X-irradiated Animals Research Articles

Biochemical effects of low-dose whole body x-irradiation on mouse liver and the protective action of ectoine

Purpose: To investigate the possible role of ectoine, which is known to protect protein hydration and folding and structural organization of biological membranes, in protecting mouse liver against low-dose x-irradiation. Methods: The study included thirty Swiss albino mice weighing 20 - 22 g each, which were divided into five groups of six animals each: group (1) naive animals serving as control, group (2) animals irradiated with a whole-body 2 Gy single dose of x-ray, and sacrificed after one day, group (3) x-irradiated and sacrificed after one week (each animal in the 3 groups received 0.2 mL saline daily by oral gavage). Group 4 consisted of x-irradiated animals dosed with ectoine 200 mg/kg in saline and sacrificed after one day. Group 5 cmoprised of x-irradiated animals and were dosed daily with ectoine 200 mg/kg and sacrificed after one week. The evaluated inflammation parameters in the animals’ liver were interleukin- 1β (IL-1β), interleukin-6 (IL-6), interleukin-10 (IL-10) and prostaglandin E2 (PGE2). Furthermore, the oxidative stress parameters, viz, malondialdehyde (MDA), reduced glutathione (GSH), oxidized glutathione (GSSG) and their ratio (GSH/GSSG) were also assessed. Results: Whole body low-dose x-irradiation resulted in statistically significant (p ≤ 0.05) increases in all ILs tested as well as PGE2 of mice liver. Indications of oxidative stress included elevated levels of MDA and oxidized glutathione with decreased reduced glutathione. The effects of radiation were progressive and the changes in the tested parameters increased from day 1 to day 7. Administration of ectoine significantly (p ≤ 0.05) ameliorated the biochemical effects induced by whole body x-irradiation. Furthermore, the modulating action was dependent on the accumulation of ectoine, as it was more effective after repeated administration. Conclusion: Ectoine has a post-irradiation protective effect on mouse liver via its action on inflammatory and oxidative stress pathways. It probably has similar action in other vital organs. Preventive treatment of healthcare personnel and technicians frequently exposed to low doses of radiation with ectoine is worth investigating. Keywords: X-irradiation, Ectoine, Oxidative stress, Mice, Radioprotection

IN VIVO RADIOPROTECTIVE EFFECTS OF WHEATGRASS (TRITICUM AESTIVUM) EXTRACT AGAINST X-IRRADAITION-INDUCED OXIDATIVE STRESS AND APOPTOSIS IN PERIPHERAL BLOOD LYMPHOCYTES IN RATS

Objectives: The present study was undertaken to investigate the possible protective potential of wheatgrass extract against radiation-induced toxicity in peripheral lymphocytes of rats exposed to a fractionated dose of X-rays.Methods: Effects of the X-irradiation with and without wheatgrass were studied on various parameters in peripheral lymphocytes including antioxidant defense system and apoptosis. Male Sprague-Dawley rats were divided into four different groups: Normal control group, X-ray-irradiated group (21 Gy over a span of 7 days), wheatgrass-treated group (80 mg/100 g bodyweight for 2 weeks), and X-rays-irradiated + wheatgrass-treated group. All the biochemical indices which included lipid peroxidation (LPO), reduced glutathione, reactive oxygen species (ROS), and activities of antioxidant enzymes were investigated in lymphocytes. Terminal deoxynucleotidyl transferase dUTP nick-end labeling assay was carried out to assess the apoptosis in lymphocytes following whole-body X-irradiation.Results: Whole-body X-irradiation to rats resulted in significant increase in LPO with concomitant depression of antioxidant enzymes activities, namely, superoxide dismutase, catalase, and glutathione peroxidise (GPx) in lymphocytes. Further, the present study witnessed a significant increase in the number of apoptotic lymphocytes in the X-irradiated animals. However, wheatgrass supplementation lowered the LPO levels, restored cellular antioxidant status, and provided significant protection against radiation-induced apoptosis.Conclusions: Based on these observations, the present study suggests that wheatgrass extract has the potential to be used as an effective radioprotectant against radiation-induced oxidative stress and apoptosis in peripheral lymphocytes of whole-body X-ray-exposed rats.

