Cardiovascular effects of carbachol microinjected into the bed nucleus of the stria terminalis of the rat brain

Water Drinking Behavior Associated with Aversive Arousal in Rats: An Integrative Approach

Cholinergic muscarinic stimulation of vast areas of the limbic brain induced a well-documented polydipsia in laboratory rats. This excessive water-drinking behavior has not received any convincing biological and physiological interpretation for the last 50 years. This review offers such an interpretation and suggests that cholinergically induced drinking response, mostly by carbachol, is associated with activation of the ascending mesolimbic cholinergic system that serves for initiation of emotional aversive arousal of the organism. The ascending cholinergic system originates from the laterodorsal tegmental nucleus, has a diffuse nature, and affects numerous subcortical limbic structures. It is proposed that the carbachol-induced drinking response is related to the state of anxiety and does not serve the regulation of thirst. Instead, the response is anxiety-induced polydipsia that might occur as a soothing procedure that decreases the aversiveness of the negative emotional state induced by carbachol. It is concluded that carbachol-induced water-drinking behavior is a rewarding process that contributes to alleviating the feeling of anxiety by bringing some relief from the cholinergically induced aversive state, and it is a homologue to anxiety-driven polydipsia in humans.

Freezing revisited: coordinated autonomic and central optimization of threat coping

Animals have sophisticated mechanisms for coping with danger. Freezing is a unique state that, upon threat detection, allows evidence to be gathered, response possibilities to be previsioned and preparations to be made for worst-case fight or flight. We propose that - rather than reflecting a passive fear state - the particular somatic and cognitive characteristics of freezing help to conceal overt responses, while optimizing sensory processing and action preparation. Critical for these functions are the neurotransmitters noradrenaline and acetylcholine, which modulate neural information processing and also control the sympathetic and parasympathetic branches of the autonomic nervous system. However, the interactions between autonomic systems and the brain during freezing, and the way in which they jointly coordinate responses, remain incompletely explored. We review the joint actions of these systems and offer a novel computational framework to describe their temporally harmonized integration. This reconceptualization of freezing has implications for its role in decision-making under threat and for psychopathology.

N-Methyl-D-aspartate Glutamate Receptor Modulates Cardiovascular and Neuroendocrine Responses Evoked by Hemorrhagic Shock in Rats

Here, we report the participation of N-methyl-D-aspartate (NMDA) glutamate receptor in the mediation of cardiovascular and circulating vasopressin responses evoked by a hemorrhagic stimulus. In addition, once NMDA receptor activation is a prominent mechanism involved in nitric oxide (NO) synthesis in the brain, we investigated whether control of hemorrhagic shock by NMDA glutamate receptor was followed by changes in NO synthesis in brain supramedullary structures involved in cardiovascular and neuroendocrine control. Thus, we observed that intraperitoneal administration of the selective NMDA glutamate receptor antagonist dizocilpine maleate (MK801, 0.3 mg/kg) delayed and reduced the magnitude of hemorrhage-induced hypotension. Besides, hemorrhage induced a tachycardia response in the posthemorrhage period (i.e., recovery period) in control animals, and systemic treatment with MK801 caused a bradycardia response during hemorrhagic shock. Hemorrhagic stimulus increased plasma vasopressin levels during the recovery period and NMDA receptor antagonism increased concentration of this hormone during both the hemorrhage and postbleeding periods in relation to control animals. Moreover, hemorrhagic shock caused a decrease in NOx levels in the paraventricular nucleus of the hypothalamus (PVN), amygdala, bed nucleus of the stria terminalis (BNST), and ventral periaqueductal gray matter (vPAG). Nevertheless, treatment with MK801 did not affect these effects. Taken together, these results indicate that the NMDA glutamate receptor is involved in the hemorrhagic shock by inhibiting circulating vasopressin release. Our data also suggest a role of the NMDA receptor in tachycardia, but not in the decreased NO synthesis in the brain evoked by hemorrhage.

