Magnetic resonance elastography of slow and fast shear waves illuminates differences in shear and tensile moduli in anisotropic tissue.

Mechanical anisotropy is an important property of fibrous tissues; for example, the anisotropic mechanical properties of brain white matter may play a key role in the mechanics of traumatic brain injury (TBI). The simplest anisotropic material model for small deformations of soft tissue is a nearly incompressible, transversely isotropic (ITI) material characterized by three parameters: minimum shear modulus (µ), shear anisotropy (ϕ=µ1µ-1) and tensile anisotropy (ζ=E1E2-1). These parameters can be determined using magnetic resonance elastography (MRE) to visualize shear waves, if the angle between the shear-wave propagation direction and fiber direction is known. Most MRE studies assume isotropic material models with a single shear (µ) or tensile (E) modulus. In this study, two types of shear waves, "fast" and "slow", were analyzed for a given propagation direction to estimate anisotropic parameters µ, ϕ, and ζ in two fibrous soft materials: turkey breast ex vivo and aligned fibrin gels. As expected, the speed of slow shear waves depended on the angle between fiber direction and propagation direction. Fast shear waves were observed when the deformations due to wave motion induced stretch in the fiber direction. Finally, MRE estimates of anisotropic mechanical properties in turkey breast were compared to estimates from direct mechanical tests.

Chronic cocaine exposure during pregnancy increases postpartum neuroendocrine stress responses.

The cycle of chronic cocaine (CC) use and withdrawal results in increased anxiety, depression and disrupted stress-responsiveness. Oxytocin and corticosterone (CORT) interact to mediate hormonal stress responses and can be altered by cocaine use. These neuroendocrine signals play important regulatory roles in a variety of social behaviours, specifically during the postpartum period, and are sensitive to disruption by CC exposure in both clinical settings and preclinical models. To determine whether CC exposure during pregnancy affected behavioural and hormonal stress response in the early postpartum period in a rodent model, Sprague-Dawley rats were administered cocaine daily (30 mg/kg) throughout gestation (days 1-20). Open field test (OFT) and forced swim test (FST) behaviours were measured on postpartum day 5. Plasma CORT concentrations were measured before and after testing throughout the test day, whereas plasma and brain oxytocin concentrations were measured post-testing only. The results obtained indicated increased CORT response after the OFT in CC-treated dams (P ≤ 0.05). CC-treated dams also exhibited altered FST behaviour (P ≤ 0.05), suggesting abnormal stress responsiveness. Peripheral, but not central, oxytocin levels were increased by cocaine treatment (P ≤ 0.05). Peripheral oxytocin and CORT increased after the FST, regardless of treatment condition (P ≤ 0.05). Changes in stress-responsiveness, both behaviourally and hormonally, may underlie some deficits in maternal behaviour; thus, a clearer understanding of the effect of CC on the stress response system may potentially lead to treatment interventions that could be relevant to clinical populations. Additionally, these results indicate that CC treatment can have long-lasting effects on peripheral oxytocin regulation in rats, similar to changes observed in persistent social behaviour and stress-response deficits in clinical populations.

Gestational ethanol and nicotine exposure: effects on maternal behavior, oxytocin, and offspring ethanol intake in the rat.

Alcohol consumption and smoking during pregnancy is common, despite the known adverse effects of these drugs on fetal development. Though studies on the effects of each drug separately are published, little is known about the effect of concurrent use of alcohol and nicotine in humans or in preclinical models. In this report, we examined the impact of continuous gestational exposure to both ethanol via liquid diet and nicotine via an osmotic minipump on maternal behavior, offspring ethanol intake, and oxytocin levels in a rat model. Dams were tested for the onset of maternal behavior with litters of unexposed surrogate pups and then killed to examine oxytocin levels within specific brain regions. Drug-exposed offspring reared by surrogate dams were tested for ethanol intake at either adolescence or adulthood, and oxytocin levels were measured in relevant brain regions after behavioral tests. Dams exhibited minor deficits in maternal care, which were associated with lower oxytocin levels in both the ventral tegmental and medial preoptic areas compared to control dams. Prenatal exposure altered sex-specific ethanol intake, with differential effects at adolescence and adulthood. Oxytocin system changes were also apparent in the ventral tegmental and medial preoptic regions of drug-exposed adolescent and adult offspring. These results suggest that dam treatment with ethanol and nicotine can somewhat negatively affect the early rearing environment, and that prenatal exposure to both of these drugs results in drinking behavior differing from what would be expected from either drug alone. Oxytocin's possible involvement in the mediation of these effects is highlighted.

