Effect of acute restraint stress on the tachycardiac and bradycardiac responses of the baroreflex in rats

The medial prefrontal cortex and the cardiac baroreflex activity: physiological and pathological implications

The cardiac baroreflex is an autonomic neural mechanism involved in the modulation of the cardiovascular system. It influences the heart rate and peripheral vascular resistance to preserve arterial blood pressure within a narrow variation range. This mechanism is mainly controlled by medullary nuclei located in the brain stem. However, supramedullary areas, such as the ventral portion of medial prefrontal cortex (vMPFC), are also involved. Particularly, the glutamatergic NMDA/NO pathway in the vMPFC can facilitate baroreflex bradycardic and tachycardic responses. In addition, cannabinoid receptors in this same area can reduce or increase those cardiac responses, possibly through alteration in glutamate release. This vMPFC network has been associated to cardiovascular responses during stressful situations. Recent results showed an involvement of glutamatergic, nitrergic, and endocannabinoid systems in the blood pressure and heart rate increases in animals after aversive conditioning. Consequently, baroreflex could be modified by the vMPFC neurotransmission during stressful situations, allowing necessary cardiovascular adjustments. Remarkably, some mental, neurological and neurodegenerative disorders can involve damage in the vMPFC, such as posttraumatic stress disorder, major depressive disorder, Alzheimer's disease, and neuropathic pain. These pathologies are also associated with alterations in glutamate/NO release and endocannabinoid functions along with baroreflex impairment. Thus, the vMPFC seems to play a crucial role on the baroreflex control, either during pathological or physiological stress-related responses. The study of baroreflex mechanism under such pathological view may be helpful to establish causality mechanisms for the autonomic and cardiovascular imbalance found in those conditions. It can explain in the future the reasons of the high cardiovascular risk some neurological and neurodegenerative disease patients undergo. Additionally, the present work offers insights on the possible contributions of vMPFC dysfunction on baroreflex alterations, which, in turn, may raise questions in what extent other brain areas may play a role in autonomic deregulation under such pathological situations.

NMDA receptors in the insular cortex modulate cardiovascular and autonomic but not neuroendocrine responses to restraint stress in rats

The insular cortex (IC) is a brain structure involved in physiological and behavioural responses during stressful events. However, the local neurochemical mechanisms involved in control of stress responses by the IC are poorly understood. Thus, this study aimed to investigate the involvement of glutamatergic neurotransmission within the IC in cardiovascular, autonomic and neuroendocrine responses to an acute session of restraint stress. For this, the selective NMDA glutamate receptor antagonist LY235959 (1 nmol/100 nL) or the selective non-NMDA glutamate receptor antagonist NBQX (1 nmol/100 nL) were microinjected into the IC 10 min before the onset of the 60 min session of restraint stress. We observed that the antagonism of NMDA receptors within the IC enhanced the restraint-evoked increase in arterial pressure and heart rate, while blockade of non-NMDA receptors did not affect these cardiovascular responses. Spontaneous baroreflex analysis demonstrated that microinjection of LY235959 into the IC decreased baroreflex activity during restraint stress. The decrease in tail skin temperature during restraint stress was shifted to an increase in animals treated with the NMDA receptor antagonist. Nevertheless, the blockade of either NMDA or non-NMDA glutamate receptors within the IC did not affect the increase in circulating corticosterone levels during restraint stress. Overall, our findings provide evidence that IC glutamatergic neurotransmission, acting via local NMDA receptors, plays a prominent role in the control of autonomic and cardiovascular responses to restraint stress, but without affecting neuroendocrine adjustments.

Physiologic Effects of Housing Rats in Metabolic Cages

Currently, metabolic cages (MC) are the only way to achieve serial sampling of urine and feces in rodents. However, the use of this caging creates a dramatic change from an animal's usual microenvironment. Here we sought to examine the effect of MC on physiologic parameters that are stress-responsive in rats. We surgically implanted 8 male Wistar rats (weight, 150 to 175 g) with telemetric transmitters and allowed them to recover for at least 2 wk. At the beginning of the study, the rats were moved to conventional open-top cages, and telemetry recording was initiated. After 24 h, the rats were moved to MC or to another conventional cage and the recording continued for another 24 h. Finally, the rats were returned to their home cages, and telemetry recording was performed for a final 24 h. After 10 days, this process was then repeated, with MC and conventional assignments switched. During the 78-h monitoring period, we recorded heart rate, arterial blood pressure, locomotor activity, body weight, and food and water consumption. Heart rate and arterial blood pressure showed transient but significant changes. Locomotor activity during the dark phase was greatly decreased in MC compared with conventional cages, perhaps due to space constraints. In addition, when the rats were housed in MC, they showed a small but significant weight loss. Food consumption did not differ between housing environments, but water consumption was lower when rats were in MC. In conclusion, the housing of rats in MC for 24 h can elicit mild and reversible cardiovascular changes. This finding is consistent with European Directive 2010/63/EU, which considers short-term (less than 24 h) restraint in MC a procedure of mild severity.

Use and perceived usefulness of a just-in-time resonance breathing intervention adjunct for substance use disorder: Contextual and physiological predictors

Craving for alcohol and other drugs is often described as a momentary hyperarousal state that interferes with one's ability to use top-down strategies. As such, it may be best interrupted 'in the moment' through bottom-up modulation. We recently reported that episodic resonance paced breathing (eRPB) delivered via mobile phone app as an add-on to outpatient treatment for substance use disorder (SUD) was effective at dampening craving over the course of an 8-week intervention (NCT#02579317). However, not all participants engaged with the eRPB app and there was high intra- and inter-individual variability in weekly ratings of usefulness. Here we examined baseline demographic, physiological, and psychiatric measures as well as time-varying exposure to positive, negative, and temptation craving triggers as predictors of frequency of eRPB app use and ratings of usefulness. Seventy-seven outpatient women were randomized to an eRPB (0.1 Hz) or a faster paced breathing sham (0.23 Hz) condition. Baseline measures were assessed within the first 3 weeks of treatment entry prior to randomization. App use frequency, ratings of usefulness, and trigger exposure were measured weekly throughout the intervention. Variables were entered into marginal means models with forward stepwise model selection and examined as predictors of use and usefulness. Frequent app use was associated with a lifetime alcohol use disorder (AUD) diagnosis (p = 0.026), higher ratings of usefulness (p < 0.001), and fewer exposures to positive triggers (e.g., celebration, socialization; p < 0.001). There was a trend-level association between frequency of app use and greater cardiovascular capacity at baseline (p = 0.088). Higher ratings of usefulness were associated with greater exposure to negative triggers (e.g,. loneliness, frustration; p < 0.001) and parasympathetic dysregulation at baseline (p = 0.05). A positive relationship between app use frequency and ratings of usefulness was present only in the eRPB group (p = 0.045). Matching ideal candidates and moments to an arousal modulation anti-craving intervention can help streamline screening and implementation of eRPB in the treatment of SUD.