Muscarinic M2 receptor promotes vasopressin synthesis in mice supraoptic nuclei

Muscarinic acetylcholine receptors have been suggested to be implicated in arginine-vasopressin secretion because intracerebroventricular muscarinic agonist administration induces arginine-vasopressin release into the circulation. Although which subtype is involved in the regulation of arginine-vasopressin secretion is unclear, M₂ receptors have been reported to be highly expressed in the hypothalamus. In the present study, M₂ receptor-knockout mice were used to elucidate whether M₂ receptor regulates arginine-vasopressin synthesis in the paraventricular nuclei and supraoptic nuclei of the hypothalamus. The number of arginine-vasopressin-immunoreactive neurons in M₂ receptor-knockout mice was significantly decreased in the supraoptic nuclei, but not in the paraventricular nuclei compared with wild-type mice. Plasma arginine-vasopressin level in M₂ receptor-knockout mice was also significantly lower than in the wild-type mice. Urinary volume and frequency as well as water intake in M₂ receptor-knockout mice were significantly higher than those in wild-type mice. The V₂ vasopressin receptor expression in kidneys of M₂ receptor-knockout mice was comparable with that of wild-type mice, and increased urination in M₂ receptor-knockout mice was significantly decreased by administration of desmopressin, a specific V₂ receptor agonist, suggesting that V₂ receptors in the kidneys of M₂ receptor-knockout mice are intact. These results suggest that M₂ receptors promote arginine-vasopressin synthesis in the supraoptic nuclei and play a role in the regulation and maintenance of body fluid.

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.

Vasopressin and sympathetic system mediate the cardiovascular effects of the angiotensin II in the bed nucleus of the stria terminalis in rat

The bed nucleus of the stria terminalis (BST) is involved in cardiovascular regulation. The angiotensin II (Ang II) receptor (AT1), and angiotensinogen were found in the BST. In our previous study we found that microinjection of Ang II into the BST produced a pressor response. This study was performed to find the mechanisms mediating this response in anesthetized rats. Ang II was microinjected into the BST and the cardiovascular responses were re-tested after systemic injection of a blocker of autonomic or vasopressin V1 receptor. The ganglionic nicotinic receptor blocker, hexamethonium dichloride, attenuated the pressor response to Ang II, indicating that the cardiovascular sympathetic system is involved in the pressor effect of Ang II. A selective vasopressin V1 receptor antagonist greatly attenuated the pressor effect of Ang II, indicating that the Ang II increases the arterial pressure via stimulation of vasopressin release as well. In conclusion, in the BST, Ang II as a neurotransmitter increases blood pressure by exciting cardiovascular sympathetic system and directly or indirectly causing vasopressin to release into bloodstream by VPN. This is an interesting new finding that not only circulating Ang II but also brain Ang II makes vasopressin release.

Role of Muscarinic Acetylcholine Receptor-2 in the Cerebellar Cortex in Cardiovascular Modulation in Anaesthetized Rats

Our previous investigations have demonstrated that microinjection of acetylcholine (ACh) or muscarinic ACh receptor activation in the cerebellar cortex induces a systemic blood pressure depressor response. This study aimed to determine the role of muscarinic ACh receptor-2 (M2 receptor) in the cerebellar cortex in cardiovascular function regulation in rats. A nonselective muscarinic receptor agonist (oxotremorine M, OXO; 30 mM), a selective M2 receptor agonist (arecaidine but-2-ynyl ester tosylate, ABET; 3, 10, and 30 mM), 30 mM OXO mixed with a selective M2 receptor antagonist (methoctramine hydrate, MCT; 0.3, 1, and 3 mM), and normal saline (0.9 % NaCl) were separately microinjected (0.5 µl/5 s) into the cerebellar cortex (lobule VI) of anaesthetized rats. We measured the mean arterial pressure (MAP), maximum change in MAP, and reactive time (RT; the duration required for the blood pressure to return to basal levels), heart rate (HR) and the maximum change in HR during the RT in response to drug activation. The results demonstrated that ABET dose-dependently decreased MAP and HR, increased the maximum change in MAP and the maximum change in HR, and prolonged the RT. Furthermore, MCT dose-dependently blocked the OXO-mediated cardiovascular depressor response. This study provides the first evidence that M2 receptors in the cerebellar cortex are involved in cardiovascular regulation, the activation of which evokes significant depressor and bradycardic responses.

