A new method for measurement of blood pressure, heart rate, and activity in the mouse by radiotelemetry.

A simple and reliable means for accurate, chronic measurement of pulsatile blood pressure (BP) from conscious, freely moving laboratory mice was developed and validated. The newly developed device consists of a small (1.9 ml, 3.4 g), fully implantable radiotelemetry transmitter. Initial frequency response tests showed an adequate dynamic response; the average -3-dB point found in five transmitters was 145 +/- 14 (SD) Hz. BP, heart rate, and locomotor activity were recorded from 16 chronically (30-150 days) implanted mice. Mean arterial and pulse pressure, checked at regular intervals, ranged from 90-140 mmHg and from 30-50 mmHg, respectively, throughout the study. Transmitter BP measurements were validated against a Millar 1.4-Fr. transducer-tipped catheter. The mean error of the transmitters for diastolic pressures was +1.1 +/- 6.9 mmHg (n = 7). The error for systolic pressures was, on average, 2.7 +/- 3.9 mmHg larger. This new device accurately monitors BP, heart rate, and locomotor activity in conscious, untethered, freely moving mice living in their home cages for periods of at least 150 days.

Central nucleus of the amygdala and the development of hypertension in spontaneously hypertensive rats.

Electrolytic lesions of the central nucleus of the amygdala (ACe) have been shown to attenuate the development of hypertension in spontaneously hypertensive rats (SHR). Whether this was due to destruction of local neurons and/or fibers is unknown. In the present study, neuronal perikarya in the ACe of 4-wk-old SHR were selectively destroyed with ibotenic acid. In two experiments, each comprising lesioned and sham-lesioned SHR, mean arterial blood pressure (MAP) was measured 7 and 15 wk after operation in the second experiment also at 22 wk. In the first experiment, in which rats were fed ad libitum, lesioned SHR had significantly lower body weights from 5 wk postoperation onward, and at 15 wk postoperation their average MAP [173 +/- 7 mmHg (SE)] was significantly lower vs. sham-lesioned SHR (201 +/- 4 mmHg). In the second experiment, food intake, and hence body weight, among the lesioned and sham-lesioned rats was equalized. Average MAP in the lesioned SHR at 7 and 15 wk postoperation was not different vs. sham-lesioned SHR but was significantly higher (191 +/- 6 mmHg) vs. sham-lesioned SHR but was significantly higher (191 +/- 6 mmHg) vs. sham-lesioned SHR (164 +/- 5 mmHg) 22 wk postoperation. These results indicate that destruction of neuronal perikarya in the ACe in young SHR merely delays the development of hypertension, due to a reduced weight gain.

Cardiovascular effects of social stress in borderline hypertensive rats.

OBJECTIVE: To test the hypothesis that chronic exposure to psychosocial stress, alone or in combination with elevated levels of dietary salt, leads to hypertension and cardiac pathology in a susceptible strain of rats. DESIGN AND METHODS: In four experiments, borderline hypertensive rats, maintained on normal or high-salt diets, were exposed to 14-16 weeks aggregation in a colony housing or in larger breeder cages. Pulsatile blood pressure was measured once a week in unrestrained male rats by pressure telemetry. Direct carotid pressures of the aggregated rats and of control rats were measured before they were killed; at necropsy cardiac and adrenal weights and ventricular design were determined. RESULTS: Despite continuous fighting, their weekly measured blood pressures remained stable; no differences in final carotid pressures between experimental and control rats were found. Rats from three aggregations showed significant increases in left and right ventricular and adrenal weights. CONCLUSION: No hypertension developed in any aggregation, although most of the rats showed signs of perceived stress (significantly reduced weight gain, enlarged adrenals and a large number of body wounds). Cardiac hypertrophy did ensue, possibly reflecting increased physical activity or intermittent increases in sympathetic activity, or both.

Cardiovascular effects of neuronal activation of the extended amygdala in rats.

