Cardiovascular responses to open-field stress in rats: sex differences and effects of gonadal hormones

Antidepressant-Like Properties of Intrastriatal Botulinum Neurotoxin-A Injection in a Unilateral 6-OHDA Rat Model of Parkinson's Disease

Parkinson’s patients often suffer from depression and anxiety, for which there are no optimal treatments. Hemiparkinsonian (hemi-PD) rats were used to test whether intrastriatal Botulinum neurotoxin-A (BoNT-A) application could also have antidepressant-like properties in addition to the known improvement of motor performance. To quantify depression- and anxiety-like behavior, the forced swim test, tail suspension test, open field test, and elevated plus maze test were applied to hemi-PD rats injected with BoNT-A or vehicle. Furthermore, we correlated the results in the forced swim test, open field test, and elevated plus maze test with the rotational behavior induced by apomorphine and amphetamine. Hemi-PD rats did not show significant anxiety-like behavior as compared with Sham 6-OHDA- + Sham BoNT-A-injected as well as with non-injected rats. However, hemi-PD rats demonstrated increased depression-like behaviors compared with Sham- or non-injected rats; this was seen by increased struggling frequency and increased immobility frequency. Hemi-PD rats intrastriatally injected with BoNT-A exhibited reduced depression-like behavior compared with the respective vehicle-receiving hemi-PD animals. The significant effects of intrastriatally applied BoNT-A seen in the forced swim test are reminiscent of those found after various antidepressant drug therapies. Our data correspond with the efficacy of BoNT-A treatment of glabellar frown lines in treating patients with major depression and suggest that also intrastriatal injected BoNT-A may have some antidepressant-like effect on hemi-PD.

Influence of pre-existing hypertension on neuroendocrine and cardiovascular changes evoked by chronic stress in female rats

This study investigated neuroendocrine, autonomic, and cardiovascular changes evoked by daily exposure to the same type of stressor (homotypic) or different aversive stressor stimuli (heterotypic) in 60-days-old female normotensive Wistar rats and female spontaneously hypertensive rats (SHR). Both strains of rats were exposed for 10 consecutive days to either the homotypic stressor repeated restraint stress (RRS) or the heterotypic stressor chronic unpredictable stress (CUS). As expected, SHR had higher baseline blood pressure values and impaired baroreflex activity in relation to normotensive animals. Besides, SHR presented higher plasma corticosterone levels and decreased thymus weight. Both RRS and CUS increased baseline plasma corticosterone concentration and decreased body weight gain in both normotensive and SHR rats. In addition, both stress protocols caused hypertrophy of adrenal glands in normotensive rats. Regarding the cardiovascular effects, RRS increased basal heart rate in both rat strains, which was mediated by an increase in sympathetic tone to the heart. Besides, RRS increased baroreflex-mediated tachycardia in SHR animals, while CUS increased cardiac parasympathetic activity and pacemaker activity in normotensive rats. Taken together, these results indicate a stress type-specific effect, as identified by a vulnerability of both strains to the deleterious cardiovascular effects evoked by the homotypic stressor and a resilience to the impact of the heterotypic stressor. Vulnerability of hypertensive rats was evidenced by the absence of CUS-evoked adaptive cardiovascular responses and an increase of baroreflex tachycardia in SHR animals subjected to RRS. The somatic and HPA axis changes were overall independent of the chronic stress regimen and pre-existing hypertension.

Sex differences in cardiovascular, neuroendocrine and behavioral changes evoked by chronic stressors in rats