Cardiovascular and single-unit responses to microinjection of angiotensin II into the bed nucleus of the stria terminalis in rat

The bed nucleus of the stria terminalis (BST) is part of the limbic system located in the rostral forebrain. BST is involved in behavioral, neuroendocrine and autonomic functions, including cardiovascular regulation. The angiotensin II (Ang II) receptor, AT1, was found in the BST, however its effects on the cardiovascular system and on single-unit responses have not been studied yet. In the present study, Ang II was microinjected into the BST of anesthetized rats and cardiovascular and single-unit responses were recorded simultaneously. Furthermore the responses were re-tested after the microinjection of a blocker of the AT1 receptor, losartan, into the BST. We found that microinjection of Ang II into the BST produced a pressor response of 11±1mmHg for a duration of 2-8min. Ang II had no consistent effect on heart rate. It also produced two types of single-unit responses in the BST, short excitatory and long inhibitory. Blockade of AT1 receptors abolished both the cardiovascular and single-unit responses, indicating that the responses were mediated through AT1 receptors. These findings imply that Ang II may be utilized as a neurotransmitter and may play a role in returning blood pressure toward normal during hypotension.

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.

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.

Presynaptic muscarinic M(2) receptors modulate glutamatergic transmission in the bed nucleus of the stria terminalis

The anterolateral cell group of the bed nucleus of the stria terminalis (BNST(ALG)) serves as an important relay station in stress circuitry. Limbic inputs to the BNST(ALG) are primarily glutamatergic and activity-dependent changes in this input have been implicated in abnormal behaviors associated with chronic stress and addiction. Significantly, local infusion of acetylcholine (ACh) receptor agonists into the BNST trigger stress-like cardiovascular responses, however, little is known about the effects of these agents on glutamatergic transmission in the BNST(ALG). Here, we show that glutamate- and ACh-containing fibers are found in close association in the BNST(ALG). Moreover, in the presence of the acetylcholinesterase inhibitor, eserine, endogenous ACh release evoked a long-lasting reduction of the amplitude of stimulus-evoked EPSCs. This effect was mimicked by exogenous application of the ACh analog, carbachol, which caused a reversible, dose-dependent, reduction of the evoked EPSC amplitude, and an increase in both the paired-pulse ratio and coefficient of variation, suggesting a presynaptic site of action. Uncoupling of postsynaptic G-proteins with intracellular GDP-β-S, or application of the nicotinic receptor antagonist, tubocurarine, failed to block the carbachol effect. In contrast, the carbachol effect was blocked by prior application of atropine or M(2) receptor-preferring antagonists, and was absent in M(2)/M(4) receptor knockout mice, suggesting that presynaptic M(2) receptors mediate the effect of ACh. Immunoelectron microscopy studies further revealed the presence of M(2) receptors on axon terminals that formed asymmetric synapses with BNST neurons. Our findings suggest that presynaptic M(2) receptors might be an important modulator of the stress circuit and hence a novel target for drug development.

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.

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.

Vasopressin and sympathetic systems mediate the cardiovascular effects of the GABAergic system in the bed nucleus of the stria terminalis

The bed nucleus of the stria terminalis (BST) is an important part of the limbic system. It has been shown that chemical stimulation of the BST elicited cardiovascular depressive and bradycardic responses. It was also demonstrated that GABA is present in the BST, though its role in cardiovascular control is not yet understood. This study was performed to find the effects of GABA receptor subtypes in the BST on cardiovascular responses and to find the possible mechanisms that mediate these responses in urethane-anesthetized rats. Microinjection of muscimol (500 pmol/100 nl), a GABA(A) agonist, into the BST produced a weak unsignificant decrease in the mean arterial pressure (MAP) and heart rate (HR). Injection of bicuculline methiodide (BMI, 100 pmol/100 nl), a GABA(A) antagonist, caused a significant increase in the MAP (41.3+/-5.1 mmHg) as well as in the HR (33.2+/-5.6 beats/min). Injection of two doses (500 and 1000 pmol/100 nl) of phaclofen, a GABA(B) antagonist, produced no significant change in either MAP or HR. Administration (i.v.) of the muscarinic receptor blocker, homatropine methyl bromide had no effect on the magnitude of mean arterial pressure or heart rate responses to BMI. This suggests that the parasympathetic system is not involved in these responses. However, administration (i.v.) of the nicotinic receptor blocker, hexamethonium bromide had no effect on the magnitude of mean arterial pressure response but abolished heart rate response to BMI. This suggests that the sympathetic system is involved in the bradycardic effect of GABA. On the other hand, administration (i.v.) of a selective vasopressin V(1) receptor antagonist abolished the pressor effect of BMI, which indicates that the GABAergic system of the BST decreases the arterial pressure via tonic inhibition of vasopressin release. In summary, we demonstrated, for the first time, that GABA exerts its influence in the BST through the activation of GABA(A), but not GABA(B), receptors that, in turn, tonically inhibit vasopressin release and sympathetic outflow to the heart.

