Teratogenic effects of static magnetic field on mouse fetuses

A short period of exposure of pregnant mice to a strong static magnetic field of 400 mT -- 8000 times that of the earth -- in a dorso-ventral direction had teratogenic effects on developing fetuses. Fetuses were exposed to the static magnetic field in utero for 6 min on 1 day from 7.5 to 14.5 days of pregnancy. Exposed and control groups consisted of 10 pregnant mice each; thus 160 animals were used in total. Various malformations were observed in 15.1%, 13.4%, 15.8%, 16.7%, 20.8%, 24.3%, 24.4%, and 14.1% of fetuses exposed on days 7.5, 8.5, 9.5, I0.5, 11.5, 12.5, 13.5, and 14.5 of pregnancy, respectively. Types of malformations were polydactylism, abdominal fissure, fused rib, vestigial 13th rib, lumbar rib, brain hernia, and curled tail, while only a low incidence (up to 2.8%) of curled tail was detected in control group. These deformations apparently caused by SMF exposure but the effect did not reflect so-called exposure period specificity.

Adaptive modification of the cats vestibulospinal reflex during sustained and combined roll tilt of the whole animal and forepaw rotation: cerebellar mechanisms

In decerebrate cats, the electromyogram (EMG) activity of the forelimb extensor triceps brachii (TB) increases during side-down roll tilt of the whole animal (vestibulospinal reflex, VSR) at about 0.15 Hz. (+/-10 degrees ), while decreases during side up tilt. On the other hand, the TB activity increases during dorsal flexion of the ipsilateral forepaw (0.15 Hz, +/-5 degrees-10 degrees ), but decreases during ventral flexion. In six experiments, these stimuli were synergistically associated (side-down tilt coincided with dorsal flexion of the forepaw), so that the EMG modulation of the TB activity was greater than that induced by the individual stimuli. During a 3-h period of this sustained stimulation, the amplitude of the pure VSR progressively increased to reach the maximum value at the end of the third hour and persisted unmodified during the post-adaptation period (1 h). In three experiments, animal tilt and forepaw rotation were antagonistically associated (side-down tilt coincided with ventral flexion of the forepaw). In these instances the VSR gain remained on the average stable, but, at the end of the 3-h period of combined stimulation, a proportion of TB responses to animal tilt showed a phase reversal. In a digitigrade animal like the cat, a dorsal flexion of the wrist is associated with a decrease in limb length and would occur when the extensor tone is not appropriate to support body weight; we propose, therefore, that somatosensory volleys elicited by wrist rotation modify the gain of VSR so as to maintain postural stability. Inactivation, on the side of muscle recording, of the corticocerebellar region which projects to the lateral vestibular nucleus of Deiters, by local microinjection of the GABA-A agonist muscimol (0.5 microl at 16 microg/microl), decreased the already adapted gain of VSR. In conclusion, the results of this study suggest that somatosensory reafferent inputs to the cerebellar vermis are used to plastically modify the gain of VSR, when external forces produce changes in the final posture of the foot during animal tilt.

Intracuneate mechanisms underlying primary afferent cutaneous processing in anaesthetized cats

The cutaneous primary afferents from the upper trunk and forelimbs reach the medial cuneate nucleus in their way towards the cerebral cortex. The aim of this work was twofold: (i) to study the mechanisms used by the primary afferents to relay cutaneous information to cuneate cuneolemniscal (CL) and noncuneolemniscal (nCL) cells, and (ii) to determine the intracuneate mechanisms leading to the elaboration of the output signal by CL cells. Extracellular recordings combined with microiontophoresis demonstrated that the primary afferent cutaneous information is communicated to CL and nCL cells through AMPA, NMDA and kainate receptors. These receptors were sequentially activated: AMPA receptors participated mainly during the initial phase of the response, whereas kainate- and NMDA-mediated activity predominated during a later phase. The involvement of NMDA receptors was confirmed by in vivo intracellular recordings. The cutaneous-evoked activation of CL cells was decreased by GABA and increased by glycine acting at a strychnine-sensitive site, indicating that glycine indirectly affects CL cells. Two subgroups of nCL cells were distinguished based on their sensitivity to iontophoretic ejection of glycine and strychnine. Overall, the results support a model whereby the primary afferent cutaneous input induces a centre-surround antagonism in the cuneate nucleus by activating (via AMPA, NMDA and kainate receptors) and disinhibiting (via serial glycinergic-GABAergic interactions) a population of CL cells with overlapped receptive fields that at the same time inhibit (via GABAergic cells) other neighbouring CL cells with different receptive fields.