This study investigated the physiological, somatic and behavioral changes evoked by daily exposure to the same type of stressor (homotypic) or different aversive stressor stimuli (heterotypic) in male and female rats. For this, adult Wistar rats were subjected to a 10days regimen of repeated restraint stress (RRS, homotypic stressor) or chronic variable stress (CVS, heterotypic stressor). Effects evoked by CVS included: (i) adrenal hypertrophy and decreased body weight gain in male animals, (ii) a sympathetically-mediated increase in basal heart rate in males, and (iii) a rise in plasma corticosterone concentration and anxiogenic effects in female animals. The homotypic stressor RRS also induced an increase in plasma corticosterone and anxiogenic effects in females, decreased body weight gain in males and evoked a sympathetically-mediated increase in heart rate in both sexes. Changes in cardiovascular function and autonomic activity evoked by both stressors were followed by impairment of baroreflex activity in males, but not female animals. Both chronic stressors evoked changes in blood pressure responsiveness to vasoconstrictor and vasodilator agents in both sexes. Taken together, these results indicate that regardless of chronic stress regimen males are more vulnerable to somatic effects of chronic stressors, while females appear to be more susceptible to neuroendocrine and behavioral changes. Present findings also indicate that females are selectively vulnerable to cardiovascular and autonomic changes evoked by homotypic stressors. Nevertheless, homotypic and heterotypic stressors similarly affect cardiovascular function and autonomic activity in males.

Botulinum Neurotoxin A Injected Ipsilaterally or Contralaterally into the Striatum in the Rat 6-OHDA Model of Unilateral Parkinson's Disease Differently Affects Behavior

Parkinson's disease (PD) is one of the most frequent neurodegenerative disorders. The loss of dopaminergic neurons in the substantia nigra leads to a disinhibition of cholinergic interneurons in the striatum. Pharmacotherapeutical strategies of PD-related hypercholinism have numerous adverse side effects. We previously showed that ipsilateral intrastriatal injections of 1 ng in unilaterally 6-hydroxydopamine (6-OHDA)-lesioned rats inhibit apomorphine-induced rotation behavior significantly up to 6 months. In this study, we extended the behavioral testing of ipsilateral botulinum neurotoxin A (BoNT-A)-injection and additionally investigated the impact of intrastriatal BoNT-A-injections contralateral to the 6-OHDA-lesioned hemisphere on the basal ganglia circuity and motor functions. We hypothesized that the interhemispheric differences of acetylcholine (ACh) concentration seen in unilateral hemi-PD should be differentially and temporally influenced by the ipsilateral or contralateral injection of BoNT-A. Hemi-PD rats were injected with 1 ng BoNT-A or vehicle substance into either the ipsilateral or contralateral striatum 6 weeks after 6-OHDA-lesion and various behaviors were tested. In hemi-PD rats intrastriatal ipsilateral BoNT-A-injections significantly reduced apomorphine-induced rotations and increased amphetamine-induced rotations, but showed no significant improvement of forelimb usage and akinesia, lateralized sensorimotor integration and also no effect on spontaneous locomotor activity. However, intrastriatal BoNT-A-injections contralateral to the lesion led to a significant increase of the apomorphine-induced turning rate only 2 weeks after the treatment. The apomorphine-induced rotation rate decreases thereafter to a value below the initial rotation rate. Amphetamine-induced rotations were not significantly changed after BoNT-A-application in comparison to sham-treated animals. Forelimb usage was temporally improved by contralateral BoNT-A-injection at 2 weeks after BoNT-A. Akinesia and lateralized sensorimotor integration were also improved, but contralateral BoNT-A-injection had no significant effect on spontaneous locomotor activity. These long-ranging and different effects suggest that intrastriatally applied BoNT-A acts not only as an inhibitor of ACh release but also has long-lasting impact on transmitter expression and thereby on the basal ganglia circuitry. Evaluation of changes of transmitter receptors is subject of ongoing studies of our group.

Pharmacologic Treatment Assigned for Niemann Pick Type C1 Disease Partly Changes Behavioral Traits in Wild-Type Mice

