Cardiorespiratory effects of electrical stimulation of the globus pallidus in cats

Placebo response in pain, fatigue, and performance: Possible implications for neuromuscular disorders

The placebo response in neuromuscular disorders is not well understood. The only available data regarding its underlying mechanisms are related to neuropathic pain. In this review, we describe the factors that contribute to improved outcomes in the placebo arm, with specific attention to pain and fatigue, as well as some of the most important psychobiological mechanisms that may explain such a response. This approach may also improve our insight into the symptomatology and therapeutic responses of other neuromuscular disorders. The fact that >90% of tested analgesics for neuropathic pain have failed in advanced phases of clinical trials should prompt a greater investment of effort and resources into understanding the mechanisms and impact of placebos in clinical research. Such an endeavor will help improve the design of clinical trials and will provide information that informs clinical neuromuscular practice. Muscle Nerve 56: 358-367, 2017.

Coronary spasm in neurosurgical patients and role of trigeminocardiac reflex

Background. Coronary artery spasm (CAS) is a rarely reported complication in neurosurgical patients and its main causative mechanism was attributed to vagal mediated responses. However, these may be the unusual manifestations of trigeminal cardiac reflex (TCR) which is a well established brain stem reflex observed in various neurosurgical patients. Methods and Results. In this review, we have searched for the case reports/papers related to intraoperative coronary spasm in neurosurgical patients and described the role of TCR in this regard. TCR is a possible mechanism in producing CAS in most of the cases in which stimulation occurred at or near the vicinity of trigeminal nerve. It is likely that TCR mediated coronary spasm may be a physiological mechanism and not related to actual myocardial insult apparent by cardiac enzymes or echocardiography studies in most of the cases. Some common risk factors may also exist related to occurrence of CAS as well as TCR. Conclusions. In conclusion, neurosurgical procedures occurring at the vicinity of trigeminal nerve may produce CAS even in previously healthy patients and may produce catastrophic consequences. There is a need for future reports and experimental studies on the interaction of TCR and pathophysiological mechanisms related to CAS.

The top-down influence of ergogenic placebos on muscle work and fatigue

Placebos have been shown to induce powerful effects in a variety of medical conditions, such as pain and movement disorders, as well as to increase physical performance and endurance in healthy subjects. Here we investigated the effects of an ergogenic placebo on the performance of the quadriceps muscle, which is responsible for the extension of the leg relative to the thigh. In a first experiment, a placebo was administered along with the suggestion that it was caffeine at high dose. This resulted in a significant increase in mean muscle work across subjects, which, however, was not accompanied by a decrease of perceived muscle fatigue. In a second experiment, the placebo caffeine was administered twice in two different sessions. Each time, the weight to be lifted with the quadriceps was reduced surreptitiously so as to make the subjects believe that the 'ergogenic agent' was effective. After this conditioning procedure, the load was restored to the original weight, and both muscle work and perceived fatigue assessed after placebo administration. Compared with the first experiment, the placebo effect was larger, with a significant increase in muscle work and decrease in perceived muscle fatigue. Within the context of the role of peripheral and/or central mechanisms in muscle performance, the present findings suggest a central mechanism of top-down modulation of muscle fatigue. In addition, the difference between the first and second experiment underscores the role of learning in increasing muscle performance with placebos.

Sympathetic activity at rest and motor brain areas: FDG-PET study

Although recent studies identified brain areas which are involved in short term activation of the sympathetic nervous system, little is known about brain mechanisms which generate the individual variability of basal autonomic activity. In this fluorodeoxyglucose positron emission tomography study (FDG-PET), we aimed to identify brain regions, which covary with function parameters of the autonomic nervous system at rest. Therefore, FDG-PET (Siemens, Germany) was performed twice in 14 healthy resting subjects (7 m, 7 f; mean age 29.5 years) while different parameters of autonomic function were assessed simultaneously: Blood pressure, heart rate, power spectra of heart rate variability (HF/LF ratio) and plasma catecholamines. In order to control for attention, subjects had to focus visual affective neutral presentations during the experiment. Correlation analysis was performed as a region of interest analysis using SPM2 software (p<0.001 uncorrected). Sympathetic activity at rest varied substantially between subjects. There were significant positive correlations between increase of regional cerebral glucose metabolism (rCGM) of the heads of caudate nuclei on both sides and the HF/LF ratio of heart rate variability. Furthermore, significant negative correlations between both heart rate and plasma catecholamines and rCGM decreases of caudate nuclei heads were found. In addition, there was a positive correlation between plasma catecholamines and primary motor cortex activation. Autonomic nervous system at rest seems to be partially interlocked with activity of motor brain regions - the caudate nuclei and the motor cortex. This might have clinical implications for the understanding of stress-related disorders, which are frequently accompanied by increased sympathetic activity as well as muscle tone.

