Enhancement of the acoustic startle reflex by an alarm pheromone in male rats

Recently, we reported that an alarm pheromone released from the perianal region of male rats aggravated stress-induced hyperthermia and increased defensive and risk assessment behaviors in recipient male rats. Based on these results, we hypothesized that the primary effect of the alarm pheromone is to increase anxiety; however, there is still no clear evidence for this pheromone effect. Therefore, we examined this issue by assessing the effect of the alarm pheromone on the acoustic startle reflex (ASR), which is a useful index for studying negative emotions such as anxiety in rats. The alarm pheromone enhanced the ASR for 105-dB auditory stimuli, but not for those of 90 and 120 dB, when these three intensities of sound were used randomly. The same results were obtained when one of these three intensities was used repeatedly. In addition, pretreatment with diazepam (i.p.) at doses of 0.7 and 2.0 mg/kg suppressed the ASR of the pheromone recipients, whereas the lower dose (0.2 mg/kg) slightly attenuated the pheromone effect and the control injection (vehicle) had no effect. These results indicate that the alarm pheromone enhances the ASR by increasing anxiety in recipient rats, suggesting that the primary effect of the alarm pheromone is to increase the anxiety level.     

Alarm pheromone increases defensive and risk assessment behaviors in male rats

Previously, we reported that alarm pheromone released from the perianal region of male rats aggravated stress-induced hyperthermia and increased Fos expression in the vomeronasal pathway and stress-related nuclei in pheromone-recipient rats. However, the alarm property of this pheromone in terms of behavior modification is still unclear. We recently found that this alarm pheromone could be trapped in water. Based on this finding, we developed an experimental paradigm to assess the effect of alarm pheromone on recipient behavior. Male Wistar rats were acclimatized for 5 min to an open field, where two pieces of filter paper soaked with 750 microl of either pheromone-containing water or vehicle water were attached to the wall. Then, a small "hiding box" was placed in one corner of the field and the behavioral responses of the subject rat were recorded for 10 subsequent minutes. Exposure to alarm pheromone significantly increased defensive and risk assessment behaviors and decreased exploratory and grooming behaviors compared to the vehicle control group, indicating the alarm property of the pheromone. In addition, the comparison with previous results suggests that the alarm pheromone released from the perianal region of the male rat increases anxiety in recipients, rather than evoking a stereotyped autonomic response.     

Alarm pheromone enhances stress-induced hyperthermia in rats

Behavioral and physiological effects of alarm pheromones emanating from stressed conspecific animals were investigated. Experimentally naive male Wistar rats were exposed to the test chambers containing alarm pheromones, which had been released by other rats receiving foot shocks in the same chamber beforehand. Along with behavioral analysis, the heart rate (HR) and core body temperature (cBT) were measured simultaneously using a biotelemetory system. Exposure to the alarm pheromones increased freezing, sniffing and walking and decreased resting as compared with rats exposed to control odors. In addition, these pheromone-exposed animals showed consistent increases in body temperature, i.e., stress-induced hyperthermia. After exposure to the alarm substances, immunoreactivity to nuclear Fos protein in the mitral cell layer in the accessory olfactory bulb (AOB) also increased compared with the reaction to control odors. These results suggest that an alarm pheromone enhances stress responses of conspecific animals both behaviorally and physiologically, and that these effects are mediated via activation of the AOB.     

Prepulse inhibition of the startle response with chronic schizophrenia: A replication study

Prepulse inhibition (PPI) deficit, the acoustic startle reflex (ASR) and habituation (HAB) impairment are considered to be endophenotypes for schizophrenia. The recent two studies have reported that a PPI deficit was detected in Japanese schizophrenic patients. We replicated that study using larger samples (115 schizophrenic patients and 111 normal controls) than the original study and a method same as original study. A startle response monitoring system was used to deliver acoustic startle stimuli, and to record and score the electromyographic activity of the orbicularis oculi muscle. We evaluated the startle measures of mean magnitude of ASR, HAB, and PPI at prepulse sound pressure intensities of 82 dB (PPI82), 86 dB (PPI86), and 90 dB (PPI90). ASR was significantly different between schizophrenic patients and controls. HAB and all PPI session data from schizophrenic patients were significantly lower than in controls. In addition, we detected significant differences for ASR, HAB and each PPI (82, 86 and 90 dB) between schizophrenic patients and controls with the use of multiple regression analysis. The gender and smoking state were not correlated with ASR, HAB or any PPI in multiple regression analysis. In conclusion, we were able to replicate the finding of HAB impairment and PPI deficit in chronic Japanese schizophrenic patients.     

