Both alpha1 and alpha2-adrenoceptors mediate the cardiovascular responses to noradrenaline microinjected into the bed nucleus of the stria terminal of rats

Both Prelimbic and Infralimbic Noradrenergic Neurotransmissions Modulate Cardiovascular Responses to Restraint Stress in Rats

The prelimbic (PL) and infralimbic (IL) subareas of the medial prefrontal cortex (mPFC) have been implicated in physiological and behavioral responses during aversive threats. The previous studies reported the noradrenaline release within the mPFC during stressful events, and the lesions of catecholaminergic terminals in this cortical structure affected stress-evoked local neuronal activation. Nevertheless, the role of mPFC adrenoceptors on cardiovascular responses during emotional stress is unknown. Thus, we investigated the role of adrenoceptors present within the PL and IL on the increase in both arterial pressure and heart rate (HR) and on the sympathetically mediated cutaneous vasoconstriction evoked by acute restraint stress. For this, bilateral guide cannulas were implanted into either the PL or IL of male rats. All animals were also subjected to catheter implantation into the femoral artery for cardiovascular recording. The increase in both arterial pressure and HR and the decrease in the tail skin temperature as an indirect measurement of sympathetically mediated cutaneous vasoconstriction were recorded during the restraint session. We observed that the microinjection of the selective α₂-adrenoceptor antagonist RX821002 into either the PL or IL decreased the pressor response during restraint stress. Treatment of the PL or IL with either the α₁-adrenoceptor antagonist WB4101 or the α₂-adrenoceptor antagonist reduced the restraint-evoked tachycardia. The drop in the tail skin temperature was decreased by PL treatment with the β-adrenoceptor antagonist propranolol and with the α₁- or α₂-adrenoceptor antagonists. The α₂-adrenoceptor antagonist into the IL also decreased the skin temperature response. Our results suggest that the noradrenergic neurotransmission in both PL and IL mediates the cardiovascular responses to aversive threats.

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.

Interaction of GABA and norepinephrine in the lateral division of the bed nucleus of the stria terminals in anesthetized rat, correlating single-unit and cardiovascular responses

The bed nucleus of the stria terminalis (BST) consists of multiple anatomically distinct nuclei. The lateral division, which receives dense noradrenergic innervation, has been implicated in cardiovascular regulation and modulation of responses to stress. This study is performed to identify the cardiovascular and single-unit responses of the lateral BST to norepinephrine (NE), involved adrenoceptors, and possible interaction with GABAergic system of the BST in urethane-anesthetized rats. NE, adrenoreceptor antagonists, and GABA_A antagonist were microinjected into the lateral division of BST, while arterial pressure (AP), heart rate (HR), and single-unit responses were simultaneously recorded. NE microinjected into the lateral division of BST produced depressor and bradycardic responses. The decrease in AP and HR to NE was blocked by prazosin, an α₁-adrenoreceptor antagonist, but not by yohimbine, an α₂ antagonist. Furthermore, injections of the GABA_A receptor antagonist, bicuculline methiodide (BMI), into the lateral BST abolished the NE-induced depressor and bradycardic responses. We also observed single-unit responses consisting of excitatory and inhibitory responses correlated with cardiovascular function to the microinjection of NE. In conclusion, these data provide the first evidence that microinjection of NE in the lateral division of BST produces depressor and bradycardic responses in urethane-anesthetized rat. The depressor and bradycardiac response are mediated by local α₁- but not α₂-adrenoceptors. α₁-AR activates the GABAergic system within the BST, which in turn produces depressor and bradycardic responses.

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.

Noradrenergic neurotransmission within the bed nucleus of the stria terminalis modulates the retention of immobility in the rat forced swimming test