Clinical Trial Registration

https://clinicaltrials.gov/ct2/show/NCT02579317, identifier NCT02579317.

Cardiovascular Reactivity to a Novel Stressor: Differences on Susceptible and Resilient Rats to Social Defeat Stress

Prolonged and heightened responses to stress are known factors that influence the development of mood disorders and cardiovascular diseases. Moreover, the coping strategies related to the experience of adverse events, i.e., resilience or the susceptibility to stress, are determinants for the individual risk of developing such diseases. Susceptible rats to the social defeat stress (SDS), identified by the social interaction test (SIT), show behavioral and cardiovascular alterations after SDS exposure that are not found in resilient rats. However, it is not elucidated yet how the cardiovascular system of susceptible and resilient phenotypes responds to a new stressor after SDS exposure. Thus, using the SDS exposure followed by the SIT, we evaluated heart rate, blood pressure (BP), tail skin temperature, and circulating corticosterone responses to an acute session of restraint stress in susceptible and resilient rats to SDS. Susceptible rats showed resting tachycardia and exaggerated BP response to restraint stress, while resilient rats did not present such alterations. In contrast, both phenotypes showed increased plasma corticosterone and a drop in tail skin temperature to restraint stress, which was similar to that observed in control animals. Our results revealed an increased cardiovascular reactivity in response to a new stressful stimulus in susceptible rats, which might be related to a greater risk for the development of cardiovascular diseases.

A functional selective effect of oxytocin secreted under restraint stress in rats

Restraint stress (RS) is an unavoidable stress model that triggers activation of the autonomic nervous system, endocrine activity, and behavioral changes in rodents. Furthermore, RS induces secretion of oxytocin into the bloodstream, indicating a possible physiological role in the stress response in this model. The presence of oxytocin receptors in vessels and heart favors this possible idea. However, the role of oxytocin secreted in RS and effects on the cardiovascular system are still unclear. The aim of this study was to analyze the influence of oxytocin on cardiovascular effects during RS sessions. Rats were subjected to pharmacological (blockade of either oxytocin, vasopressin, or muscarinic receptors) or surgical (hypophysectomy or sinoaortic denervation) approaches to study the functional role of oxytocin and its receptor during RS. Plasma levels of oxytocin and vasopressin were measured after RS. RS increased arterial pressure, heart rate, and plasma oxytocin content, but not vasopressin. Treatment with atosiban (a Gi biased agonist) inhibited restraint-evoked tachycardia without affecting blood pressure. However, this effect was no longer observed after sinoaortic denervation, homatropine (M2 muscarinic antagonist) treatment or hypophysectomy, indicating that parasympathetic activation mediated by oxytocin secreted to the periphery is responsible for blocking the increase in tachycardic responses observed in the atosiban-treated group. Corroborating this, L-368,899 (oxytocin antagonist) treatment showed an opposite effect to atosiban, increasing tachycardic responses to restraint. Thus, this provides evidence that oxytocin secreted to the periphery attenuates tachycardic responses evoked by restraint via increased parasympathetic activity, promoting cardioprotection by reducing the stress-evoked heart rate increase.

The AT-1 Angiotensin Receptor is Involved in the Autonomic and Neuroendocrine Responses to Acute Restraint Stress in Male Rats

The renin-angiotensin system (RAS) is involved in cardiovascular and hydroelectrolytic control, being associated with the development of hypertension. The restraint stress (RS) model is an aversive situation, which promotes a sustained increase in blood pressure and heart rate, and stimulation of the hypothalamic-pituitary-adrenal axis. Stress leads to an increase of angiotensin-II contents both in the circulation and the central nervous system (CNS), as well as an increased expression of AT-1 receptors in CNS structures related to stress. Stressful stimuli are associated with the modulation of autonomic nervous system, as well as baroreflex; changes in this adjustment mechanism are related to cardiovascular diseases. We hypothesized that RAS is involved in the modulation of autonomic, neuroendocrine, and functional RS-caused alterations. The intravenous (i.v) pretreatment of rats with lisinopril, an angiotensin-converting-enzyme inhibitor, reduced the RS-evoked pressor response. The doses of 0.1 and 0.3 mg/kg also reduced the RS-evoked tachycardia, while in the dose of 1 mg/kg of lisinopril potentiated the tachycardic one. Additionally, i.v. pretreatment with losartan, a selective AT-1 receptor antagonist, reduced the pressor and the tachycardic responses caused by RS. Pretreatment with lisinopril 0.3 mg/kg increased the power of the low frequency (LF) band of the systolic BP spectrum after the treatment without affecting this parameter during RS. The pretreatment with losartan 1 mg/kg increased the power of the high frequency (HF) band and reduced the LF (n.u.) and the LF/HF ratio of the pulse interval spectrum in the first hour of RS. Concerning baroreflex sensitiveness (SBR), pretreatments with losartan or lisinopril did not affect the gain of the baroreflex sequences. However, the pretreatment with losartan reduced the baroreflex effectiveness index of the total sequences in the third hour of the RS. These results indicate that Ang-II, via the AT-1 receptor, plays a facilitating influence on the cardiovascular response caused by RS; facilitates sympathetic activation and reduces parasympathetic activity related to RS; facilitates the baroreflex activation during RS and favors corticosterone release under this stress model. The impairment of Ang-II synthesis, as well as the blockade of AT-1 receptors, may constitute an important pharmacological strategy to treat cardiovascular consequences caused by stress.

Chronic ethanol vapor exposure potentiates cardiovascular responses to acute stress in male but not in female rats

BACKGROUND

Ethanol use is related to a wide variety of negative health outcomes, including cardiovascular diseases. Stress is also involved in numerous pathologies, such as cardiovascular diseases and psychiatric disorders. Sexual dimorphism is an important factor affecting cardiovascular response and has been proposed as a potential risk factor for sex-specific health problems in humans. Here, we evaluated the effect of prolonged ethanol vapor inhalation on arterial pressure, heart rate, and tail skin temperature responses to acute restraint stress, investigating differences between male and female rats.