Effects of sex and estrous cycle on modulation of the acoustic startle response in mice

Potential sex differences in amplitude, habituation, prepulse inhibition (PPI) and prepulse facilitation (PPF) of the acoustic startle response (ASR) were investigated using male and female mice from the two different inbred mouse strains C57BL/6J (C57) and C3H. Furthermore, the effects of the estrous cycle were tested. The estrous cycle appeared to have no effect on ASR amplitude, habituation, PPF and PPI, the latter being in contrast to results in rats and humans. While sex had no effect on PPI or PPF, males exhibited higher startle amplitudes than females, irrespective of strain, which we discuss to be due to increased male anxiety. In addition, long-term habituation was stronger in C57 males and short-term habituation was weaker in C3H males with respect to females. These results provide evidence for influence of the reproductive hormones on startle reactivity and startle habituation; we therefore conclude that future studies involving genetic influences on behavior using inbred strains are only complete if both sexes are included.     

Leukocytosis,muscle damage and increased lymphocyte proliferative response after an adventure sprint race

The effect of an adventure sprint race (ASR) on T-cell proliferation, leukocyte count and muscle damage was evaluated. Seven young male runners completed an ASR in the region of Serra do Espinhaço, Brazil. The race induced a strong leukocytosis (6.22±2.04×10³ cells/mm³ before vs 14.81±3.53×10³ cells/mm³ after the race), marked by a significant increase of neutrophils and monocytes (P<0.05), but not total lymphocytes, CD3⁺CD4⁺ or CD3⁺CD8⁺ cells. However, the T-cell proliferative response to mitogenic stimulation was increased (P=0.025) after the race, which contradicted our hypothesis that ASR, as a high-demand competition, would inhibit T-cell proliferation. A positive correlation (P=0.03, r=0.79) was observed between the proliferative response of lymphocytes after the race and the time to complete the race, suggesting that the proliferative response was dependent on exercise intensity. Muscle damage was evident after the race by increased serum levels of aspartate amino transferase (24.99±8.30 vs 50.61±15.76 U/L, P=0.003). The results suggest that humoral factors and substances released by damaged muscle may be responsible for lymphocyte activation, which may be involved in muscle recovery and repair.     

Alarm substance emitted by rats in the forced-swim test is a low volatile pheromone.

A series of studies was conducted to determine if the alarm substance produced by rats in the forced-swim test satisfies criteria for pheromones: well-defined behavioral effect, species specificity, minimal influence of experience and control for nonspecific arousal. The alarm substance satisfied these criteria. Additional studies involving activity testing in the presence of the alarm pheromone and preference/avoidance for odors emanating from cylinders containing the pheromone indicated it has very low volatility.     

Low dietary sodium is anxiogenic in rats

Noise exposure during the critical period of postnatal development in rats results in anomalous processing of acoustic stimuli in the adult auditory system. In the present study, the behavioral consequences of an acute acoustic trauma in the critical period are assessed in adult rats using the acoustic startle reflex (ASR) and prepulse inhibition (PPI) of ASR. Rat pups (strain Long-Evans) were exposed to broad-band noise of 125 dB SPL for 8 min on postnatal day 14; at the age of 3-5 months, ASR and PPI of ASR were examined and compared with those obtained in age-matched controls. In addition, hearing thresholds were measured in all animals by means of auditory brainstem responses. The results show that although the hearing thresholds in both groups of animals were not different, a reduced strength of the startle reflex was observed in exposed rats compared with controls. The efficacy of PPI in exposed and control rats was also markedly different. In contrast to control rats, in which an increase in prepulse intensity was accompanied by a consistent increase in the efficacy of PPI, the PPI function in the exposed animals was characterized by a steep increase in inhibitory efficacy at low prepulse intensities of 20-30 dB SPL. A further increase of prepulse intensity up to 60-70 dB SPL caused only a small and insignificant change of PPI. Our findings demonstrate that brief noise exposure in rat pups results in altered behavioral responses to sounds in adulthood, indicating anomalies in intensity coding and loudness perception.     

Response to alarm substance in different rat strains.

