Intrapericardial injections using a novel technique.

Intrapericardial injections have been proposed as a means to specifically treat diseases of the myocardium, pericardium, and coronary vasculature. The pericardial space is potential drug reservoir, allowing sustained delivery of drug to the target tissue. In this study we have demonstrated a novel method for pericardial delivery in the mouse.

Testing awareness of heart disease among West Australian women.

Cardiovascular disease [CVD] is the top cause of death in Australian women. Large studies in the US and Europe have shown that the majority of women do not consider CVD as their greatest health threat. Australian women's awareness has not previously been investigated. The aim of this cross-sectional survey [TAWDAH] was to assess Australian women's awareness of CVD their leading causes of death [LCD].

Reciprocal connection between nucleus ambiguus and caudal ventrolateral medulla.

To investigate interactions between parasympathetic preganglionic neurons in the nucleus ambiguus (NA) and sympathoinhibitory neurons in the caudal ventrolateral medulla (CVLM) the activity of CVLM neurons was recorded during glutamate stimulation of cardioinhibitory sites in the NA of urethane-anesthetized rats. Neurons in the CVLM were identified as cardiovascular neurons if they increased their activity after i.v. phenylephrine and displayed cardiac cycle-related rhythmicity. Of 23 cardiovascular neurons studied, 10 decreased activity after glutamate (GLU) microinjection in the NA, five neurons were excited and eight did not respond. In another series of experiments, the nature of the influence of the CVLM on unit activity in the NA was investigated. Sites in the CVLM from which decreases in arterial pressure and heart rate were elicited after GLU microinjection were identified and the activity of cardiovascular neurons in the NA was recorded. Of 22 NA cardiovascular neurons studied, eight decreased activity after microinjection of GLU in the CVLM and 14 did not change firing frequency. These results demonstrate the existence of a reciprocal pathway between the NA and CVLM and provide evidence for functional interactions between medullary sites implicated in the control of the parasympathetic and sympathetic nervous systems.

Nucleus ambiguus inhibits activity of cardiovascular units in RVLM.

To investigate interactions between sites in the medulla which control the sympathetic (SNS) and the parasympathetic (PNS) nervous system, the activity of cardiovascular neurons in the rostral ventrolateral medulla (RVLM) was recorded during chemical stimulation of cardioinhibitory neurons in the nucleus ambiguus (NA). Cardioinhibitory sites in the NA were identified in urethane anesthetized rats. The spontaneous activity of single units in the RVLM was recorded and cardiovascular units were identified as units which displayed a cardiac cycle-related rhythmicity (CR) and decreased activity after i.v. phenylephrine. Of 55 units studied, 36 units were identified as cardiovascular and of these, 24 decreased activity after glutamate (GLU) microinjection in the NA, two units were excited and ten did not respond. Decreases in RVLM unit activity were positively correlated with the magnitude and duration of heart rate decreases elicited by GLU. Seven of the 24 units were tested for their response to microinjection of glycine (GLY) in the NA. GLY did not change firing frequency but did accentuate CR. These results demonstrate an inhibitory connection between the NA and RVLM which influences the rhythmicity of RVLM unit activity and provide clear evidence for functional interactions between the SNS and PNS within the central nervous system.

Expression of Fos in rat central nervous system elicited by afferent stimulation of the femoral nerve.

To investigate the distribution of Fos-like immunoreactivity (FLI) in the central nervous system of urethane anesthesized rats after activation of a somatosympathetic reflex pathway, the cut central end of the right femoral nerve of 17 male Wistar rats was stimulated electrically for 1 h at parameters such that increases in heart rate and arterial pressure were elicited. Sections of brain and spinal cord were incubated in anti-Fos antibody and the presence of FLI was detected using the ABC immunoperoxidase method. In the spinal cord FLI was present in the ipsilateral lumbar spinal cord (laminae 1 and 2, 4-6 and 10) and contralateral intermediolateral nucleus in the thoracic spinal cord. In the hindbrain, FLI was present in the contralateral rostral ventrolateral medulla and bilaterally in the cochlear nucleus, external cuneate nucleus, locus coeruleus and lateral parabrachial nucleus. In the midbrain, label appeared in the Edinger-Westphal nucleus and peripeduncular nucleus on both sides. In the forebrain, FLI appeared bilaterally in the central nucleus of the amygdala, para- and periventricular hypothalamus, supraoptic nucleus, paraventricular thalamus, reuniens nucleus, subfornical organ and bed nucleus of the stria terminalis. These results define the central nervous system pathways of somatosympathetic reflexes and demonstrate that areas in the forebrain not previously known to be activated by somatosympathetic reflexes, but previously implicated in mediating the defense reaction, are activated by these reflexes.