Niemann-Pick Type C1 (NPC1) is an autosomal recessive inherited disorder characterized by accumulation of cholesterol and glycosphingolipids. Previously, we demonstrated that BALB/c-npc1nihNpc1-/- mice treated with miglustat, cyclodextrin and allopregnanolone generally performed better than untreated Npc1-/- animals. Unexpectedly, they also seemed to accomplish motor tests better than their sham-treated wild-type littermates. However, combination-treated mutant mice displayed worse cognition performance compared to sham-treated ones. To evaluate effects of these drugs in healthy BALB/c mice, we here analyzed pharmacologic effects on motor and cognitive behavior of wild-type mice. For combination treatment mice were injected with allopregnanolone/cyclodextrin weekly, starting at P7. Miglustat injections were performed daily from P10 till P23. Starting at P23, miglustat was embedded in the chow. Other mice were treated with miglustat only, or sham-treated. The battery of behavioral tests consisted of accelerod, Morris water maze, elevated plus maze, open field and hot-plate tests. Motor capabilities and spontaneous motor behavior were unaltered in both drug-treated groups. Miglustat-treated wild-type mice displayed impaired spatial learning compared to sham- and combination-treated mice. Both combination- and miglustat-treated mice showed enhanced anxiety in the elevated plus maze compared to sham-treated mice. Additionally, combination treatment as well as miglustat alone significantly reduced brain weight, whereas only combination treatment reduced body weight significantly. Our results suggest that allopregnanolone/cyclodextrin ameliorate most side effects of miglustat in wild-type mice.

Effects of estrogen replacement on stress-induced cardiovascular responses via renin-angiotensin system in ovariectomized rats

The purpose of this study was to determine whether chronic estrogen replacement in ovariectomized rats inhibits the pressor response to psychological stress by attenuating the activation of the renin-angiotensin system. Female Wistar rats aged 9 wk were ovariectomized. After 4 wk, the rats were randomly assigned to be implanted subcutaneously with pellets containing either 17β-estradiol (E2) or placebo (Pla). After 4 wk of treatment, the rats underwent cage-switch stress and, in a separate experiment, a subset received an infusion of angiotensin II. The cage-switch stress rapidly elevated blood pressure (BP) and heart rate (HR) as measured by radiotelemetry in both groups. However, the BP and HR responses to the stress were significantly attenuated in the E2 group compared with the Pla group. An angiotensin II type 1 receptor blocker, losartan, given in drinking water, abolished the difference in the pressor response to stress between the two groups. Moreover, the stress-induced elevation in plasma renin activity and angiotensin II concentration was significant in the Pla group, but not in the E2 group. In addition, the expression of renin mRNA in the kidney was lower in the E2 group relative to the Pla group. Finally, we found that intravenous angiotensin II infusion increased BP and decreased HR to a similar degree in both groups. These results suggest that the inhibitory effects of estrogen on psychological stress-induced activation of the renin-angiotensin system could be at least partially responsible for the suppression of the pressor responses to psychological stress seen in estrogen-replaced ovariectomized rats.

Lifelong caloric restriction increases working memory in mice

Caloric restriction (CR) is argued to positively affect general health, longevity and the normally occurring age-related reduction of cognition. This issue is well examined, but most studies investigated the effect of short-term periods of CR. Herein, 4 weeks old female mice were fed caloric restricted for 4, 20 and especially for 74 weeks. CR mice received 60% of food eaten by their ad libitum (AL) fed littermates, and all age-matched groups were behaviorally analyzed. The motor coordination, which was tested by rotarod/accelerod, decreased age-related, but was not influenced by the different periods of CR. In contrast, the age-related impairment of spontaneous locomotor activity and anxiety, both being evaluated by open field and by elevated plus maze test, was found aggravated by a lifelong CR. Measurement of cognitive performance with morris water maze showed that the working memory decreased age-related in AL mice, while a lifelong CR caused a better cognitive performance and resulted in a significantly better spatial memory upon 74 weeks CR feeding. However, a late-onset CR feeding in 66 weeks old mice did not ameliorate the working memory. Therefore, a lifelong CR seems to be necessary to improve working memory.

