Rostral pontine and caudal mesencephalic control of arterial pressure and iliac, celiac and renal vascular resistance. I. Anatomic regions

Brain Research, 361 ( 19851 284-3(10

284

Elsevier BRE 11322

Rostral Pontine and Caudal Mesencephalic Control of Arterial Pressure and Iliac, Celiac and Renal Vascular Resistance. I. Anatomic Regions DANIEL N. DARLINGTON* and DAVID G. WARD

Department of Physiology, University of Virginia, Charlottesville, VA 22908 (U.S.A.) (Accepted April 23rd, 1985)

Key words: pons - - mesencephalon - - electrical stimulation - - arterial pressure - - vascular resistance

The rostral pons and caudal mesencephalon in 26 cats were electrically stimulated (>2400 sites) while measuring arterial pressure and iliac, celiac and renal vascular resistance. Areas active in control of arterial pressure and iliac vasoconstriction were located in the marginal nucleus of the brachium eonjunctivum (BCM) and in parts of.the central tegmentat fields (FFC) of the mesencephalon. Areas active in control of celiac and renal vasoconstriction were confined to the BCM. Areas active in control of iliac and celiac vasodilation were generally found ventral to the constrictor areas in the FTC of the mesencephalon. Stimulation of the caudal periaqueductal grey, locus caeruleus and underlying reticular formation eficited no change in any parameter measured. These findings surest that multiple pathways for control of arterial pressure and vasoconstriction pass through or synapse in a discrete region of the dorsal rostral ports that is limited to the BCM.

INTRODUCTION

itary and autonomic nervous system. Pathways that

Central neural control of the cardiovascular system has been said to be diffusely organized because electrical stimulation of large areas in the medulla. pons and m e s e n c e p h a l o n lead to changes in cardiovascular p a r a m e t e r s 5,14,4°. Recently however, small

ascend from the nucleus tractus solitarii and t h a t carry cardiovascular signals for control of adrenocorticotrophin ( A C T H ) release and for control of water intake traverse the medial rostral ports and caudal mesencephalon, specifically the p e n a q u e d u c t a l grey and locus caeruleus 41,43:5,47. T h e r e are also pathways

and discrete areas of the hindbrain have been described from which electrical stimulation leads to cardiovascular changes, thus contrasting with the theories of diffuse autonomic control These areas melude the ventrolateral medulla and pons (A1. C1 and A5 catecholamine areas) 4,23, the spinal trigeminal nucleus2L nucleus ambiguus 8. the solitary tract nucleilO,27, the fastigial nucleus t2,25, the paraventricular and lateral hypothalamic nuclei t3.14,17, the central nucleus of the amygdala ~8 and parts of the cortex 9.39. These nuclei are anatomically interconnected and communication between t h e m is highly likely. A r e a s in the dorsal rostral pons and caudal mesencephalon have recently been implicated in cardiovascular control because of their influence on the pitu-

that descend from limbic and hypothalamic structures implicated in control of heart rate and arterial pressure14,18 that traverse the periaqueductal grey and ventrolateral m e s e n c e p h a l o n to terminate in the marginal nucleus of the brachium conjunctivuml5,19, 41. F u r t h e r m o r e . the integrity of the marginal nucleus of the brachium conjunctivum is necessary for hypothalamic control of renal vasoconstriction 42. It has recently b e e n shown that electrical stimulation of the periaqueductal grey, the locus caeruleus and the marginal nucleus of the brachium conjunctivum lead to changes in release of ACTH45: and that electrical stimulation of the marginal nucleus of the brachium conjunctivum and possibly the locus caeruleus lead to changes in heart rate and vasocons-

*

Present address: Department of Physiology, UCSF, San Francisco, CA 94143, U . S . A .