Expectation enhances autonomic responses to stimulation of the human subthalamic limbic region

Recent studies show that the placebo component of a treatment can be investigated by administering therapies either overtly or covertly, without the administration of any placebo. Here, we analyze the effects of open (i.e., expected) versus hidden (i.e., unexpected) stimulations of the human subthalamic region on autonomic responses in Parkinson patients. To do this, we mapped the whole subthalamic region, from the dorsal to the ventral part, and recorded both heart rate and sympathetic responses by using spectral analysis of heart rate variability. We found that open stimulations were more effective than hidden ones only in the ventral subthalamic region, whereas no difference between the two conditions was found in the dorsal aspect. By analyzing the stimulus-response curves in the dorsal, middle, and ventral subthalamic regions, we found that the autonomic response threshold was higher in the hidden than open condition for both heart rate and sympathetic responses only in the ventral part. As this ventralmost portion of the subthalamic region is involved in associative-limbic functions, these data suggest that expectation enhances autonomic responses only if these are elicited in the limbic system. These results extend previous findings on the open-hidden paradigm in deep brain stimulation [Benedetti, F., Colloca, L., Lanotte, M., Bergamasco, B., Torre, E., Lopiano, L., 2004a. Autonomic and emotional responses to open and hidden stimulations of the human subthalamic region. Brain Res. Bull. 63, 203-211.], and indicate that expectation plays a major role in the therapeutic outcome. In light of the interactions between the sympathetic adrenergic system and the immune system, the open-hidden difference in autonomic responses might be relevant to the understanding of how expectations might affect the immune system.

Autonomic and emotional responses to open and hidden stimulations of the human subthalamic region

We performed a microstimulation study of the subthalamic region of Parkinsonian patients who underwent bilateral electrode implantation in the subthalamic nuclei and whose heart rate and heart rate variability were recorded. The stimulation of the dorsalmost region, which includes the zona incerta and the dorsal pole of the subthalamic nucleus, produced autonomic responses that were constant over time. In fact, hidden stimulations (the patient is not aware of being stimulated) and open stimulations (the patient is aware of being stimulated) always induced the same responses. By contrast, the stimulation of the ventralmost region, which includes the ventral pole of the subthalamic nucleus and the substantia nigra pars reticulata, produced autonomic and emotional responses that were inconstant over time and varied according to the condition. In fact, different responses were elicited with hidden and open stimulations. These data suggest that the dorsal subthalamic nucleus and/or the zona incerta are involved in autonomic control, whereas the ventral subthalamic nucleus and/or the substantia nigra reticulata are involved in associative/limbic-related autonomic activity. The difference between the open and hidden stimulations in the ventral subthalamic region can explain previous studies in which open and hidden stimulations produced different therapeutic outcomes.

Differential blood pressure and heart rate responses to supramedullary brain stimulation in cats

The purpose of this study was to compare the cardiovascular responses to electrical stimulation of different supramedullary brain regions. Arterial blood pressure (BP) and heart rate (HR) effects were elicited by electrical stimulation of the lateral hypothalamus (LH), mamillary bodies (Mm), substantia nigra (SN), globus pallidus (GP), and the subthalamic nucleus (Sub) in conscious, freely moving cats. Pressor responses were obtained from all of these regions. The higher intensity of stimulation the higher increase in BP and HR was obtained. However, clear-cut differences occurred in the effects both during and after the termination of stimulations. Namely, a continuous increase in BP and HR was obtained from the LH and SN. In contrast, the initial increase in BP and HR was followed by a reduction compared to the peak value of the effects of stimulation in the GP and the Sub. However, the BP and HR never reduced to the pre-stimulaion level during the stimulation. Also the changes following the cessation of stimulation at the different brain loci were dissimilar. The BP and HR either returned gradually to the pre-stimulation level, or long-lasting oscillation occurred. The electrical activity of the nucleus of the solitary tract (NTS) and the vagus nerve co-varied with the changes in BP and HR. It is concluded that the supramedullary stimulations produce differential cardiovascular effects, and these effects are modified by the baroreflexes that are activated by the electrically elicited rise in blood pressure.