Estradiol replacement enhances cocaine-stimulated locomotion in female C57BL/6 mice through estrogen receptor alpha

Psychostimulant effects are enhanced by ovarian hormones in women and female rodents. Estradiol increases behavioral responses to psychostimulants in women and female rats, although the underlying mechanism is unknown. This study utilized mice to investigate the time frame and receptor mediation of estradiol's enhancement of cocaine-induced behavior as mice enable parallel use of genetic, surgical and pharmacological methods. The spontaneous behavior of Sham and Ovariectomized (Ovx) female wildtype (WT) mice was determined during habituation to a novel environment and after cocaine administration. Ovx mice were replaced with vehicle (sesame oil) or 17β-estradiol (E2) for 2 days or 30 min prior to a cocaine challenge to investigate the time course of E2's effects. To examine receptor mediation of estradiol effects, Ovx mice replaced for 2 days with either the ERα-selective agonist PPT or the ERβ-selective agonist DPN were compared to Sham mice, and mice lacking either ERα (αERKO) or ERβ (βERKO) were compared to WT littermates. Ovx mice exhibited fewer ambulations during habituation than Sham females. Cocaine-induced increases in behavioral ratings were greater in Sham than in Ovx mice. Two days but not 30 min of E2 replacement in Ovx mice increased cocaine responses to Sham levels. PPT replacement also increased the cocaine response relative to vehicle- or DPN- treated Ovx mice. αERKO mice displayed modestly attenuated behavioral responses to novelty and cocaine compared to αWT littermates, but no behavioral differences were found between βERKO and βWT mice. These results suggest that E2 enhances cocaine-stimulated locomotion in mice predominantly through ERα.

Effect of sex and ovarian hormones on carotid baroreflex resetting and function during dynamic exercise in humans

To date, no studies have examined whether there are either sex- or ovarian hormone-related alterations in arterial baroreflex resetting and function during dynamic exercise. Thus we studied 16 young men and 18 young women at rest and during leg cycling at 50% heart rate (HR) reserve. In addition, 10 women were studied at three different phases of the menstrual cycle. Five-second pulses of neck pressure (NP) and neck suction (NS) from +40 to -80 Torr were applied to determine full carotid baroreflex (CBR) stimulus response curves. An upward and rightward resetting of the CBR function curve was observed during exercise in all groups with a similar magnitude of CBR resetting for mean arterial pressure (MAP) and HR between sexes (P > 0.05) and at different phases of the menstrual cycle (P > 0.05). For CBR control of MAP, women exhibited augmented pressor responses to NP at rest and exercise during mid-luteal compared with early and late follicular phases. For CBR control of HR, there was a greater bradycardic response to NS in women across all menstrual cycle phases with the operating point (OP) located further away from centering point (CP) on the CBR-HR curve during rest (OP-CP; in mmHg: -13 ± 3 women vs. -3 ± 3 men; P < 0.05) and exercise (in mmHg: -31 ± 2 women vs. -15 ± 3 men; P < 0.05). Collectively, these findings suggest that sex and fluctuations in ovarian hormones do not influence exercise resetting of the baroreflex. However, women exhibited greater CBR control of HR during exercise, specifically against acute hypertension, an effect that was present throughout the menstrual cycle.

Longitudinal assessment of the effects of oestrogen on blood pressure and cardiovascular autonomic activity in female rats

1. Published data concerning the effects of ovarian hormones on haemodynamic variability are contradictory. For the first time, the present study used radiotelemetric haemodynamic monitoring to investigate the long-term effects of chronic oestrogen depletion and repletion on cardiovascular autonomic control and arterial baroreflex sensitivity (BRS) in female rats. 2. Blood pressure (BP), heart rate (HR) and +dP/dt(max) of arterial pressure (an estimate of myocardial contractility) were monitored in sham-operated (SO), ovariectomized (OVX) and oestrogen-replaced OVX rats (OVXE2) for 16 weeks. Cardiovascular autonomic control and baroreflexes were assessed by frequency domain analysis of interbeat intervals (IBI) and systolic BP (SBP). 3. Compared with SO rats, OVX rats exhibited no changes in BP, short-lived decreases in HR and sustained reductions in +dP/dt(max) of arterial pressure. The high- (HF; 0.75-3 Hz) and low-frequency (LF; 0.25-0.75 Hz) components of spectral power of IBI were significantly decreased and increased, respectively, by ovariectomy. An increase in the IBI(LF/HF) ratio in OVX rats suggests a shift in the cardiac sympathovagal balance towards sympathetic dominance. Index alpha, the spectral index of spontaneous BRS, was reduced by OVX. 4. Oestrogen replacement caused significant reductions in BP and HR and reversed OVX-induced changes in +dP/dt(max) of arterial pressure and cardiac autonomic activity. The LF oscillations of SBP were reduced in OVXE2 rats, suggesting a reduction in vascular sympathetic tone by oestrogen. 5. These findings highlight the importance of long-term oestrogen therapy in rectifying the detrimental effects of depletion of ovarian hormones on the cardiovascular system and baroreflex.