Correspondence." D.G. Ward. Present address: H.M. Ward Memorial Laboratory, P.O. Box 207, Valley Home, CA 95384, U.S.A. 0006-8993/85/$03.30 © 1985 Elsevier Science Publishers B.V. (Biomedical Division)

285 triction11,16A7,26,45. These data are consistent with a medial ascending pathway for pituitary control in the medial pons and mesencephalon that traverses the periaqueductal grey and locus caeruleus and with a more lateral descending pathway for autonomic control of arterial pressure and vascular resistance that traverses the marginal nucleus of the brachium conjunctivum41. The purpose of the following experiments is to precisely identify areas in the rostral pons and caudal mesencephalon from which small electrical stimulations lead to rapid neurally mediated changes in arterial pressure and in iliac, celiac and renal vasoconstriction. Electrical stimulation is chosen in order to reveal the location of pathways, inclusive of cell bodies or fibers of passage, active in cardiovascular control. MATERIALS AND METHODS Experiments were performed on 26 cats of either sex. They were housed in the University of Virginia Vivarium for a period of 1-3 months and were maintained on a 12-h on, 12-h off light cycle. The animal weights ranged between 2.5 and 4.4 kg. Each animal was brought into the laboratory at 08.00-09.00 h and sedated with chloroform gas or ketamine (5 mg/lb). Infusion catheters were placed in the cephalic vein and chloralose/urethane was administered (40 mg/kg and 200 mg/kg). Supplementary doses of chloralose/urethane (up to 40 mg/ 200 mg) were given if pupillary dilation or retraction of the nictitating membranes occurred. Atropine, 0.04 mg, was administered intramuscularly to prevent nasal and oral secretions from interfering with respiration. The animal was placed on a water-filled heating pad that was regulated between 37 and 39 °C by a rectal probe monitor feeding back to a temperature controller. An endotracheal tube was inserted to prevent obstruction and to allow positive ventilation of paralyzed animals. The animals were paralyzed with Gallamine (10 mg) and maintained on positive ventilation with a Harvard pump to minimize the mechanical effects of breathing on changes in MAP and vascular resistance. Supplemental doses (10 mg) were administered as needed when spontaneous breathing occurred. The femoral artery and vein were cannulated for

measurement of arterial pressure and administration of drugs, respectively. For any given experiment, electromagnetic flow probes were placed on two of the three arteries: iliac, celiac and renal. The renal and celiac arteries were approached retroperitoneally on the left side and the iliac artery was approached through a cutdown on the right side of the femoral region. The animal's head was placed in a stereotaxic frame and a line of burr holes was drilled laterally from the interparietal ridge in the parietal bone. The rostral pons and caudal midbrain was approached stereotaxically at a 45 ° angle to the horizontal plane. Electrical stimulation was carried out using monophasic square waves of constant current derived from a Grass S-88 stimulator through bipolar coaxial electrodes (Rhodes SNE 100, tip to barrel separation 0.25 mm) with cathodal current at the tip. The tip of the electrode at the end of a track was marked by passing a direct current (DC) of 100/~A for 10 s. The electrode was raised 5 mm and a second marking lesion was made. Upon completion of the stimulation protocol (6-8 h, see below) the animal was hemorrhaged to zero flow for baseline calibration of flow probes. In these sorts of experiments, this method provides measures of 'zero' flow that corresponds extremely well to measures obtained using occluding devices. The brains were removed after perfusion through the left ventrical with saline followed by 10% formalin, and were stored in formalin for 1 week, sectioned frozen at 35 pm in the sagittal plane, and stained with thionine in order to locate electrode tracks and marking lesions. Stimulation parameters were based on previous studies of the thresholds for eliciting consistent changes in arterial pressure and in release of ACTH 44, and consisted of: current intensity, 100pA; frequency, 50 Hz; pulse duration, 0.2 ms; stimulus duration, 30 s. All parameters were monitored on an oscilloscope. In each animal, a total of six electrode penetrations were made in a pseudorandom order 1 mm apart in the medial-lateral plane. For each penetration, a total of sixteen stimulations were applied 0.5 mm apart and at time intervals of 3-5 min. Systolic and diastolic measures of arterial pressure and blood flows were obtained immediately before and between 5-10 s after onset of stimulation when peak pressure and flow changes occurred. Care was taken to obtain all measurements during the same phase of

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Fig. 1. A representative sagittal section showing stimulation sites and responses of arterial pressure. The photomicrograph is a ~agittal section from cat number 14, with arrows showing the electrode track. The sagittal drawing represents electrode track and stimulation sites located on it. Each site was stimulated at 100/~A intensity, 0.2 ms duration at a frequency of 50 Hz. Polygraph tracings for each site show response of arterial pressure to 30 s train of stimulation (between on and off).