Electrical stimulation of the midbrain increases heart rate and arterial blood pressure in awake humans

Electrical stimulation of the hypothalamus, basal ganglia or pedunculopontine nucleus in decorticate animals results in locomotion and a cardiorespiratory response resembling that seen during exercise. This has led to the hypothesis that parallel activation of cardiorespiratory and locomotor systems from the midbrain could form part of the 'central command' mechanism of exercise. However, the degree to which subcortical structures play a role in cardiovascular activation in awake humans has not been established. We studied the effects on heart rate (HR) and mean arterial blood pressure (MAP) of electrically stimulating the thalamus and basal ganglia in awake humans undergoing neurosurgery for movement disorders (n = 13 Parkinson's disease, n = 1 myoclonic dystonia, n = 1 spasmodic torticollis). HR and MAP increased during high frequency (> 90 Hz) electrical stimulation of the thalamus (HR 5 +/- 3 beats min(-1), P = 0.002, MAP 4 +/- 3 mmHg, P = 0.05, n = 9), subthalamic nucleus (HR 5 +/- 3 beats min(-1), P = 0.002, MAP 5 +/- 3 mmHg, P = 0.006, n = 8) or substantia nigra (HR 6 +/- 3 beats min(-1), P = 0.001, MAP 5 +/- 2 mmHg, P = 0.005, n = 8). This was accompanied by the facilitation of movement, but without the movement itself. Stimulation of the internal globus pallidus did not increase cardiovascular variables but did facilitate movement. Low frequency (< 20 Hz) stimulation of any site did not affect cardiovascular variables or movement. Electrical stimulation of the midbrain in awake humans can cause a modest increase in cardiovascular variables that is not dependent on movement feedback from exercising muscles. The relationship between this type of response and that occurring during actual exercise is unclear, but it indicates that subcortical command could be involved in 'parallel activation' of the locomotor and cardiovascular systems and thus contribute to the neurocircuitry of 'central command'.

Subthalamic influences on the cardiorespiratory functions in the cat

The electrical stimulation of the subthalamic nucleus (STN) caused a conspicuous increase in arterial blood pressure (BP), heart rate (HR) and respiratory rate (RR) in freely moving cats. The pulse pressure (PP) increased significantly following an initial decrease at the beginning of the 10 s long stimulation. A rebound bradycardia occurred after switching off the stimulation. Cardiorespiratory responses might be elicited also during ketamine-induced anaesthesia. The BP responses reduced highly under the blockade of the alpha(1)-adrenergic receptors. The neurotoxic lesions of the ipsilateral globus pallidus caused no significant alterations in the cardiorespiratory responses to STN stimulation. It is concluded that, besides its role in the motor control, STN is also involved in adjusting the cardiorespiratory functions to the somatomotor activity.

Characterization of cardiorespiratory responses to electrical stimulation of the globus pallidus in cat

The aim of the present study was to describe the characteristics of the electrically elicited cardiorespiratory responses from the globus pallidus (GP) in cat. GP stimulation caused an increase in the arterial blood pressure (BP), heart rate (HR), and respiratory rate (RR) in freely moving cats. Threshold, medium, and high intensity for stimulation at 100 Hz were determined by the somatomotor effects of stimulation. The higher stimulus intensity the higher increase in cardiorespiratory functions was obtained. The electrical stimulation within different segments of the GP caused changed effects. A continuous rise in BP, HR, and RR was induced by stimulating in the external segment (GPe). On the contrary, the stimulation in the internal segment (GPi) produced complex sequence of changes. At the beginning of the 10-s long stimulation the increase in diastolic pressure was more steep than that of the systolic pressure, so the pulse pressure decreased. However, 2-3 s after the onset of stimulation the diastolic pressure reduced; therefore, the pulse pressure increased. Simultaneously, the HR decreased below the prestimulation level. Occasionally, similar slowing in RR appeared as well. The blockade of the alpha 1-receptors by phentolamine, or neurotoxic lesion within the GP by kainic acid, reduced significantly the BP effects of GP stimulation of identical parameters. It is concluded that GP plays an intricate role in the adjustment of cardiorespiratory functions to the somatomotor activities.