The bed nucleus of the stria terminalis (BST) and the sublenticular substantia innominata (SI) are considered rostral extensions of the medical and central amygdaloid nuclei. In contrast to amygdaloid nuclei proper, the involvement of BST and SI neurons in cardiovascular control has not been studied. These areas were systematically explored in 35 urethane-anesthetized Wistar rats for sites from which changes in arterial pressure (AP) and heart rate (HR) could be obtained by injection of 20 nl of glutamate solutions (Glu, 0.5 M). Injections into 84 of the 130 histologically verified sites were followed after an 8.0 +/- 0.7 s latency by depressor responses ranging from -4 to -33 (mean -13.3 +/- 0.8) mmHg, accompanied by variable changes in HR. Pressor responses were elicited from only 3 sites; 43 sites were not responsive. An additional group of 10 rats was instrumented for bilateral Glu injections (0.1 M, 200 nl per side) into the ventral division of the lateral BST and ventral BST and for the recording of AP, HR and regional blood flows measured with pulsed Doppler probes in the conscious state. In these rats, decreases in AP (-11.9 +/- 1.7 mmHg) were accompanied by significant increases in hindquarter conductance (44.2 +/- 11.4%), while renal and mesenteric vascular conductances remained unchanged. The fall in AP usually preceded the rise in hindquarter flow. These results suggest the existence of a depressor area in regions of the BST and SI, but the contribution of the elicited depressor effects in the overall central control of the circulation remains to be established.

Inhibition of rostral VLM by baroreceptor activation is relayed through caudal VLM.

Experiments were done to test the hypothesis that inhibition of neurons in the rostral ventrolateral medulla (RVLM) elicited by stimulation of the nucleus tractus solitarii (NTS) is relayed through the caudal ventrolateral medulla (CVLM). We recorded activity from 56 spontaneously firing units in the right RVLM of urethan-anesthetized and artificially ventilated rats. Eleven of these units were classified as cardiovascular neurons, because they were silenced by baroreceptor activation (1-3 micrograms phenylephrine iv) and showed rhythmicity of their spontaneous activity in synchrony with the cardiac cycle. Single pulses (0.1 ms, 30-75 microA) delivered 1/s to depressor sites in the ipsilateral NTS inhibited the activity of all these cardiovascular neurons. Microinjection of the glutamate antagonist kynurenic acid (0.15 M, 50 nl) into the ipsilateral CVLM blocked the inhibitory response of RVLM units to the administration of phenylephrine and increased the firing frequency of cardiovascular neurons in the RVLM by 43%. Moreover, kynurenic acid administration attenuated the inhibitory response of cardiovascular neurons in the RVLM to NTS stimulation. Finally, stimulation of the NTS that elicited depressor responses under control conditions produced a pressor response after kynurenic acid administration. The remaining 45 RVLM neurons were barosensitive but lacked cardiac cycle-related rhythmicity. These results provide direct evidence for the existence of a tonic inhibitory pathway from NTS to RVLM that is relayed through the CVLM probably by a glutamatergic projection from NTS to CVLM.

Neurons in rostral VLM are inhibited by chemical stimulation of caudal VLM in rats.

Recent evidence suggests that neurons in the caudal ventrolateral medulla (CVLM) exert a tonic inhibition on the neurons in the rostral ventrolateral medulla (RVLM) that are essential for the maintenance of arterial pressure (AP). To test the hypothesis that selective activation of cell bodies in the CVLM can inhibit the discharge of neurons in the RVLM, activity from 88 neurons in the RVLM was recorded extracellularly while 2-30 nl sodium glutamate (Glu; 0.15 M) were microinjected into depressor sites of the CVLM of urethan-anesthetized male Wistar rats. Results obtained from spontaneously breathing and artificially ventilated rats were essentially similar and are presented together. Twenty-five neurons were characterized as cardiovascular because they were inhibited by baroreceptor activation and showed rhythmicity of their spontaneous activity in synchrony with the cardiac cycle. Activation of cell bodies in the CVLM inhibited the firing rate of 23 of these cardiovascular neurons and excited 2. The remaining 63 neurons could not be considered cardiovascular because they either were not barosensitive or lacked cardiac cycle-related rhythmicity. Injection of Glu into the CVLM inhibited 26 of these neurons, excited 22, and had no effect on 15. These results provide direct evidence for the existence of an inhibitory pathway from neurons located in the CVLM to cardiovascular neurons in the RVLM.

Cardiovascular responses and changes in neural activity in the rostral ventrolateral medulla elicited by electrical stimulation of the amygdala of the rat.