287 respiration in all experiments. A schematic sagittal section of the pons with stimulation sites and arterial pressure tracings during stimulation is shown in Fig. 1. M e a n arterial pressure and m e a n b l o o d flow at each time of m e a s u r e m e n t were calculated as diastolic + (systolic - diastolic)/3. Resistance in each artery was calculated by dividing the m e a n arterial pressure by the mean flow in each artery at the same time point. Changes in m e a n arterial pressure and regional vascular resistance were d e t e r m i n e d by subtracting the a p p r o p r i a t e measures before stimulation from the corresponding measures during stimulation. Calculation of percent changes in m e a n arterial pressure and regional vascular resistance during a stimulation were calculated based on the values m e a s u r e d before that stimulation. Negative and positive changes in resistance were interpreted as dilations and constrictions, respectively. If an electrode track could not be located histologically, then the results of electrical stimulation of that track were ignored. E a c h stimulation site was plotted on s t a n d a r d sagittal sections and then transferred to standard coronal sections derived from B e r m a n 3 as is shown in Fig. 2. Composite drawings of all stimulation sites were prepared. A d j a c e n t sites from which electrical stimulation led to consistent changes in arterial pressure or regional vascular resistance were g r o u p e d t o g e t h e r into areas. Changes in pressure and resistance within areas and between areas was evaluated using analysis of variance for r e p e a t e d measures as. The t o p o g r a p h y of the regions from which areas were constructed was modified systematically until the areas contained sites of stimulation associated with the least variability within areas and the most difference c o m p a r e d to adjacent areas. RESULTS O v e r 2400 stimulations were p e r f o r m e d in the 26 cats. A cumulative m a p of sites stimulated while measuring arterial pressure and the corresponding magnitudes of the changes is shown in Fig. 3. The average m e a n arterial pressure prior to stimulations for all experiments was 131 + 5 m m Hg. Changes in m e a n arterial pressure ranged from 0 to 110% of prestimulus levels with most changes failing b e t w e e n 0 and 60%. Most sites eliciting changes in mean arterial pressure greater than 10% were located in the lat-

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Fig. 2. Illustration of how stimulation sites plotted on sagittal sections were replotted on coronal sections. The anterior-posterior sagittal coordinate is marked near the lower right hand corner of each sagittal section. Each sagittal section has three coronal sections plotted onto it. These are represented by black vertical lines running down the center of each sagittal section. The vertical lines are continuous with representations of the coronal sections to the right of the figure. Each vertical line is numbered with the anterior-posterior coordinate of the sagittal section 3. Stimulation sites on the sagittal sections were replotted on coronal sections by determining which sites were on or close to a vertical line representing a coronal section. Each stimulation site represents a change in mean arterial pressure as specified in the key in the lower right hand corner of the figure.

eral rostral pons and in small areas of the caudal mesencephalon. The active areas are shown schematically in Fig. 4 where clusters of three or m o r e sites that elicited changes greater than 10% are drawn. The active areas include the marginal nucleus of the brachium conjunctivum and the dorsal central tegmental

