Evaluation of Cardiovascular Risk Factors in the Wistar Audiogenic Rat (WAR) Strain.

Risk factors for life-threatening cardiovascular events were evaluated in an experimental model of epilepsy, the Wistar Audiogenic Rat (WAR) strain.We used long-term ECG recordings in conscious, one year old, WAR and Wistar control counterparts to evaluate spontaneous arrhythmias and heart rate variability, a tool to assess autonomic cardiac control. Ventricular function was also evaluated using the pressure-volume conductance system in anesthetized rats.Basal RR interval (RRi) was similar between WAR and Wistar rats (188 ± 5 vs 199 ± 6 ms). RRi variability strongly suggests that WAR present an autonomic imbalance with sympathetic overactivity, which is an isolated risk factor for cardiovascular events. Anesthetized WAR showed lower arterial pressure (92 ± 3 vs 115 ± 5 mmHg) and exhibited indices of systolic dysfunction, such as higher ventricle end-diastolic pressure (9.2 ± 0.6 vs 5.6 ± 1 mmHg) and volume (137 ± 9 vs 68 ± 9 μL) as well as lower rate of increase in ventricular pressure (5266 ± 602 vs 7320 ± 538 mmHg.s-1). Indices of diastolic cardiac function, such as lower rate of decrease in ventricular pressure (-5014 ± 780 vs -7766 ± 998 mmHg.s-1) and a higher slope of the linear relationship between end-diastolic pressure and volume (0.078 ± 0.011 vs 0.036 ± 0.011 mmHg.μL), were also found in WAR as compared to Wistar control rats. Moreover, Wistar rats had 3 to 6 ventricular ectopic beats, whereas WAR showed 15 to 30 ectopic beats out of the 20,000 beats analyzed in each rat.The autonomic imbalance observed previously at younger age is also present in aged WAR and, additionally, a cardiac dysfunction was also observed in the rats. These findings make this experimental model of epilepsy a valuable tool to study risk factors for cardiovascular events in epilepsy

ECG recordings illustrating ectopic beats (arrows) in 3 different WAR studied at 1 year of age.

<p>(A) One isolated ectopic beat, (B) two ectopic beats from distinct ventricular origins and (C) a period of bigeminy.</p

Hemodynamic parameters and indices of systolic and diastolic function derived from left ventricle pressure-volume relationship in one-year old pentobarbital anesthetized WAR and Wistar control rats.

<p>*P<0.05 compared with Wistar control rats.</p><p>HR: heart rate, MAP: mean arterial pressure, LVSP: left ventricular systolic pressure, ESV: end-systolic volume, EDP: end-diastolic pressure, EDV: end-diastolic volume, CO: cardiac output, TPR: total peripheral resistance, EF: ejection fraction, dP/dt_max maximal slopes of the systolic pressure increment (+dP/dt_max) and diastolic pressure decrement (-dP/dt_max), ESPVR and EDPVR: slope of end-systolic and end-diastolic pressure-volume relationships, τ: relaxation time constant, PRSW: preload recruitable stroke work.</p><p>Values are mean ± SEM.</p><p>Hemodynamic parameters and indices of systolic and diastolic function derived from left ventricle pressure-volume relationship in one-year old pentobarbital anesthetized WAR and Wistar control rats.</p

Mean values of RR interval (RRi) and RRi variability in time and frequency domain in one-year old conscious freely moving WAR and Wistar control rats.

<p>*P<0.05 compared with Wistar control rats.</p><p>RRi: interval between successive R waves, SDNN: standard deviation of normal RRi, VLF, LF and HF: power of oscillatory components of RRi series at very low (<0.2 Hz), low (0.2–0.8 Hz) and high (0.8–3.0 Hz) frequency bands. nu: normalized units. LF and HF (Hz): central frequency of the main oscillatory component modeled at low- and high-frequency bands.</p><p>Values are mean ± SEM.</p><p>Mean values of RR interval (RRi) and RRi variability in time and frequency domain in one-year old conscious freely moving WAR and Wistar control rats.</p