The bed nucleus of the stria terminalis (BNST) is a limbic structure that has a direct influence on the autonomic, neuroendocrine, and behavioral responses to stress. It was recently reported that reversible inactivation of synaptic transmission within this structure causes antidepressant-like effects, indicating that activation of the BNST during stressful situations would facilitate the development of behavioral changes related to the neurobiology of depression. Moreover, noradrenergic neurotransmission is abundant in the BNST and has an important role in the regulation of emotional processes related to the stress response. Thus, this study aimed to test the hypothesis that activation of adrenoceptors within the BNST facilitates the development of behavioral consequences of stress. To investigate this hypothesis, male Wistar rats were stressed (forced swimming, 15 min) and 24 h later received intra-BNST injections of vehicle, WB4101, RX821002, CGP20712, or ICI118,551, which are selective α(1), α(2), β(1), and β(2) adrenoceptor antagonists, respectively, 10 min before a 5-min forced swimming test. It was observed that administration of WB4101 (10 and 15 nmol), CGP20712 (5 and 10 nmol), or ICI118,551 (5 nmol) into the BNST reduced the immobility time of rats subjected to forced swimming test, indicating an antidepressant-like effect. These findings suggest that activation of α(1), β(1), and β(2) adrenoceptors in the BNST could be involved in the development of the behavioral consequences of stress.

Effects of hypocretin and norepinephrine interaction in bed nucleus of the stria terminalis on arterial pressure

Forebrain neuronal circuits containing hypocretin-1 (hcrt-1) and norepinephrine (NE) are important components of central arousal-related processes. Recently, these two systems have been shown to have an overlapping distribution within the bed nucleus of the stria terminalis (BST), a limbic structure activated by stressful challenges, and which functions to adjust arterial pressure (AP) and heart rate (HR) to the stressor. However, whether hcrt-1 and NE interact in BST to alter cardiovascular function is unknown. Experiments were done in urethane-α-chloralose anesthetized, paralyzed, and artificially ventilated male Wistar rats to investigate the effect of hcrt-1 and NE on the cardiovascular responses elicited by l-glutamate (Glu) stimulation of BST neurons. Microinjections of hcrt-1, NE or tyramine into BST attenuated the decrease in AP and HR to Glu stimulation of BST. Additionally, combined injections of hcrt-1 with NE or tyramine did not elicit a greater attenuation than either compound alone. Furthermore, injections into BST of the α2-adrenergic receptor (α2-AR) antagonist yohimbine, but not the α1-AR antagonist 2-{[β-(4-hydroxyphenyl)ethyl]aminomethyl}-1-tetralone hydrochloride, blocked both the hcrt-1 and NE-induced inhibition of the BST cardiovascular depressors responses. Finally, injections into BST of the GABAA receptor antagonist bicuculline, but not the GABAB receptor antagonist phaclofen, blocked the hcrt-1 and NE attenuation of the BST Glu-induced depressor and bradycardia responses. These data suggest that hcrt-1 effects in BST are mediated by NE neurons, and hcrt-1 likely acts to facilitate the synaptic release of NE. NE neurons, acting through α2-AR may activate Gabaergic neurons in BST, which in turn through the activation of GABAA receptors inhibit a BST sympathoinhibitory pathway. Taken together, these data suggest that hcrt-1 pathways to BST through their interaction with NE and Gabaergic neurons may function in the coordination of cardiovascular responses associated with different behavioral states.

Facilitation of sodium intake by combining noradrenaline into the lateral parabrachial nucleus with prazosin peripherally

Injections of noradrenaline into the lateral parabrachial nucleus (LPBN) increase arterial pressure and 1.8% NaCl intake and decrease water intake in rats treated with the diuretic furosemide (FURO) combined with a low dose of the angiotensin converting enzyme inhibitor captopril (CAP). In the present study, we investigated the influence of the pressor response elicited by noradrenaline injected into the LPBN on FURO+CAP-induced water and 1.8% NaCl intake. Male Holtzman rats with bilateral stainless steel guide-cannulas implanted into LPBN were used. Bilateral injections of noradrenaline (40 nmol/0.2 μl) into the LPBN increased FURO+CAP-induced 1.8% NaCl intake (12.2±3.5, vs., saline: 4.2±0.8 ml/180 min), reduced water intake and strongly increased arterial pressure (50±7, vs. saline: 1±1 mmHg). The blockade of the α1 adrenoceptors with the prazosin injected intraperitoneally abolished the pressor response and increased 1.8% NaCl and water intake in rats treated with FURO+CAP combined with noradrenaline injected into the LPBN. The deactivation of baro and perhaps volume receptors due to the cardiovascular effects of prazosin is a mechanism that may facilitate water and NaCl intake in rats treated with FURO+CAP combined with noradrenaline injected into the LPBN. Therefore, the activation of α2 adrenoceptors with noradrenaline injected into the LPBN, at least in dose tested, may not completely remove the inhibitory signals produced by the activation of the cardiovascular receptors, particularly the signals that result from the extra activation of these receptors with the increase of arterial pressure.

