Simultaneous recording of electroencephalogram and blood pressure in conscious telemetered rats during ictal state

Surgical implantation and functional assessment of an invasive telemetric system to measure autonomic responses in domestic pigs

The first aim of this study was to establish a surgical procedure to implant a new telemetric device for the continuous recording of electrocardiogram (ECG) and blood pressure (BP) in freely moving pigs. A second aim was the functional assessment of cardiovascular parameters, including heart rate variability (HRV) and blood pressure variability (BPV), so that these data could be used as the basis for the objective evaluation of autonomic activity and balance in different behavioural contexts. Eleven domestic pigs (German Landrace) underwent surgery for the placement of a telemetric device. At day 15 after surgery, 512 consecutive inter-beat intervals and pressure waves were analysed using different detection methods (automatic and manually corrected) while the animals were resting or feeding, respectively. HRV and BPV were calculated. Incomplete datasets were found in four pigs due to missing ECG or BP signals. Technical and surgical issues concerning catheterisation and detachment of the negative ECG lead were continuously improved. In the remaining pigs, excellent signal quality (manually corrected data of 1%) was obtained during resting and acceptable signal quality (<10%) was obtained during feeding. Automatic triggering was sufficiently reliable to eliminate errors in BP recordings during active behaviour, but this was not the case for ECG recordings. Sympathetic arousal with accompanying vagal withdrawal during feeding was documented. The established surgical implantation and functional assessment of the telemetric system with the reliable registration of cardiovascular parameters in freely moving pigs could serve as a basis for future studies of autonomic regulation in context of stress and animal welfare.

Interchangeability of Electrocardiography and Blood Pressure Measurement for Determining Heart Rate and Heart Rate Variability in Free-Moving Domestic Pigs in Various Behavioral Contexts

This study assessed the interchangeability between heart rate (HR) and heart rate variability (HRV) measures derived from a series of interbeat intervals (IBIs) recorded via electrocardiogram (ECG) and intra-arterial blood pressure (BP) in various behavioral contexts. Five minutes of simultaneously recorded IBIs from ECG and BP signals in 11 female domestic pigs during resting, feeding, and active behavior were analyzed. Comparisons were made for measures of HR, the standard deviation of IBIs, and the root mean of the squared distances of subsequent IBIs derived from ECG and BP signals for each behavior category using statistical procedures with different explanatory power [linear regression, intraclass correlation coefficient (ICC), Bland and Altman plots, and analysis of variance (ANOVA)]. Linear regression showed a strong relationship for HR during all behaviors and for HRV during resting. Excellent ICCs [lower 95% confidence intervals (CI) >0.75] and narrow limits of agreement in all behavior categories were found for HR. ICCs for HRV reached the critical lower 95% CI value of 0.75 only during resting. Using Bland and Altman plots, HRV agreement was unacceptable for all of the behavior categories. ANOVA showed significant differences between the methods in terms of HRV. BP systematically overestimated HRV compared with ECG. Our findings reveal that HR data recorded via BP agree well those recorded using ECG independently of the activity of the subject, whereas ECG and BP cannot be used interchangeably in the context of HRV in free-moving domestic pigs.

Both Ox1r and Ox2r orexin receptors contribute to the cardiovascular and locomotor components of the novelty stress response in the rat

