036 I-Y23O/Y2 85.00 ’ .oo (‘opynght r lYY2 Pergamon PreysI.td.
Rrcr/,l Rc\t,uv~II H~r//o/,n. Vol. 28. pp. 565m.67I, lYY2 Printed in the USA. ,111nghts reserved.
Influence of Nucleus Tractus Solitarius Stimulation and Baroreceptor Activation on Rat Parabrachial Neurons JACK
H. JHAMANDAS’
Received
AND
76 August
KIM
H. HARRIS
199 I
JHAMANDAS. J. H. AND K. H. HARRIS. Infl~rcncv o/ n/rc,/crc.t/I’NC’(~~\\o//f~r.clr\ \//v1!~/01/off trrir/ hilr-cv~‘tc,/,/or nc’//vrrl/o,~ O/I ~(11 paruhruch~a/ w~~ro~~.~ BRAIN RES BULL 28(4) 565-57 I. 1992.-The parabrachial nucleus (PBN) within the dorsolateral pons is a major recipient of autonomic-related inputs from more caudal levels of the hrainstem and. in particular. the nucleus of the solitary tract (NTS). Although the anatomical projections from the NTS to the PBN are well characterized. less is known concerning the influence of activating NTS efferents on PBN neurons and the response of the latter to cardiovascular-related inputs. The present study examined the response of PBN neurons to electrical stimulation of the depressor area wittun the NTS in urethancanesthetized rats. and subsequently. the influence of arterial baroreceptor activation and systemic angiotensin II (ANCi II) on these cells. Extracellular single-unit PBN recordings indicated that 92 of 217 (40.5”; ) cells were orthodromicallq excited and 35 of 227 (15.4%) inhibited consequent to NTS stimulation. Ten (4.5%) PBN cells displayed antidromic activation from the NTS. Of 41 of I I9 neurons responding to both NTS stimulation and baroreceptor activation. 29.3”;’ revealed a excitator! and 31.7”; an inhibitory response to the two stimuli. Fifteen PBN cells responded to NTS stimulation. barorcceptor activation. and the administration of systemic ANG II. with six cells displa>:ing either an excitatory or Inhibitory response to all three stimuli. fhese observations provide electrophysiological support for reciprocal connections bctmeen the NTS and PBN and indicate the presence of both excitatory and inhibitory projections to the pontine nucleus. A population of neurons influenced by activatmn of NTS ctferents also reveal a similarity of responses to inputs originating from peripheral arterial haroreceptors and systemic ,ANG II. Brainstem
Angiotensin
II
Electrophysiolog!
Blood pressure
THE parabrachial nucleus (PBN) has been proposed as a major relay for the transfer of a wide array of autonomic-related information from the more caudal levels of the neuraxis to the forebrain (1.h, 15.2223). Anatomical studies identified the PBN as a prominent target of ascending projections originating within the medulla, including the nucleus of the solitary tract (NTS). caudal and rostra1 ventrolateral medulla. and the area postrema (8. I2- 14.22-24). However, ventrolateral portions of the PBN and the adjacent KGlliker-Fuse (KF) nuclei also provided a reciprocal input to these medullary sites (6,7) and in particular to the NTS. The bidirectional anatomical linkage between the parabrachial complex and the NTS provides a framework for the modulation of autonomic responses at both rostra1 and caudal levels of the brainstem. However, the nature of the synaptic input from the NTS to PBN. that is, whether it is excitatory, inhibitory, or both, is not as well defined. In the rat. neurons within the lateral PBN have been identified to be responsive to hemorrhage (29). baroreceptor activation (IO), and stimulation of buffer nerves (1). In addition, systemic
angiotensin II (ANG II) has shown to alter the excitability of PBN neurons through mechanisms other than baroreceptor activation consequent to the pressor effects of the peptidc ( 10). Subnuclei located in lateral division of the PBN that contain neurons responsive to cardiovascular stimuli also receive significant projections arising from the caudal medial and commissural portions of the NTS (8.12,13). The NTS receives and processes a wide variety of visceral inputs including those originating from taste receptors. gastrointestinal alferents, lung stretch receptors, and somatic afferents. but the caudal medial and commissural compartments of this nucleus also encompass the site of primary termination of cardiovascular afferents originating in the periphery ( I I ). Electrophysiological data confirmed the presence of neurons within this relay area of the NTS that respond to baro- and chemoreceptor stimulation (3.25). In the present study. we first examined electrophysiologically. the orthodromic influence of NTS stimulation on PBN neurons, and also antidromically identified neurons within the PBN that project to the NTS. In addition. we assessed the response of NTS-
’ Requests for repnnts should be addressed to Dr. Jack H. Jhamandas. Alberta. Edmonton, Alberta. T6G 287. Canada.