Quantitative and Noninvasive Assessment of Prenatal X-Ray-Induced CNS Abnormalities Using Magnetic Resonance Imaging

Our purpose was to noninvasively assess formation of the microvasculature, blood-brain barrier (BBB) and blood-CSF barrier formation of prenatal X-ray-induced CNS abnormalities using quantitative MRI. Eight pregnant female Sprague-Dawley rats were divided into two groups consisting of control and X-irradiated animals. After birth, 20 neonatal male rats were divided into four groups of five rats. To evaluate the development of the BBB, changes in T(1) induced by Gd-DTPA were compared quantitatively in normal and prenatally irradiated animals in the formative period 1 to 2 weeks after birth. To assess the abnormalities of the microvasculature, quantitative perfusion MRI and MR angiography were also used. Histology was also performed to evaluate the BBB (albumin) and vascular endothelial cells (laminin). Decreased cerebral blood flow (CBF) and angioarchitectonic abnormalities were observed in the prenatally irradiated rats. However, abnormalities of the BBB and blood-CSF barrier were not observed using Gd-enhanced MRI and albumin staining. Quantitative perfusion MRI, MR angiography and Gd-enhanced T(1) mapping are useful for assessing CNS disturbance after prenatal exposure to radiation. These techniques provide important diagnostic information for assessing the condition of patients during the early stages of life after accidental or unavoidable prenatal exposure to radiation.

Efficacy of Intracerebral Delivery of Carboplatin in Combination With Photon Irradiation for Treatment of F98 Glioma-Bearing Rats

To evaluate the efficacy of prolonged intracerebral (i.c.) administration of carboplatin by means of ALZET osmotic pumps, in combination with radiotherapy for the treatment of intracranial F98 glioma in rats. Seven days after stereotactic implantation of F98 glioma cells into the brains of Fischer rats, carboplatin was administrated i.c. by means of ALZET pumps over 6 days. Rats were treated at the European Synchrotron Radiation Facility with a single 15-Gy X-ray dose, either given alone or 24 h after administration of carboplatin. Untreated rats had a mean survival time (MST) +/- SE of 23 +/- 1 days, compared with 44 +/- 3 days for X-irradiated animals and 69 +/- 20 days for rats that received carboplatin alone, with 3 of 13 of these surviving >195 days. Rats that received carboplatin followed by X-irradiation had a MST of >142 +/- 21 days and a median survival time of >195 days, with 6 of 11 rats (55%) still alive at the end of the study. The corresponding percentage increases in lifespan, based on median survival times, were 25%, 85%, and 713%, respectively, for carboplatin alone, radiotherapy alone, or the combination. Our data demonstrate that i.c. infusion of carboplatin by means of ALZET pumps in combination with X-irradiation is highly effective for the treatment of the F98 glioma. They provide strong support for the approach of concomitantly administering chemo- and radiotherapy for the treatment of brain tumors.

The effect of prenatal X-irradiation on the developing cerebral cortex of rats. II: A quantitative assessment of glial cells in the somatosensory cortex

The developing central nervous system is known to be highly vulnerable to X-irradiation. Although glial cells are involved in various brain functions, knowledge on the effects of X-irradiation on glial cells is limited. Therefore, the purpose of the present study was to evaluate the effects of prenatal X-irradiation on glial cells. Pregnant Wistar rats were exposed to X-irradiation at a dose of 1.0Gy on day 15 of gestation. Their offspring were examined at 7 weeks of age. The forebrain weight of X-irradiated rats was significantly lower than that of the age-matched controls. Histological quantification with stereology of the somatosensory cortex (SC) revealed no significant difference in the numerical density of glial cells between the X-irradiated and control rats. However, the glial cells in the X-irradiated animals had significantly larger nuclear size. We had previously reported that a similar X-irradiation paradigm resulted in no significant change in the numerical density of neurons in the SC. According to the results of the present study, there were no significant differences in the glial cell-to-neuron ratios between the X-irradiated and control animals. Taken together, it is speculated that prenatal X-irradiation has an equal effects on the numerical densities of glial cells and neurons.

GM1 ganglioside treatment protects against long-term neurotoxic effects of neonatal X-irradiation on cerebellar cortex cytoarchitecture and motor function