Cardiovascular and single unit responses elicited by stimulation of the islands of Calleja and by changes in arterial pressure.

Recent experiments in this laboratory have investigated the distribution of the nuclear protein Fos in the rat brain after unilateral electrical stimulation of the aortic depressor nerve and have revealed intense ipsilateral straining in the islands of Calleja. To test the hypothesis that the islands of Calleja may have a role in cardiovascular control, we tested the effect on arterial pressure and heart rate of microinjection of L-glutamate into the islands of Calleja of the artificially ventilated, urethane anesthetized rat. Microinjection of glutamate into the islands of Calleja resulted in a decrease in arterial pressure (24.5 +/- 1.5 mmHg) and heart rate (16.6 +/- 1.6 bpm). These responses were eliminated by i.v. injection of propranolol or by transection of the spinal cord at the C1 level. These results are the first demonstration that the islands of Calleja are involved in mediating cardiovascular reflexes primarily through an influence on sympathetic outflow to the heart and vessels. To determine the effects of increases or decreases of arterial pressure on single unit activity in the islands of Calleja, responses of single units in the islands to i.v. injection of phenylephrine or sodium nitroprusside were recorded. Of 87 units recorded from in the islands of Calleja, 40 (46%) responded to phenylephrine and 27 (68%) decreased their firing frequency. Of these 27, 16 (59.3%) increased their firing frequency to administration of nitroprusside. In addition, in 11 (31%) of 35 units recorded from in the islands, glutamate microinjection in the nucleus tractus solitarius decreased the firing frequency in 9 (82%) units.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of c-fos protein in rat brain after electrical stimulation of the aortic depressor nerve.

To reveal central nervous system (CNS) structures involved in the baroreceptor reflex we studied the distribution of Fos protein-like immunoreactivity in the rat brain after one hour of electrical stimulation of the aortic depressor nerve (ADN). In 13 male Wistar rats under urethane the ADN was cut on both sides and the central ends were placed on stimulating electrodes. Intermittent (11 s on, 6 s off) electrical stimulation at parameters set to elicit a drop in mean arterial pressure of 15-30 mmHg was applied to one, both or neither ADNs for 1 h. CNS sections were incubated for 48 h in anti-Fos antibody and prepared for visualization of the reaction product using the ABC immunoperoxidase technique. Label was found in several discrete brain nuclei primarily on the side ipsilateral to the side of stimulation. In the medulla labelled nuclei were found in the nucleus tractus solitarius, area postrema, rostral and caudal ventrolateral medulla, nucleus ambiguus and medullary reticular formation. In the pons labelled neurons were found in the lateral and ventrolateral parabrachial nucleus, locus coeruleus, pontine reticular field and A5 region. In the forebrain labelled nuclei were observed in the peri- and paraventricular hypothalamus, supraoptic nucleus, subfornical organ, preoptic area, central nucleus of the amygdala, median preoptic area, horizontal limb of the diagonal band, bed nucleus of the stria terminalis and islands of Calleja. In control animals moderate amounts of label were present in the supraoptic nucleus and periventricular hypothalamus bilaterally. These results define central pathways involved in mediating the baroreceptor reflex.

Neurokinin-1 receptor immunoreactivity in hypotension sensitive sympathetic preganglionic neurons.

Substance P activation of neurokinin-1 (NK1) receptors on spinal sympathetic preganglionic neurons (SPN) influences blood pressure. We identified SPN likely to subserve the baroreceptor reflex and established if these neurons showed NK1 receptor-immunoreactivity. Nitroprusside (NP) infusion or inferior vena cava (IVC) constriction activated similar numbers of SPN. Of these, about 40% were NK1 receptor-immunoreactive after NP infusion, but only about 20% were NK1 receptor-immunoreactive after IVC constriction. The distribution of Fos/NK1 receptor SPN suggested that substance P may preferentially target sympathoadrenal SPN.

Expression of fos in the hypothalamus of rats exposed to warm and cold temperatures.