Two studies were conducted. In the first study, four strains of male rats--Long-Evans (LE), Sprague-Dawley (SD), Wistar, Fisher 344--were immersed in fresh water or water soiled by a rat of the same strain which presumably contains an alarm substance. LE rats were less immobile than SD, Wistar, and Fisher rats in fresh water. All strains were significantly less immobile in soiled water; however, relative to immobility times in fresh water, the decrease in immobility in soiled water was greatest for SD rats and least for Wistar rats. A second study tested SD and Wistar rats in water soiled by animals of the same strain compared to water soiled by animals of the other strain. This study indicated that Wistar rats produce less alarm substance or less potent substance and are also less reactive to it than SD rats. The results of these two studies indicate that some strains are more affected by alarm substance than others and the differential response is due both to decreased production/potency and reaction to the substance.     

Enhancement of the breathing frequency response to hypoxia by neonatal caffeine treatment in adult male rats: The role of testosterone

Caffeine is a common treatment for apnea of prematurity. Although relatively safe, little is known about the potential long-term effects of this treatment on respiratory control development. We previously showed that adult male (but not female) rats previously subjected to neonatal caffeine treatment (NCT; 15 mg/kg/day, postnatal days 3–12) show a higher breathing frequency response during the early phase of hypoxic exposure. To address the role of sexual hormones in this sexual dimorphism, the present study tested the hypothesis that in adult male rats, circulating testosterone contributes to NCT-related augmentation of the acute breathing frequency response to hypoxia. Whole body plethysmography was used to compare the acute ventilatory response to moderate hypoxia (FIO₂ = 0.12; 20 min) between rats previously subjected to NCT or neonatal water treatment (NWT; same treatment as NCT but using water). In each group, rats were either sham-operated or gonadectomized (GDX) 14 days prior to ventilatory measurements. In sham-operated rats, the increase in breathing frequency measured during the first 8 min of hypoxia was greater in NCT rats versus NWT. The hypoxic ventilatory response measured at the end of the hypoxia was not affected by treatment, thus indicating that NCT mainly affected the peripheral component of the chemoreflex. Gonadectomy had no effect on NCT but augmented the frequency response of NWT rats to the same level of NCT, thus eliminating the between-group difference. NCT may interfere with the inhibitory effect of circulating testosterone on carotid body function. Although appealing, additional experiments are necessary to substantiate this interpretation.     

Progesterone exerts neuroprotective effects by inhibiting inflammatory response after stroke

Objective and design  We evaluated the inhibitory effects of progesterone (PROG) on inflammatory response and its influence on the structure of blood–brain barrier in a permanent model of stroke. Material  One hundred and twenty adult male Sprague-Dawley rats were used in this study. Treatments  PROG was dissolved in 22.5% 2-hydroxypropyl-bcyclodextrin and given in a dose of 15 mg/kg by intraperitoneal injection 1 h after permanent occlusion of middle cerebral artery (pMCAO). Additional injections of 15 mg/kg were administered subcutaneously 6, 24, and 48 h after pMCAO. Methods  The expression of tumor necrosis factor-alpha (TNF-α) and claudin5 was measured by immunohistochemistry and western blot technique. Brain water content was determined by the dry–wet weight method. Results  TNF-α were increased, but claudin5 were reduced in vehicle-treated rats after pMCAO. PROG-treated rats showed a substantial reduction in the expression of TNF-α compared to vehicle controls. In addition, there was significant increase in the expression of claudin5 in the pMCAO rats treated with PROG compared to vehicle. Examination of the water content of the brain also revealed that administration of PROG significantly attenuated the amount of water compared to vehicle in the ipsilateral hemispheres. Conclusions  These data indicate that PROG is beneficial in this animal model, and may warrant further test in future clinical trials for human stroke.     