Exposure of neonatal rats to a 5 Gy dose of X-irradiation induces permanent abnormalities in cerebellar cortex cytoarchitecture (disarrangement of Purkinje cells, reduction of thickness of granular cortex) and neurochemistry (late increase in noradrenaline levels), and motor function (ataxic gait). The neuroprotective effects of gangliosides have been demonstrated using a variety of CNS injuries, including mechanical, electrolytic, neurotoxic, ischemic, and surgical lesions. Here, we evaluated whether systemically administered GM1 ganglioside protects against the long-term CNS abnormalities induced by a single exposure to ionizing radiation in the early post-natal period. Thus, neonatal rats were exposed to 5 Gy X-irradiation, and subcutaneously injected with one dose (30 mg/kg weight) of GM1 on h after exposure followed by three daily doses. Both at post-natal days 30 and 90, gait and cerebellar cytoarchitecture in X-irradiated rats were significantly impaired when compared to age-matched controls. By contrast, both at post-natal days 30 and 90, gait in X-irradiated rats that were treated with GM1 was not significantly different from that in non-irradiated animals. Furthermore, at post-natal day 90, cerebellar cytoarchitecture was still well preserved in GM1-treated, X-irradiated animals. GM1 failed to modify the radiation-induced increase in cerebellar noradrenaline levels. Present data indicate that exogenous GM1, repeatedly administered after neonatal X-irradiation, produces a long-term radioprotection, demonstrated at both cytoarchitectural and motor levels.

Intestinal and extra-intestinal tumor multiplicities in the Apc1638N mouse model after exposure to X-rays

Seven-week-old Apc1638N mice were exposed to a single dose of 5 Gy total-body X-irradiation resulting in a 8-fold increase in the number of intestinal tumors and a reduction of the lifespan to an average of 6 months. The distribution of tumors along the intestinal tract as well as the adenoma/carcinoma ratio, were similar between non-irradiated and irradiated animals. Semi-quantitative PCR analysis of intestinal-tumor DNA revealed that 10 out of 14 tumors had lost the wild-type Apc allele. However, in contrast to spontaneous Apc1638N intestinal tumors in which the LOH event at the Apc locus involves the entire chromosome 18 (1), in 6 out of 10 tumors derived from X-irradiated animals the Apc loss is associated with only a partial intrachromosomal deletion. The remaining tumors have lost all chromosome 18 markers tested. In addition to the intestinal tumors, female Apc1638N mice are susceptible to the development of mammary tumors. Upon X-irradiation, Apc1638N mice show a striking 15-fold increase in mammary tumors. Moreover, Apc1638N mice spontaneously develop other extra-intestinal neoplasia, such as desmoid-like lesions similar to those associated with familial adenomatous polyposis (FAP), the human syndrome caused by germline mutations in the APC gene. Spontaneous desmoid growth is sex-dependent, as male Apc1638N mice develop 3-fold more desmoids than female mice. Interestingly, X-irradiation seemed to increase the number of desmoids per animal nearly twofold only in female Apc1638N mice. Five out of 9 desmoids found in Apc1638N mice exposed to X-ray displayed loss of the wild-type Apc allele.

Quantification of 5-hydroxytryptamine 1a receptors in the cerebellum of normal and X-irradiated rats during postnatal development

5-Hydroxytryptamine 1A receptors were studied in rats during the first postnatal month in the normal cerebellum and in the granule cell-deprived cerebellum produced by X-irradiation at postnatal day 5. Quantitive autoradiographic studies on sagittal sections of cerebellar vermis, using [ 125I]BH-8-MeO-N-PAT as radioligand or specific anti-receptor antibodies, revealed that 5-hydroxytryptamine 1A receptors existed in the molecular/Purkinje cell layer but at variable density from one lobule to another. Thus, in both normal and X-irradiated rats, the posterior lobules were more heavily labelled than the anterior ones, and the density of 5-hydroxytryptamine 1A sites decreased progressively in all the cerebellar folia down to hardly detectable levels at postnatal day 21. However, the intensity of labelling remained higher at postnatal day 8 and postnatal day 12 in X-irradiated rats than in age-paired controls. Measurements of [ 3H]8-OH-DPAT specific binding to membranes from whole cerebellum confirmed that the density of 5-hydroxytryptamine 1A sites per mg membrane protein (B max) was higher in X-irradiated animals than in age-paired controls. However, on a “per cerebellum” basis, no significant difference could be detected between the total number of 5-hydroxytryptamine 1A sites, which progressively increased in both control and X-irradiated animals during the first postnatal month. These results therefore show that 5-hydroxytryptamine 1A receptors are not located on developing granule cells. The progressive decrease in 5-hydroxytryptamine 1A receptor density during the first postnatal month did not reflect a transient expression of 5-hydroxytryptamine 1A receptors in the cerebellum of newborn rats, but resulted from the progressive “dilution” of these sites in this growing structure. The higher density of 5-hydroxytryptamine 1A sites in X-irradiated rats simply reflected a lower “dilution” due to the delayed growth of the cerebellum in these animals.

