278: 195–202, 2005)