The effect of methylprednisolone on treatment in rats with induced sepsis

In this study, an appropriate sepsis model was created in rats. Additionally, the effects of steroid treatments on survival, in connection with antibiotic treatment, were investigated. The sepsis model performed via intraperitoneal injection of 3 ml/kg fecal suspension was determined as the most appropriate model for our study. Fifteen rats were used to investigate the effect of piperacillin–tazobactam on sepsis treatment. Forty-five randomly selected rats were used to investigate the efficacy of the antibiotic-plus-steroid combination. The rats were divided into three groups of 15 rats each. Twelve hours after the administration of fecal suspension, methylprednisolone (MP) at the dose of 0.25, 0.5, and 2 mg/kg/day was given to each group, respectively, in addition to an antibiotic administered intravenously. In order to investigate the effect of steroids alone in the treatment of sepsis, 0.5 mg/kg/day MP was given intravenously to 15 rats, 12 h after the fecal suspension was administered. It was concluded that administration of MP alone shortens survival time in rats with sepsis, whereas antibiotic therapy alone increases survival time significantly in rats with sepsis. It was seen that the antibiotic-plus-steroid treatment increases survival significantly compared to rats with no treatment (p < 0.05). In addition, steroids, when added to an antibiotic treatment in sepsis, affect survival positively when compared to the group with antibiotic therapy alone, depending on the dose given. Although, not statistically significant, high doses decrease survival (p > 0.05), and very low doses increase survival and mean survival time (p > 0.05) on the basis of clinical observation and average life time. However, low doses were found to increase survival significantly (p < 0.05). We concluded that low-dose MP, in addition to the appropriate antibiotic therapy, is the optimal in the treatment of rats with intraabdominal sepsis.     

Trans-beta-farnesene as a feeding stimulant for the sand fly Lutzomyia longipalpis (Diptera: Psychodidae).

The aphid alarm pheromone, trans-beta-farnesene (TBF), was found to stimulate feeding in both male and female Lutzomyia longipalpis Lutz & Neiva. Four other structurally related compounds (farnesol; 808 farnesene; trans, trans-farnesyl acetate; farnesyl methyl ether) were slightly less stimulating to these insects. The effect of TBF varied with sand fly age and the concentration of the chemical used. In contrast, TBF did not stimulate feeding in either sex of four other sand fly species (L. shannoni Dyar, Phlebotomus papatasi (Scopoli), P. argentipes Annandale & Brunetti, P. perniciosus Newstead). TBF might be useful in enhancing L. longipalpis field collections or in developing a poison bait for the control of this species.     

Behavioral characterization of the alarm reaction and anxiolytic-like effect of acute treatment with fluoxetine in piauçu fish

In Ostariophysan fish, the detection of the alarm substance liberated into the water as a consequence of an attack by a predator elicits an alarm reaction or anti-predatory behavior. In this study, experiments were performed to: (i) describe and quantitatively characterize the behavioral and ventilatory responses in piauçu fish (Leporinus macrocephalus), individually and as part of a school, to conspecific alarm substance (CAS) and; (ii) test the effect of acute fluoxetine treatment on alarm reaction. Histological analysis revealed the presence of club cells in the intermediate and superficial layers of the epidermis. The predominant behavioral response to CAS was freezing for fish held individually, characterized by the cessation of the swimming activity as the animal settles to a bottom corner of the aquarium. Fish exposed to CAS showed decrease in the mean ventilatory frequency (approximately 13%) relative to control. In schools, CAS elicited a biphasic response that was characterized by erratic movements followed by increased school cohesion and immobility, reflected as an increased school cohesion (65.5% vs. ? 5.8% for controls) and in the number of animals near the bottom of the aquarium (42.0% vs. 6.5% for controls). Animals treated with single i.p. injections of fluoxetine (10 μg/g b.w.) did not exhibit alarm behavior following CAS stimulation. These results show that an alarm pheromone system is present in piauçu fish, evidenced by the presence of epidermal club cells and an alarm reaction induced by CAS and consequently of a chemosensory system to transmit the appropriate information to neural structures responsible for initiating anti-predator behavioral responses. In addition, fluoxetine treatment caused an anxiolytic-like effect following CAS exposure. Thus, the alarm reaction in piauçu can be a useful model for neuroethological and pharmacological studies of anxiety-related states.     

Aging effects on exercise-induced alternations in plasma acylated ghrelin and leptin in male rats

Ghrelin and exercise have been known to stimulate the release of growth hormone which is related to the glucose metabolism. However, the age effects of exercise on ghrelin in energy consumption remain unclear. Young (3 month old) and middle-aged (12 month old) Sprague–Dawley male rats were overnight fasted, and then randomly partitioned into exercise and control groups. Exercise groups swam for 20 min in 25°C water. Rats immersed in 25°C water for 20 min were used as control animals. All blood samples were collected before and 10, 20, 30, and 60 min after initiation of exercise via the right jugular vein. Our results indicated that the swimming regimen decreased the secretion of acylated ghrelin and insulin, but increased the secretion of leptin, lactate, and glucose. In addition, exercise significantly amplified the inverse correlation between leptin and acylated ghrelin (r < −0.6) in middle-age group. Both the above findings were not emphasized in related articles before. Moreover, the time courses of these changes were slightly different in young and middle-aged rats. In basal metabolic characteristics, body weight and the plasma lactate, glucose, insulin, and leptin are higher in middle-age group than that in young group. In conclusion, compared with young rats, middle-aged rats have higher basal body weight, plasma glucose, insulin, and leptin, but age had no effect on the level of plasma acylated ghrelin. A 20-min exercise regimen decreased acylated ghrelin and increased leptin with inverse correlation between them which was strengthened during exercise, but were not influenced by age.     