Behavioral and Cardiorespiratory Responses to Bilateral Microinjections of Oxytocin into the Central Nucleus of Amygdala of Wistar Rats, an Experimental Model of Compulsion

<div><p>Introduction</p><p>The central nucleus of amygdala plays an important role mediating fear and anxiety responses. It is known that oxytocin microinjections into the central nucleus of amygdala induce hypergrooming, an experimental model of compulsive behavior. We evaluated the behavioral and cardiorespiratory responses of conscious rats microinjected with oxytocin into the central nucleus of amygdala.</p><p>Methods</p><p>Male Wistar rats were implanted with guide cannulae into the central nucleus of amygdala and microinjected with oxytocin (0.5 µg, 1 µg) or saline. After 24 h, rats had a catheter implanted into the femoral artery for pulsatile arterial pressure measurement. The pulsatile arterial pressure was recorded at baseline conditions and data used for cardiovascular variability and baroreflex sensitivity analysis. Respiratory and behavioral parameters were assessed during this data collection session.</p><p>Results</p><p>Microinjections of oxytocin (0.5 µg) into the central nucleus of amygdala produced hypergrooming behavior but did not change cardiorespiratory parameters. However, hypergrooming evoked by microinjections of oxytocin (1 µg) into the central nucleus of amygdala was accompanied by increase in arterial pressure, heart rate and ventilation and augmented the power of low and high (respiratory-related) frequency bands of the systolic arterial pressure spectrum. No changes were observed in power of the low and high frequency bands of the pulse interval spectrum. Baroreflex sensitivity was found lower after oxytocin microinjections, demonstrating that the oxytocin-induced pressor response may involve an inhibition of baroreflex pathways and a consequent facilitation of sympathetic outflow to the cardiovascular system.</p><p>Conclusions</p><p>The microinjection of oxytocin (1 µg) into the central nucleus of amygdala not only induces hypergrooming but also changes cardiorespiratory parameters. Moreover, specific oxytocin receptor antagonism attenuated hypergrooming but did not affect pressor, tachycardic and ventilatory responses to oxytocin, suggesting the involvement of distinct neural pathways.</p></div

Behavioral, hemodynamic and respiratory responses to oxytocin antagonist.

<p>(A) Grooming score average count of the 5-min behavior sampling window of the saline+oxytocin (SAL+OT) 1 µg and vasotocin+OT (OTA+OT) 1 µg groups. (B) Grooming score (mean of 60 min) of the SAL+OT 1 µg (open bar) and OTA+OT 1 µg (black bar) groups. Time-course of (C) mean arterial blood pressure (ΔMABP, mmHg), (E) heart rate (ΔHR, bpm) and (G) minute ventilation (ΔV_E, mL.Kg⁻¹.min⁻¹) changes for 60 min after bilateral microinjections of OT 1 µg into the central nucleus of amygdala (CeA) in the SAL+OT 1 µg and OTA+OT 1 µg groups. Maximum responses in (D) mean arterial blood pressure (ΔMABP, mmHg) at 50 min, (F) heart rate (ΔHR, bpm) at 5 min and (H) minute ventilation (ΔV_E, mL.Kg⁻¹.min⁻¹) at 5 min after bilateral microinjections of OT 1 µg into the CeA in the SAL+OT 1 µg (open bars) and OTA+OT 1 µg (black bars) groups. The arrow indicates the moment of microinjections. Data shown represent the means ± standard error of mean. (*) SAL+OT 1 µg group <i>vs</i> VASO+OT 1 µg group; p<0.05, <i>Poisson</i> model.</p

Grooming score following oxytocin microinjection into the central nucleus of amygdala.