Electrical stimulation of the central nucleus of the amygdala (ACe) in anesthetized animals produces a decrease in arterial pressure (AP) as a result of an overall decrease in peripheral resistance. As the cardiovascular neurons that presumably mediate these changes are located in the rostral ventrolateral medulla (RVLM), we recorded spontaneous activity from 89 histologically verified units in the RVLM of urethan-anesthetized rats. Twenty-two of these units were classified as cardiovascular neurons because their spontaneous activity was inhibited by baroreceptor stimulation (2-4 micrograms phenylephrine i.v.) and displayed a cardiac cycle-related rhythmicity. Single or twin pulses (0.5 ms, 180 +/- 55 microA) delivered once per second to arterial depressor sites in the ipsilateral ACe inhibited the activity of 18 of these neurons and excited 4. In 27 additional barosensitive neurons that lacked cardiac cycle rythmicity, a similar distribution of effects was obtained by electrical stimulation of the ACe: 13 inhibited, 5 excited, 9 not affected. Finally, 40 non-barosensitive units were found; stimulation of the ACe inhibited the activity of 16, excited 12 and had not effect in 12. These results are interpreted to indicate that the differential effects of ACe stimulation on different vascular beds are mediated probably by differential influences on cardiovascular neurons in the RVLM, and that functions other than respiratory and cardiovascular control are represented in the RVLM.

Neurally mediated cardiovascular responses to stimulation of cell bodies in the hypothalamus of the rat.

To study the cardiovascular responses to selective activation of neuronal cell bodies in the hypothalamus, DL-homocysteate (5-50 nl of a 0.15-M solution, pH 7.4) was injected into 417 histologically verified sites in the hypothalamus of 46 urethan-anesthetized, paralyzed and artificially ventilated rats. Injections resulted in depressor responses (-5 to -32 mm Hg) in 271 sites, in pressor responses (5-47 mm Hg) in 77 sites and 69 sites were not responsive. Depressor effects had a shorter latency (85% started within 5 s) than pressor effects (42% started within 5 s). Control injections of 0.15 M NaCl into 126 of the responsive sites were ineffective. Arterial pressure (AP) responses showed a positive correlation (r = 0.61, P less than 0.001) with changes in heart rate (HR). Analysis of the anatomical distribution of responsive sites showed that in all hypothalamic subdivisions depressor responses predominated except in the paraventricular nucleus, where mainly pressor effects and tachycardia were elicited. These results demonstrate that excitation of cell bodies in most hypothalamic regions elicits neurally mediated changes in AP and HR and that the traditional functional division of the hypothalamus into a rostral depressor and a caudal pressor area is probably based on the combined excitation of fibers of passage and cell bodies.

Septal neurons respond to activation of baro- and chemoreceptors in the rat.

Because it has recently been shown that selective activation of neuronal perikarya in the septal area elicits arterial depressor responses, it seems reasonable to expect that information from receptors in the cardiovascular system may be related to the septum. This possibility was investigated by searching for single units in the medial and lateral septal nuclei responding to activation of baroreceptors, elicited either by electrical stimulation of the aortic depressor nerve (ADN) or by systemic injection of phenylephrine (PE), or responding to activation of chemoreceptors, elicited by intracarotid injection of sodium cyanide. Fifty-four male Wistar rats weighing 300-400 g were anesthetized with urethan (1.4 g/kg ip) or alpha-chloralose-urethan (35 and 400 mg/kg ip, respectively) and allowed to breathe spontaneously. One-third of spontaneously firing units tested responded to ADN stimulation; these 93 units were divided into two groups according to their response patterns; 62 (67%) showed an increase and 31 (33%) a decrease in their discharge. Of 35 units tested, 6 responded to intravenous injection of PE. The majority of the units (48 of 60) affected by chemoreceptor activation were excited, and the remaining 12 were inhibited. These experiments suggest that sensory information from cardiovascular receptors may play an important role in the control of the circulation by the septum.

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.

Chemical microstimulation of the septal area lowers arterial pressure in the rat.