Division
565
of Neurology.
2E3.17
Walter
Mackenzie
Centre.
liniverslty
of
566
HAKKlS
FIG. 1.(A) Schematic coronal section of the rat brainstem at the level of the NTS depicting location of electrode tips (+) where electrical stimulation evoked a depressor response [as in (B)] and an alteration in the excitability of PBN neurons. Stimulation at sites outside the NTS region (II) produced neither a change in blood pressure nor an influence in the activity of PBN neurons. (B) Blood pressure (BP) and heart rate changes evoked as a consequence of a brief (1 s duration) burst of stimuli applied through the electrode positioned within the NTS at 50 Hz with varying current intensities (FA). (C) Photomice~raph of a lesion within the NTS denoting the position of the tip of the stimulating electrode. Calibration bar = 100 pm.
activated PBN cells to peripheral arterial baror~~ptor activation and administration of systemic .ANG II. METHOD
Surgical Preparaiio~ Experiments were performed on 25 male Sprague-Dawley rats (200-350 g) in which anesthesia was induced with urethane (1.2-I .5 g/kg). The femoral artery and vein were catheterized (PE 50 Intmmedic) to monitor arterial blood pressure continuously and permit the administration of drugs, respectively.
Heart rate was monitored c~utinuously from the direct arterial (pulse) pressure trace, and body temperature maintained at 37°C using a feedback-controlled heating blanket. Animals were then placed in a stereotaxic frame and burr holes drilled in the skull for subsequent placement of stimulating and recording electrodes. Electrophpiology Concentric bipolar stimulating electrodes (tip-ring separation < 0.25 mm; impedance 2~-4~ kQ) were stereotaxically implanted within the NTS. Prior to fixation with dental cement,
TABLE 1 SUMMARY OF NTS ST~MUL~r~ON-EVO~D
No. of PBN neurons Latency (ms) Duration (ms)
RESPONSES IN PBN NEURONS
n @J)
Excited
Inhibited
Antidromic
No Response
227 (100%) -
92 (40.5%) 14.8 rfi 1.0 28.2 f 2.9
35 ( i 5.4%) 14.6 r 1.2 6 I.5 I 4.9
IO (4.5%) 15.5 f 1.0 -
90 (39.6%) -
NTS AND
BARORECEPTOR
INPUT
TO RAT PARABRACHIAL
567
NEURONS
stimuli applied with interstimulus interval < IO ms. and evidence of collision cancellation of the antidromic response with a spontaneous action potential. In cases where stable, baseline recording was obtained for more than 3 min. the responsiveness of these neurons to NTS stimulation and baroreceptor activation was assessed. Single cathodal pulses (200 PCS,50- I50 PA) were applied through the NTS electrode and the influence on the excitability of PBN neurons was assessed. Activation of peripheral arterial baroreceptors was achieved by a brief intravenous (i.v.) administration of 210 pg of Ihe cu-adrenergic agonist, metaraminol. that was sufficient to elevate mean arterial pressure by at least 40-60 mmHg (2.9). In some cells. the effect of systemlcally administered angiotensin II (ANG II) was also assessed. The doses for ANocalization of aortic and carotid baroreceptor and chemoreceptor primary afferents in the brainstem. In: Buckley J. P.; Ferrario C. M., eds. Central nervous system mechanisms in hypertension. New York: Raven Press; I98 I 12. King. G. Topology of ascending brainstem projections to nucleus parabrachialis in the cat. J. Comp. Neural. 191:615-638; 1980. 13. Loewy, A. D.: Burton. H. Nuclei of the solitary tract: Efferent projections to the lower brainstem and spinal cord in the cat. J. Camp. Neural. IX I :42 I-450; 1978.
