X-irradiated Rats Research Articles

Degranulation of rat cerebellum induces selective variations in gene expression.

Selective variations in the composition of poly(A)-containing mRNA were found to be induced in the rat cerebellum by X-irradiation. mRNA populations prepared from normal and X-irradiated rat cerebella at different stages of their development displayed equal efficiencies when translated in vitro in reticulocyte lysates. Specific differences were revealed, however, when the labeled translation products of both mRNA preparations were subjected to two-dimensional gel electrophoresis followed by fluorography of the dried gels. Of more than 100 polypeptide products, several showed marked intensity differences, indicating changes in the abundance of their directing mRNA species. These differences appear both in developing and in mature cerebellar mRNA, and the extent of modification in mRNA is much higher than the consequent changes in the composition of proteins in the irradiated cerebellum. The degranulation-induced modifications in levels of specific cerebellar mRNA species can be used to identify proteins whose biosynthesis depends on the presence of interneurons.

Mossy fiber and Purkinje cell axon collateral arborization patterns in normal and X-irradiated rat cerebellum: A light microscopic study using horseradish peroxidase fiber filling techniques

The horseradish peroxidase neuronal staining technique was applied to reveal through anterograde and retrograde staining the detailed morphology of fiber arborization patterns in the cerebella of normal adult rats as well as those treated with neonatal X-irradiation. Morphological features of anterogradely-filled mossy fibers including the axonal arborization and glomerular-type synaptic specializations were found to be similar in all groups studied. In addition, retrogradely-filled Purkinje cell axon collaterals in the cerebella degranulated by X-irradiation exhibited much more elaborate branching and arborization of recurrent collaterals than those labeled in the normal cerebellar cortex. The presence of glomerular-type specializations in the degranulated cerebellum suggests that mossy fibers develop and maintain their normal features independent of major influences from granule cells. The hypertrophy observed after destruction of the cerebellar interneurons suggests the hypothesis that the growth of the normal Purkinje cell collateral system is normally suppressed by extrinsic factors within the neuronal circuit.

Behavioral correlates of focal hippocampal x-irradiation in rats II. Behavior related to adaptive function in a natural setting.

Prior investigations have shown the effects of hippocampal degranulation on behaviors such as two-way avoidance, open-field behavior, and operant schedules of reinforcement. Little, however, has been done with behaviors related to adaptive function in a natural setting; the present study has addressed this issue. Long-Evans hooded rats, subjected to focal neonatal X-irradiation of the hippocampus, were tested in passive avoidance and four dominance situations. The experimental animals, which had approximately a 70% reduction in the granule cells of the hippocampal dentate gyrus, showed response perseveration in the passive avoidance task and were generally non-competitive in the dominance situations when compared to non-irradiated control animals. The single exception to this was noted in the test where an experimental rat and control animal were competing for a receptive female rat. Here the degranulated animals were strikingly superior to the control subjects with many more successful mounts. Some support for the response suppression model of hippocampal functioning was noted.

Cyclic 3′,5′-adenosine monophosphate levels during the developmental cycle of Trypanosoma brucei brucei in the rat

Intracellular content of cyclic 3′,5′-adenosine monophosphate was determined in several strains of Trypanosoma brucei brucei during their growth in rats. In non-relapsing infections with the cloned monomorphic strain 110M and with the cloned pleomorphic strain YTatl, the amount of cyclic AMP per 10 9 trypanosomes increased from 30 to over 90 pmol as the parasitemia increased from patency to over 10 9 organisms per ml. This increase was not observed during non-relapsing infections with strain 427. During infections with strain YTatl in both immunocompetent and lethally X-irradiated rats, cyclic AMP content of the parasite increased from 20-20 pmol per 10 9 cells early in logarithmic growth to 65–70 pmol per 10 9 cells at peak parasitemia, then decreased as the transition to intermediate and short stumpy forms commenced. At crisis, basal levels were reestablished when long slender forms were the lowest percentage of the total population and intermediate and short stumpy forms predominated, suggesting a correlation between morphologic type and level of cyclic AMP per cell during fluctuations in parasitemia. Increases in intracellular cyclic AMP were measured during in vitro incubation of the parasite in medium containing potential effectors of the trypanosome cyclic AMP system. Sodium fluoride, adenosine and methyl xanthines stimulated increases in cyclic AMP content while isoproterenol, prostaglandin E 1, serotonin, histamine and several trypanocidal drugs were ineffective. The results are discussed in terms of the possible regulatory role of cyclic AMP in differentiation of trypanosomes.