Fos-like immunoreactivity was investigated in hypothalamic areas involved in central thermoregulatory processes. Different groups of urethane anaesthetized rats (n = 36) were exposed to: (1) 23.5 degrees C for 1 h (control); (2) 5 degrees C for 20 min (short cold); (3) 5 degrees C for 1 h (long cold); (4) 47 degrees C for 10 min (short warm) and (5) 47 degrees C for 1 h (long warm). Fos was present in the supramammillary nucleus, supraoptic nucleus and paraventricular hypothalamus of all (control and long and short, warm- and cold-exposed) rats. Fos was seen in the dorsomedial, medial and ventromedial hypothalamus of rats with long or short exposure to both warm and cold temperatures, and in the medial preoptic area and lateral anterior hypothalamus of long and short warm-exposed, and long cold-exposed, rats. Fos was present in the hypothalamus of long and short cold-exposed animals only in the posterior hypothalamus, and in the anterior hypothalamus (central and anterior divisions), suprachiasmatic nucleus and ventrolateral preoptic area of short and long warm-exposed rats. These results provide information on the location of neurons in rat hypothalamus activated by exposure to warm and cold temperatures and may aid in the functional identification of central thermoregulatory pathways.

Rapid and reliable induction of partial status epilepticus in naive rats by low-frequency (3-Hz) stimulation of the amygdala.

Naive rats were electrically stimulated in the amygdala with biphasic square wave pulses at 3 Hz in a model of partial status epilepticus (SE). This treatment led to the rapid kindling of seizures in all rats, and the subsequent induction of SE in 100% of rats stimulated for approximately 30-60 min. Extensive gliosis and degeneration was seen in the basal forebrain of the SE brains. This method of inducing SE is simpler, more rapid, and more reliable than similar methods reported previously.

Absence of a hemispheric difference in seizure sensitivity and kindling rate in the rat brain.

The question of a population hemispheric asymmetery in initial seizure sensitivity and in rate of kindling in the amygdala was examined in an unbiased sample of 80 rats studied in our laboratory during the past six years. Afterdischarge threshold, initial and final afterdischarge duration, and kindling rate were the same in rats kindled in the left or right basolateral amygdala. The results suggest that there is no systematic difference between the hemispheres in initial seizure sensitivity or rate of amygdala kindling.

Intrathecal cGMP elicits pressor responses and maintains mean blood pressure during haemorrhage in anaesthetized rats.

The intracellular second messenger, cyclic guanosine monophosphate (cGMP), a soluble guanylate cyclase (GC) product, is a primary mechanism for the transduction of a nitric oxide (NO)-initiated signal in the central nervous system. NO is produced from L-arginine by neuronal nitric oxide synthase (NOS), which is found in sympathetic preganglionic neurons of the intermediolateral cell column. This suggests the possibility that NO is a modulator of sympathetic nervous activity (SNA) through a cGMP-mediated mechanism. The aim of this study was to determine the effects of intrathecally injected membrane-permeant 8-bromo-cGMP and 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ), a selective inhibitor of the soluble form of GC, on arterial pressure in urethane anaesthetized (1.4 g kg(-1) I.P.) rats. The effects of intrathecal cGMP and ODQ on haemodynamic responses to haemorrhage were also investigated. Finally, L-arginine, the NO precursor, was also injected intrathecally, alone and in the presence of ODQ. Baseline mean arterial pressure (MAP) increased significantly after intrathecal 8-Br-cGMP injection (10 microl, 1, 3, 10, 30, 100 microm). A dose-effect relationship (1 microm to 100 microm) was also established (EC(50)=6.03 microm). During continuous haemorrhage, MAP was maintained in animals injected with 8-Br-cGMP, relative to the control group. Although no change in baseline MAP was observed as a result of intrathecal ODQ injection (10 microl, 100 mM), a greater rate of fall in MAP was observed during haemorrhage. Injecting L-arginine (10, 100, 1000 microm, 10 microl) showed a pressor effect that was consistent with the effect of the downstream messenger, cGMP. Furthermore, its pressor effect was blocked by ODQ pre-administration. The results indicate that cGMP increases blood pressure, and thus suggest that cGMP increases SNA. This supports the hypothesis that the sympathoexcitatory effects of spinal delivery of NO are mediated by a cGMP-dependent mechanism.

Cardiovascular responses to microinjection of ANF into dorsal medulla of rats.