Intergenerational effects of cocaine on maternal aggressive behavior and brain oxytocin in rat dams.

Gestational cocaine treatment results in significantly increased maternal aggression towards an intruder by postpartum day six, while acute postpartum treatment dose dependently decreases maternal aggressive (MA) behavior. Both increased and decreased aggression in the cocaine-treated dams are correlated with either decreased or increased levels of oxytocin in the amygdala, respectively. The current study was an effort to determine whether the effect of gestational cocaine on maternal aggression is transient or would continue into the postpartum period; whether an intermittent cocaine treatment regimen, which incorporates gestational and postpartum intermittent cocaine treatment, would differ from chronic daily gestational treatment; and finally, whether next generation female offspring of cocaine-treated or control dams would have altered MA behavior and oxytocin system changes attributable to either prenatal drug exposure, rearing condition or both. We now report no increase in maternal aggression following chronic gestational treatment and significantly lower levels of aggression in intermittently treated dams on postpartum day eight, with no significant effects in either group on postpartum day 12. Young adult female offspring of the cocaine-treated and control dams, who reared their own natural litters and were tested on postpartum day eight for maternal aggression, had higher levels of maternal aggression towards an intruder attributable to both prenatal cocaine exposure and rearing condition. Higher aggression in cocaine-reared next generation dams was associated with lower levels of oxytocin in the amygdala. Intergenerational effects of cocaine were apparent with respect to aggression and oxytocin system changes.

Impact of gestational cocaine treatment or prenatal cocaine exposure on early postpartum oxytocin mRNA levels and receptor binding in the rat.

Prior research reported decreased oxytocin levels in specific brain regions correlated with disruptions in maternal care following gestational cocaine treatment in rats. Similarly, prenatal exposure to cocaine impaired subsequent maternal behavior in adulthood, but behavioral alterations were not associated with decreases in oxytocin levels in the same brain regions as were found in their cocaine-treated rat dams. To determine if other aspects of the oxytocin system are disrupted by cocaine treatment or prenatal exposure to cocaine during critical time points associated with maternal care, oxytocin mRNA transcription and receptor binding were examined on postpartum day two in relevant brain regions following gestational treatment with, or prenatal exposure to, either cocaine or saline. We hypothesized that oxytocin mRNA levels and receptor binding would be differentially affected by cocaine in the early postpartum period of dams and their offspring. Our findings indicate that gestational cocaine treatment resulted in significant increases in oxytocin mRNA levels in only the paraventricular nucleus of cocaine-treated dams, with almost significant increases in both generations in the supraoptic nucleus, but no significant effects of cocaine on receptor binding in either generation of dams. These findings indicate that in addition to oxytocin levels, cocaine treatment or prenatal exposure primarily affects oxytocin mRNA synthesis, with little effect on receptor binding in specific brain regions associated with maternal behavior in the early postpartum period of the rat.

Cocaine treatment alters oxytocin receptor binding but not mRNA production in postpartum rat dams.

Gestational cocaine treatment in rat dams results in decreased oxytocin (OT) levels, up-regulated oxytocin receptor (OTR) binding density and decreased receptor affinity in the whole amygdala, all concomitant with a significant increase in maternal aggression on postpartum day six. Rat dams with no gestational drug treatment that received an infusion of an OT antagonist directly into the central nucleus of the amygdala (CeA) exhibited similarly high levels of maternal aggression towards intruders. Additionally, studies indicate that decreased OT release from the hypothalamic division of the paraventricular nucleus (PVN) is coincident with heightened maternal aggression in rats. Thus, it appears that cocaine-induced alterations in OT system dynamics (levels, receptors, production, and/or release) may mediate heightened maternal aggression following cocaine treatment, but the exact mechanisms through which cocaine impacts the OT system have not yet been determined. Based on previous studies, we hypothesized that two likely mechanisms of cocaine's action would be, increased OTR binding specifically in the CeA, and decreased OT mRNA production in the PVN. Autoradiography and in situ hybridization assays were performed on targeted nuclei in brain regions of rat dams on postpartum day six, following gestational treatment twice daily with cocaine (15 mg/kg) or normal saline (1 ml/kg). We now report cocaine-induced reductions in OTR binding density in the ventromedial hypothalamus (VMH) and bed nucleus of the stria terminalis (BNST), but not the CeA. There was no significant change in OT mRNA production in the PVN following cocaine treatment.