<p>(A) Grooming score average count showing 5-min behavior sampling curve of oxytocin (OT) 0.5 µg, OT 1 µg or saline (SAL) into the central nucleus of amygdala (CeA) group and OT 1 µg outside CeA group. (B) grooming score (sum of grooming behavior over 60 min) of OT 0.5 µg (checkered bar), OT 1 µg (black bar, n = 8) or SAL (open bar) inside CeA group and OT 1 µg outside CeA group (striped bar). The arrow indicates the moment of microinjections. Data shown represent the means. (‡ ‡) SAL inside CeA group <i>vs</i> OT 0.5 µg inside CeA group; (*) SAL inside CeA group <i>vs</i> OT 1 µg inside CeA group; (**) OT 0.5 µg inside CeA group <i>vs</i> OT 1 µg outside CeA group; (‡) OT 1 µg inside CeA group <i>vs</i> OT 1 µg outside CeA group. p<0.05, <i>Poisson</i> model.</p

Systolic arterial blood pressure and pulse interval variability following oxytocin microinjection into central nucleus of amygdala.

<p>(A–C) Systolic arterial blood pressure (SABP) and (D–F) pulse interval (PI) variability analysis at 10 min after bilateral microinjections of oxytocin (OT) (black-white bar, n = 4), OT 1 µg (black bar, n = 8) or SAL (open bar, n = 8) into the central nucleus of amygdala (CeA) group and OT 1 µg outside CeA group (striped bar, n = 7). A and D: variance (σ²); B, C, E and F: power of the low and high frequency (LF; HF) bands. Data shown represent the means ± standard error of mean. (*) SAL inside CeA group <i>vs</i> OT 1 µg inside CeA group; (**) OT 0.5 µg inside CeA group <i>vs</i> OT 1 µg inside CeA group; (‡) OT 1 µg inside CeA group <i>vs</i> OT 1 µg outside CeA group.p<0.05, One-way ANOVA followed by Bonferroni's <i>post hoc</i> test.</p

Respiratory responses to oxytocin microinjection into the central nucleus of amygdala.

<p>(A) Time-course of respiratory frequency (Δf_R, cpm), (C) tidal volume (ΔV_T, mL.Kg⁻¹) and (E) minute ventilation (ΔV_E, mL.Kg⁻¹.min⁻¹) changes for 60 min after bilateral microinjections of oxytocin (OT) 0.5 µg, OT 1 µg or saline (SAL) into the central nucleus of amygdala (CeA) group and OT 1 µg outside CeA group. Maximum responses in (B) respiratory frequency (Δf_R, cpm), (D) tidal volume (ΔV_T, mL.Kg⁻¹) and (F) minute ventilation (ΔV_E, mL.Kg⁻¹.min⁻¹) 5 min after bilateral microinjections of OT 0.5 µg (black-white bar), OT 1 µg (black bar) or SAL (open bar) inside CeA group and OT 1 µg outside CeA group (striped bar). The arrow indicates the moment of microinjections. Data shown represent the means ± standard error of mean. (*) SAL inside CeA group <i>vs</i> OT 1 µg inside CeA group; p<0.05, Two-way ANOVA followed by Bonferroni's <i>post hoc</i> test.</p

Hemodynamic responses to oxytocin microinjection into the central nucleus of amygdala.

<p>(A) Time-course of mean arterial blood pressure (ΔMABP, mmHg) and (C) heart rate (ΔHR, bpm) changes for 60 min after bilateral microinjections of oxytocin (OT) 0.5 µg, OT 1 µg or saline (SAL) into the central nucleus of amygdala (CeA) group and OT 1 µg outside CeA group. (B) Maximum responses in mean arterial blood pressure (ΔMABP, mmHg) at 50 min and (D) heart rate (ΔHR, bpm) at 5 min after bilateral microinjections of OT 0.5 µg (black-white bar), OT 1 µg (black bar) or SAL (open bar) inside CeA group and OT 1 µg outside CeA group (striped bar). The arrow indicates the moment of microinjections. Data presented are the means ± standard error of the mean. (*) SAL inside CeA group <i>vs</i> OT 1 µg inside CeA group; (**) OT 0.5 µg inside CeA group <i>vs</i> OT 1 µg inside CeA group; (‡) OT 1 µg inside CeA group <i>vs</i> OT 1 µg outside CeA group. p<0.001, Two-way ANOVA followed by Bonferroni's <i>post hoc</i> test.</p