In vivo demonstration of the ultrasound-modulated light technique

We present, to our knowledge for the first time, results of ultrasound-modulated light signals on living tissues. In particular, we analyze, both theoretically and experimentally, the effect of speckle fluctuations on the signal. We find that two different kinds of noise compete--shot noise and speckle noise--and are present at different levels in static phantoms and ex vivo tissue samples on the one hand and in dynamic phantoms and living tissues on the other hand.

Unexpected changes of rat cervical spinal cord tolerance caused by inhomogeneous dose distributions

PURPOSE

The effects of dose distribution on dose-effect relationships have been evaluated and, from this, iso-effective doses (ED(50)) established.

METHODS AND MATERIALS

Wistar rats were irradiated on the cervical spinal cord with single doses of unmodulated protons (150 MeV) to obtain sharp lateral penumbras, using the shoot-through technique, which employs the plateau of the depth-dose profile rather than the Bragg peak. Two types of inhomogeneous dose distributions have been administered: (1) 2 4-mm fields with 8- or 12-mm spacing between the center of the fields (referred to as split-field) were irradiated with variable single doses and (2) cervical spinal cord was irradiated with various combinations of relatively low doses to a large volume (20 mm) combined with high doses to a small volume (4 mm) (referred to as bath and shower). The endpoint for estimating the dose-response relationships was paralysis of the fore or hind limbs.

RESULTS

The split-field experiments (2 x 4 mm) showed a shift in the dose-response curves, giving significant higher ED(50) values of 45.4 Gy and 41.6 Gy for 8- and 12-mm spacing, respectively, compared with the ED(50) of 24.9 Gy for the single 8 mm (same total tissue volume irradiated). These values were closer to the ED(50) for a single 4-mm field of 53.7 Gy. The bath and shower experiments showed a large decrease of the ED(50) values from 15-22 Gy when compared with the 4-mm single field, even with a bath dose as low as 4 Gy. There were no histologic changes found in the low dose bath regions of the spinal cord at postmortem.

CONCLUSIONS

Not only the integral irradiated volume is a determining factor for the ED(50) of rat cervical spinal cord, but also the shape of the dose distribution is of great importance. The high ED(50) values of a small region or shower (4 mm) decreases significantly when the adjacent tissue is irradiated with a subthreshold dose (bath), even as low as 4 Gy. The significant shift to lower ED(50) values for induction of paralysis of the limbs by adding a low-dose bath was not accompanied by changes in histologic lesions. These observations may have implications for the interpretation of complex treatment plans and normal tissue complication probability in intensity-modulated radiotherapy.

Inter-species extrapolation of skin heating resulting from millimeter wave irradiation: modeling and experimental results

This study reports measurements of the skin surface temperature elevations during localized irradiation (94 GHz) of three species: rat (irradiated on lower abdomen), rhesus monkey (posterior forelimb), and human (posterior forearm). Two exposure conditions were examined: prolonged, low power density microwaves (LPM) and short-term, high power density microwaves (HPM). Temperature histories were compared with calculations from a bio-heat transfer model. The mean peak surface temperature increase was approximately 7.0 degrees C for the short-term HPM exposures for all three species/locations, and 8.5 degrees C (monkey, human) to 10.5 degrees C (rat) for the longer-duration LPM exposures. The HPM temperature histories are in close agreement with a one-dimensional conduction heat transfer model with negligible blood flow. The LPM temperature histories were compared with calculations from the bio-heat model, evaluated for various (constant) blood flow rates. Results suggest a variable blood flow model, reflecting a dynamic thermoregulatory response, may be more suited to describing skin surface temperature response under long-duration MMW irradiation.