Selective survival of ß 1-adenergic receptors in rat cerebellum following neonatal X-irradiation

Although beta 2-adrenergic receptors predominate in adult rat cerebellum, a small number of beta 1-receptors are also present. To investigate the cellular localization of beta 1- and beta 2-adrenergic receptors, the effects of intermittent neonatal X-irradiation focused on the cerebellum were determined on the densities of the two subtypes of beta-adrenergic receptor. This treatment destroys the late-maturing cerebellar interneurons including the granule, basket and stellate cells. A 60--70% loss of cerebellar mass was observed in 2-, 6- and 12-week-old animals. The large early-maturing Purkinje cells are resistant to the effects of X-irradiation. The total number of beta-adrenergic receptors per cerebellum, measured by Scatchard analysis of saturation isotherms of specific [125I]iodohydroxybenzylpindolol (IHYP) binding, was reduced by 70--80% in 2-, 6- and 12-week-old animals. The relative proportion of beta 1- and beta 2-receptors was determined by analyzing the inhibition of specific IHYP binding by the beta 1 selective antagonist practolol. The total number of beta 2-adrenergic receptors per cerebellum was reduced by 81--83% in 6- and 12-week-old X-irradiated rats. However, the number of beta 1-adrenergic receptors per cerebellum in 6- and 12-week-old X-irradiated rats was not significantly different from that in control animals. The results suggest that beta 2 receptors in the rat cerebellum are primarily associated with the small interneurons destroyed by neonatal X-irradiation. The beta 1 receptors may be located on a cell population which is unaffected by this treatment, possibly on cerebellar Purkinje cells.

Fate of the multiple innervation of cerebellar Purkinje cells by climbing fibers in immature control, X-irradiated and hypothyroid rats

The fate of the multiple innervation of Purkinje cells (PCs) by climbing fibers (CFs) was studied as a function of age in immature rats rendered agranular by X-irradiation, in immature hypothyroid rats, and compared to that in controls. This was done by examining in each group the intracellular activities of PCs mediated via CFs throughout maturation. From the third day in control rats, CF responses of PCs evoked by juxta fastigial region (JF) stimulation or occurring spontaneously already resembled the adult responses with, however, some important differences: (1) most of these responses were graded by steps with the intensity of the stimulation before day 13, due to the multiple innervation of PCs by CFs (see below); (2) immature CF responses exhibited a longer duration and their initial spike started near the peak of the EPSP instead of near the baseline later on. Finally, an anlage of CF response was already present in most PCs on day 2, and consisted of a single fast spike elicited near the peak of an underlying all-or-none EPSP. In the 3 groups of rats, CF EPSPs already closely resembled the adult ones as early as 3 days, although their total duration and especially their time to peak were longer. In control rats, these CF EPSPs reversed with depolarizing currents from day 3 and currents for reversal were much lower than in the adult. ‘Dual’ CF EPSPs of PCs 37 were encountered in immature 7- to 10-day-old controls, and persisted in hypothyroid rats until the end of the third postnatal week. The mono- or the multiple innervation of PCs by CFs was ascertained in the 3 groups according to the graded or the all-or-none character of CF EPSPs, and the number of CFs impinging on a given PC was estimated by the number of steps in the response. In control rats, most of PCs were already multiply innervated by CFs as early as 3 days. The multiple innervation culminated on day 5 with an average number of 3.5 CFs for PC, and rapidly regressed later on, so that the adult-type mono-innervation was the rule after day 13. In hypothyroid rats, the establishment of the redundancy and its regression was delayed by 2–3 days. In X-irradiated rats, the settlement and the involution of the multiple innervation of PCs by CFs was exactly superimposed with that seen in controls until day 8. Later on, regression of the supernumerary contacts no longer occurred so that most PCs remained multiply innervated until adulthood. Finally, the first clear-cut IPSPs were detected in PCs on day 9 in control and X-irradiated rats and 2–3 days later in hypothyroid animals.

Effects of environmental enrichment upon maze performance in rats with microcephaly induced by prenatal X-irradiation.