Evaluation of the role of germ cells in regulating the route of secretion of immunoactive inhibin from the rat testis.

During normal sexual maturation of the male rat there is a progressive change in the route of secretion of inhibin by the Sertoli cell, from a predominantly basal route of secretion in prepuberty to a predominantly apical route of secretion in adulthood. This change may be monitored by comparing the levels of inhibin in testicular (TV), spermatic and peripheral (PV) venous blood and the levels in testicular interstitial fluid (IF). This study has assessed the role of germ cells in effecting this change by assessing (a) the effect of total germ cell depletion by X-irradiation of the males in utero, and (b) the effect of selective germ cell depletion in adulthood using the testicular toxicant, methoxyacetic acid (MAA). Female rats were X-irradiated on day 20 of gestation to produce male offspring whose testes were germ-cell deficient. Blood and IF samples were collected from groups of these offspring and age-matched controls at 35 and 100 days of age. In blood and IF samples, inhibin concentrations were significantly higher at 35 days of age than at 100 days. The absence of germ cells in X-irradiated animals did not affect the age-related fall in inhibin levels, nor the change in the predominant route of secretion of inhibin from the testis into blood. Testosterone was almost undetectable in 35-day-old controls, but was raised significantly by 100 days of age. In X-irradiated animals, testosterone levels were increased significantly at 35 days of age, and the levels in most samples were increased even more substantially by 100 days of age. However, PV levels of testosterone in 100-day-old X-irradiated animals were significantly lower than in controls. LH and FSH levels were raised in X-irradiated animals compared with their age-matched controls, but FSH levels in X-irradiated animals still fell with age, as in the controls. The role of specific germ cell types in regulating the route of secretion of inhibin from the normal adult testis was studied after depletion (80-100%) of pachytene and later spermatocytes by a single oral administration of MAA (650 mg/kg) to adult rats. At 3 days after MAA treatment, coincident with the loss of pachytene spermatocytes, plasma inhibin levels were increased significantly in blood and IF samples, and this was associated with a dramatic change in the route of secretion of inhibin from the testis, with increased secretion of this peptide via the base of the Sertoli cell into IF and TV blood.(ABSTRACT TRUNCATED AT 400 WORDS)

Increased activity of tyrosine hydroxylase in the cerebellum of the X-irradiated dystonic rat

The exposure of the cephalic end of rats to repeated doses of X-irradiation (150 rad) immediately after birth induces a long-term increase in the noradrenaline (NA) content of cerebellum (CE) (+ 37.8%), and a decrease in cerebellar weight (65.2% of controls), which results in an increased NA concentration (+ 109%). This increase in the neurotransmitter level is accompanied by a dystonic syndrome and histological abnormalities: Purkinje cells (the target cells for NA afferents to CE) fail to arrange in a characteristic monolayer, and their primary dendritic tree appears randomly oriented. The injection of reserpine 0.9 and 1.2 mg/kg ip to adult rats for 18 h depletes cerebellar NA content in both controls (15.7 +/- 4 ng/CE and 2.8 +/- 1.5 ng/CE, respectively) and X-irradiated rats (17.1 +/- 1 ng/CE and 8.3 +/- 2 ng/CE, respectively). The activity of tyrosine hydroxylase (TH) in CE of adult rats, measured by an in vitro assay, is significantly increased in neonatally X-irradiated animals when compared to age-matched controls (16.4 +/- 1.4 vs 6.32 +/- 0.6 nmol CO2/h/mg prot., p less than 0.01). As observed for NA levels, a net increase in TH activity induced by the ionizing radiation is also measured: 308.9 +/- 23.8 vs 408.2 +/- 21.5 nmol CO2/h/CE, p less than 0.01 (controls and X-treated, respectively). These results suggest that X-irradiation at birth may induce an abnormal sprouting of noradrenergic afferents to CE. The possibility that these changes represent a response of the NA system to the dystonic syndrome is discussed.

Resistance of human and mouse myeloid leukemia cells to UV radiation.

Sensitivity of mouse bone marrow and myeloid leukemia cells as well as the sensitivity of human myeloid leukemia cells to UV light was tested. Criteria were the in vivo colony-forming ability of UV exposed cells and the inhibition of DNA synthesis during post-irradiation incubation for 24 h in vitro. Mouse bone marrow cells irradiated with a small dose of UV light (5 J/m2) and injected into x-irradiated animals did not form hemopoietic colonies on the recipients' spleens, and the recipients died. However, mouse leukemia cells, after irradiation with higher doses of UV light, retained the ability to form colonies on the spleens, and all recipient mice died with typical symptoms of leukemia. In vitro, mouse bone marrow cells exhibited high sensitivity to UV light as compared to mouse myeloid leukemia cells. Human leukemia cells were also resistant to UV light, but more sensitive than mouse leukemia cells. These results indicate that myeloid leukemia cells are resistant to UV light as compared with normal bone marrow cells.