Prenatal exposure to antibodies from mothers of children with autism produces neurobehavioral alterations: A pregnant dam mouse model

A pregnant mouse model was used to compare the effect of IgG, administered E13-E18, from mothers of children with autistic disorder (MCAD), to controls (simple- and IgG-) on behavioral testing in offspring. Mice, exposed in-utero to MCAD-IgG, as adolescents, were more active during the first ten minutes of central field novelty testing and, as adults, displayed anxiety-like behavior on a component of the elevated plus maze and had a greater magnitude of startle following acoustic stimulation. On a social interaction paradigm, adult mice had alterations of sociability. Pilot studies of immune markers in MCAD IgG-exposed embryonic brains suggest evidence of cytokine and glial activation. These studies demonstrate that the transplacental passage of IgG from MCAD is capable of inducing long-term behavioral consequences.

Progesterone withdrawal-evoked plasticity of neural function in the female periaqueductal grey matter

Cyclical changes in production of neuroactive steroids during the oestrous cycle induce significant changes in GABA_A receptor expression in female rats. In the periaqueductal grey (PAG) matter, upregulation of α4β1δ GABA_A receptors occurs as progesterone levels fall during late dioestrus (LD) or during withdrawal from an exogenous progesterone dosing regime. The new receptors are likely to be extrasynaptically located on the GABAergic interneurone population and to mediate tonic currents. Electrophysiological studies showed that when α4β1δ GABA_A receptor expression was increased, the excitability of the output neurones in the PAG increased, due to a decrease in the level of ongoing inhibitory tone from the GABAergic interneurones. The functional consequences in terms of nociceptive processing were investigated in conscious rats. Baseline tail flick latencies were similar in all rats. However, acute exposure to mild vibration stress evoked hyperalgesia in rats in LD and after progesterone withdrawal, in line with the upregulation of α4β1δ GABA_A receptor expression.

Effects of sex hormones on associative learning in spontaneously hypertensive rats

Pavlovian conditioning of a visual stimulus paired with food was examined in spontaneously hypertensive rats (SHR), which are a commonly used model for Attention-Deficit/Hyperactivity Disorder (ADHD), and in Wistar rats (normoactive control). In gonadally intact rats of both strains, males spent more time in the food cup following onset of the light than did females, indicating a stronger association of the conditioned stimulus (CS) with reward. Gonadectomy carried out in adulthood affected conditioning differently in the two strains. In Wistar rats, gonadectomy had no effect on conditioned responding in females, but reduced conditioned responding in males, effectively eliminating the sex difference in behavior. This result suggests that circulating androgens in male Wistar rats normally aid conditioning in this task. In contrast, gonadectomy enhanced conditioning in both sexes in the SHR rats, indicating that androgens and/or estrogens impair conditioned associations in this strain. These data indicate that gonadal steroids can influence conditioning in rats and that the valence of steroid action on this behavior is strain-dependent. To the extent that SHR serves as a model of ADHD in humans, the influence of steroids on associative learning may play a role in the expression of ADHD-like behaviors.