On again, off again effects of gonadectomy on the acoustic startle reflex in adult male rats

Numerous studies have shown sex and/or estrous cycle differences in the acoustic startle reflex (ASR) and its prepulse inhibition (PPI) in humans and animals. However, few have examined the effects of hormone manipulations on these behaviors. This study paired gonadectomy (GDX) in adult male rats with testing for ASR and PPI at 2, 4, 9, 16, 23, 30 and 37 days after surgery. Initial studies of control, GDX and GDX rats given testosterone propionate revealed no group differences in PPI, but did reveal phasic facilitation of the ASR in GDX rats that was greatest on the first and final testing sessions and that was attenuated by testosterone. A second study addressing roles for estrogen and androgen signaling tested new control and GDX rats along with GDX rats given estradiol or the non-aromatizable androgen, 5-alpha-dihydrotestosterone and revealed no group differences in PPI, and increases in ASR in GDX rats that were largest during the first and final testing sessions and that were attenuated by both hormone replacements. However, while responses in GDX rats given testosterone were similar to those of controls, ASR in estradiol- and to a lesser extent in dihydrotestosterone-treated GDX rats were typically lower than in controls. This may suggest that hormone modulation of the ASR requires synergistic estrogen and androgen actions. In the male brain where this can be achieved by local steroid metabolism, the enzymes responsible, e.g., aromatase, could help identify loci in the startle circuitry that may be especially relevant for the hormone modulation observed.     

Non-linear shrinkage of Batson's #17 resin during vascular corrosion casting

Many studies of cardiovascular function require a realistic representation of vascular geometry. Corrosion casting has been used to acquire such geometries for many decades. However, the fidelity with which this method reproduces vascular anatomy has not been completely determined. Here we report on the non-linear shrinkage characteristics and exothermic properties of Batson's #17, a widely used casting resin, in model systems and in aortas of rats and rabbits. The setting process was captured using high-resolution photography. Shrinkage ranged from 3.4 ± 1.5% of the diameter in 1 ml plastic syringes (inner diameter 4.8 mm) to 19.6 ± 5.6% in the aorta of rats (diameter 1.5–2.6 mm). In addition, aortic curvature and branching angles changed during setting. These effects should be determined and corrected in studies of vascular geometry where high accuracy is required.     

Naltrexone effects on male sexual behavior, corticosterone, and testosterone in stressed male rats

Chronic physical or psychological stress disrupts male reproductive function. Studies in our laboratory have shown that stress by immersion in cold water (ICW) and by electrical foot shocks (EFS) has inhibitory effects on male sexual behavior; these effects do not seem to be mediated by an increase in corticosterone, nor by a decrease in testosterone. On the other hand, it is known that endogenous opioids are released in the brain in response to these same stressors; consequently, they could be participating in the impairment of sexual behavior, as well as in the changes in corticosterone and testosterone caused by stress. The aim of this study was to analyze the effects of the opioid antagonist naltrexone (NTX) on male sexual behavior, corticosterone, and testosterone in both stressed sexually experienced and naive male rats. Sexually experienced adult male rats were assigned to one of the following groups (n = 10 each): 1) control group, males without sexual evaluation; 2) control group, rats injected ip with saline, non-stressed; 3) control group, rats injected with NTX (3 mg/kg) non-stressed; 4) rats injected ip with saline, and stressed by EFS; 5) rats injected ip with NTX (1.5 mg/kg) and stressed by EFS; 6) rats injected ip with saline and stressed by ICW; 7) rats injected ip with NTX (1.5 mg/kg) and stressed by ICW; 8) rats injected ip with NTX (3 mg/kg) and stressed by ICW. Naive males were assigned to the same control groups but only stressed by ICW and the NTX dose used was 3 mg/kg. Injections were given 30 min before stress sessions. Stress was applied on 20 consecutive days. Male sexual behavior was assessed 15 min after EFS or 30 min after ICW, on days 1, 4, 8, 12, 15, and 20. Trunk blood was collected at the end of the experiments on day 20 of stress. Corticosterone and testosterone were evaluated by HPLC.Mount, intromission and ejaculation latencies were longer in control saline naive males compared to control saline sexually experienced males on the first day. NTX administration to control naive males caused a decrease in mount, intromission, and ejaculation latencies, as well as an increase in ejaculatory frequency/30 min, compared to control-saline only on day 1. Stressed naive males showed higher mount, intromission and ejaculation latencies, compared to control and stressed sexually experienced males, as well as comparable increase in corticosterone and decrease in testosterone plasma levels. NTX administration before exposure to stress prevented the modifications caused by stress in sexual parameters. Sexual behavior in control sexually-active males injected with saline or NTX was not modified. Saline stressed males showed the previously reported alterations in sexual behavior, as well as an increase in corticosterone and a decrease in testosterone plasma levels. Stressed males injected with NTX before exposure to stress showed no alterations in male sexual behavior. NTX in control non-stressed males did not modify corticosterone plasma levels, but did cause a significant increase in plasma testosterone. The increase in corticosterone and the decrease in testosterone due to stress, were attenuated with the opioid antagonist, both in naive and sexually experienced males. Prevention of ICW stress effects was more effective with higher doses of NTX (3 mg/kg). These data suggest that endogenous opioids could be participating in the effects caused by stress on male sexual behavior, corticosterone, and testosterone.     