Mechanisms in the bed nucleus of the stria terminalis involved in control of autonomic and neuroendocrine functions: a review

The bed nucleus of the stria terminalis (BNST) is a heterogeneous and complex limbic forebrain structure, which plays an important role in controlling autonomic, neuroendocrine and behavioral responses. The BNST is thought to serve as a key relay connecting limbic forebrain structures to hypothalamic and brainstem regions associated with autonomic and neuroendocrine functions. Its control of physiological and behavioral activity is mediated by local action of numerous neurotransmitters. In the present review we discuss the role of the BNST in control of both autonomic and neuroendocrine function. A description of BNST control of cardiovascular and hypothalamus-pituitary-adrenal axisactivity at rest and during physiological challenges (stress and physical exercise) is presented. Moreover, evidence for modulation of hypothalamic magnocellular neurons activity is also discussed. We attempt to focus on the discussion of BNST neurochemical mechanisms. Therefore, the source and targets of neurochemical inputs to BNST subregions and their role in control of autonomic and neuroendocrine function is discussed in details.

Both α1- and β1-adrenoceptors in the bed nucleus of the stria terminalis are involved in the expression of conditioned contextual fear

BACKGROUND AND PURPOSE

The bed nucleus of the stria terminalis (BNST) is a limbic structure that is involved in the expression of conditioned contextual fear. Among the numerous neural inputs to the BNST, noradrenergic synaptic terminals are prominent and some evidence suggests an activation of this noradrenergic neurotransmission in the BNST during aversive situations. Here, we have investigated the involvement of the BNST noradrenergic system in the modulation of behavioural and autonomic responses induced by conditioned contextual fear in rats.

EXPERIMENTAL APPROACH

Male Wistar rats with cannulae bilaterally implanted into the BNST were submitted to a 10 min conditioning session (6 footshocks, 1.5 ma/ 3 s). Twenty-four hours later freezing and autonomic responses (mean arterial pressure, heart rate and cutaneous temperature) to the conditioning box were measured for 10 min. The adrenoceptor antagonists were administered 10 min before the re-exposure to the aversive context.

KEY RESULTS

L-propranolol, a non-selective β-adrenoceptor antagonist, and phentolamine, a non-selective α-adrenoceptor antagonist, reduced both freezing and autonomic responses induced by aversive context. Similar results were observed with CGP20712, a selective β(1) -adrenoceptor antagonist, and WB4101, a selective α(1) -antagonist, but not with ICI118,551, a selective β(2) -adrenoceptor antagonist or RX821002, a selective α(2) -antagonist.

CONCLUSIONS AND IMPLICATIONS

These findings support the idea that noradrenergic neurotransmission in the BNST via α(1) - and β(1) -adrenoceptors is involved in the expression of conditioned contextual fear.

Hypothalamic supraoptic but not paraventricular nucleus is involved in cardiovascular responses to carbachol microinjected into the bed nucleus of stria terminalis of unanesthetized rats

Microinjection of the cholinergic agonist carbachol into the bed nucleus of the stria terminalis (BST) has been reported to cause pressor response in unanesthetized rats, which was shown to be mediated by an acute release of vasopressin into the systemic circulation and followed by baroreflex-mediated bradycardia. In the present study, we tested the possible involvement of the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei in the pressor response evoked by carbachol microinjection into the BST of unanesthetized rats. For this, cardiovascular responses following carbachol (1 nmol/100 nL) microinjection into the BST were studied before and after PVN or SON pretreatment, either ipsilateral or contralateral in relation to BST microinjection site, with the nonselective neurotransmission blocker cobalt chloride (CoCl₂, 1 mM/100 nL). Carbachol microinjection into the BST evoked pressor response. Moreover, BST treatment with carbachol significantly increased plasma vasopressin levels, thus confirming previous evidences that carbachol microinjection into the BST evokes pressor response due to vasopressin release into the circulation. SON pretreatment with CoCl₂, either ipsilateral or contralateral in relation to BST microinjection site, inhibited the pressor response to carbachol microinjection into the BST. However, CoCl₂ microinjection into the ipsilateral or contralateral PVN did not affect carbachol-evoked pressor response. In conclusion, our results suggest that pressor response to carbachol microinjection into the BST is mediated by SON magnocellular neurons, without significant involvement of those in the PVN. The results also indicate that responses to carbachol microinjection into the BST are mediated by a neural pathway that depends on the activation of both ipsilateral and contralateral SON.