The effects of dopaminergic/serotonergic reuptake inhibition on maternal behavior, maternal aggression, and oxytocin in the rat.

Studies using dopaminergic and serotonergic agonists or antagonists implicate involvement of these systems in various aspects of early maternal behavior and postpartum aggression towards an intruder in rats, both of which are associated with the presence of oxytocin in specific brain regions. It is unclear however, if or how long-term uptake inhibition of either neurotransmitter system alone or in combination, affects oxytocin system dynamics or maternal behavior/aggression. Pregnant women frequently take drugs (antidepressants, cocaine) that induce long-term reuptake inhibition of dopamine and/or serotonin, thus it is important to understand these effects on behavior and biochemistry. Rat dams were treated throughout gestation with amfonelic acid, fluoxetine, or a combination of both, to investigate effects of reuptake inhibition of dopamine and serotonin systems respectively, on maternal behavior, aggression and oxytocin. The more appetitive aspects of maternal behavior (nesting, licking, touching) and activity were increased by the low dose of amfonelic acid, high dose of fluoxetine, or the high dose combination more than other treatments. Aggression was decreased by amfonelic acid and somewhat increased by fluoxetine. Dopamine uptake inhibition appears to have a strong effect on hippocampal oxytocin levels, while receptor dynamics may be more strongly affected by serotonin uptake inhibition.

Biochemical indicators of hepatotoxic effects of pesticides.

Pesticides can cause damage to man and beneficial organisms. Some sub-lethal effects of pesticides were studied in birds with a view to identifying characteristic biochemical responses that may be useful for the monitoring of exposure to sub-lethal levels in the field. Pesticides were used: demeton-S-methyl, (DSM), chlorpyriphos, chlorfenviphos, triazophos, pirimicarb, methiocarb and permethrin. Blood was collected before dosing, and 2, 6, 24, 48 and 72 hours after the treatment from the brachial vein of birds. Enzyme activities were assayed in the plasma or serum samples obtained. The assays used were GOT, MDH, GDH, SDH, GAMMA GT and ChE. The results showed an increase in plasma and serum GOT and gamma-GT levels were found in all animals treated with the previous pesticides. The level of ChE increased in birds after treatment with permethrin. It was concluded that the pesticides cause structural and functional changes in the liver and also, the measurement of the previous parameter activities may be useful for assessing exposure and sub-lethal effects of pesticides on the wildlife.

Neurotoxic pesticides and behavioural effects upon birds.

Organochlorine, organophosphorus, carbamate, pyrethroid and neonicotinoid insecticides and organomercury fungicides are all neurotoxic and therefore have the potential to cause behavioural disturbances in birds. A number of studies have described behavioural effects caused to captive birds by neurotoxic pesticides, but it is very difficult to measure such effects in the field, which is a serous limitation given their potential to cause adverse effects at the population level. The mode of action, and the neurotoxic and behavioural effects of these compounds are briefly reviewed before considering evidence for their effects in the laboratory and field. Behavioural effects may cause adverse changes at the population level either directly or indirectly. Direct effects upon avian populations may be due to disturbances of reproduction, feeding, or avoidance of predation. Indirect effects on predators may be the consequence of direct action upon the prey population leading to either (1) reduction of numbers of the prey population, or (2) selective predation by the predator upon the most contaminated individuals within the prey population. Attention is given to the historic evidence for neurotoxic and behavioural effects of persistent organochlorine insecticides, raising the question of retrospective analysis of existing data for this once important and intensively studied class of compounds. Less persistent pesticides currently in use may also have neurotoxic effects upon birds in the field. Sometimes, as with some OPs, their effects may outlast the persistence of their residues, and the ecotoxicity and persistence of some may be affected by interactions with other environmental chemicals. The development of new mechanistic biomarker assays could improve understanding of behavioural effects and possible associated effects at the population level caused by such compounds in the field.

Dose-related effects of chronic gestational cocaine treatment on maternal aggression in rats on postpartum days 2, 3, and 5.