288 ARTERIAL

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291 fields of the mesencephalon. Notice that the periaqueductal grey, locus caeruleus and adjacent reticular formation are not active. Sites stimulated while recording iliac vascular resistance is shown in Fig. 5. The average mean iliac blood flow prior to stimulations was 15 + 4 ml/min. Changes in iliac vascular resistance ranged from -34 to +374% of prestimulus levels with most changes falling between -20 and +150%. The sites eliciting changes in iliac vascular resistance greater than 10% were located in the marginal nucleus of the brachium conjunctivum and central tegmental fields. These areas are shown schematically in Fig. 6. Areas active for iliac vasoconstriction are located in the marginal nucleus of the brachium conjunctivum and dorsal central tegmental fields and generally overlap the areas that represent increases in mean arterial pressure. Areas active for iliac vasodilation are only located in the ventral portions of the central tegmental fields, usually below the areas representing constriction (P0.2-A1.6). The periaqueductal grey, locus caeruleus and underlying reticular formation are not active in control of iliac resistance. Sites stimulated while recording celiac vascular resistance are shown in Fig. 7. The average mean celiac blood flow prior to stimulations was 54 ___12 ml/min. Changes in celiac vascular resistance ranged from -35 to +64% of prestimulus levels with most changes falling between -10 and +20. Only a few sites elicited celiac vasoconstriction while more elicited dilations. Areas that elicited changes greater than 10% are shown schematically in Fig. 8. Areas active for celiac vasoconstriction were found only in the lateral marginal nucleus of the brachium conjunctivum (P4.0P3.1). The areas active for celiac vasodilation were located in the ventral central tegmental fields (P1.5A0.6) analogous to the area for iliac vasodilation (Fig. 6). The periaqueductal grey, locus caeruleus and underlying reticular formation are not active in control of celiac resistance. Sites stimulated while recording changes in renal vascular resistance are shown in Fig. 9. The average mean renal blood flow prior to stimulations was 52 + 16 ml/min. Changes in renal vascular resistance ranged from 0 to 365% of prestimulus levels with most changes falling between 0 and 150%. Only increases in renal vasoconstriction were obtained, and only in response to stimulation of the marginal nucle-

us of the brachium conjunctivum. Areas eliciting changes greater than 10% are shown schematically in Fig. 10. Areas active for renal vasoconstriction comprised a subset of areas active for iliac vasoconstriction and for increases in arterial pressure. Again, the periaqueductal grey, locus caeruleus and underlying reticular formation are not active in control of renal resistance. DISCUSSION This study indicates that neural structures in the marginal nucleus of the brachium conjunctivum and in areas of the central tegmental fields of the midbrain are involved in the control of arterial pressure and vascular resistance. At the time these experiments were conducted, few data were available about pontine and mesencephalic control of arterial pressure and vascular resistance. Previous studies had shown that electrical stimulation of the marginal nucleus of the brachium conjunctivum, locus caeruleus and underlying reticular formation elicited changes in heart rate and arterial pressureS.30.40. Of these areas, this study and other recent studies26. 45 implicate only the marginal nucleus of the brachium conjunctivum. This discrepancy may be because, (a) studies obtaining responses from stimulation of the locus caeruleus generally used large stimulation intensities and current spread may have activated neighboring structures and (b) studies obtaining responses from only the marginal nucleus of the brachium conjunctivum used small stimulation intensities that may have been ineffective in activating sufficient neural units in other areas to obtain a measurable response. This study also suggests the anatomical location of neural structures active in control of iliac, celiac and renal vascular resistance (Figs. 6, 8 and 10). The areas active in control of iliac vasoconstriction comprise the marginal nucleus of the brachium conjunctivum and a large portion of the mesencephalic central tegmental fields (Fig. 6). This is not the case for areas active in control of renal and celiac vasoconstriction (Figs. 8 and 10). Areas active in renal vasoconstriction are confined to the marginal nucleus of the brachium conjunctivum (P4.0-P2.1 in Fig. 10) and central tegmental fields of the caudal mesencephalon (P1.5). Areas active in celiac vasoconstriction are re-

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Fig. 10. Location of areas active in controlling changes in renal vascular resistance. Areas from which electrical stimulation led to increases and decreases in renal resistance are shown with vertical and horizontal lines, respectively. Areas from which electrical stimulation led to no change are represented with dot stippling.