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.

Increased circulating vasopressin may account for ethanol-induced hypertension in rats

BACKGROUND

Long-term ethanol intake has been reported to evoke both hypertension and increase of systemic vasopressin levels in rats.

METHODS

In this work, we investigated the involvement of systemic vasopressin in the hypertension evoked in rats by long-term ethanol (20% vol/vol) intake for 2 weeks, by systemic treatment with the V1-vasopressin receptor antagonist dTyr(CH2)5(Me)AVP (50 microg/kg). Moreover, plasma arginine-vasopressin (AVP) content was quantified using an AVP radioimmunoassay and the expression of vasopressin mRNA in the supraoptic (SON) and paraventricular (PVN) nuclei was measured using real-time PCR.

RESULTS

Mild hypertension was observed after 2 weeks of ethanol treatment when compared with control animals. Moreover, an increase in both the expression of vasopressin mRNA and the vasopressin blood content was observed in ethanol-treated rats in comparison to the control group. Basal blood pressure levels of ethanol-treated animals were significantly reduced by IV treatment with the V1-vasopressin receptor antagonist dTyr(CH2)5(Me)AVP. However, dTyr(CH2)5(Me)AVP had no effect on the blood pressure of control animals.

CONCLUSIONS

The results indicate that mild hypertension is already observed at an early phase of ethanol consumption in rats. Because the content of circulating vasopressin was increased in ethanol-treated rats and their basal blood pressure returned to control levels after IV treatment with a V1-vasopressin receptor antagonist, it is proposed that increased circulating vasopressin content may mediate the hypertension observed in ethanol-treated rats.

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.

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

BACKGROUND AND PURPOSE

We have previously shown that noradrenaline microinjected into the bed nucleus of stria terminalis (BST) elicited pressor and bradycardiac responses in unanaesthetized rats. In the present study, we investigated the subtype of adrenoceptors that mediates the cardiovascular response to noradrenaline microinjection into the BST.

EXPERIMENTAL APPROACH

Cardiovascular responses following noradrenaline microinjection into the BST of male Wistar rats were studied before and after BST pretreatment with different doses of the selective alpha(1)-adrenoceptor antagonist WB4101, the alpha(2)-adrenoceptor antagonist RX821002, the combination of WB4101 and RX821002, the non-selective beta-adrenoceptor antagonist propranolol, the selective beta(1)-adrenoceptor antagonist CGP20712 or the selective beta(2)-adrenoceptor antagonist ICI118,551.

KEY RESULTS

Noradrenaline microinjected into the BST of unanaesthetized rats caused pressor and bradycardiac responses. Pretreatment of the BST with different doses of either WB4101 or RX821002 only partially reduced the response to noradrenaline. However, the response to noradrenaline was blocked when WB4101 and RX821002 were combined. Pretreatment with this combination also shifted the resulting dose-effect curve to the left, clearly showing a potentiating effect of this antagonist combination. Pretreatment with different doses of either propranolol or CGP20712 increased the cardiovascular responses to noradrenaline microinjected into the BST. Pretreatment with ICI118,551 did not affect cardiovascular responses to noradrenaline.

CONCLUSION AND IMPLICATIONS

The present results indicate that alpha(1) and alpha(2)-adrenoceptors mediate the cardiovascular responses to noradrenaline microinjected into the BST. In addition, they point to an inhibitory role played by the activation of local beta(1)-adrenoceptors in the cardiovascular response to noradrenaline microinjected into the BST.