Rats receiving prenatal X-ray irradiation showed great deficit in learning of the Hebb-Williams maze. The deficit of the maze learning was only slightly improved even when the X-irradiated rats were reared in an environmentally enriched condition.

Factors specifying the development of synapse number in the rat dentate gyrus: effects of partial target loss

The development of the dentate gyrus has been studied under conditions of partial reduction of granule cell number. Neonatal rats were subjected to X-irradiation, a procedure which reduces the number of granule cells to 20% of control values. In X-irradiated rats, quantitative analyses were performed on cells in the entorhinal cortex which give rise to the perforant path projection to the dentate granule cells, and on the remaining, undamaged dentate granule cells. These residual cells were examined morphologically for possible hyperdevelopment in comparison to granule cells from control animals. Granule cells in X-irradiated animals were similar to granule cells in control animals with respect to dendritic structure and synaptic density. The number of neurons in both the medial and lateral entorhinal cortices in X-irradiated animals appeared normal until day 12, at which time a selective reduction in cell numbers became apparent. By day 30, 25–55% of the cells of origin of the perforant path were absent in X-irradiated animals. It is hypothesized that these cells are subject to retrograde transynaptic degeneration as a result of target removal. Further, it appears that granule cells play an important role in determining the density of their innervation.

Separation of the Dead Cell Fraction from X-irradiated Rat Thymocyte Suspensions by Density Gradient Centrifugation

Separation of the Dead Cell Fraction from X-irradiated Rat Thymocyte Suspensions by Density Gradient Centrifugation

Reaction of Blood Pressure and Mesenteric Blood Flow to Infusion of Biogenic Amines in Normal and Supralethally X-Irradiated Rats

The responses of blood pressure and mesenteric blood flow were recorded during infusion of biogenic amines (noradrenaline, dopamine, serotonin, acetylcholine, and histamine) to control and X-irradiated rats (first and third days after 2 kR X irradiation). Responses to different doses of the amines were evaluated, and the results obtained correspond to those seen in other species (e.g., an increase in pressure and a decrease in flow with an overshoot after infusion of noradrenaline, an increase in pressure and flow after dopamine, an increase in pressure and a decrease in flow after serotonin, a decrease in pressure and flow after acetylcholine, and a decrease in pressure and an increase in flow after histamine). Irradiated animals are more responsive to pressure-raising agents, in particular to noradrenaline. They also have an altered dose-pressure response curve for dopamine.

Dendritic and axonic fields of purkinje cells in developing and X-irradiated rat cerebellum. a comparative study using intracellular staining with horseradish peroxidase

Intracellular staining of cerebellar Purkinje cells with horseradish peroxidase was achieved in normal developing rats (8–13 days old), in normal adult rats and in adult rats in which the cerebellum had been degranulated by X-ray treatment. The mono- and multiple innervation of Purkinje cells by climbing fibres was electrophysiologically determined and correlated with their dendritic pattern and axonal field. In immature rats, considerable variations in dendritic arborization were observed between cells at the same age, according to their position in the vermis. In adult X-irradiated animals, a large variety of dendritic shapes was found, confirming previous anatomical data, but no obvious correlation was found between the morphology of the dendrites of Purkinje cells and their synaptic investment by climbing fibres. As regards the axonal field, the adult branching pattern of recurrent axon collaterals was almost established by postnatal day 8, except for some cells which exhibited richer recurrent collaterals. On the other hand, in X-irradiated animals, profuse plexuses were the rule and they originated either from one collateral stem, or from several collaterals, also independently of the number of afferent climbing fibres. The existence of these enlarged recurrent collateral plexuses can be explained by the persistence of an immature stage, and certainly also by collateral sprouting following the largely impaired innervation of the terminal field during development. These results emphasize the role of the cellular interactions that occur during Purkinje cell growth in the formation of both its axonal and dendritic fields.

Soybean diet lowers breast tumor incidence in irradiated rats.

This paper examines the relationship between feeding a diet rich in protease inhibitors and the reduction of mammary cancer induced by x-irradiation in Sprague-Dawley rats. Of a total of 145 irradiated animals, 44% of the 45 rats fed a raw soybean diet containing a high concentration of protease inhibitor developed mammary tumors as compared to 74% of 50 rats fed a casein diet containing no protease inhibitor. Animals fed Purina rat chow which contained low levels of protease inhibitor exhibited a 70% mammary tumor incidence. No spontaneous neoplasms were found in any of the non-irradiated animals on the raw soybean diet whereas about 10% of the animals on the protease-free diet developed tumors. Thus, soybeans which are rich in protease inhibitors reduced the induction of mammary cancer in x-irradiated rats. This work suggests that diets rich in protease inhibitors may contribute to reducing cancer incidence in man.