METHODS

We exposed male and female Long-Evans rats to ethanol vapor for 14 h, followed by ethanol withdrawal for 10 h, for 30 consecutive days, or to room air (control groups). The animals underwent surgical implantation of a cannula into the femoral artery for assessment of arterial pressure and heart rate values. The tail skin temperature was measured as an indirect measurement of sympathetic vasomotor response.

RESULTS

Chronic ethanol vapor inhalation reduced basal heart rate in both female and male rats. Sex-related difference was observed in the decrease of tail cutaneous temperature evoked by stress, but not in the pressor and tachycardiac responses. Furthermore, prolonged ethanol inhalation enhanced the blood pressure and heart rate increase caused by acute restraint stress in male, but not in female rats. However, no effect of chronic ethanol vapor was observed in the tail cutaneous temperature response to restraint in either sex.

CONCLUSION

Chronic ethanol vapor exposure increased the cardiovascular reactivity to stress in male, but not in female rats.

Bed nucleus of the stria terminalis modulates baroreflex cardiac activity: an interaction between alpha-1 receptors and NMDA/nitric oxide pathway

The bed nucleus of the stria terminalis (BNST) is a forebrain structure, involved in the modulation of neuroendocrine, cardiovascular and autonomic responses. One of the responses is baroreflex activity, which consists in a neural mechanism responsible for keeping the blood pressure within a narrow range of variation. It has been reported that blockade of BNST α1-adrenoceptors increased the bradycardic component of baroreflex. In addition, such receptors are able to modulate glutamate release in this structure. Interestingly, BNST NMDA receptor antagonism and neuronal nitric oxide synthase (nNOS) inhibition led to the same effect of the α1-adrenoceptors blockade on baroreflex bradycardic response. Therefore, the hypothesis of the present study is that BNST noradrenergic transmission interacts with NMDA/NO pathway through α1 adrenoceptors to modulate the baroreflex activity. Male Wistar rats had stainless steel guide cannulas bilaterally implanted in the BNST. Subsequently, a catheter was inserted into the femoral artery for cardiovascular recordings, and into the femoral vein for assessing baroreflex activation. Injection of the noradrenaline reuptake inhibitor reboxetine in the BNST did not modify the tachycardic, but significantly decreased the bradycardic component of baroreflex. Administration of an α1, but not an α2 antagonist into the BNST prior to reboxetine prevented this effect. Likewise, previous injection of NMDA/NO pathway blockers inhibited the effect of reboxetine on bradycardic response. In conclusion, it was demonstrated for the first time the existence of an interaction between BNST noradrenergic, glutamatergic and nitrergic neurotransmissions in the modulation of bradycardic baroreflex response.

Corticotropin-releasing factor neurotransmission in the lateral hypothalamus modulates the tachycardiac response during acute emotional stress in rats

The lateral hypothalamus (LH) is implicated in the physiological and behavioral responses during stressful events. However, the local neurochemical mechanisms related to control of stress responses by this hypothalamic area are not completely understood. Therefore, in this study we evaluated the involvement of CRFergic neurotransmission acting through the CRF₁ receptor within the LH in cardiovascular responses evoked by an acute session of restraint stress in rats. For this, we investigated the effect of bilateral microinjection of different doses (0.01, 0.1 and 1 nmol/100 nL) of the selective CRF₁ receptor antagonist CP376395 into the LH on arterial pressure and heart rate increases and decrease in tail skin temperature evoked by acute restraint stress. We found that all doses of the CRF₁ receptor antagonist microinjected into the LH decreased the restraint-evoked tachycardia, but without affecting the arterial pressure and tail skin temperature responses. Additionally, treatment of the LH with CP376395 at the doses of 0.1 and 1 nmol/100 nL increased the basal values of both heart rate and arterial pressure, whereas the dose of 0.1 nmol/100 nL decreased the skin temperature. Taken together, these findings indicate that CRFergic neurotransmission in the LH, acting through activation of local CRF₁ receptors, plays a facilitatory role in the tachycardia observed during aversive threats, but without affecting the pressor and tail skin temperature responses. Our results also provide evidence that LH CRFergic neurotransmission in involved in tonic maintenance of cardiovascular function.

Hyper-reactivity of HPA axis in Fischer 344 rats is associated with impaired cardiovascular and behavioral adaptation to repeated restraint stress

Fischer 344 (F344) rats are characterized by the hyper-reactive hypothalamic-pituitary-adrenal axis to stressful stimuli, while Lewis (LEW) rats are considered to be hypo-reactive. We studied stress-induced cardiovascular, neuroendocrine, and behavioral responses of adult male F344 and LEW rats subjected to the single (120 min) or the repeated restraint stress (daily 120 min for 1 week). Mean arterial pressure (MAP) and heart rate (HR) were measured in the restrained rats (n = 7-8 for each group) via a catheter inserted into the femoral artery. Baroreceptor sensitivity was evaluated using NO donor sodium nitroprusside and α₁-adrenoceptor agonist phenylephrine. The plasma levels of adrenocorticotropic hormone (ACTH), corticosterone, aldosterone, and adrenaline were determined before and during the restraint. Exploratory behavior was tested in open field test. F344 rats exerted the augmented stress-induced increase in plasma ACTH, corticosterone, and adrenaline as well as the impaired endocrine adaptation to the repeated stress compared to LEW rats. F344 rats exhibited higher MAP than LEW rats during single and repeated restraint. Moreover, repeatedly restrained F344 showed elevated HR and diminished baroreflex sensitivity. F344 and LEW rats exhibited similar total locomotor activity and the time spent in the center of open field arena, both parameters being decreased by the repeated restraint. The detailed analysis revealed altered pattern of locomotor behavior in F344 rats subjected to repeated restraint. In conclusion, F344 rats showed the impaired endocrine adaptation that resulted in allostatic overload, which might contribute to the impaired cardiovascular and behavioral adaptation to chronic stress observed in this strain. Lay summary F344 rats, characterized by HPA axis hyper-reactivity, exhibited higher blood pressure during restraint than LEW rats. Moreover, repeatedly restrained F344 rats showed elevated heart rate and impaired baroreflex sensitivity. It can be concluded that a poor adaptation to the repeated stress in F344 rats is not only limited to the neuroendocrine response but also has important cardiovascular consequences.