Midgestational exposure of pregnant [formula omitted] mice to magnetic resonance imaging conditions

The potential for producing reproductive toxicity or teratogenesis in mice by exposure to magnetic resonance imaging (MRI) conditions was evaluated by means of reproduction studies and the homeotic shift test. Embryos from pregnant BALB c mice were exposed in vivo for 16 hours beginning on gestation day 8.75 to MRI conditions of modest field strength (static field, 0.35 tesla (T); pulsed gradients, 2.3 × 10 −4 T/cm for 2.5 to 10 msec; and radio frequency, 15 MHz at an average of 61.2 mW). Unexposed, sham-exposed (both MRI and X-ray) and X-irradiated (0.5 Gy) animals were the control groups. Neither placental resorptions nor stillbirths were increased by MRI. Fetal weight at birth and crown-rump length were proportional; however, crown-rump length was significantly less ( p < 0.001) in the MRI-exposed fetuses (respective mean values for MRI-exposed fetuses were 21.8 ± 0.2 mm compared to 22.4 ± 0.1 for sham-exposed fetuses). Both crown-rump length and fetal weight were significantly reduced after X-irradiation. The percentage of homeotic skeletal shifts was scored for each of eight anatomic sites. Only X-radiation produced significant increases in skeletal shifts. Prolonged midgestational exposure of mice to MRI conditions currently used for human clinical imaging, therefore, failed to reveal overt embryotoxicity (resorptions, stillbirths) or teratogenicity (homeotic shifts), consistent with the non-ionizing properties of MR. However, the slight but significant reduction in fetal crown-rump length after prolonged exposure justifies further study of higher MRI energy levels and consideration of other endpoints for establishing with greater confidence the safety of MRI during pregnancy.

The role of new vessels and macrophages in the development and resolution of edema following a cortical freeze lesion in the mouse.

The role of an influx of macrophages and neovascularity in the resolution of vasogenic edema is not well defined. The inhibition of these processes with x-irradiation or parenteral corticosteroid administration was used to evaluate their contribution to the resolution of edema around a cortical freeze lesion in mice. The resorption of Evans blue, a marker of protein extravasation, was delayed in x-irradiated mice on the second day following a freeze lesion (p = 0.0075), which correlates with a delay in macrophage infiltration around the lesion. The specific gravity of the lesion and its border regions was significantly less in x-irradiated animals on day 7 than in controls (p = 0.00062), which correlates with a delay in new vessel formation around the lesion. Administration of corticosteroids from the time of production of the freeze lesion resulted in a specific gravity significantly less than control when measured eight days after the lesion (p = 0.01). Macrophages may participate by inhibiting the development of the macromolecular portion of vasogenic edema. The development of neovascularity correlates with the resorption of the aqueous portion of vasogenic edema. As with x-irradiation, corticosteroids administered from the time of freeze lesion inhibited the resorption of the aqueous portion of vasogenic edema, but they may suppress the spread of edema in this experimental model.

Repopulation of spleens of irradiated mice after injection of spleen cell subpopulations.

Haemopoietic stem cells present in the spleen of adult mice were analysed by grafting X-irradiated animals with polystyrene-nonadherent (NABS) and polystyrene-adherent (ABS) B-enriched splenocytes from syngeneic donors. The progeny of the haemopoietic stem cells present in NABS and ABS subsets were studied with respect to size, surface markers, and response to mitogens and antigens. Ninety-six per cent of the precursors of the myeloid cell lineage (CFU-S) were present in the NABS fraction (50-fold enrichment). The presence in NABS of progenitors of functional T and B lymphocytes was also demonstrated. Twelve days after grafting with NABS, more than 80% of the recipient splenocytes were large and nonadherent granulocyte-like cells. These cells had surface similarities with NABS from normal mice, since both populations reacted with peanut agglutinin and with a rabbit anti-NABS (RAN) serum.