Gravid Sprague-Dawley rats received subcutaneous injections of saline, 3.5, 7.5 or 15 mg/kg of cocaine, twice daily, throughout gestation. On postpartum days 2, 3, and 5, dams and their litters (surrogate or natural) were videotaped for 10 minutes in the presence of a male rat for assessment of aggression towards the intruder. Oxytocin levels in discrete brain areas were assayed on postpartum day 5. The 30 mg/kg dose group had a significantly greater increase in the frequency of threats from postpartum day2 through postpartum day 5 than the 7.5 mg/kg cocaine and the non-yoke-fed saline control groups. Dams with natural litters exhibited a significantly greater frequency of receptive behavior compared to dams with surrogate litters. There were no significant differences in oxytocin levels between the 30 mg/kg cocaine-treated group and the other treatment or control groups on postpartum day 5. There are very few statistically significant cocaine-induced increases in maternal aggressive behavior and no dose-dependent decreases in amygdaloid OT levels in the early postpartum period.

Effects of chronic cocaine administration on aggressive behavior in virgin rats.

Virgin Sprague-Dawley rats received subcutaneous injections of saline, 3.5, 7.5 or 15 mg/kg of cocaine, twice daily, for 20 consecutive days. Females were videotaped for 10 minutes in the presence of a male rat for assessment of aggression towards the intruder 2, 3, and 5 days following cessation of cocaine or saline administration. Oxytocin levels in discrete brain areas were assayed following behavioral testing, 5 days following cessation of cocaine or saline administration. The 30 mg/kg-dose group tended to have a lower frequency of fight attacks and aggressive postures compared to saline-treated controls across sessions. The frequency of most of the behaviors analyzed were represented by quadratic functions across time, such that the highest frequency of behavior occurred 2 days following the final injection with relatively less activity 3 and 5 days following cessation of saline or cocaine administration. The 30 mg/kg cocaine-treated group had significantly lower hippocampal OT levels than the 15 mg/kg group 5 days following cessation of cocaine or saline administration.

Acute cocaine alters oxytocin levels in the medial preoptic area and amygdala in lactating rat dams: implications for cocaine-induced changes in maternal behavior and maternal aggression.

Acute cocaine administration has been correlated with disruptions in the onset and maintenance of maternal behavior as well as decreases in maternal aggressive behavior in rat dams. A growing body of evidence suggests that cocaine may alter oxytocin levels leading to impairments in maternal behavior and aggression. The current study assessed whether acute cocaine injections alter oxytocin (OT) levels in the medial preoptic area (MPOA), ventral tegmental area (VTA), amygdala (AMY), and hippocampus (HIP) on postpartum day (PPD) 1 or PPD 6. On PPD 1, 30 mg/kg cocaine reduced OT levels by approximately 26.9% (picograms/milligram) in the MPOA (t (18) = 3.44, P<.01) compared to saline. On PPD 6, 30 mg/kg cocaine significantly increased OT levels by approximately 20.9% (picograms/brain area) in the AMY (F (2,25) = 3.44, P=.05) relative to saline. These findings suggest that acute cocaine may disrupt maternal behavior and maternal aggression at least in part through its action on the oxytocinergic system.

Radioligand assays for oestradiol and progesterone conjugated to protein reveal evidence for a common membrane binding site in the medial preoptic area-anterior hypothalamus and differential modulation by cholera toxin and GTPgammaS.

In this study membrane oestradiol (E) binding sites in the medial preoptic area-anterior hypothalamus (MPOA-AH) of ovariectomized (OVX) rats were characterized using standard radioligand binding techniques employing E conjugated to bovine serum albumin (BSA) at position 6 and radiolabeled with 125I (E-6-[125I-BSA]). In previous studies binding of a radioactive conjugate of progesterone (P) and BSA (P-3-[125I-BSA]) was examined using the same membrane preparation. E-6-[125I-BSA] binding was linear across a tissue concentration range of 0.005-0.02 mg protein/0.1 ml of membrane suspension. An association T1/2 of 9.5 min and a dissociation T1/2 of 52.1 min for E-6-[125I-BSA] were derived from kinetic experiments. Competition binding experiments revealed high (Ki=0.63+/-(0.50 nM) and low (Ki=161.5(96.5 nM) affinity binding sites for E-6-[125I-BSA], demonstrating different binding parameters than shown in our previous work for P-3-[125I-BSA] binding. Further studies on MPOA-AH membranes treated with cholera toxin (CTX) and GTPgammaS suggested that E-6-BSA binding sites are associated with G proteins. E-6-[125I-BSA] binding demonstrated both high-and low-affinity sites. GTPgammaS added to the assay reduced both E-6-[125I-BSA] and P-3-[125I-BSA] binding suggesting that G proteins are associated with both binding sites. Extensive analysis of both E-6-[125I-BSA] and P-3-[125I-BSA] binding sites demonstrated a reciprocal relationship such that high-affinity E-6-[125I-BSA] binding sites exhibit low affinity for P-3-[125I-BSA] and low-affinity E-6-[125I-BSA] binding sites exhibit high affinity for P-3-[125I-BSA]. Preincubating membranes with CTX or GTPgammaS reduced high-affinity E-6-[125I-BSA] binding and enhanced high-affinity P-3-[125I-BSA] binding. These results suggest that, in the MPOA-AH, membrane steroid binding sites exist in two interconvertible conformations that preferentially bind either E-6-BSA or P-3-BSA, depending on their association with a G protein. Additional studies with free steroids revealed that: (1) oestrogens (17beta-oestradiol, diethylstilbestrol) as well as synthetic oestrogen antagonists tamoxifen and ICI 182 780 displaced P-3-[125I-BSA] further suggesting a relationship between membrane binding sites for E and P-3-[125I-BSA] binding sites; and (2) treatment of OVX rats with E decreased displacement by P-3-BSA and increased displacement by ICI 182,780 and tamoxifen suggesting these antagonists affect membrane P-3-[125I-BSA] binding sites after in-vivo E treatment. The membrane binding sites for E and P demonstrate interrelationships not demonstrated by their nuclear receptors.

