Non-exposed Animals Research Articles

Prenatal exposure to diazepam alters central and peripheral responses to stress in adult rat offspring

Central and peripheral responses to restraint stress were evaluated in 90-day-old rats exposed prenatally to diazepam (1.0, 2.5, or 10.0 mg/kg/day) over gestational days 13–20. As a measure of a central response to stress, the utilization of norephinephrine (NE) by hypothalamic NE neurons was assessed by determining the effect of stress on the loss of NE after synthesis inhibition. The stress-induced changes in plasma corticosterone and prolactin levels were evaluated as a physiologic index of stress. While stress increased the loss of NE after synthesis inhibition in the non-exposed control animals, it totally prevented any loss of NE after synthesis inhibition in offspring prenatally exposed to DZ. Additionally, the stress-induced change in plasma corticosterone was attenuated in a dose-related manner by prenatal exposure to DZ. The stress-induced change in plasma prolactin was also altered in a dose-related manner by the prenatal exposure. Both the altered response to stress within hypothalamic NE neurons and the attenuated change in plasma corticosterone induced by prenatal exposure to DZ (2.5 mg/kg) were prevented by concurrent administration of the centrally acting benzodiazepine antagonist Ro15-1788 to the pregnant dam, indicating that the effects of DZ were mediated via binding of the drug to central sites during gestation. These results indicate that activation of specific binding sites during early development can induce neural alterations in the adult offspring which can be reflected in functional changes which may compromise the organism.

A purge-and-trap method for the analysis of acetone in biological tissues

A method for the detection and quantitation of acetone in biological tissues is described. The solvent was extracted with nitrogen gas from the biological specimen and adsorbed on a porous polymer (Porapak Q). The acetone content of the adsorbent was determined by conventional gas chromatographic analysis (FID) after heat desorption. The reliability of the method was tested both with in vitro- and in vivo-exposed specimens. A complete recovery was obtained after in vitro additions of acetone. The method error was about 9% as calculated from both in vitro and in vivo experiments. Acetone concentrations ranging between 17 nmol/g tissue in nonexposed animals and 1.8 μmol/g tissue in mice exposed to acetone vapor were determined.

Chronic Effects of Dietary Exposure to Amosite Asbestos and Tremolite in F344 Rats

Carcinogenesis bioassays of blocky (nonfibrous) tremolite and amosite asbestos alone or in combination with the intestinal carcinogen 1,2-dimethylhydrazine dihydrochloride (DMH) were conducted with male and female Fischer 344 rats. The minerals were administered at a concentration of 1% in pelleted diet for the entire lifetime of the rats starting with the dams of the test animals. One group of amosite rats also received chrysotile asbestos via gavage during lactation. Group sizes varied from 100 to 250 animals. The offspring from mothers exposed to tremolite or amosite asbestos were smaller at weaning than those from untreated mothers and remained smaller throughout their life. The administration of dimethylhydrazine (DMH) did not affect body weight gain, either in amosite-exposed or nonexposed animals. Survival was comparable in the tremolite and control groups. The amosite-exposed rats showed enhanced survival compared to the untreated controls. DMH exposure reduced survival by approximately one year, although the amosite plus DMH groups survived slightly better than the DMH alone groups. No toxicity or increase in neoplasia was observed in the tremolite-exposed rats compared to the controls. Significant increases (p less than 0.05) in the rates of C-cell carcinomas of the thyroid and monocytic (mononuclear cell) leukemia in male rats were observed in amosite-exposed groups. However, the biological significance of the C-cell carcinomas in relation to amosite asbestos exposure is discounted because of a lack of significance when C-cell adenomas and carcinomas were combined and the positive effect was not observed in the amosite plus preweaning gavage group. The biological significance of an increased incidence of mononuclear cell leukemia is questionable, because of a lack of statistical significance in the amosite group when evaluated using life table analysis, lack of significance when compared to the tremolite control group, and the fact that no toxic or neoplastic lesions were observed in the target organs, i.e., gastrointestinal tract and mesothelium. DMH caused a high rate of (62-74%) of intestinal neoplasia in amosite and nonamosite-exposed groups. Neither an enhanced carcinogenic nor protective effect was demonstrated by exposure to amosite asbestos.