Acute restraint stress increases blood pressure and oxidative stress in the cardiorenal system of rats: a role for AT1 receptors

We evaluate whether acute restraint stress may affect the oxidative state of the cardiorenal system and the possible contribution of angiotensin II/AT₁ receptors in such response. Male Wistar rats were restrained for 60 min within wire mesh chambers. Some rats were treated with losartan (selective AT₁ receptor antagonist, 10 mg/kg, p.o., gavage) 30 min before being stressed. Biochemical analyses were conducted after the 60-min period of restraint. Treatment with losartan prevented the increase in mean arterial pressure (MAP), but not heart rate (HR) induced by acute stress. Phenylephrine-induced contraction of endothelium-intact aortas was not affected by acute stress. Losartan prevented the increase in both superoxide anion (O₂^•-) and hydrogen peroxide (H₂O₂) levels induced by acute stress in the aorta and renal cortex. Similarly, the augmented activity of superoxide dismutase (SOD) induced by acute stress in the aorta and renal cortex was prevented by losartan. Enhanced levels of O₂^•- and thiobarbituric acid reactive species (TBARS) were detected in the left ventricle (LV) of stressed rats, but losartan did not prevent these responses. Similarly, losartan did not inhibited stress-induced decrease in the concentration of nitrate/nitrite (NOx) and H₂O₂ in the left ventricle. Stress increased ROS generation and affected the enzymatic antioxidant system in the cardiorenal system. In addition to its well-known cardiovascular changes during acute stress, angiotensin II also induces ROS generation in the cardiorenal system in a tissue-specific manner. The increase in oxidative stress mediated by angiotensin II/AT₁ receptors could be one mechanism by which acute stress predisposes to cardiorenal dysfunctions.

Effect of chronic stress on cardiovascular and ventilatory responses activated by both chemoreflex and baroreflex in rats

Chronic stress results in physiological and somatic changes. It has been recognized as a risk factor for several types of cardiovascular dysfunction and changes in autonomic mechanisms, such as baroreflex and chemoreflex activity. However, the effects of different types of chronic stress on these mechanisms are still poorly understood. Therefore, in the present study, we investigated, in adult male rats, the effect of repeated restraint stress (RRS) or chronic variable stress (CVS) on baroreflex, chemoreflex and heart rate variability in a protocol of 14 days of stress sessions. Exposure to RRS and CVS indicated no changes in the basal level of either arterial pressure or heart rate. However, RRS and CVS were able to attenuate sympathovagal modulation and spontaneous baroreflex gain. Additionally, only RRS was able to increase the power of the low-frequency band of the systolic blood pressure spectrum, as well as the slope of linear regression of baroreflex bradycardic and tachycardic responses induced by vasoactive compounds. Additionally, our study is one of the first to show that exposure to RRS and CVS decreases the magnitude of the pressor response and potentiates respiratory responses to chemoreflex activation, which can trigger cardiovascular and respiratory pathologies. Furthermore, the basal respiratory parameters, such as minute ventilation and tidal volume, were significantly decreased by both protocols of chronic stress. However, only CVS increased the basal respiratory frequency. In this way, the findings of the present study demonstrate the impact of chronic stress in terms of not only depressive-like behavior but also alterations of the autonomic baroreflex responses and cardiocirculatory variability (systolic blood pressure and pulse interval).Our results provide evidence that chronic stress promotes autonomic dysregulation, and impairment of baroreflex, chemoreflex and heart rate variability.

Differential roles of hippocampal nNOS and iNOS in the control of baroreflex function in conscious rats

The baroreflex is a prominent moment-to-moment mechanism regulating the blood pressure. The hippocampus is a limbic structure in which has been pointed out as part of central network regulating baroreflex. However, the local neurochemical mechanisms involved in control of baroreflex function are not completely understood. Thus, this study aimed to investigate the involvement of nitrergic neurotransmission present in the dorsal hippocampus in baroreflex control of heart rate in conscious rats. For this, we evaluated the effect of bilateral microinjection into the dorsal hippocampus of either the nitric oxide (NO) scavenger carboxy-PTIO, the selective neuronal nitric oxide synthase (nNOS) inhibitor Nω-Propyl-l-arginine (NPLA) or the selective inducible nitric oxide synthase (iNOS) inhibitor 1400 W in bradycardia evoked by blood pressure increases in response to intravenous infusion of phenylephrine, and tachycardia caused by blood pressure decreases evoked by intravenous infusion of sodium nitroprusside. Bilateral microinjection of carboxy-PTIO into the dorsal hippocampus decreased the baroreflex tachycardic response without affecting the reflex bradycardia. Hippocampus treatment with NPLA increased the baroreflex bradycardia gain without affecting the reflex tachycardia. Bilateral hippocampal treatment with 1400 W decreased the reflex tachycardia and increased the baroreflex bradycardic response. Overall, these findings provide evidence that hippocampal nitrergic mechanisms acting in a NOS isoform-specific manner plays a prominent role in control of baroreflex function. Indeed, the results indicate that nNOS and iNOS exerts an inhibitory influence on reflex bradycardia, whereas iNOS mediates the reflex tachycardia.

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.

Medial prefrontal cortex TRPV1 and CB1 receptors modulate cardiac baroreflex activity by regulating the NMDA receptor/nitric oxide pathway

The ventral medial prefrontal cortex (vMPFC) facilitates the cardiac baroreflex response through N-methyl-D-aspartate (NMDA) receptor activation and nitric oxide (NO) formation by neuronal NO synthase (nNOS) and soluble guanylate cyclase (sGC) triggering. Glutamatergic transmission is modulated by the cannabinoid receptor type 1 (CB₁) and transient receptor potential vanilloid type 1 (TRPV₁) receptors, which may inhibit or stimulate glutamate release in the brain, respectively. Interestingly, vMPFC CB₁ receptors decrease cardiac baroreflex responses, while TRPV₁ channels facilitate them. Therefore, the hypothesis of the present study is that the vMPFC NMDA/NO pathway is regulated by both CB₁ and TRPV₁ receptors in the modulation of cardiac baroreflex activity. In order to test this assumption, we used male Wistar rats that had stainless steel guide cannulae bilaterally implanted in the vMPFC. Subsequently, a catheter was inserted into the femoral artery, for cardiovascular recordings, and into the femoral vein for assessing baroreflex activation. The increase in tachycardic and bradycardic responses observed after the microinjection of a CB₁ receptors antagonist into the vMPFC was prevented by an NMDA antagonist as well as by the nNOS and sGC inhibition. NO extracellular scavenging also abolished these responses. These same pharmacological manipulations inhibited cardiac reflex enhancement induced by TRPV₁ agonist injection into the area. Based on these results, we conclude that vMPFC CB₁ and TRPV₁ receptors inhibit or facilitate the cardiac baroreflex activity by stimulating or blocking the NMDA activation and NO synthesis.