Sex difference in norepinephrine surge in response to psychological stress through nitric oxide in rats

Psychological stress elevates blood pressure through sympathetic nerve activation. This pressor response is supposedly associated with cardiovascular events. We investigated a sex difference in the pressor response and norepinephrine surge to cage-switch stress in rats. Wistar male and female rats were catheterized for blood pressure monitoring and blood sampling. Six days post-surgery, the rats were exposed to the cage-switch stress and blood samples were collected at rest and 30 min after the start of the stress. The stress-induced pressor response was greater in the male than in the female rats. The stress significantly increased the norepinephrine level in the male, but not in the female rats. Pre-treatment with N(G)-nitro-l-arginine methyl ester (L-NAME), a nitric oxide (NO) synthase inhibitor, attenuated the norepinephrine response significantly in the male rats. There was no sex difference in the endothelial NO synthase expression in the gastrocnemius muscle. However the phosphorylation at serine 1177, a marker for eNOS activation, was higher in the male than in the female rats. These results suggest that NO is involved in the norepinephrine surge to psychological stress in the male rats, but not in the female rats. This is the first report on a sex difference in the norepinephrine surge in response to psychological stress through NO, in association with pressor response.

Early deprivation, but not maternal separation, attenuates rise in corticosterone levels after exposure to a novel environment in both juvenile and adult female rats

Separation from the maternal nest alters the hypothalamic-pituitary-adrenal (HPA) axis stress response in adult male rats, but little research has addressed how separation affects female rats. The following experiments investigated how early maternal separation from postnatal day (PND) 2 to 14 affected stress-induced corticosterone and ACTH after exposure to an open field in juvenile and adult female rats. Female rats were separated for 5 h daily from mother and littermates (early deprivation: ED), separated from mother but not littermates (maternal separation: MS), or animal facility reared (AFR). Male siblings were left with the mother rat during separation. Female rats were exposed to an open field arena either during the juvenile period (PND 30) or during adulthood (PND 80-100). Results show that ED juvenile female rats showed a lower corticosterone stress response than MS and AFR female rats when measured at 5 min post-stress, but no difference at 20 or 60 min post-stress. In adulthood, ED female rats showed comparable elevations of corticosterone as MS and AFR rats at 5 min post-stress but lower elevations at 20 min. In terms of behavior, there were no significant effects of early experience. However, in adulthood, ED and MS rats tended to show a decreased proportion of inner grid crossings of the open field compared to AFR rats, suggesting a tendency for increased anxiety in these two separation groups.

Exogenous progesterone attenuates the subjective effects of smoked cocaine in women, but not in men

In a previous study, we showed that the positive subjective effects of cocaine were higher during the follicular phase compared to the luteal phase of the menstrual cycle. The purpose of the present study was to determine if exogenously administered progesterone during the follicular phase in females would attenuate the response to cocaine compared to the normal follicular phase, thus making the response to cocaine similar to the luteal phase. To address the role of sex differences, males were also administered exogenous progesterone during one inpatient stay. In all, 11 female and 10 male non-treatment-seeking cocaine smokers participated. Females had three inpatient stays: one during a normal follicular phase, one during a normal luteal phase, and one during a follicular phase when exogenous progesterone was administered. Males had two inpatient stays: one when exogenous progesterone was administered and the other when placebo was administered. During each inpatient admission, there were four smoked cocaine administration sessions: participants were administered six doses of cocaine (0, 6, 12, or 25 mg cocaine base) at 14 min intervals. Smoked cocaine increased heart rate, blood pressure and several subjective effects such as 'good drug effect' and 'drug quality' cluster scores. Administration of progesterone during the follicular phase in women attenuated the positive subjective effects of cocaine, whereas only minimal changes were observed in men. These results indicate that progesterone modulates the response to cocaine in women and suggests that fluctuations in endogenous progesterone levels account for some of the sex differences observed in humans.