Infectious bovine keratoconjunctivitis: Bacteriologic, immunologic, and clinical responses of cattle to experimental exposure with Moraxella bovis

The bacteriologic, immunologic, and clinical responses of 3- to 4-month old Holstein-Friesian calves to experimental exposure with Moraxella bovis type 10900 has been investigated. After u.v. radiation and intraconjunctival exposure with 1.9 × 10 7 microorganisms, each eye of 16 calves exhibited signs of blepharospasm, photophobia, and increased lacrimation. Bacteria were recovered from exposed eyes for 2–7 consecutive weeks before maximal clinical response occurred. The severity of the cases varied from eyes that exhibited mild signs to severe clinical cases with profuse lacrimation, conjunctival swelling, corneal opacity, and ulceration. By 70 days after exposure, M. bovis could not be recovered from any conjunctival swabs, and clinical signs were not observed. Four non-exposed control animals did not develop clinical signs nor was M. bovis recovered from conjunctival swabs. Lacrimal secretions collected at the time of and 1 week after maximal clinical response had significantly elevated levels of total protein as compared to those collected 3, 2, and 1 week before, and 2 and 3 weeks after maximal clinical response. A passive hemagglutination test, using tanned formalized sheep erythrocytes sensitized with M. bovis sonicate antigen, detected antibody in lacrimal secretions from 22 of 32 eyes. The appearance of specific antibody in lacrimal secretions correlated with the amelioration of clinical signs and the decline in numbers of M. bovis microorganisms recovered from conjunctival swabs.

Longitudinal distribution of cochlear potentials and the K + concentration in the endolymph after acoustic trauma

Guinea pigs were exposed to 142 dB third-octave band of noise centred at 1 kHz for 1 h. At different times after exposure the endocochlear potential (EP), the anoxic negative endocochlear potential (-EP), the concentration of K + (K e +) and microphonic potentials were recorded in scala media in four cochlear turns. The remaining hair cells were counted in each animal. Immediately after the exposure, the EP and K e + decreased evenly in all four cochlear turns and gradually returned to normal physiological values in 5–20 days. When measured 20 days after the exposure, essentially normal EP and K e + values were observed, with an apicalwards decline, which was similar to that found along the cochlea in nonexposed animals. Abnormal increased EP was observed in some animals 20 days after the exposure in the first and second turns. In contrast to positive EP and K e + values, the anoxic negative EP attained less negative values in the second turn of exposed animals i.e., in the turn where the narrow band noise exerted the major destructive effect. An almost normal distribution of hair cells and most negative EP values were found in the fourth turn. The distribution of persistent hair cells correlated positively with the values of the anoxic negative EP and amplitudes of the microphonic potentials. It is assumed that, in addition to the difference in K + concentration between endolymph and perilymph, the anoxic negative EP is dependent upon the functional state of the organ of Corti.

Environmental modulation of analgesic tolerance induced by morphine pellets

The development of analgesic tolerance to the nociceptive tail flick test was examined in morphine implanted rats. Animals repeatedly exposed to a nonfunctional tail flick apparatus after implantation, were significantly more tolerant than nonexposed animals, on subsequent tests with the functional apparatus. In contrast, prior exposure to an alternate nociceptive, hot plate test, did not significantly modify tolerance on the tail flick. Facilitation of tolerance, produced by prior tail flick assessment, was maintained for at last one week following the last test, but only if the morphine pellet was not removed. If the pellet was removed the influence of prior analgesic assessment was not retained. The substantial plasticity exhibited by the spinal tail flick reflex suggests the utility of this response for investigations of neural correlates of behavior.