Cardiovascular responses to microinjection of noradrenaline into the medial amygdaloid nucleus of conscious rats result from α₂-receptor activation and vasopressin release

The medial amygdaloid nucleus (MeA) is involved in the modulation of physiological and behavioral processes, as well as regulation of the autonomic nervous system. Moreover, MeA electrical stimulation evokes cardiovascular responses. Thus, as noradrenergic receptors are present in this structure, the present study tested the effects of local noradrenaline (NA) microinjection into the MeA on cardiovascular responses in conscious rats. Moreover, we describe the types of adrenoceptor involved and the peripheral mechanisms involved in the cardiovascular responses. Increasing doses of NA (3, 9, 27 or 45 nmol/100 nL) microinjected into the MeA of conscious rats caused dose-related pressor and bradycardic responses. The NA cardiovascular effects were abolished by local pretreatment of the MeA with 10 nmol/100 nL of the specific α₂-receptor antagonist RX821002, but were not affected by local pretreatment with 10 nmol/100 nL of the specific α₁-receptor antagonist WB4101. The magnitude of pressor response evoked by NA microinjected into the MeA was potentiated by intravenous pretreatment with the ganglion blocker pentolinium (5 mg/kg), and blocked by intravenous pretreatment with the selective V₁-vasopressin antagonist dTyr(CH₂)₅ (Me)AVP (50 μg/kg). In conclusion, our results show that microinjection of NA into the MeA of conscious rats activates local α₂-adrenoceptors, evoking pressor and bradycardic responses, which are mediated by vasopressin release.

Acute reversible inactivation of the bed nucleus of stria terminalis induces antidepressant-like effect in the rat forced swimming test

BACKGROUND

The bed nucleus of stria terminalis (BNST) is a limbic forebrain structure involved in hypothalamo-pituitary-adrenal axis regulation and stress adaptation. Inappropriate adaptation to stress is thought to compromise the organism's coping mechanisms, which have been implicated in the neurobiology of depression. However, the studies aimed at investigating BNST involvement in depression pathophysiology have yielded contradictory results. Therefore, the objective of the present study was to investigate the effects of temporary acute inactivation of synaptic transmission in the BNST by local microinjection of cobalt chloride (CoCl2) in rats subjected to the forced swimming test (FST).

METHODS

Rats implanted with cannulae aimed at the BNST were submitted to 15 min of forced swimming (pretest). Twenty-four hours later immobility time was registered in a new 5 min forced swimming session (test). Independent groups of rats received bilateral microinjections of CoCl2 (1 mM/100 nL) before or immediately after pretest or before the test session. Additional groups received the same treatment and were submitted to the open field test to control for unspecific effects on locomotor behavior.

RESULTS

CoCl2 injection into the BNST before either the pretest or test sessions reduced immobility in the FST, suggesting an antidepressant-like effect. No significant effect of CoCl2 was observed when it was injected into the BNST immediately after pretest. In addition, no effect of BNST inactivation was observed in the open field test.

CONCLUSION

These results suggest that acute reversible inactivation of synaptic transmission in the BNST facilitates adaptation to stress and induces antidepressant-like effects.

Neural regulation of endocrine and autonomic stress responses

The survival and well-being of all species requires appropriate physiological responses to environmental and homeostatic challenges. The re- establishment and maintenance of homeostasis entails the coordinated activation and control of neuroendocrine and autonomic stress systems. These collective stress responses are mediated by largely overlapping circuits in the limbic forebrain, the hypothalamus and the brainstem, so that the respective contributions of the neuroendocrine and autonomic systems are tuned in accordance with stressor modality and intensity. Limbic regions that are responsible for regulating stress responses intersect with circuits that are responsible for memory and reward, providing a means to tailor the stress response with respect to prior experience and anticipated outcomes.