Susceptibility of normal and X-irradiated animals toAeromonas hydrophila infections

The virulence of threeAeromonas hydrophila strains isolated from humans and water were compared by intramuscular inoculation of normal and x-irradiated mice and goldfish. Selected strains, irrespective of source, were pathogenic for mice and goldfish with maximum mortality of normal hosts observed at 24–48 h after injection. Immunosuppression resulted in increased mortality of hosts by two of the threeA. hydrophila strains. The variation in virulence potential of differentA. hydrophila isolates may depend upon the in vivo interaction of endotoxins, surface antigens, and extracellular bacterial products.

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Repeated exposure of female C3H/HeNCR- mice to sunlight prevented the normal immunologic rejection of a UV-induced tumor. This systemic immunologic alteration was transferred to syngeneic lethally X-irradiated animals with lymphoid cells from mice exposed to sunlight. The lymphoid cells also were able to suppress the capacity of lymphoid cells from normal animals to reject a UV-induced tumor. The 295- to 320-nm wave band appeared to be responsible for this immunosuppressive effect of sunlight because suppression was prevented by filtration of the radiation through Mylar and by application of a sunscreen containing para-aminobenzoic acid. These observations may have importance in understanding the pathogenesis of sunlight-induced skin cancer in humans.

Attempts to transfer experimental allergic neuritis with lymphocytes

Attempts have been made to transfer experimental allergic neuritis (EAN) both by the intraneutral and the intravenous injection of cells derived from Lewis rats with the disease into naive recipients of the same strain. Lymph node cells obtained 12 and 15 days after inoculation with bovine dorsal root in Freund's complete adjuvant were injected intrneurally. A small number of demyelinated axons were observed, but clinical weakness was not evident. Lymph node cells, lymph node cells cultured with concanavalin A, or cultured spleen cells from animals with EAN were transferred intravenously to normal rats. Uncultured lymph node cells were transferred to X-irradiated animals. There were no clinical or histological differences between these recipients and controls receiving cells from rats inoculated with Freund's adjuvant alone. The findings are discussed in relation to previous reports of attempts to transmit EAN by cell transfer.

Effects of environmentally differential rearing upon maze performance in prenatally irradiated microcephalic rats.

Pregnant rats received 100 rads of X-irradiation on day 17 of gestation. Control pregnant rats were sham-irradiated on the same gestation day. The male offspring were reared under environmentally enriched, standard colony, and impoverished conditions for 30 days after weaning. Then the Hebb-Williams maze test was carried out. All the prenatally X-irradiated rats were microcephalic: their mean cerebral wet weight was 15.5% less than controls. The effect of X-irradiation was not significant in error scores and running times, whereas the effect of environment was significant in these items; initial and total error scores and running times were decreased in enriched groups compared to impoverished groups in controls as well as in X-irradiated animals.

Environmental enrichment to alleviate maze performance deficits in rats with microcephaly induced by X-irradiation

Pregnant rats received 150 R of X-irradiation on day 17 of gestation. The male offspring were reared under environmentally enriched (EC), standard colony (SC) or impoverished conditions (IC) for 30 days after weaning. Then the Hebb-Williams maze test was carried out. The effects of X-irradiation and Environment were both significant in initial, repetitive and total error scores and running time. Further analysis revealed that both EC-SC and EC-IC differences in initial, repetitive and total error scores were significant in X-irradiated animals, whereas only the EC-IC difference in initial and total error scores was significant in sham-irradiated control animals. Total protein, protein/g cortex, total benzodiazepine and muscarine cholinergic receptor bindings, and muscarinic cholinergic receptor binding/mg protein in the cerebral cortex were decreased in X-irradiated groups compared to controls, but the effect of Environment was not significant in these items. The results confirmed that environmental enrichment is a useful tool to alleviate the learning decrements in prenatally X-irradiated microcephalic rats.

Regulation of antibody synthesis in the X-irradiated Mexican axolotl.

The effects of X-irradiation were studied on the Mexican axolotl antibody synthesis. To reduce the anti-horse red blood cell (HRBC) antibody titers, 150 rd and smaller doses are ineffective, 200-450 rd are increasingly effective, and 700 rd are maximally effective (and lethal). A significant enhancement of the anti-HRBC titers was observed in low doses (50-150 rd X-irradiated animals). This enhancement was also observed when a low X-ray dose was applied only on the thymic areas. In whole body, but thymus area-shielded, 100 rd X-irradiated animals, the anti-HRBC titers were similar to those of the nonirradiated, HRBC-immunized control group. To explain these phenomena, it is suggested that a radiosensitive, adult thymectomy-sensitive and hydrocortisone-sensitive suppressor T cell subpopulation regulates the antibody synthesis in the axolotl.