INVESTIGATIONS ON THE EFFECTS OF 2,3,7,8‐TETRACHLORODIBENZO‐p‐DIOXIN (TCDD) ON PARAMETERS OF VARIOUS IMMUNE FUNCTIONS

The effects of TCDD exposure on parameters of immune function during the developmental period were investigated. Exposures were performed in Fischer/Wistar rats. Fetal and neonatal rats were exposed to TCDD through maternal dosing (5 micrograms/Kg) on day 18 of gestation and on days 0, 7, and 14 of postnatal life (group 1). Another group of neonatal rats were exposed to TCDD through maternal dosing on days 0, 7, and 14 of postnatal life only (group 2). Body weights and relative thymus weights were found to be suppressed up to 135 days of age in group 1 but only up to 35 days of age in group 2. Parameters of cell-mediated and humoral immune function were investigated. TCDD suppressed cell-mediated immune function without affecting humoral immune function. TCDD-exposed animals had recovered normal cell-mediated immune function by 270 days of age. A group of inbred Fischer rats was exposed to TCDD as described for group 1 above. At 45 days of age these animals were utilized in lymphocyte homing studies. It was found that TCDD exposure alters homing patterns of lymphocytes from exposed animals when adoptively transferred to untreated animals. In addition, lymphocytes from nonexposed animals did not home normally when injected into TCDD-exposed recipients.

Effects of noise exposure on the cochlea and neurons of the inferior colliculus

Guinea pigs were exposed for 30 or 60 min to high-intensity stimuli (1/3-octave band noise centered at 1 or 2 kHz tone, intensity from 130 to 145 dB SPL). Several electrophysiological measurements were made in the cochlea and in the inferior colliculus before and after the exposure. Potassium concentration in the perilymph of scala vestibuli (measured with ion-selective double barrel microelectrodes) which was 3.07 ± 0.50 mm K+ in the control group of nonexposed animals, increased after the exposure to 4.70 ± 1.55 mm K+. Threshold tuning curves for the inferior colliculus neurons were elevated by about 30–50 dB, when compared with the pre-exposure levels. The threshold values gradually decreased, reaching the pre-exposure level approximately after 48 hours. Similar time course was observed in the endochochlear potentials, which was decreased after the exposure. Despite the threshold elevation the excitability of neurons ot polarizing currents was not greatly affected by the exposure.

Hippocampal lesions during rearing and transfer of perceptual learning in rats

Bilateral lesions of the hippocampus in humans result in severe deficits of recent memory which consist of an inability to recall events a few minutes after they have occurred. On the other hand, such patients demonstrate normal abilities to recall events that transpired before the operation. Studies employing animals as subjects have produced contrary evidence concerning a memory-consolidation view of hippocampal functioning because hippocampal animals are not deficient in learning a variety of tasks. In the present research, the recent memory hypothesis was reexamined employing the early experience paradigm of Gibson and Walk (1956). This methodological variation provided a testing situation more analogous to the human testing situation in that animals were required to utilize salient cues from their environment and to transfer this information to a subsequent discrimination task. It was found that animals receiving bilateral hippocampectomy before exposure to the to-be-discriminated stimuli fared no better in a subsequent discrimination test than animals not exposed to the stimuli. In addition, animals undergoing hippocampal ablation after exposure to the forms demonstrated significantly better performance in the test situation than nonexposed animals. The findings of the present research provide some support for the recent memory hypothesis of hippocampal functioning.