Control of cardiovascular responses to stress by CRF in the bed nucleus of stria terminalis is mediated by local NMDA/nNOS/sGC/PKG signaling

The aims of the present study were to assess an interaction of corticotropin-releasing factor (CRF) neurotransmission within the bed nucleus of the stria terminalis (BNST) with local nitrergic signaling, as well as to investigate an involvement of activation of local NMDA glutamate receptor and nitric oxide (NO) signaling in control of cardiovascular responses to acute restraint stress by BNST CRF neurotransmission in rats. We observed that CRF microinjection into the BNST increased local NO release during restraint stress. Furthermore, bilateral microinjection of CRF into the BNST enhanced both the arterial pressure and heart rate increases evoked by restraint stress, but without affecting the sympathetically-mediated cutaneous vasoconstriction. The facilitation of both pressor and tachycardiac responses to restraint stress evoked by BNST treatment with CRF were completely inhibited by local pretreatment with either the selective NMDA glutamate receptor antagonist LY235959, the selective neuronal nitric oxide synthase (nNOS) inhibitor Nω-Propyl-l-arginine (NPLA), the soluble guanylate cyclase (sGC) inhibitor 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) or the protein kinase G (PKG) inhibitor KT5823. Taken together, these results provide evidence that BNST CRF neurotransmission facilitates local NMDA-mediated glutamatergic neurotransmission and activates nitrergic signaling, and this pathway is involved in control of cardiovascular responses to stress.

Nitric oxide-cGMP-PKG signaling in the bed nucleus of the stria terminalis modulates the cardiovascular responses to stress in male rats

The bed nucleus of the stria terminalis (BNST) constitutes an important component of neural substrates of physiological and behavioral responses to aversive stimuli, and it has been implicated on cardiovascular responses evoked by stress. Nevertheless, the local neurochemical mechanisms involved in BNST control of cardiovascular responses during aversive threats are still poorly understood. Thus, the aim of the present study was to assess the involvement of activation in the BNST of the neuronal isoform of the enzyme nitric oxide synthase (nNOS), as well as of signaling mechanisms related to nitric oxide effects such as soluble guanylate cyclase (sGC) and protein kinase G (PKG) on cardiovascular responses induced by an acute session of restraint stress in male rats. We observed that bilateral microinjection of either the nonselective NOS inhibitor Nω-Nitro-L-arginine methyl ester (L-NAME), the selective nNOS inhibitor Nω-Propyl-L-arginine (NPLA) or the sGC inhibitor 1H-[1,2,4]Oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) into the BNST enhanced the tachycardic response and decreased the drop in tail cutaneous temperature evoked by acute restraint stress, but without affecting the increase on blood pressure. Bilateral BNST treatment with the selective PKG inhibitor KT5823 also facilitated the heart rate increase and decreased the drop in cutaneous temperature, in addition to enhancing the blood pressure increase. Taken together, these results provide evidence that NO released from nNOS and activation of sGC and PKG within the BNST play an inhibitory influence on tachycardia to stress, whereas this signaling mechanism mediates the sympathetic-mediated cutaneous vasoconstriction.

Prelimbic cortex GABAA receptors are involved in the mediation of restraint stress-evoked cardiovascular responses

Stress is a response of the organism to homeostasis-threatening stimuli and is coordinated by two main neural systems: the hypothalamic-pituitary-adrenal and the autonomic nervous system. Acute restraint stress (RS) is a model of unavoidable stress, which is characterized by autonomic responses including an increase in mean arterial pressure (MAP) and heart rate (HR), as well as a drop in tail temperature. The prelimbic cortex (PL) has been implicated in the modulation of functional responses caused by RS. The present study aimed to evaluate the role of PL GABAergic neurotransmission in the modulation of autonomic changes induced by RS. Bilateral microinjection of the GABA_A receptor antagonist bicuculline methiodide into the PL reduced pressor and tachycardic responses evoked by RS, in a dose-dependent manner, without affecting the tail temperature drop evoked by RS. In order to investigate which peripheral autonomic effector modulated the reduction in RS-cardiovascular responses caused by the blockade of PL GABA_A receptors, rats were intravenously pretreated with either atenolol or homatropine methylbromide. The blockade of the cardiac sympathetic nervous system with atenolol blunted the reducing effect of PL treatment with bicuculline methiodide on RS-evoked pressor and tachycardic responses. The blockade of the parasympathetic nervous system with homatropine methylbromide, regardless of affecting the beginning of the tachycardic response, did not impact on the reduction of RS-evoked tachycardic and pressor responses caused by the PL treatment with bicuculline methiodide. The present results indicate that both cardiac sympathetic and parasympathetic activities are involved in the reduction of RS-evoked cardiovascular responses evidenced after the blockade of PL GABA_A receptors by bicuculline methiodide.

Ventrolateral periaqueductal grey matter neurotransmission modulates cardiac baroreflex activity

Baroreflex activity is a neural mechanism responsible for short-term adjustments in blood pressure (BP). Several supramedullary areas, which send projections to the medulla, are able to control this reflex. In this context, the ventrolateral part of the periaqueductal grey matter (vlPAG), which is a mesencephalic structure, has been suggested to regulate the cardiovascular system. However, its involvement in baroreflex control has never been addressed. Therefore, our hypothesis is that the vlPAG neurotransmission is involved in baroreflex cardiac activity. Male Wistar rats had stainless steel guide cannulae unilaterally or bilaterally implanted in the vlPAG. Afterward, a catheter was inserted into the femoral artery for BP and HR recording. A second catheter was implanted into the femoral vein for baroreflex activation. When the nonselective synaptic blocker cobalt chloride (CoCl₂ ) was unilaterally injected into the vlPAG, in either the left or the right hemisphere, it increased the tachycardic response to baroreflex activation. However, when CoCl₂ was bilaterally microinjected into the vlPAG it decreased the tachycardic response to baroreflex stimulation. This work shows that vlPAG neurotransmission is involved in modulation of the tachycardic response of the baroreflex. Moreover, we suggest that the interconnections between the vlPAG of both hemispheres are activated during baroreflex stimulation. In this way, our work helps to improve the understanding about brain-heart circuitry control, emphasizing the role of the autonomic nervous system in such modulation.