14. Loewy, A. D.; Wallach. J. H.; McKellar. S. Efferent connections of the ventral medulla oblongata in the rat. Brain Res. Rev. 3:63-80: 1981. 15. Moga. M. M.; Herbert. H.; Hurley, K. M.: Yasui. Y.; Gray, 7. S.: Saper. C. B. Organization of central basal forebrain, and hypothalamus afferents to the parabrachial nucleus in the rat. J. Comp. Neurol. 295:624-66 1; 1990. 16. Mraovitch. S.: Kumada. M.: Reis. D. J. Role of the nucleus parabrachialis in cardiovascular regulation in the cat. Brain Res. 232: 57-75: 1982. 17. Norgren. R. Projections from the nucleus of the solitary tract in the rat. Neuroscience 3:207-2 18; 1978. 18. Ohman. L. E.; Johnson, A. K. Lesions in lateral parabrachial nucleus enhance drinking to angiotensin II and isoproterenol. Am. J. Physiol. (Reg. Integr. Comp. Physiol., 25) 25l:R504-R509: 1986. 19. Ohman. L. E.; Shade. R. E.: Hayvvood, J. R. Parabrachial nucleus modulation of vasopressin release. Am. J. Physiol. (Reg. Integr. Comp. Physiol.. 27) 258:R358-R364: 1990. 20. Papas, S.: Ferguson. A. V. Electrophysiological characterization of reciprocal connections between the parabrachial nucleus and the area postrema in the rat. Brain Res. Bull. 24:577-582: 1990. 2 I. Pellegrino, I.. J.: Pellegrino. A. S.; Cushman. A. J. A stereotaxic atlas of the rat brain (2nd ed.). New York: Plenum: 1979, 22. Ricardo. J. A.; Koh. E. T. Anatomical evidence ofdirect projections from the nucleus ofthe solitary tract to the hypothalamus. amygdala and other forebrain structures in the rat. Brain Res. 153: l-26: 1978. 23. Saper, C. B.: Loewy. A. D. Efferent connections of the parabrachial nucleus in the rat. Brain Res. I97:29 l-3 17: 1980. 24. Shapiro. R. E.: Miselis. R. R. The central neural connections of the area postrema of the rat. J. Comp. Neurol. 234:344-364; 1985. 25. Spyer, K. M. Neural organization and control of the baroreceptor reflex. Rev. Physiol. Biochem. Pharmacol. XX:I’- 124; 198 I. 26. Sved. A. F. Pontine pressor sites which release vasopressin. Brain Res. 369: 14% 150: 1986. 27. Talman. W. T.: Robertson. S. C. Glycine. like glutamate. microinjetted into the nucleus tractus solitarii of rat decreases blood pressure and heart rate. Brain Res. 477:7-l 3; 1989. 28. Urbanski, R. W.: Sapru. H. N. Putative neurotransmitters involved in medullary cardiovascular regulation. J. .Auton. Nerv. Syst 25: IXI-193: 198X. 29. Ward. D. G. Neurons m the parabrachial nuclei respond to hemorrhage. Brain Res. 49 I :80-92: 1989.
Rrcr/,l Rc\t,uv~II H~r//o/,n. Vol. 28. pp. 565m.67I, lYY2 Printed in the USA. ,111nghts reserved.
Influence of Nucleus Tractus Solitarius Stimulation and Baroreceptor Activation on Rat Parabrachial Neurons JACK
H. JHAMANDAS’
Received
AND
76 August
KIM
H. HARRIS
199 I
JHAMANDAS. J. H. AND K. H. HARRIS. Infl~rcncv o/ n/rc,/crc.t/I’NC’(~~\\o//f~r.clr\ \//v1!~/01/off trrir/ hilr-cv~‘tc,/,/or nc’//vrrl/o,~ O/I ~(11 paruhruch~a/ w~~ro~~.~ BRAIN RES BULL 28(4) 565-57 I. 1992.-The parabrachial nucleus (PBN) within the dorsolateral pons is a major recipient of autonomic-related inputs from more caudal levels of the hrainstem and. in particular. the nucleus of the solitary tract (NTS). Although the anatomical projections from the NTS to the PBN are well characterized. less is known concerning the influence of activating NTS efferents on PBN neurons and the response of the latter to cardiovascular-related inputs. The present study examined the response of PBN neurons to electrical stimulation of the depressor area wittun the NTS in urethancanesthetized rats. and subsequently. the influence of arterial baroreceptor activation and systemic angiotensin II (ANCi II) on these cells. Extracellular single-unit PBN recordings indicated that 92 of 217 (40.5”; ) cells were orthodromicallq excited and 35 of 227 (15.4%) inhibited consequent to NTS stimulation. Ten (4.5%) PBN cells displayed antidromic activation from the NTS. Of 41 of I I9 neurons responding to both NTS stimulation and baroreceptor activation. 29.3”;’ revealed a excitator! and 31.7”; an inhibitory response to the two stimuli. Fifteen PBN cells responded to NTS stimulation. barorcceptor activation. and the administration of systemic ANG II. with six cells displa>:ing either an excitatory or Inhibitory response to all three stimuli. fhese observations provide electrophysiological support for reciprocal connections bctmeen the NTS and PBN and indicate the presence of both excitatory and inhibitory projections to the pontine nucleus. A population of neurons influenced by activatmn of NTS ctferents also reveal a similarity of responses to inputs originating from peripheral arterial haroreceptors and systemic ,ANG II. Brainstem
Angiotensin
II
Electrophysiolog!