The effects of scopolamine on preexposure to a learning apparatus

Forty-eight random-bred male mice (CFW, Carsworth Laboratory) were divided randomly into saline or scopolamine (1.0 mg/kg) treatment groups, with each of these groups being subdivided into either an exposed or a nonexposed group. The exposed group animals were given the appropriate injections (ip) 20 min prior to being allowed to explore both sides of a shuttlebox for 30 min for 10 preexposure sessions. The nonexposed group animals were injected and placed in a carrying cage for each of the 10 sessions. After these sessions, all animals were placed in the shuttlebox and given a series of signaled one-way shuttle avoidance trials. The saline exposed group required significantly fewer trials to criteria than the scopolamine exposed group. It was also found that scopolamine was capable of attenuating the normally occurring decrement in locomotor activity across exposure sessions.

Radiation-induced life shortening in germfree mice

The life span, prevalence of disease and a variety of aging parameters were evaluated in 358 conventional and germfree virgin female mice of the CD-1 line, some of which were exposed to 700 R cobalt-60-γ-radiation at 6 weeks of age. In comparison with the conventional groups, the exposed and nonexposed germfree animals showed a reduction in life span accentuated by irradiation, a reduced prevalence but accelerated appearance-rate of benign and malignant tumors, an increased incidence of amyloidosis and displacement of a series of aging parameters consistent with accelerated aging. These observations are tentatively attributed to the characteristic hyporeactivity of lymphoreticular structures associated with the germfree state and particularly the attendant decrease in the pool of thymic-dependent recirculating small lymphocytes.

The effects of preexposure to a learning apparatus

ICR mice were given exposure to a one-way shuttle apparatus until locomotor activity had been habituated. When compared with nonexposed animals, the exposed animals displayed superior shuttle avoidance learning. Animals exposed to both the apparatus and the CS did not differ from the nonexposed group. It was concluded that preexposure to the learning apparatus facilitated acquisition, while preexposure to the apparatus in the presence of the CS did not. The relationship between this effect and habituation was considered.

Effect of Cold Exposure on the Immunologic Response of Rabbits to Human Serum Albumin

Abstract The effect of low environmental temperature on the response of rabbits to a single injection of human albumin was examined. Animals exposed to cold (4°C ± 2°C) had faster catabolism of antigen and earlier appearance and higher levels of circulating antibody. Mercaptoethanol-resistant antibody was produced early (12 days) in coldexposed animals and late (26 days) in non-exposed animals. The effects of cold exposure on the immune response were as apparent after acute exposure (1 to 2 days) as after chronic exposure (3 to 8 wk).

Mammary Neoplasia in the Rat as Related to Dose of Partial-Body Irradiation

Female Sprague-Dawley rats were exposed to 250-kvp X-rays at 42 days of age so that the anterior half of the animal received either 0, 222 R, 444 R, 666 R, 888 R, or 1110 R in a single exposure. The animals were studied over their entire life span. The life span was reduced increasingly with increasing dose. The non-exposed animals had similar rates of mammary neoplasia in the anterior and posterior areas. Mammary neoplasia was much more prevalent in the anterior, exposed area than in the posterior, shielded area. Within the anterior, exposed area the incidence of mammary neoplasia increased in an approximately regular manner as the dose was increased from 222 R to 88 8R. The mammary neoplastic response to 1110 R was less than the response to 888 R and often less than the response to 666 R when calculated on a rat-day at risk basis. The decline in mammary neoplastic response at 1110 R was thought to be the result of cell death of mammary tissue cells, some of which would have been expected to develop neop...

Studies on Radiation-Induced Mammary Gland Neoplasia in the Rat: VI. The Effect of Changes in Thyroid Function, Ovarian Function, and Pregnancy