Involvement of endocannabinoid neurotransmission in the bed nucleus of stria terminalis in cardiovascular responses to acute restraint stress in rats

BACKGROUND AND PURPOSE

Endocannabinoid signalling has been reported as an important neurochemical mechanism involved in responses to stress. Previous studies provided evidence of endocannabinoid release in the bed nucleus of the stria terminalis (BNST) during aversive stimuli. Nevertheless, a possible involvement of this neurochemical mechanism in stress responses has never been evaluated. Therefore, in the present study we investigated the involvement of BNST endocannabinoid neurotransmission, acting via local CB1 receptors, in the cardiovascular responses to acute restraint stress in rats.

EXPERIMENTAL APPROACH

The selective CB1 receptor antagonist AM251 (1, 30 and 100 pmol 100 nL(-1) ) and/or the fatty acid amide hydrolase (FAAH) enzyme inhibitor URB597 (30 pmol 100 nL(-1) ) or the monoacylglycerol lipase (MAGL) enzyme inhibitor JZL184 (30 pmol 100 nL(-1) ) was microinjected into the BNST before the acute restraint stress.

KEY RESULTS

Microinjection of AM251 into the BNST enhanced the tachycardia caused by restraint stress, without affecting the increase in arterial pressure and the sympathetic-mediated cutaneous vasoconstrictor response. Conversely, the increased endogenous levels of AEA in the BNST evoked by local treatment with the FAAH enzyme inhibitor URB597 decreased restraint-evoked tachycardia. Inhibition of the hydrolysis of 2-arachidonoylglycerol (2-AG) in the BNST by local microinjection of the MAGL enzyme inhibitor JZL184 also decreased the HR response. These effects of URB597 and JZL184 were abolished by BNST pretreatment with AM251.

CONCLUSIONS AND IMPLICATIONS

These findings indicate an involvement of BNST endocannabinoid neurotransmission, acting via CB1 receptors, in cardiovascular adjustments during emotional stress, which may be mediated by the local release of either AEA or 2-AG.

Involvement of Type 1 Angiontensin II Receptor (AT1) in Cardiovascular Changes Induced by Chronic Emotional Stress: Comparison between Homotypic and Heterotypic Stressors

Consistent evidence has shown an important role of emotional stress in pathogenesis of cardiovascular diseases. Additionally, studies in animal models have demonstrated that daily exposure to different stressor (heterotypic stressor) evokes more severe changes than those resulting from repeated exposure to the same aversive stimulus (homotypic stressor), possibly due to the habituation process upon repeated exposure to the same stressor. Despite these pieces of evidence, the mechanisms involved in the stress-evoked cardiovascular dysfunction are poorly understood. Therefore, the present study investigated the involvement of angiotensin II (Ang II) acting on the type 1 Ang II receptor (AT₁) in the cardiovascular dysfunctions evoked by both homotypic and heterotypic chronic emotional stresses in rats. For this purpose, we compared the effect of the chronic treatment with the AT₁ receptor antagonist losartan (30 mg/kg/day, p.o.) on the cardiovascular and autonomic changes evoked by the heterotypic stressor chronic variable stress (CVS) and the homotypic stressor repeated restraint stress (RRS). RRS increased the sympathetic tone to the heart and decreased the cardiac parasympathetic activity, whereas CVS decreased the cardiac parasympathetic activity. Additionally, both stressors impaired the baroreflex function. Alterations in the autonomic activity and the baroreflex impairment were inhibited by losartan treatment. Additionally, CVS reduced the body weight and increased the circulating corticosterone; however, these effects were not affected by losartan. In conclusion, these findings indicate the involvement of angiotensin II/AT₁ receptors in the autonomic changes evoked by both homotypic and heterotypic chronic stressors. Moreover, the present results provide evidence that the increase in the circulating corticosterone and body weight reduction evoked by heterotypic stressors are independent of AT₁ receptors.

Effects of Panax ginseng extracts prepared at different steaming times on thermogenesis in rats

BACKGROUND

Panax ginseng (PG) has a long history of use in Asian medicine because of its multiple pharmacological activities. It has been considered that PG in a type of white ginseng may induce undesirable thermogenic effects, but not in a type of red ginseng. However, there is a lack of evidence about the correlation between ginsenoside and thermogenesis.

METHODS

We investigated the effects of PG with different ginsenoside compositions on body temperature, blood pressure, and thermogenesis-related factors in rats.

RESULTS

With increasing steaming time (0 h, 3 h, 6 h, and 9 h), the production of protopanaxadiol ginsenosides increased, whereas protopanaxatriol ginsenosides decreased in white ginseng. In both short- and long-term studies, administration of four ginseng extracts prepared at different steaming times did not induce significant changes in body temperature (skin, tail, and rectum) and blood pressure of rats compared to saline control. In addition, there were no significant differences in the molecular markers related to thermogenesis (p > 0.05), mRNA expressions of peroxisome proliferator-activated receptor-gamma coactivator-1α and uncoupling protein 1 in brown adipose tissue, as well as the serum levels of interleukin-6, inducible nitric oxide synthase, and nitrite among the treatment groups.

CONCLUSION

These observations indicate that the potential undesirable effects of PG on body temperature could not be explained by the difference in ginsenoside composition.

Emotional Stress and Cardiovascular Complications in Animal Models: A Review of the Influence of Stress Type

Emotional stress has been recognized as a modifiable risk factor for cardiovascular diseases. The impact of stress on physiological and psychological processes is determined by characteristics of the stress stimulus. For example, distinct responses are induced by acute vs. chronic aversive stimuli. Additionally, the magnitude of stress responses has been reported to be inversely related to the degree of predictability of the aversive stimulus. Therefore, the purpose of the present review was to discuss experimental research in animal models describing the influence of stressor stimulus characteristics, such as chronicity and predictability, in cardiovascular dysfunctions induced by emotional stress. Regarding chronicity, the importance of cardiovascular and autonomic adjustments during acute stress sessions and cardiovascular consequences of frequent stress response activation during repeated exposure to aversive threats (i.e., chronic stress) is discussed. Evidence of the cardiovascular and autonomic changes induced by chronic stressors involving daily exposure to the same stressor (predictable) vs. different stressors (unpredictable) is reviewed and discussed in terms of the impact of predictability in cardiovascular dysfunctions induced by stress.