297 stricted to the dorsal marginal nucleus of the brachium conjunctivum (P4.0-P3.1 in Fig. 8). It is possible that the ventral portion of the marginal nucleus of the brachium conjunctivum is also active in celiac vasoconstriction. In this study, that area was not stimulated and other studies have shown intense mesenteric constrictions during electrical stimulation of the marginal nucleus of the brachium conjunctivum 26. Since the areas active in vasoconstriction in each vascular bed vary in size according to the bed they innervate, it is possible that the size of the area active in controlling a vascular bed is proportional to the size of that bed. This notion is consistent with areas active in iliac and renal vasoconstriction but not with celiac vasoconstriction. The areas active in control of iliac vasodilation were located in the ventral central tegmental fields of the mesencephalon (P0.9-A1.6 in Fig. 6) and is in agreement with earlier findings 36. The areas active in control of celiac vasodilation were also located in areas similar to those representing iliac vasodilation (P1.5-A0.6 in Fig. 8). At no point did electrical stimulation elicit renal vasodilations. However, other studies using large stimulation intensities, have elicited renal dilation from stimulation of the ventral mesencephalon and hypothalamus 1. Generally, the dilations seen in the present study in the iliac and celiac vascular beds were not as intense as the constrictions. This difference in intensity may occur in part because, (a) neural units that mediate vasodilations have higher thresholds than those that mediate vasoconstrictions, (b) neural units that mediate vasodilation are sparse and a given stimulus may activate too few neural units to elicit a response in the vascular bed studied, (c) the anesthesia influences the neural circuitry mediating vasodilation to a greater degree than the circuitry mediating vasoconstriction, or (d) the vascular beds are initially near maximal dilation. In the present study, prestimulation measures of regional vascular flows suggested an intermediate level of constriction. The typical cardiovascular response seen during electrical stimulation of the marginal nucleus of the brachium conjunctivum was a rapid rise in arterial presstire and a decrease in heart rate, in agreement with previous reportsZ6,45. Hamilton et al. demonstrated that electrical stimulation of the marginal nucleus of the brachium conjunctivum in the rabbit

leads to bradycardia that occurs before the increase in arterial pressure and which is severely attenuated by prior bilateral cervical vagotomy 17, and suggested that the marginal nucleus of the brachium conjunctivum directly controlled vagal parasympathetics to the heart. In the present study, the animals were treated with Gallamine which suppresses vagal control of the heart, and decreases in heart rate were not as pronounced. In separate studies of ours not using Gallamine, large decreases in heart rate were often seen (Ward, D.G., unpublished). By using electrical stimulation, the overall course of central neural pathways mediating changes in arterial pressure and regional vascular resistance are likely to be revealed. This is because electrical stimulation tends to activate fibers of passage as well as cell bodies. At the level of the rostral pons, electrical stimulation of only the marginal nucleus of the brachium conjunctivum led to changes in arterial pressure and regional vascular resistance. Accordingly, this finding suggests strongly that most if not all pathways mediating rapid changes in arterial pressure and vascular resistance pass through or terminate in a discrete region of the rostral pons. Consistent with this suggestion, anatomical studies have shown two major pathways descending from cardiovascular active areas of the hypothalamus that course through the ventrolateral mesencephalon and the periaqueductal grey7,14,15,31,34. A ventrolateral pathway originates in limbic and anterolateral hypothalamic areas and courses in the ventrolateral mesencephalon to end in the caudal central tegmental fields and marginal nucleus of the brachium conjunctivum. A route through the periaqueductal grey originates in the posterior hypothalamus, descends through the periaqueductal grey to terminate around the level of the 3rd cranial nucleus. Secondary fibers from this region then radiate laterally and ventrally to terminate in the caudal central tegmental fields and marginal nucleus of the brachium conjunctivum2.6.15. 29. The mesencephalic areas described in the present study that are active in increasing arterial pressure and iliac vasoconstriction seem to coincide with the ventrolateral pathway (A3.3-A1.6 in Figs. 4 and 6). The dorsal pontine areas active in increasing arterial pressure and vasoconstriction seem to coincide in large part with the end of these pathways. Consistent with these observations, lesions of both the rostral periaqueduc-