Atrial natriuretic factor (ANF) has been suggested as a putative neurotransmitter in central pathways involved in the control of the cardiovascular system. To investigate this possibility, 50 nl of 10(-7) M ANF were microinjected into discrete sites in the nucleus of the tractus solitarius (NTS) where baro- and chemoreceptor afferents terminate. Injections into 36 of a total of 66 sites in the NTS of paralyzed artificially ventilated Wistar rats under urethan anesthesia were found to produce a significant decline in heart rate [HR; -9.2 +/- 2.9 (SE) beats/min, P less than 0.05] and mean arterial pressure [MAP; -11.1 +/- 1.2 (SE) mmHg, P less than 0.01]. Similar responses were also present in anesthetized animals breathing spontaneously. Microinjection of an inactive peptide analogue or of saline did not produce cardiovascular changes. It was also found that ANF injection into the cuneate nucleus (20 of 38 sites) and the spinal trigeminal complex (28 of 42 sites) produced a decrease in MAP and HR that were of the same magnitude as those seen in the NTS. Injections of ANF into the medial longitudinal fasciculus (n = 22), hypoglossal nucleus (n = 9), area postrema (n = 16), and dorsal motor nucleus of the vagus (n = 11) did not change HR or MAP. These results suggest that ANF may serve as a neurotransmitter involved in cardiovascular reflexes mediated by specific nuclei in the dorsal medulla.

Baroreceptor activation or glutamate coinjection facilitates depressor responses to ANF microinjection into NTS.

As microinjection of atrial natriuretic factor (ANF) into the nucleus of the solitary tract (NTS) has been shown to elicit depressor responses [D. J. McKitrick and F. R. Calaresu. Am. J. Physiol. 255 (Regulatory Integrative Comp. Physiol. 24): R182-R187, 1988], we investigated the possibility that these responses might be facilitated either by electrical stimulation of arterial baroreceptor fibers in the aortic depressor nerve (ADN) or by simultaneous microinjection of L-glutamate (Glu) into the same sites in the NTS. Male Wistar rats (n = 51) were anesthetized with urethan (1.4 g/kg ip), artificially ventilated, and the dorsal medulla was exposed. The ADN was isolated, cut distally, and the central end was placed on bipolar stimulating electrodes. Threshold doses of 10(-7) M ANF microinjected into the NTS were combined with threshold electrical stimulation of the ADN (n = 37) or threshold doses of 0.13-0.5 M Glu (n = 14) microinjected into the NTS. There was a significant interaction between ANF microinjection and ADN stimulation in producing changes in mean arterial pressure (MAP) and heart rate [HR; P less than 0.05; -20.2 +/- 2.3 (SE) mmHg and -30.8 +/- 6.9 (SE) beats/min, respectively; n = 18]. There was also a significant interaction between ANF and Glu in producing changes in MAP and HR [P less than 0.05; -16.3 +/- 1.8 (SE) mmHg and -15.0 +/- 3.0 (SE) beats/min, respectively; n = 8]. These results indicate that ANF influences neurons in the NTS, which are also influenced by activation of arterial baroreceptors, and ANF and Glu interact in the NTS to produce facilitated cardiovascular responses.

Interaction of putative transmitters in central nervous pathways involved in the control of heart rate and arterial pressure.

As many putative transmitter substances have been shown to be co-localized in areas of the central nervous system involved in cardiovascular control, we have investigated the possibility that some of these substances may interact in eliciting changes in heart rate and arterial pressure in anesthetized rats. In a first set of experiments, interactions between atrial natriuretic factor and glutamate were investigated by microinjection into the nucleus of the tractus solitarius, the site of termination of baroreceptor fibers of the aortic depressor nerve. In addition, interactions between the transmitter released in the nucleus tractus solitarius by electrical stimulation of the aortic depressor nerve and atrial natriuretic factor microinjected into the nucleus tractus solitarius were investigated. Combined microinjection of atrial natriuretic factor and glutamate into the nucleus tractus solitarius, or stimulation of the aortic depressor nerve combined with atrial natriuretic factor in the nucleus tractus solitarius, elicited decreases in heart rate and arterial pressure which were greater than the responses to either substance or stimulation alone or their algebraic sum. In a second set of experiments, interactions between substance P and acetylcholine were investigated in the intermediolateral nucleus of the spinal cord, the location of sympathetic preganglionic neurons. Furthermore, we investigated the possibility that the cardiovascular responses to microinjection of substance P and acetylcholine into the intermediolateral nucleus could be potentiated by the transmitter released in the intermediolateral nucleus by microinjection of glutamate into the rostral ventrolateral medulla, a region with known sympatho-excitatory function.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular responses to combined microinjection of substance P and acetylcholine in the intermediolateral nucleus of the rat.