Blood pressure
THE parabrachial nucleus (PBN) has been proposed as a major relay for the transfer of a wide array of autonomic-related information from the more caudal levels of the neuraxis to the forebrain (1.h, 15.2223). Anatomical studies identified the PBN as a prominent target of ascending projections originating within the medulla, including the nucleus of the solitary tract (NTS). caudal and rostra1 ventrolateral medulla. and the area postrema (8. I2- 14.22-24). However, ventrolateral portions of the PBN and the adjacent KGlliker-Fuse (KF) nuclei also provided a reciprocal input to these medullary sites (6,7) and in particular to the NTS. The bidirectional anatomical linkage between the parabrachial complex and the NTS provides a framework for the modulation of autonomic responses at both rostra1 and caudal levels of the brainstem. However, the nature of the synaptic input from the NTS to PBN. that is, whether it is excitatory, inhibitory, or both, is not as well defined. In the rat. neurons within the lateral PBN have been identified to be responsive to hemorrhage (29). baroreceptor activation (IO), and stimulation of buffer nerves (1). In addition, systemic
angiotensin II (ANG II) has shown to alter the excitability of PBN neurons through mechanisms other than baroreceptor activation consequent to the pressor effects of the peptidc ( 10). Subnuclei located in lateral division of the PBN that contain neurons responsive to cardiovascular stimuli also receive significant projections arising from the caudal medial and commissural portions of the NTS (8.12,13). The NTS receives and processes a wide variety of visceral inputs including those originating from taste receptors. gastrointestinal alferents, lung stretch receptors, and somatic afferents. but the caudal medial and commissural compartments of this nucleus also encompass the site of primary termination of cardiovascular afferents originating in the periphery ( I I ). Electrophysiological data confirmed the presence of neurons within this relay area of the NTS that respond to baro- and chemoreceptor stimulation (3.25). In the present study. we first examined electrophysiologically. the orthodromic influence of NTS stimulation on PBN neurons, and also antidromically identified neurons within the PBN that project to the NTS. In addition. we assessed the response of NTS-
’ Requests for repnnts should be addressed to Dr. Jack H. Jhamandas. Alberta. Edmonton, Alberta. T6G 287. Canada.
Division
565
of Neurology.
2E3.17
Walter
Mackenzie
Centre.
liniverslty
of
566
HAKKlS
FIG. 1.(A) Schematic coronal section of the rat brainstem at the level of the NTS depicting location of electrode tips (+) where electrical stimulation evoked a depressor response [as in (B)] and an alteration in the excitability of PBN neurons. Stimulation at sites outside the NTS region (II) produced neither a change in blood pressure nor an influence in the activity of PBN neurons. (B) Blood pressure (BP) and heart rate changes evoked as a consequence of a brief (1 s duration) burst of stimuli applied through the electrode positioned within the NTS at 50 Hz with varying current intensities (FA). (C) Photomice~raph of a lesion within the NTS denoting the position of the tip of the stimulating electrode. Calibration bar = 100 pm.
activated PBN cells to peripheral arterial baror~~ptor activation and administration of systemic .ANG II. METHOD
Surgical Preparaiio~ Experiments were performed on 25 male Sprague-Dawley rats (200-350 g) in which anesthesia was induced with urethane (1.2-I .5 g/kg). The femoral artery and vein were catheterized (PE 50 Intmmedic) to monitor arterial blood pressure continuously and permit the administration of drugs, respectively.