Correlation of measurement of optic nerve sheath diameter using ultrasound with magnetic resonance imaging

Background and Aims:

Analysis to correlate the measurements of optic nerve sheath diameter (ONSD) obtained by using ultrasound to magnetic resonance imaging (MRI) techniques in order to establish the accuracy of ocular sonography as a noninvasive modality for detecting raised intracranial pressure (ICP).

Materials and Methods:

A prospective, observational study was performed in 100 cases of adult meningoencephalitis patients admitted to Intensive Care Unit in whom MRI was performed for neurodiagnosis. ONSD was measured in such patients, 3 mm behind the globe in each eye. A mean binocular ONSD >4.6 mm in female and 4.8 mm in male was taken as cut-off values for diagnosing raised ICP. This was compared with ONSD measured on T2-weighted MRI image measured 3 mm behind the globe. The reading obtained from both the methods were compared with Bland–Altman analysis for correlation and the findings were tabulated.

Results:

The mean ONSD values measured with ultrasonography (USG) and MRI for female were 5.48 ± 0.43 mm and 5.68 ± 0.44 mm and for male were 5.40 ± 0.37 mm and 5.56 ± 0.38 mm, respectively. The mean age of the female and male was 53.90 ± 17.84 and 56.06 ± 15.67 years, respectively. On comparing ultrasound with MRI-derived ONSD values, we found acceptable agreement between both methods for measurements at a depth of 3 mm (r = 0.02, P < 0.001).

Conclusion:

In our study, we have found a good correlation between ocular USG and MRI of ONSD. The study has shown agreement with the fact that ocular sonography can be used as a noninvasive tool for detecting raised ICP with accuracy.     

Effect of the cholinesterase inhibitor donepezil on cardiac remodeling and autonomic balance in rats with heart failure

In an earlier study we demonstrated the beneficial effect of direct vagal electrical stimulation on cardiac remodeling and survival. In the study reported here, we attempted to reproduce the effect of vagal enhancement through the administration of an acetylcholinesterase inhibitor, donepezil. A rat model of heart failure following extensive healed myocardial infarction was used. Compared to their nontreated counterparts, rats given donepezil (5 mg/kg/day) in their drinking water had a smaller biventricular weight (3.40 ± 0.13 vs. 3.02 ± 0.21 g/kg body weight, P < 0.05), and maximal rate of rise (3256 ± 955 vs. 3822 ± 389 mmHg/s, P < 0.05) and the end-diastolic value (30.1 ± 5.6 vs. 23.2 ± 5.7 mmHg, P < 0.05) of left ventricular pressure were improved. Neurohumoral factors were suppressed in donepezil-treated rats (norepinephrine 1885 ± 1423 vs. 316 ± 248 pg/ml, P < 0.01; brain natriuretic peptide 457 ± 68 vs. 362 ± 80 ng/ml, P < 0.05), and the high-frequency component of heart rate variability showed a nocturnal increase. These findings indicated that donepezil reproduced the anti-remodeling effect of electrical vagal stimulation. Further studies are warranted to evaluate the clinical usefulness of donepezil in heart failure.