Orexin contributes to the expression of the cardiovascular and behavioural response of some forms of stress, including novelty stress. Thus, Almorexant, a dual receptor antagonist that blocks the two known orexin receptors, Ox1R and Ox2R, reduces these responses. However, it is not known if the reduction results from blockade of one receptor only or both. To answer this question, the selective Ox1R antagonist ACT335827 and the selective Ox2R antagonist EMPA were injected intragastrically (300 mg/kg) or intraperitoneally (30 and 100 mg/kg) either alone or as a cocktail and compared to Almorexant in rats exposed to novelty stress. Cardiovascular and locomotor responses were recorded by radio-telemetry. Triple immunolabelling was also conducted to establish the distribution of Ox1R and Ox2R in sympathetic preganglionic neurons and orexin neurons. Intraperitoneal injections of ACT335827 (100 mg/kg) reduced the pressor and tachycardic but not the locomotor response of novelty (by 32% and 48%, respectively). Intraperitoneal injections of EMPA (100 mg/kg) only reduced the pressor response (42%). However when given together, ACT335827 and EMPA reduced all 3 components (65%, 60% and 57% of the tachycardic, pressor and locomotor responses, respectively) as Almorexant (100 mg/kg) did (69%, 87% and 72%, respectively). Triple immunolabelling revealed that sympathetic preganglionic neurons were mainly Ox1R positive only while orexin neurons were both Ox1R and Ox2R positive. This study shows that orexin's contribution to the cardiovascular and locomotor components of the novelty stress response is not mediated by one receptor alone, but by both receptors and at different levels of the neuraxis.

EEG characterization of audiogenic seizures in the hamster strain GASH:Sal

The study was performed to characterize GASH:SAL audiogenic seizures as true epileptic activity based on electroencephalographic markers acquired with a wireless implanted radiotelemetry system. We analyzed cortical EEG patterns synchronized with video recordings of convulsive behavior of the GASH:Sal hamster following an acoustic stimulus. All GASH:Sal presented archetypal motor symptoms comparable to current animal models of generalized tonic-clonic epilepsy. Seizures consisted of an initial bout of wild running, followed by opisthotonus, tonic-clonic convulsions, tonic limb extension, and terminated in postictal depression. EEG patterns correlated with behavior and displayed phase appropriate spike-wave complexes, low-amplitude desynchronized activity, and high frequency large-amplitude peaks. Our results confirm that electroencephalographic profiles of the audiogenic seizures of the hamster GASH:Sal are parallel to EEG patterns of other animal models of generalized tonic-clonic seizures. Therefore, this animal may serve as an appropriate model for epilepsy research.

Repeated amygdala-kindled seizures induce ictal rebound tachycardia in rats

It is thought that cardiovascular changes may contribute to sudden death in patients with epilepsy. To examine cardiovascular alterations that occur during epileptogenesis, we measured the heart rate of rats submitted to the electrical amygdala kindling model. Heart rate was recorded before, during, and after the induced seizures. Resting heart rate was increased in stages 1, 3, and 5 as compared with the unstimulated control condition. In the initial one third of the seizures, we observed bradycardia, which increased in intensity with increasing stage and was blocked by injecting methyl atropine. During stage 5 seizures, a rebound tachycardia was observed that also increased in intensity with increasing number of seizures. This study demonstrated the influence of seizure frequency on cardiac autonomic modulation, providing a basis for discussion of potential mechanisms that cause patients with epilepsy to die suddenly.

Epileptic seizure-induced hypertension and its prevention by calcium channel blockers: a real-time study in conscious telemetered rats

Epileptic seizures are accompanied by changes in autonomic function that in turn influence the cardiovascular system (hypertension and bradyarrhythmia). We have studied possible cardioprotective activity (during the ictal state in conscious animals) of valproic acid, nifedipine, and verapamil, alone and in combination, during pentylenetetrazole (PTZ)-induced seizures. Telemetry system was used for recording EEG, blood pressure, and heart rate in conscious, freely moving rats during seizures. We observed that PTZ-induced seizures were accompanied by hypertension and bradyarrhythmia. Pretreatment with valproic acid did not block seizure-induced hypertension and bradyarrhythmia. Nifedipine alone and in combination with valproic acid blocked seizure-induced hypertension and bradyarrhythmia significantly. We also observed that pretreatment with verapamil alone and in combination with valproic acid did not block seizure-induced hypertension and bradyarrhythmia significantly. Our results suggest that pretreatment with nifedipine alone or in combination with valproic acid provides protection against seizure-induced hypertension and bradyarrhythmia.