Role of the bed nucleus of the stria terminalis in the cardiovascular responses to acute restraint stress in rats

The aim of this work was to test the hypothesis that the bed nucleus of the stria terminalis (BST) and noradrenergic neurotransmission therein mediate cardiovascular responses to acute restraint stress in rats. Bilateral microinjection of the non-specific synaptic blocker CoCl(2) (0.1 nmol/100 nl) into the BST enhanced the heart rate (HR) increase associated with acute restraint without affecting the blood pressure increase, indicating that synapses within the BST influence restraint-evoked HR changes. BST pretreatment with the selective alpha(1)-adrenoceptor antagonist WB4101 (15 nmol/100 nl) caused similar effects to cobalt, indicating that local noradrenergic neurotransmission mediates the BST inhibitory influence on restraint-related HR responses. BST treatment with equimolar doses of the alpha(2)-adrenoceptor antagonist RX821002 or the beta-adrenoceptor antagonist propranolol did not affect restraint-related cardiovascular responses, reinforcing the inference that alpha(1)-adrenoceptors mediate the BST-related inhibitory influence on HR responses. Microinjection of WB4101 into the BST of rats pretreated intravenously with the anticholinergic drug homatropine methyl bromide (0.2 mg/kg) did not affect restraint-related cardiovascular responses, indicating that the inhibitory influence of the BST on the restraint-evoked HR increase could be related to an increase in parasympathetic activity. Thus, our results suggest an inhibitory influence of the BST on the HR increase evoked by restraint stress, and that this is mediated by local alpha(1)-adrenoceptors. The results also indicate that such an inhibitory influence is a result of parasympathetic activation.

Mechanisms involved in the pressor response to noradrenaline microinjection into the supraoptic nucleus of unanesthetized rats

We report on the cardiovascular effects of noradrenaline (NA) microinjection into the hypothalamic supraoptic nucleus (SON) as well as the central and peripheral mechanisms involved in their mediation. Microinjections of NA 1, 3, 10, 30 or 45 nmol/100 nL into the SON caused dose-related pressor and bradycardiac response in unanesthetized rats. The response to NA 10 nmol was blocked by SON pretreatment with 15 nmol of the alpha(2)-adrenoceptor antagonist RX821002 and not affected by pretreatment with equimolar dose of the selective alpha(1)-adrenoceptor antagonist WB4101, suggesting that local alpha(2)-adrenoceptors mediate these responses. Pretreatment of the SON with the nonselective beta-adrenoceptor antagonist propranolol 15 nmol did not affect the pressor response to NA microinjection of into the SON. Moreover, the microinjection of the 100 nmol of the selective alpha(1)-adrenoceptor agonist methoxamine (MET) into the SON did not cause cardiovascular response while the microinjection of the selective alpha(2)-adrenoceptor agonists BHT920 (BHT, 100 nmol) or clonidine (CLO, 5 nmol) caused pressor and bradycardiac responses, similar to that observed after the microinjection of NA. The pressor response to NA was potentiated by intravenous pretreatment with the ganglion blocker pentolinium and was blocked by intravenous pretreatment with the V(1)-vasopressin receptor antagonist dTyr(CH2)5(Me)AVP, suggesting an involvement of circulating vasopressin in this response. In conclusion, our results suggest that pressor responses caused by microinjections of NA into the SON involve activation of local alpha(2)-adrenoceptor receptors and are mediated by vasopressin release into circulation.

Anxiolytic-like effects induced by acute reversible inactivation of the bed nucleus of stria terminalis

There is conflicting evidence concerning the role of the bed nucleus of the stria terminalis (BNST) in fear and anxiety-elicited behavior. Most of the studies investigating this role, however, employed irreversible lesions of this nucleus. The objective of the present study was to investigate the effects of an acute and reversible inactivation of the BNST in rats submitted to the Vogel conflict test (VCT) and contextual fear conditioning, two widely employed animal models that are responsive to prototypal anxiolytic drugs. Male Wistar rats were submitted to stereotaxic surgery to bilaterally implant cannulae into the BNST. Ten minutes before the test they received bilateral microinjections of cobalt chloride (CoCl(2)) (1 mM/100 nL), a nonselective synapse blocker. CoCl(2) produced anxiolytic-like effects in tests, increasing the number of punished licks in the VCT and decreasing freezing behavior and the increase in mean arterial blood pressure and heart rate of animals re-exposed to the context where they had received electrical foot shocks 24 h before. The results indicate that the BNST is engaged in behavioral responses elicited by punished stimuli and aversively conditioned contexts, reinforcing its proposed role in anxiety.