Inter-individual vs line/strain differences in psychogenetically selected Roman High-(RHA) and Low-(RLA) Avoidance rats: neuroendocrine and behavioural aspects

Inter-individual differences in neuroendocrine and behavioural responses to environmental challenges will be considered within the context of psychogenetic selection, using the Roman High-(RHA) and Low-(RLA) Avoidance rat lines as an example. We assume that the selected genotypes, by interacting with environmental factors, determine specific 'biobehavioural profiles'. Practical and theoretical problems regarding the measurement of inter-individual vs line/strain differences, the definition of 'traits' vs experimental variables, and possible correlations between physiological and behavioural parameters will be discussed. We will argue that environmental influences are the main cause of inter-individual variability, and that the genotype only constitutes a 'blueprint' from which typical biobehavioural profiles are established, notably under the influence of early environmental factors. These biobehavioural profiles may correspond in part to human categories known as 'types', 'temperaments' or 'personality traits'. Within each category (including those which can be obtained by psychogenetic selection), more individual personality traits can evolve, notably as a result of social interactions and particular life events.

The effect of enalapril on the cardiac remodelling in ovariectomized spontaneously hypertensive rats

Angiotensin-converting enzyme inhibitors reduce the blood pressure (BP) and inhibit the generation of the angiotensin II from the inactive angiotensin I. Ten 28-week-old spontaneously hypertensive rats (SHRs) had their ovaries bilaterally removed and five rats were left intact and studied for 7 additional weeks: intact group, ovariectomized group (ovx SHRs) and ovariectomized + enalapril group (ovx + en). BP was higher in ovx SHRs and lower in treated ovx SHRs. Left ventricular (LV) mass index was greater in untreated ovx SHRs and smaller in ovx + en group. The LV cardiomyocyte (cmy) mean cross-sectional area, measured by stereology, was greater in ovx SHRs and smaller in both intact and ovx + en SHRs. Ovx significantly decreased the density of intramyocardial blood vessels (ive), but administration of enalapril was able to restore the density of the ive to that seen in intact group. The worst ive:cmy ratio was found in untreated ovx SHRs, the intact group showed a 90% greater ratio, and the treated ovx group showed a 150% greater ratio than the untreated ovx group. In conclusion, ovariectomy, in SHRs, causes cardiac hypertrophy and an unfavourable myocardial remodelling. Of the spectrum of changes seen, the major effect of enalapril appears to be mediated via an increase in the density of ive.

Estrogen replacement suppresses stress-induced cardiovascular responses in ovariectomized rats

We assessed the hypothesis that chronic estrogen replacement in ovariectomized rats has the beneficial effect of suppressing stress-induced cardiovascular responses through endothelial nitric oxide synthase (eNOS). We employed a radiotelemetry system to measure blood pressure and heart rate (HR). Female Wistar rats aged 11 wk were ovariectomized and implanted with radiotelemetry devices. After 4 wk, the rats were assigned either to a placebo-treated group (Placebo; n = 6) or a group treated with 17β-estradiol (Estrogen; n = 8) subcutaneously implanted with either placebo- or 17β-estradiol (1.5 mg/60-day release) pellets under anesthesia. These rats underwent either of the two types of stress after 4 wk of estrogen or placebo treatment. Cage-switch stress and restraint stress rapidly and continuously elevated the mean arterial pressure (MAP) and HR both in the Placebo and Estrogen groups. However, the MAP and HR responses to cage-switch stress and the MAP but not HR response to restraint stress were attenuated significantly in the Estrogen group compared with the Placebo group. A NOS inhibitor, NG-nitro-l-arginine methyl ester, given in drinking water, reduced the difference in the pressor response to cage-switch between the Estrogen and Placebo groups. In addition, Western blot analysis showed that eNOS expression in the mesentery was increased in the Estrogen group compared with the Placebo group. Thus for the first time we showed that mesenteric eNOS overexpression could explain at least partly why chronic estrogen treatment suppressed the enhanced cardiovascular responses to psychological stress in the ovariectomized rat.