Separation of the Dead Cell Fraction from X-irradiated Rat Thymocyte Suspensions by Density Gradient Centrifugation

Separation of the Dead Cell Fraction from X-irradiated Rat Thymocyte Suspensions by Density Gradient Centrifugation

Separation of the Dead Cell Fraction from X-irradiated Rat Thymocyte Suspensions by Density Gradient Centrifugation

Separation of the Dead Cell Fraction from X-irradiated Rat Thymocyte Suspensions by Density Gradient Centrifugation

Cerebellar malformations in prenatally X-irradiated rats: quantitative analysis and detailed description.

Pregnant WKA/Hok rats were exposed to 100 R or 200 R X-irradiation on one of gestation days 16 through 21. Offspring were killed at 60 days of age and the cerebellum was examined. The cerebellum of animals exposed to 200 R was slightly reduced in weight but not in width. The observed reduction in the dorsoventral length of the cerebellum was more evident when the X-irradiation was early in gestation. The anteroposterior length of the hemispheres increased following exposure to X-ray on days 16 through 19, and that of the vermis and paravermis decreased following treatment on days 17 through 21. Therefore, the anterior portions of hemispheres were situated anterior to the culmen in every 200 R group. Somewhat anteroposteriorly and horizontally directed lobules, as opposed to the normal transverse arrangement, were seen in the cerebellum of rats treated on day 16 or 17. Lobule contortion and fragmentation and an increased number of sublobules were striking in cases treated later. Histologically, ectopic Purkinje cells in the granule cell layer and white matter appeared following X-irradiation on day 20 or 21, but they were not found following earlier treatment. In the cerebellum of animals exposed to 100 R the reduction in size was mild and the folial abnormalities were rare, but the number of sublobules decreased.

Responses of vibrissa-sensitive cortical neurons in normal and prenatally X-irradiated rat.

1. Rats were irradiated by 200 R of X ray on day 17 (the 18th day) of gestation through the body wall of the mother. When they underwent the following electrophysiological tests at the age of 3-4 mo, the somatosensory cortex showed a lack of layers II, III, IV, and Va, as described by previous investigators (3, 4). 2. Spike responses to quick whisker deflections were recorded from single cells in the somatosenory cortex of normal and prenatally X-irradiated rats. 3. In normal animals, single units often responded to several whiskers, but the magnitudes (response latency and firing probability) of the responses were graded around a whisker in the "center" of the field that gave rise to the strongest response. During electrode penetration perpendicular to the cortical surface, such a center remained unchanged or shifted to another whisker that was immediately adjacent. As for the large-sized, initially positive unitary spikes (typically 2 mV or higher) sampled in this study, no systematic change in the response latency, the size of receptive field, or response probability was detected during the penetration. 4. The above description holds also for the irradiated rats except that the response latency was prolonged when compared to the normal controls. 5. Cortical laminar analysis of field potentials revealed that while the earliest electric sink appeared in layer IV in the controls, that in the irradiated rats was observed in layer Vb. However, there was no difference in the latency of these potentials between the two groups, suggesting that vibrissal sensory signals reach the cortical level normally even in the irradiated rats. The prolonged latency of the irradiated cortical neuronal response could thus be ascribed to an abnormal intracortical delay, which was most likely associated with the failure of development of layer IV stellate cells in these preparations. 6. A possibility as to how the layer IV stellate cells are involved in input-output relationships in the normal somatosensory cortex is presented and discussed.

Effect of bovine testicular extracts on plasma gonadotrophins of X-irradiated rats.

SummaryThe effect of bovine testicular extracts (bTE) on plasma FSH levels in both castrate and X-irradiated male rats has been examined. Biological activity was demonstrated in 34-day-old, orchidectomized rats with doses ranging from 50 to 250 mg. Testicular weights of X-irradiated rats 49 days after X irradiation were decreased by approximately 67%, whereas the ventral prostate weights were unaffected. Plasma FSH levels (383 ng/ml) increased significantly as a result of X irradiation (873 ng/ml). Plasma LH (51 ng/ml) also rose as a result of X irradiation (93 ng/ml), suggesting that there was some interstitial cell damage or some Sertoli cell damage. Two hundred and fifty milligrams of bTE administered in 4% gelatin given once daily for 3 days suppressed the elevated plasma FSH, but was without effect on plasma LH. Castration and a further 3 days of treatment resulted in a significant postcas-tration suppression in plasma FSH (control = 1942 ng/ml; bTE = 1283 ng/ml), and resulted in a suppression of LH ...