298 tal grey and midbrain tegmentum prevent changes in arterial pressure and heart rate elicited by electrical stimulation of the hypothalamus 2°, but lesions of the rostral periaqueductal grey alone merely attenuate the responses. Furthermore, lesions of only the marginal nucleus of the brachium conjunctivum severely attenuate the responses of renal vasoconstriction to electrical stimulation of the medial and lateral hypothalamus 42. The final pathways responsible for the cardiovascular responses seen during stimulation of the marginal nucleus of the brachium conjunctivum appear to involve descending pathways through the ventrolateral medulla and not ascending pathways to hypothalamic and limbic structures 28,33,38 because lesions of the ventrolateral medulla eliminate the responses26,46 and midcollicular transection has no measured effect on the responses 26.46. Also, the cardiovascular responses seen during electrical stimulation of the marginal nucleus of the brachium conjunctivum apparently is not due to activation of fibers of passage from the fastigial nucleus because cerebeilectomy does not affect the response26, 46. However, the relative roles of ascending and descending pathways through the marginal nucleus of the brachium conjunctivum can-

not be determined from these sorts of data alone, The marginal nucleus of the brachium conjunctivum receives projections from numerous /i~rebrain structures that are implied in cardiovascular regulation, including the fastigial nucleus 37, hypothalamus~, the amygdala 17,J9.33,38 and parts of the cortex 32. The marginal nucleus of the brachium conjunctivum also receives fibers from areas in the medulla that are involved in cardiovascular regulation, including the nuclei around the solitary tract and underlying reticular formation21,33, the nucleus ambiquus 33 and the A1 and A5 catecholamine groups 4,24,33. It is evident that the marginal nucleus of the brachium conjunctivum is not only a likely part of a descending pathway but is also a site for neural integration of ascending and descending signals that ultimately influence cardiovascular regulation.

ABBREVIATIONS USED IN THE FIGURES

FTL FTP IC ICC ICX IP KF LC LLD LLV MGP P PAG PG PON RM RR SNC SNR SOM T I'B TD TR TV VTA

Taken from A.L. Berman, The Brain Stem of the Cat, University of Wisconsin Press, Madison, WI, 1968. 3 4 5MD 5MV 5N 5PD 5SM 5ST 6N 7N AQ BC BCM BCX BP CAE CI CNF CS DR FTC FTG

third cranial nucleus fourth cranial nucleus motor trigeminal nucleus: dorsal division motor trigeminal nucleus: ventral division fifth nerve principle sensory trigeminat nucleus alaminar spinal trigeminal nucleus spinal trigeminal tract sixth nerve facial nerve aqueduct of sylvius brachium conjunctivum marginal nucleus of the brachium conjunctivum decussation of the brachium conjunctivum brachium pontis locus caeruleus inferior central nucleus cuneiform nucleus superior central nucleus dorsal nucleus of the raphe central tegmental fields gigantocellular tegmental fields

ACKNOWLEDGEMENTS The authors gratefully acknowledge the superb technical assistance of Jane H. Ward. This research was supported by Grants HL26349, RR05431 and HL00837 to D . G . W . from the United States Public Health Service, National Institutes of Health.

lateral tegmental fields paralemniscal tegmental fields central nucleus of the interpeduncular central nucleus of the inferior colliculus external nucleus of the inferior colliculus interpeduncular nucleus KoUiker-Fuse nucleus central linear nucleus dorsal nucleus of the lateral lemniscus ventral nucleus of the lateral lemniscus medial geniculate pyramidal tract periaqueductal grey pontine grey preolivary nucleus red nucleus retrorubral nucleus substantia nigra compacta substantia nigra reticularis superior olive medial nucleus nucleus of the trapezoid trapezoid dorsal tegmental nucleus tegmental recticular nucleus ventral tegmental nucleus ventral tegmental nucleus of Tsai

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