Long-term moderate exercise accelerates the recovery of stress-evoked cardiovascular responses

Psychological stress is an important global health problem. It is well documented that stress increases the incidences of various cardiovascular disorders. Regular exercise is known to reduce resting blood pressure (BP) and heart rate (HR). This study was designed to clarify the effects of long-term exercise on stress-evoked cardiovascular responses and to emphasize post-stress recovery effects. Male Wistar rats underwent 8 weeks of moderate treadmill training, with cardiovascular responses, autonomic nervous system activities and local Fos reactivity changes in the cardiovascular regulation center were monitored before, during and after immobilization stress. A spectral analysis of cardiovascular parameters was used to examine autonomic nervous activities. We found that long-term exercise (i) lowered resting BP, HR and sympathetic activity, but increased resting parasympathetic activity and baroreflex sensitivity (BRS); (ii) accelerated post-stress recovery of stress-evoked cardiovascular and sympathetic responses along with increased BRS and (iii) accelerated post-stress recovery of stress-evoked neuron activations in the paraventricular nucleus, but delayed it in the nucleus of the tractus solitarius. We conclude that, in rats, long-term exercise accelerated recovery of stress-evoked cardiovascular responses differentially altering hypothalamic and medullar neuron activities.

Medial prefrontal cortex TRPV1 channels modulate the baroreflex cardiac activity in rats

BACKGROUND AND PURPOSE

The ventral portion of the medial prefrontal cortex (vMPFC) comprises the infralimbic (IL), prelimbic (PL) and dorsopenducular (DP) cortices. The IL and PL regions facilitate the baroreceptor reflex arc. This facilitatory effect on the baroreflex is thought to be mediated by vMPFC glutamatergic transmission, through NMDA receptors. The glutamatergic transmission can be modulated by other neurotransmitters, such as the endocannabinoids, which are agonists of the TRPV1 receptor. TRPV1 channels facilitate glutamatergic transmission in the brain. Thus, we hypothesized that TRPV1 receptors in the vMPFC enhance the cardiac baroreflex response.

EXPERIMENTAL APPROACH

Stainless steel guide cannulae were bilaterally implanted into the vMPFC of male Wistar rats. Afterwards, a catheter was inserted into the femoral artery, for recording MAP and HR, and into the femoral vein for assessing baroreflex activation.

KEY RESULTS

Microinjections of the TRPV1 receptor antagonists capsazepine and 6-iodo-nordihydrocapsaicin (6-IODO) into the vMPFC reduced the cardiac baroreflex activity in unanaesthetized rats. Capsaicin microinjected into the vMPFC increased the cardiac baroreflex activity in unanaesthetized rats. When an ineffective dose of the TRPV1 receptor antagonist 6-IODO was used, the capsaicin-induced increase in the cardiac baroreflex response was abolished. The higher doses of capsaicin administered into the vMPFC after the ineffective dose of 6-IODO displaced the dose-response curve of the baroreflex parameters to the right, with no alteration in the maximum effect of capsaicin.

CONCLUSIONS AND IMPLICATIONS

The results of the present study show that stimulation of the TRPV1 receptors in the vMPFC increases the cardiac baroreceptor reflex response.

The medial amygdaloid nucleus modulates the baroreflex activity in conscious rats

The medial amygdaloid nucleus (MeA) is involved in cardiovascular control. In the present study we report the effect of MeA pharmacological ablations caused by bilateral microinjections of the nonselective synaptic blocker CoCl2 on cardiac baroreflex responses in rats. MeA synaptic inhibition evoked by local bilateral microinjection of 100 nL of CoCl2 (1 mM) did not affect blood pressure or heart rate baseline, suggesting no tonic MeA influence on resting cardiovascular parameters. However, 10 min after CoCl2 microinjection into the MeA of male Wistar rats, the reflex bradycardic response evoked by intravenous infusion of phenylephrine was significantly enhanced when compared with the reflex bradycardic response observed before CoCl2. The treatment did not affect the tachycardic responses to the intravenous infusion of sodium nitroprusside (SNP). Baroreflex activity returned to control values 60 min after CoCl2 microinjections, confirming a reversible blockade. The present results indicate an involvement of the MeA in baroreflex modulation, suggesting that synapses in the MeA have an inhibitory influence on the bradycardic component of the baroreflex in conscious rats.

CRF1 and CRF2 receptors in the bed nucleus of the stria terminalis modulate the cardiovascular responses to acute restraint stress in rats

The corticotropin-releasing factor (CRF) is involved in behavioral and physiological responses to emotional stress through its action in several limbic structures, including the bed nucleus of the stria terminalis (BNST). Nevertheless, the role of CRF1 and CRF2 receptors in the BNST in cardiovascular adjustments during aversive threat is unknown. Therefore, in the present study we investigated the involvement of CRF receptors within the BNST in cardiovascular responses evoked by acute restraint stress in rats. For this, we evaluated the effects of bilateral treatment of the BNST with selective agonists and antagonists of either CRF1 or CRF2 receptors in the arterial pressure and heart rate increase and the decrease in tail skin temperature induced by restraint stress. Microinjection of the selective CRF1 receptor antagonist CP376395 into the BNST reduced the pressor and tachycardiac responses caused by restraint. Conversely, BNST treatment with the selective CRF1 receptor agonist CRF increased restraint-evoked arterial pressure and HR responses and reduced the fall in tail skin temperature response. All effects of CRF were inhibited by local BNST pretreatment with CP376395. The selective CRF2 receptor antagonist antisalvagine-30 reduced the arterial pressure increase and the fall in tail skin temperature. The selective CRF2 receptor agonist urocortin-3 increased restraint-evoked pressor and tachycardiac responses and reduced the drop in cutaneous temperature. All effects of urocortin-3 were abolished by local BNST pretreatment with antisalvagine-30. These findings indicate an involvement of both CRF1 and CRF2 receptors in the BNST in cardiovascular adjustments during emotional stress.

Acute restraint stress induces endothelial dysfunction: role of vasoconstrictor prostanoids and oxidative stress

We hypothesized that acute stress would induce endothelial dysfunction. Male Wistar rats were restrained for 2 h within wire mesh. Functional and biochemical analyses were conducted 24 h after the 2-h period of restraint. Stressed rats showed decreased exploration on the open arms of an elevated-plus maze (EPM) and increased plasma corticosterone concentration. Acute restraint stress did not alter systolic blood pressure, whereas it increased the in vitro contractile response to phenylephrine and serotonin in endothelium-intact rat aortas. NG-nitro-l-arginine methyl ester (l-NAME; nitric oxide synthase, NOS, inhibitor) did not alter the contraction induced by phenylephrine in aortic rings from stressed rats. Tiron, indomethacin and SQ29548 reversed the increase in the contractile response to phenylephrine induced by restraint stress. Increased systemic and vascular oxidative stress was evident in stressed rats. Restraint stress decreased plasma and vascular nitrate/nitrite (NOx) concentration and increased aortic expression of inducible (i) NOS, but not endothelial (e) NOS. Reduced expression of cyclooxygenase (COX)-1, but not COX-2, was observed in aortas from stressed rats. Restraint stress increased thromboxane (TX)B(2) (stable TXA(2) metabolite) concentration but did not affect prostaglandin (PG)F2α concentration in the aorta. Restraint reduced superoxide dismutase (SOD) activity, whereas concentrations of hydrogen peroxide (H(2)O(2)) and reduced glutathione (GSH) were not affected. The major new finding of our study is that restraint stress increases vascular contraction by an endothelium-dependent mechanism that involves increased oxidative stress and the generation of COX-derived vasoconstrictor prostanoids. Such stress-induced endothelial dysfunction could predispose to the development of cardiovascular diseases.