The effect of extracorporeal shock wave treatment (ESWT) on bone defects. An experimental study

The aim of this study was to investigate the effects of extracorporeal shock wave therapy (ESWT) on the formation of callus in bone defects created in rabbit radii. this study searches for an answer to whether ESWT may have a therapeutic effect on bone defects. A bone defect with a radius of 1 cm was created in both forelimbs of 20 rabbits. At the 7th, 14th, and 21st days ESWT treatment was applied to the forming callus in the right radius under fluoroscopic control. At the 6th and 12th weeks, the animals were sacrificed and callus analysis was performed by computerized scan, dual energy x-ray absorptiometer. Histological analyses were also performed. The results revealed that the average callus area in the right (ESWT applied) radial defect was greater in both groups and statistically significant at the 12th week (p < 0.05). There was no difference in bone density between defects. Histologically the callus area was greater on the right side (ESWT applied side) in both groups. However in the first group trabeculae were occupying less space on the right side. Granulation tissue areas and chondroid areas were greater on the right side. We conclude that ESWT has a disorganizing and dispersing rather than a direct osteoinductive effect on forming callus. This effect may play a therapeutic role in bone defects and in situations like callus lengthening where a greater amount of callus is necessary.

Radiation-induced apoptosis and limb teratogenesis in embryonic mice

In utero irradiation of the fetus during the period of organogenesis induces a dramatic increase in malformation. However, the mechanisms underlying the teratogenesis remain to be elucidated. In the present study, the correlation between radiation-induced apoptosis and limb malformation was examined in mice. The mice were exposed to X rays in utero on day 11 of gestation during the period of organogenesis of limb buds. A marked increase in the number of apoptotic cells in the predigital regions in the forelimb buds was detected 4 h after irradiation. The preinterdigital regions of the forelimb buds did not show such an increase at the same time. Aphlangy and ectrodactyly were the main types of anomalies observed on day 19 in the limbs of the fetuses irradiated with 5 Gy. The increases in prenatal death and teratogenesis in limb digits in living fetuses were dependent on dose. The possible mechanisms involved are discussed.

Response of rat spinal cord to very small doses per fraction: lack of enhanced radiosensitivity

Our previous work with rat spinal cord demonstrated that the linear quadratic (LQ) model based on data for large fraction sizes (alpha/beta of 2.4 Gy) failed to predict isoeffective doses between 1 and 2 Gy per fraction, and under-estimated the sparing effect of small doses per fraction given once daily. In contrast, data from mouse skin and kidney, and recent in vitro results revealed a paradoxical increase in radiosensitivity at below 1 Gy per fraction. To assess whether enhanced radiosensitivity is present in the spinal cord below 1 Gy per fraction, the rat spinal cord (C2-T2) was irradiated initially with three daily doses of 10.25 Gy (top-up doses representing 90% of tolerance), followed by graded single doses or fractionated doses in 1.5, 1.0, 0.8, 0.6 or 0.4 Gy fractions given once daily. To limit the overall treatment time to < or = 8 weeks, a small number of the 0.6- and 0.4-Gy fractions were given twice daily with an interfraction interval of 16 h. The end-point was forelimb paralysis secondary to white matter necrosis, confirmed histologically. The ED50 values, excluding the top-up doses, were 5.8, 10.6, 14.8, 15.2, 15.9 and 19.1 Gy for a single dose and doses in 1.5-, 1.0-, 0.8-, 0.6- and 0.4-Gy fractions, respectively. The data gave an alpha/beta of 2.1 Gy (95% CI, 1.4, 2.7 Gy). Pooling the data separately, the alpha/beta value was 2.3 Gy (95% CI, 0.82, 3.7 Gy) for fraction sizes > or = 1 Gy, and 1.2 Gy (95% CI, 0.16, 2.3 Gy) for the 0.8-, 0.6- and 0.4-Gy experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Irradiation inhibits the regeneration of aneurogenic limbs

The developing arms of axolotl larvae from the 2-digit stage onward and the aneurogenic arms of surgically denervated larvae maintained in parabiosis are able to regenerate after amputation. Such regeneration is uniformly inhibited by local irradiation of the arm, whether innervated or not. This demonstration refutes a recent hypothesis that X-rays interfere with a special activity of nerves required for regeneration, and supports the earlier concept that X-rays act directly on those cells which must proliferate to form the regenerated tissues.