Heart rate was monitored c~utinuously from the direct arterial (pulse) pressure trace, and body temperature maintained at 37°C using a feedback-controlled heating blanket. Animals were then placed in a stereotaxic frame and burr holes drilled in the skull for subsequent placement of stimulating and recording electrodes. Electrophpiology Concentric bipolar stimulating electrodes (tip-ring separation < 0.25 mm; impedance 2~-4~ kQ) were stereotaxically implanted within the NTS. Prior to fixation with dental cement,
TABLE 1 SUMMARY OF NTS ST~MUL~r~ON-EVO~D
No. of PBN neurons Latency (ms) Duration (ms)
RESPONSES IN PBN NEURONS
n @J)
Excited
Inhibited
Antidromic
No Response
227 (100%) -
92 (40.5%) 14.8 rfi 1.0 28.2 f 2.9
35 ( i 5.4%) 14.6 r 1.2 6 I.5 I 4.9
IO (4.5%) 15.5 f 1.0 -
90 (39.6%) -
NTS AND
BARORECEPTOR
INPUT
TO RAT PARABRACHIAL
567
NEURONS
stimuli applied with interstimulus interval < IO ms. and evidence of collision cancellation of the antidromic response with a spontaneous action potential. In cases where stable, baseline recording was obtained for more than 3 min. the responsiveness of these neurons to NTS stimulation and baroreceptor activation was assessed. Single cathodal pulses (200 PCS,50- I50 PA) were applied through the NTS electrode and the influence on the excitability of PBN neurons was assessed. Activation of peripheral arterial baroreceptors was achieved by a brief intravenous (i.v.) administration of 210 pg of Ihe cu-adrenergic agonist, metaraminol. that was sufficient to elevate mean arterial pressure by at least 40-60 mmHg (2.9). In some cells. the effect of systemlcally administered angiotensin II (ANG II) was also assessed. The doses for ANocalization of aortic and carotid baroreceptor and chemoreceptor primary afferents in the brainstem. In: Buckley J. P.; Ferrario C. M., eds. Central nervous system mechanisms in hypertension. New York: Raven Press; I98 I 12. King. G. Topology of ascending brainstem projections to nucleus parabrachialis in the cat. J. Comp. Neural. 191:615-638; 1980. 13. Loewy, A. D.: Burton. H. Nuclei of the solitary tract: Efferent projections to the lower brainstem and spinal cord in the cat. J. Camp. Neural. IX I :42 I-450; 1978.
14. Loewy, A. D.; Wallach. J. H.; McKellar. S. Efferent connections of the ventral medulla oblongata in the rat. Brain Res. Rev. 3:63-80: 1981. 15. Moga. M. M.; Herbert. H.; Hurley, K. M.: Yasui. Y.; Gray, 7. S.: Saper. C. B. Organization of central basal forebrain, and hypothalamus afferents to the parabrachial nucleus in the rat. J. Comp. Neurol. 295:624-66 1; 1990. 16. Mraovitch. S.: Kumada. M.: Reis. D. J. Role of the nucleus parabrachialis in cardiovascular regulation in the cat. Brain Res. 232: 57-75: 1982. 17. Norgren. R. Projections from the nucleus of the solitary tract in the rat. Neuroscience 3:207-2 18; 1978. 18. Ohman. L. E.; Johnson, A. K. Lesions in lateral parabrachial nucleus enhance drinking to angiotensin II and isoproterenol. Am. J. Physiol. (Reg. Integr. Comp. Physiol., 25) 25l:R504-R509: 1986. 19. Ohman. L. E.; Shade. R. E.: Hayvvood, J. R. Parabrachial nucleus modulation of vasopressin release. Am. J. Physiol. (Reg. Integr. Comp. Physiol.. 27) 258:R358-R364: 1990. 20. Papas, S.: Ferguson. A. V. Electrophysiological characterization of reciprocal connections between the parabrachial nucleus and the area postrema in the rat. Brain Res. Bull. 24:577-582: 1990. 2 I. Pellegrino, I.. J.: Pellegrino. A. S.; Cushman. A. J. A stereotaxic atlas of the rat brain (2nd ed.). New York: Plenum: 1979, 22. Ricardo. J. A.; Koh. E. T. Anatomical evidence ofdirect projections from the nucleus ofthe solitary tract to the hypothalamus. amygdala and other forebrain structures in the rat. Brain Res. 153: l-26: 1978. 23. Saper, C. B.: Loewy. A. D. Efferent connections of the parabrachial nucleus in the rat. Brain Res. I97:29 l-3 17: 1980. 24. Shapiro. R. E.: Miselis. R. R. The central neural connections of the area postrema of the rat. J. Comp. Neurol. 234:344-364; 1985. 25. Spyer, K. M. Neural organization and control of the baroreceptor reflex. Rev. Physiol. Biochem. Pharmacol. XX:I’- 124; 198 I. 26. Sved. A. F. Pontine pressor sites which release vasopressin. Brain Res. 369: 14% 150: 1986. 27. Talman. W. T.: Robertson. S. C. Glycine. like glutamate. microinjetted into the nucleus tractus solitarii of rat decreases blood pressure and heart rate. Brain Res. 477:7-l 3; 1989. 28. Urbanski, R. W.: Sapru. H. N. Putative neurotransmitters involved in medullary cardiovascular regulation. J. .Auton. Nerv. Syst 25: IXI-193: 198X. 29. Ward. D. G. Neurons m the parabrachial nuclei respond to hemorrhage. Brain Res. 49 I :80-92: 1989.