Behavioral phenotyping of mice in pharmacological and toxicological research

The evaluation of behavioral effects is an important component for the in vivo screening of drugs or potentially toxic compounds in mice. Ideally, such screening should be composed of monitoring general health, sensory functions, and motor abilities, right before specific behavioral domains are tested. A rational strategy in the design and procedure of testing as well as an effective composition of different well-established and reproducible behavioral tests can minimize the risk of false positive and false negative results in drug screening. In the present review we describe such basic considerations in planning experiments, selecting strains of mice, and propose groups of behavioral tasks suitable for a reliable detection of differences in specific behavioral domains in mice. Screening of general health and neurophysiologic functions (reflexes, sensory abilities) and motor function (pole test, wire hang test, beam walking, rotarod, accelerod, and footprint) as well as specific hypothesis-guided testing in the behavioral domains of learning and memory (water maze, radial maze, conditioned fear, and avoidance tasks), emotionality (open field, hole board, elevated plus maze, and object exploration), nociception (tail flick, hot plate), psychiatric-like conditions (porsolt swim test, acoustic startle response, and prepulse inhibition), and aggression (isolation-induced aggression, spontaneous aggression, and territorial aggression) are described in further detail. This review is designed to describe a general approach, which increases reliability of behavioral screening. Furthermore, it provides an overview on a selection of specific procedures suitable for but not limited to behavioral screening in pharmacology and toxicology.

Involvement of corticosterone in cardiovascular responses to an open-field novelty stressor in freely moving rats

The aim of the present study was to investigate the modulatory action of different concentrations of circulating corticosterone occupying either predominantly mineralocorticoid receptors (MR) or both MR and glucocorticoid receptors (GR) in control of cardiovascular responses to a novelty stressor. Six groups of rats were instrumented with radiotelemetry transmitters: sham-operated controls, adrenalectomised (ADX) controls, ADX with chronic implantation of a 20-mg corticosterone pellet, ADX with chronic implantation of a 100-mg corticosterone pellet, ADX receiving acute bolus injection of 0.25 mg/kg of corticosterone, and ADX with both implantation of a 20-mg corticosterone pellet and bolus treatment. Exposure to the novelty of an open field caused an increase in blood pressure, heart rate, body temperature and exploratory locomotor activity. The pressor response was dose-dependently increased in ADX rats implanted with a corticosterone pellet. Bolus injection of corticosterone at 10 min prior to novelty had no effect. The tachycardia was reduced in ADX rats compared to sham-operated controls, and this effect was restored by implantation of a 20-mg, but not 100-mg, corticosterone pellet. Bolus injection of corticosterone facilitated the return of heart rate towards baseline levels. The increase in body temperature was reduced in ADX rats, a deficit that was normalised by implantation of either corticosterone dose but not by acute bolus treatment. Locomotor activity was not different between the groups except for a slightly more rapid decline of locomotor activity in both groups treated with a bolus injection of corticosterone. These data show an important role of putative brain MR in maintaining adequate cardiovascular and behavioural responsiveness to a mild psychological stressor, while additional acute or chronic occupation of GR has further differential and sometimes opposing effects.

Estrogen increases prepulse inhibition of acoustic startle in rats

Epidemiological studies have shown gender differences in the age of onset and symptoms of schizophrenia. Because sensorimotor gating mechanisms are deficient in schizophrenia, we studied the effect of administration of estrogen on prepulse inhibition of startle in rats, an animal model of sensorimotor gating. Rats were tested in an automated startle apparatus for their responses to random combinations of 115-dB sound pulses and prepulses of various intensity. Startle responses were reduced by increasing intensities of prepulses, indicating prepulse inhibition. Repeated administration of startle pulses caused gradual habituation of startle responses. Ovariectomy did not induce significant changes in either habituation of the startle response or prepulse inhibition of startle. Treatment with 17beta-estradiol caused an increase in percentage prepulse inhibition at all prepulse intensities at 18 h, but only at higher prepulse intensities at 30 min after injection. Habituation of startle responses was not affected. The enhancing effect of estradiol on prepulse inhibition was mimicked by testosterone, but not by dihydrotestosterone. Estradiol treatment increased prepulse inhibition similarly in controls or after disruption of prepulse inhibition induced by treatment with apomorphine or dizocilpine (MK-801). Our results may help to explain gender differences in schizophrenia and some of the beneficial clinical effects of estrogen treatment in this disease.