When 3l female Sprague-Dawley rats were exposed to a single total-body dose of 400 r of 250 kvp x rays on the fortieth day of age, 24 of the rats so exposed developed 43 mammary neoplasms within a 1-year period. Of 3l littermate control rats studied during the same period, only 3 rats exhibited single mammary neoplasms. When diethylstilbestrol was given to irradiated rats, both the incidence and the number of mammary neoplasms was depressed, indicating that for the maximum mammary neoplastic response to radiation the irradiation breast tissue must be subjected to the proper hormonal environment, and this appears to be provided by a normal estrus cycle. Diethylstilbestrol given to nonexposed rats did not induce any more mammary neoplasms than were found in nonexposed control rats. Hyperthyroidism, induced by exogenous triiodothyronine given after irradiation and maintained for 12 months, did not infiuence the incidence of rats with mammary neoplasia or the total number of mammary neoplasms. Hypothyroidism, induced by a continuous administration of propylthiouracil in the drinking water beginning after irradiations, reduced the incidence of rats with mammary neoplasia only slightly and further reduced the total number of mammary neoplasms, suggesting that hypothyroidism provides less than the optimum hormonalmore » pattern for the maximum mammary neoplastic response to radiation exposure. When the ovarian area was shielded, including a portion of mammary tissue, the incidence and number of mammary neoplasms were reduced. This reduction of neoplastic response appears to be due to the fact that, as less breast tissue is exposed, the smaller the total neoplastic response becomes. When 30 rats were irradiated with the ovarian area shielded and then allowed to become pregnant (with and without lactation), 19 of these rats exhibited 29 mammary neoplasms. This slight increase in neoplastic response was not proved to be significant, although it is suggestive that the changes in hormonal patterns brought about by pregnancy may also influence the neoplastic potential of irradiated breast tissue. Immediately after parturition, with or without lactation permitted, the growth rate of the adenocarcinoma type of mammary neoplasm was diminished, suggesting that in this type of mammary neoplasm the growth rate may be hormone-dependent, a conclusion reached previously by others. Twenty-nine per cent of the mammary neoplasms found in the irradiated groups were of the adenocarcinoma type; no adenocarcinomas were found in non-irradiated rats. Neoplasms of the adenofibroma or fibroadenoma types were the most common types found in either exposed or nonexposed animals. The period between exposure and appearanee of the first mammary neoplasm was 2 months in all irradiated groups. The comparable period for the nonirradiated was 12 months. Thus the irradiated female Sprague-Dawley rat develops a relatively high incidence of rapidly appearing mammary neoplasms as compared to nonirradiated rats, although the mammary neoplastic response to irradiation is subject to hormonal modification. This suggests that radiation- induced neoplasia, of this type in this strain of rat, is at least a two-stage proccss consisting of the induction phase, i.e., radiation injury, and thc promoting phase, i.e., the hormonal influence to which the radiation injured tissue is subjected. The total incidence of neoplasia of the pituitary, thyroid, and adrenal glands and of the ovaries did not exceed 6% in the exposed animals, as compared to an absence of these neoplasms in the nonexposed animals. The numbers of these neoplasms were ioo small to permit meaningful conclusions to be drawn as to the effects of changes in thyroid function, ovarian function, or pregnancy and lactation superimposed on radiation exposure on neoplasia of the endocrine system. (auth)« less

Embryonal iron turnover.

Summary. Seventeen hours after labelling the circulating iron‐βrglobulin, with 59Fe, 14–34 p. c. of the labeled iron is found in the 21 days old foetus of the rabbit.Exposure of the rabbit to 500 r of X‐rays increases the amount of 59Fe passing the placenta to almost twice the value in non‐exposed animals.Seventy‐three–eighty‐three p. c. of the 59Fe content of the embryo is found in the liver.The specific activity of the hemoglobin iron present in the nuclear fraction of the liver amounts to one fourth of that of the circulating hemoglobin in the maternal, to about twice in the embryonic organism.Exposure to radiation one day prior to labeling the plasma depresses the fraction of embryonal 59Fe incorporated into the hemoglobin of the nuclear liver fraction to about half of the value observed in non‐irradiated rabbits.The valuable assistance of Miss Jutta Schliack and the generous support of this investigation by the Riksföreningen fijr kräft‐sjukdomarnas bekämpande, Cancernämnden and the Knut och Alice Wallenbergs Stiftelse is gratefully acknowledged.