As microinjection of either substance P (SP) or acetylcholine (ACh) into the right intermediolateral cell nucleus (IML) at the T2 level elicits increases in heart rate (HR) in the anesthetized rat, we investigated the possibility of a synergistic effect on HR and arterial pressure (AP) of ACh and SP microinjected in this nucleus. Moreover, we studied the effect on HR and AP of microinjection of either ACh or SP into the IML combined with activation of cardiovascular neurons in the ipsilateral rostral ventrolateral medulla (RVLM) by microinjection of glutamate (Glu). Male Wistar rats (n = 16) were anesthetized with urethane (1.4 g/kg i.p.), artificially ventilated, and the dorsal medulla and spinal cord (T1-T3) were exposed. Micropipettes containing SP and ACh were positioned in the right IML at the T2 level. Microinjection of threshold amounts of ACh (5 x 10(-2) M, 2-10 nl) and SP (3 x 10(-6) M, 2-10 nl) that caused small or no changes in HR or AP (less than 10 bpm or mmHg) elicited statistically significant synergistic increases in HR (22.9 +/- 3.3 bpm) but no changes in AP. Threshold microinjections of Glu (0.18 M, 2-10 nl) into the right RVLM combined with microinjections of threshold amounts of SP or ACh into the ipsilateral IML elicited significant synergistic increases in HR of 13.1 +/- 1.9 bpm and 10.6 +/- 1.9 bpm and in AP of 9.7 +/- 1.9 mmHg and 10.8 +/- 1.7 mmHg, respectively. These results indicate that SP and ACh interact to influence cardioacceleratory spinal preganglionic neurons (SPN) and interact with the transmitter released in the IML by RVLM stimulation to elicit increases in HR.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of treatment with scopolamine and naloxone, singly and in combination, on amygdala kindling.

Scopolamine and naloxone were administered singly and in combination to different groups of rats undergoing electrical kindling of the amygdala. Scopolamine significantly reduced the maximal seizure stage attained during 15 drug sessions and increased the total number of afterdischarges required to kindle a generalized convulsion. Naloxone had a similar but weaker and nonsignificant effect. The results confirm that antagonism of muscarinic receptors by scopolamine retards amygdala kindling.

Effect of anaesthetic and rat strain on heart rate responses to simulated haemorrhage.

AIM AND METHODS: Haemorrhage is characterized by two distinct responses, sympathoexcitation that evokes tachycardia and supports blood pressure, followed by sympathoinhibition contributing to bradycardia and hypotension. It has been shown that anaesthetics alter the response to haemorrhage and we hypothesized that rat strain may also influence the response. We investigated the effect of simulated haemorrhage on heart rate (HR) responses in three strains of conscious rats, and the effect of three common anaesthetics, by comparing HR responses under anaesthesia to the conscious response. Haemorrhage was simulated by constricting the inferior vena cava. We demonstrate differential effects of anaesthetics, including both maintenance and elimination of HR responses to haemorrhage depending on anaesthetic. RESULTS: We also show that both phases of the HR response differ in different conscious rat strains, and we have demonstrated a transient increase in HR during the decompensatory phase of haemorrhage, a novel 'second HR peak' with advanced hypotension. CONCLUSION: Both rat strain and anaesthetic influence HR responses to haemorrhage, and some anaesthetics appear less suitable than others for studies of haemodynamic responses in rats. There was evidence of an additional compensatory mechanism that operates at advanced levels of hypotension in the rat.

Cardiovascular responses to chemical and electrical stimulation of amygdala in rats.

Electrical stimulation of the amygdala has been shown to produce changes in cardiovascular variables. To locate neuronal cell bodies responsible for these changes, responses of arterial pressure (AP) and heart rate (HR) to DL-homocysteate (DLH, 0.15 M, 50-100 nl) microinjected into sites in three amygdaloid nuclei were compared with responses to electrical (90-150 microA) stimulation of the same sites in 35 artificially ventilated, paralyzed, urethan-anesthetized rats. Electrical stimulation resulted in depressor responses in most sites (89%). Changes in AP were accompanied by variable changes in HR. Chemical stimulation produced significantly fewer (25%) depressor responses. Similar results were obtained with injections of 1.0 M DLH. To eliminate the influence of the anesthetic on these responses, AP was recorded in nine conscious rats while stimulating the amygdala. Changes in behavior and AP in these animals could be obtained only by electrical stimulation. These results may be interpreted to indicate either that cell bodies responsible for changes in cardiovascular variables during electrical stimulation are not located in the amygdala or that chemical and electrical stimulation affect different neuronal elements in circuits located in the same anatomic site.