Ultrastructural features of spironucleosis (hexamitiasis) in x-irradiated rat small intestine.

An alteration in the host response to the intestinal protozoan Spironucleus (Hexamita) muris was noted in x-irradiated rat small intestine. When few were present in the crypt lumina, the intestinal microvillar border was normal. However, when larger numbers were present, the microvilli were greatly reduced in numbers or entirely absent in some regions. The organism was identified in the base of the crypt lumen, in apical portions of mucous cells, and near the basement membrane. Spironucleus enclosed by digestive vacuoles occasionally appeared to be in the process of being extruded through the basement membrane. Not all intracellular protozoa were surrounded by such digestive vacuoles. Spironucleus was never seen in association with the digestive vacuoles of Paneth cells. Since it has been suggested that Paneth cells have a role as a fixed phagocyte, ingesting protozoa and other microorganisms, the results presented here suggest that this function may have been impaired in irradiated animals.

Distribution of climbing fibres on cerebellar Purkinje cells in X-irradiated rats. An electrophysiological study.

1. The distribution of climbing fibres on cerebellar Purkinje cells has been studied with intracellular recordings in X-irradiated and normal rats. 2. In the treated rats, multiple steps in the post-synaptic potential were elicited in 57% of the Purkinje cells by graded stimulation of the climbing fibres, the response was all-or-none in character in the other cells and in all Purkinje cells recorded in normal animals. In the neurones exhibiting the former type of response, no collision was seen along the afferent fibres during interaction experiments between just-threshold juxtafastigial and maximal olivary stimulations, whereas a collision always occurred when all-or-none responses were recorded. 3. These results show that in X-irradiated rats, the majority of Purkinje cells have a multiple innervation by two to four climbing fibres, instead of the one-to-one relationship seen normally. 4. Input resistances and total electrotonic lengths of Purkinje cells were measured in normal and treated rats. Mean values for these two parameters were higher than normal in multiply innervated cells. 5. Mean time course and mean current for reversal of the post-synaptic potential elicited in Purkinje cells by stimulation of the climbing fibres were nearly the same in mono- and in multiply innervated neurones. In multiply innervated cells, time courses and currents for reversal were independent of the size of the response or varied slightly with it, suggesting that the climbing fibres involved innervated territories whose electrotonic distance from the recording site were either the same or slightly different. 6. Interactions between two all-or-none steps of the graded post-synaptic potential evoked in multiply innervated cells by juxtafastigial and olivary stimulations revealed either a very weak or a very marked shunting effect between synapses of the two climbing fibres involved. 7. These results indicate that the over-all distribution of climbing fibre synapses on multiply innervated Purkinje cells is not grossly abnormal and that two fibres contacting a given cell can be either intermingled on the same dendrites, or segregated on distinct dendritic branches. 8. In general, the present study does not suggest the existence of a strong competition among climbing fibres innervating each Purkinje cell during development at least when granule cells are absent.

Avoidance of and anticipatory responses to shock in prenatally X-irradiated rats

Male MP1 albino rats were exposed to X-irradiation in utero at a single dose of 200 R on Day 17 of gestation. This experiment was aimed to determine just how irradiated rats could differ from controls in a shuttlebox avoidance response. Irradiated rats had a significantly higher anticipatory response to CS which predicts shock, and also made a significantly higher incidence of consecutive anticipatory responses during the CS-US interval. Thus, facilitated avoidance behavior in irradiated rats is probably a consequence of a strong tendency to running induced by shock in shuttlebox. Since cell destruction caused by irradiation was evident in the primordial hippocampus, a smaller hippocampus developed. The dendrites of pyramidal neurons in Ammon's horn were abnormally oriented. Behavioral changes in shuttlebox after irradiation may be related to the hippocampus abnormality, based on stress-arousal interpretation of hippocampal functioning in a situation employing noxious stimulation.