Role of the autonomic nervous system and baroreflex in stress-evoked cardiovascular responses in rats

Restraint stress (RS) is an experimental model to study stress-related cardiovascular responses, characterized by sustained pressor and tachycardiac responses. We used pharmacologic and surgical procedures to investigate the role played by sympathetic nervous system (SNS) and parasympathetic nervous system (PSNS) in the mediation of stress-evoked cardiovascular responses. Ganglionic blockade with pentolinium significantly reduced RS-evoked pressor and tachycardiac responses. Intravenous treatment with homatropine methyl bromide did not affect the pressor response but increased tachycardia. Pretreatment with prazosin reduced the pressor and increased the tachycardiac response. Pretreatment with atenolol did not affect the pressor response but reduced tachycardia. The combined treatment with atenolol and prazosin reduced both pressor and tachycardiac responses. Adrenal demedullation reduced the pressor response without affecting tachycardia. Sinoaortic denervation increased pressor and tachycardiac responses. The results indicate that: (1) the RS-evoked cardiovascular response is mediated by the autonomic nervous system without an important involvement of humoral factors; (2) hypertension results primarily from sympathovascular and sympathoadrenal activation, without a significant involvement of the cardiac sympathetic component (CSNS); (3) the abrupt initial peak in the hypertensive response to restraint is sympathovascular-mediated, whereas the less intense but sustained hypertensive response observed throughout the remaining restraint session is mainly mediated by sympathoadrenal activation and epinephrine release; (4) tachycardia results from CSNS activation, and not from PSNS inhibition; (5) RS evokes simultaneous CSNS and PSNS activation, and heart rate changes are a vector of both influences; (6) the baroreflex is functional during restraint, and modulates both the vascular and cardiac responses to restraint.

Both α1- and α2-adrenoceptors in the insular cortex are involved in the cardiovascular responses to acute restraint stress in rats

The insular cortex (IC) is a limbic structure involved in cardiovascular responses observed during aversive threats. However, the specific neurotransmitter mediating IC control of cardiovascular adjustments to stress is yet unknown. Therefore, in the present study we investigated the role of local IC adrenoceptors in the cardiovascular responses elicited by acute restraint stress in rats. Bilateral microinjection of different doses (0.3, 5, 10 and 15 nmol/100 nl) of the selective α1-adrenoceptor antagonist WB4101 into the IC reduced both the arterial pressure and heart rate increases elicited by restraint stress. However, local IC treatment with different doses (0.3, 5, 10 and 15 nmol/100 nl) of the selective α2-adrenoceptor antagonist RX821002 reduced restraint-evoked tachycardia without affecting the pressor response. The present findings are the first direct evidence showing the involvement of IC adrenoceptors in cardiovascular adjustments observed during aversive threats. Our findings indicate that IC noradrenergic neurotransmission acting through activation of both α1- and α2-adrenoceptors has a facilitatory influence on pressor response to acute restraint stress. Moreover, IC α1-adrenoceptors also play a facilitatory role on restraint-evoked tachycardiac response.

Cannabidiol administration into the bed nucleus of the stria terminalis alters cardiovascular responses induced by acute restraint stress through 5-HT₁A receptor

Systemic administration of cannabidiol (CBD) is able to attenuate cardiovascular responses to acute restraint stress through activation of 5-HT1A receptors. Previous results from our group suggest that the bed nucleus of the stria terminalis (BNST) is involved in the antiaversive effects of the CBD. Moreover, it has been proposed that synapses within the BNST influence restraint-evoked cardiovascular changes, in particular by an inhibitory influence on the tachycardiac response associated to restraint stress. Thus, the present work investigated the effects of CBD injected into the BNST on cardiovascular changes induced by acute restraint stress and if these effects would involve the local activation of 5-HT1A receptors. The exposition to restraint stress increased both blood pressure and heart rate (HR). The microinjection of CBD (30 and 60 nmol) into the BNST enhanced the restraint-evoked HR increase, in a dose-dependent manner, without affecting the pressor response. The selective 5-HT1A receptor antagonist WAY100635 by itself did not change the cardiovascular responses to restraint stress, but blocked the effects of CBD. These results showed that CBD microinjected into the BNST enhanced the HR increase associated with acute restraint stress without affecting the blood pressure response. Although these results are not in agreement with those observed after systemic administration of CBD, they are similar to effects observed after reversible inactivation of the BNST. Moreover, similar to the effects observed after systemic administration, CBD effects in the BNST seem to depend on activation of 5-HT1A receptors.

Influence of the single or combined administration of cocaine and testosterone in autonomic and neuroendocrine responses to acute restraint stress

Abuse of cocaine and androgenic-anabolic steroids (AASs) has become a serious public health problem. Despite reports of an increase in the incidence of simultaneous abuse of these substances, potential toxic interactions between cocaine and AASs are poorly known. In the present study, we investigated the effects of either single or combined administration of testosterone and cocaine for one or 10 consecutive days on autonomic (arterial pressure, heart rate and tail cutaneous temperature) and neuroendocrine (plasma corticosterone) responses induced by acute restraint stress in rats. Combined administration of testosterone and cocaine for 10 days reduced the increase in heart rate and plasma corticosterone level, as well as the fall in tail skin temperature induced by restraint stress. Furthermore, repeated administration of cocaine inhibited the increase in arterial pressure observed during restraint, and this effect was not affected by coadministration of testosterone. Ten-day combined administration of testosterone and cocaine increased basal values of arterial pressure. Moreover, chronic administration of testosterone induced rest bradycardia and elevated basal level of plasma corticosterone. One-day single or combined administration of the drugs did not affect any parameter investigated. In conclusion, the present study demonstrated that combined administration of testosterone and cocaine changed the autonomic and neuroendocrine responses to acute restraint stress. These findings suggest that interaction between AASs and cocaine may affect the ability to cope with stressful events.