Effects of dieldrin on life stages of the African catfish, Clarias gariepinus (Burchell).

Early life stages of Clarias gariepinus were found to be less sensitive to acute dieldrin toxicity than were those of Nile tilapia, Oreochromis niloticus; 96-h LC50 values for 37-day-old fry were 11. 7 and 4.95 microg liter-1, respectively. The growth of C. gariepinus fry was unaffected by 30 days of exposure to 2.4 microg liter-1 dieldrin under static conditions with water renewal every 96 h, whereas growth of O. niloticus fry was significantly reduced. Adult C. gariepinus exposed to dieldrin for 30 days, with water changes every 96 h, rapidly absorbed dieldrin from aqueous solution. Dieldrin concentration was measured just before water changes and from an initial concentration of 4.0 microg liter-1, stabilized after 12 days at about 0.075 microg liter-1, indicating that a balance between uptake and excretion and metabolism had been achieved. Dieldrin accumulated in the tissues during these exposures, especially in the liver, where after 30 days the bioconcentration factor relative to initial concentration was about 900. Chronic exposure of C. gariepinus to dieldrin had no effect on blood hematocrit and hemoglobin, but appeared to slow the growth of catfish and had a clear negative effect on the reproductive potential of mature females.

Dose-dependent effects of multiple acute cocaine injections on maternal behavior and aggression in Sprague-Dawley rats.

Rat dams, which had no prior drug treatment, were either nontreated controls or were injected subcutaneously 4 times during a 10-day period with a single dose of 30, 15 or 7.5 mg/kg of cocaine hydrochloride HCl, or normal saline. Injections were given immediately postpartum following delivery of their final pup (PPD 1), and again on postpartum day 3 (PPD 3), postpartum day 6 (PPD 6) and postpartum day 10 (PPD 10). Dams were observed 30 min following injections for maternal behavior (MB) towards 8 surrogate male pups on PPD 1 and PPD 3 and for aggression towards a male or female intruder in the presence of their litter on PPD 6 and PPD 10. Compared to saline and untreated controls, cocaine-treated dams exhibited more disruptions in MB on both PPD 1 and PPD 3 and were less aggressive towards an intruder, regardless of intruder sex, on PPD 6 and PPD 10. In most cases MB was altered in a dose-dependent manner with the higher doses of cocaine resulting in a greater disruption of behavior.

A dose-response study of chronic cocaine on maternal behavior in rats.

To determine if there was a dose-response relationship with regard to cocaine treatment and maternal behavior exhibited by lactating rats at doses that had not been previously investigated, we examined the effects of three doses of chronic cocaine administration throughout gestation on both onset and established maternal behavior. Dams were injected (SC) with 6.3, 13, or 25 mg/kg cocaine HCl or an equivalent volume of saline throughout gestation; maternal behavior was tested on postpartum days 1 and 3. At the doses employed, cocaine disrupted the onset of only one pup-directed component of maternal behavior significantly in a dose-response manner, although there were several statistically nonsignificant dose-dependent trends of behavioral disruptions. No pup-directed behaviors were disrupted during testing for established maternal behavior. These results indicate that gestational cocaine treatment at doses of 25 mg/kg and less have only minimal effects on the onset and no effect on the maintenance of maternal behavior using our paradigm. The relationship of the present findings to previous work is discussed.