Electrical stimulation of the septal area has been previously reported to result in either an increase or a decrease in arterial pressure (AP) and heart rate (HR) depending on the site of stimulation within the septum or on the anesthetic. These conflicting results could be due to the different proportions of cell bodies and fibers activated by electrical stimulation at different sites and to the different anesthetics acting differently on cell bodies and fibers. To study the cardiovascular responses to activation of cell bodies, DL-homocysteate (20-50 nl) was injected into histologically verified sites in the lateral septum (LS), the medial septum (MS), the nucleus of the vertical limb of the diagonal band of Broca (NDBB), and in the bed nucleus of the stria terminalis (BST) in urethananesthetized, paralyzed, and artificially ventilated rats. Injections in the LS, MS, and NDBB elicited a decrease in AP [-12.6 +/- 0.9 (SE) mmHg, n = 111] accompanied by variable changes in HR. In a group of spontaneously breathing rats anesthetized with urethan, AP responses were not significantly different from those obtained in paralyzed animals. Finally, in a group of animals under alpha-chloralose, AP responses were not significantly different from those observed in animals under urethan. Homocysteate application in the BST resulted in either depressor [-10.8 +/- 0.9 (SE) mmHg, n = 20] or pressor responses [13.7 +/- 1.9 (SE) mmHg, n = 9].(ABSTRACT TRUNCATED AT 250 WORDS)

Short-latency tachycardia evoked by stimulation of muscle and cutaneous afferents.

The short-latency effect on heart rate of peripheral nerve stimulation was studied in decerebrate cats. Selective activation (17-40 microA, 100 Hz, 1 s long) of low-threshold fibers in the nerves to the triceps surae muscle yielded isometric contractions of maximal force that were accompanied by a cardiac cycle length shortening within 0.4 s from the start of stimulation. This effect was abolished by pharmacologically induced neuromuscular blockade. The cardiac cycle length shortening during paralysis reappeared after a 6- to 10-fold increase of the stimulation strength. Cutaneous (sural) nerve stimulation (15-25 microA, 100 Hz, 1 s long) elicited reflex contractions in the stimulated limb, which were also accompanied by a cardiac acceleration with similar latency. Paralysis prevented the reflex contractions and reduced the cardiac response in some cats and abolished it in others. The response reappeared in either case after a 5- to 10-fold increase of the stimulus strength. It is concluded that muscle nerve and cutaneous nerve activity both cause a similar cardiac acceleration with a latency of less than 0.4 s. The response to muscle nerve stimulation is elicited by activity in group III afferents. It is excluded that the cardiac response to nerve stimulation is secondary to a change in the respiratory pattern.

Instantaneous cardiac acceleration in the cat elicited by peripheral nerve stimulation.

The short-latency effect of peripheral nerve stimulation on heart rate was studied in decerebrate cats. Stimulus trains (100 Hz) of 1-s duration were given to the tibial nerve or to muscle nerves with an intensity yielding a maximal force of isometric contraction of the triceps surae muscle. The first detectable sign and the maximum of cardiac cycle length shortening were found at 0.5-0.6 and 2.1 +/- 0.4 (SD) s, respectively, after the onset of stimulation. A positive correlation exists between the basic cycle length (i.e., before nerve stimulation) and the stimulation-induced shortening of cycle length. The average maximum shortening was found to be 6.7% of basic cycle length. Atropine (0.05-0.1 mg/kg) or bilateral vagotomy suppresses the heart rate response almost completely, whereas the administration of propranolol (2 mg/kg) leaves the response intact. When the nerve is cut proximal to the site of stimulation, the response disappears. Paralysis of the muscle diminishes the response upon nerve stimulation. It is concluded that the short-latency response studied here can be considered as a muscle-heart reflex that is similar to the one previously found in humans.

Apparent lack of effect on alpha-bungarotoxin on the spike-induced release of acetylcholine at the mammalian motor end-plate.

During intoxication with alpha-bungarotoxin (alpha-BGT) the amplitude of end-plate potentials (EPPs) decreased more slowly than the amplitude of potentials evoked by iontophoretically applied acetylcholine. Mean quantal content of EPPs, however, remained constant. The results do not support the notion that alpha-BGT influences, the spike-evoked transmitter release.

Electron microscopy of the rabbit pineal organ in vitro. Evidence of norepinephrine-stimulated secretory activity of the Golgi apparatus.

The results presented in this study show that the rabbit pineal organ cultured in vitro retained its in vivo fine structure for at least eight days. However, the Golgi complex in the light pinealocytes stopped forming dense core vesicles while vesicle-crowned ribbons increased in number. After addition of norepinephrine to the culture medium, the Golgi complex once more began the production of dense core vessicles. Terminals of light pinealocytic processes then often contained Golgi dense core vesicles in close contact with the cell membrane, suggesting the release of the vesicular content into the intercellular and perivascular spaces. A close topographical relationship between Golgi dense core vesicles and vesicle-crowned ribbons was observed.