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Convergence of sensory input from tooth pulp, optic chiasm and sciatic nerve onto locus coeruleus neurons in the rat
Neuroscience Letters, 12 (1979) 189--193
189
© Elsevier/North-HoUand Scientific Publishers Ltd.
CONVERGENCE OF SENSORY INPUT F R O M T O O T H PULP, OPTIC CHIASM AND SCIATIC NERVE ONTO LOCUS C O E R U L E U S N E U R O N S IN THE RAT
SEISHI IGARASHI, M A S A S H I S A S A and SHUJI T A K A O R I
Department of Pharmacology, Faculty of Medicine, Kyoto University, Kyoto 606 (Japan) (Received December 18th, 1978) (Revised versionreceived February 12th, 1979) (Accepted February 14th, 1979)
SUMMARY Electrophysiological studies using rats were performed to determine whether or n o t neurons in the locus coeruleus (LC), subcoeruleus and parabrachial areas receive convergence of sensory input from t o o t h pulp (TP), optic chiasm (OC) and sciatic nerve (SN). Convergence of input from these nerves was observed in 23% and 33% of LC and subcoeruleus neurons, respectively, and from t w o nerves in 31% and 20% of LC and subcoeruleus neurons, respectively, while convergence was rarely detected in parabrachial neurons. These results suggest that there is a convergence of peripheral sensory input onto more than half the noradrenergic coerulear neurons.
It has been d o c u m e n t e d that activation of noradrenaline-containing neurons originating in the locus coeruleus (LC) produces an inhibition of neuronal activity in the cerebral and cerebellar cortices, hippocampus, spinal trigeminal nucleus and superior colliculus [1,3,8--11,13]. Furthermore, stimulation of the peripheral nerves and skin transiently inhibits or accelerates the firing of LC neurons [ 5,6,14] ;however, these observations have been mainly based on the spontaneous firing discharge of LC neurons. We recently reported that more than 70% of LC neurons fired spikes upon ipsilateral t o o t h pulp (TP) stimulation [4]. The unilateral LC of rats contains approx. 1500 cells, which number is small from the standpoint of input from various areas of the peripheral and central nervous system. Therefore, the present study was an a t t e m p t to elucidate that different sensory input may converge onto the same neurons in the LC and subcoeruteus area. Male Wistar rats weighing 280--320 g were anesthetized with a-chloralose (70 mg/kg, i.p.). A bipolar stainless steel electrode with a tip diameter of 0.1 mm was inserted into the pulp of left lower incisor and fixed with dental
190 cement. A pair of platinum wire electrodes was twined round the right sciatic nerve (SN) exposed in the gluteal muscle. The skull was partially removed and a bipolar stimulating electrode was introduced stereotaxically into the optic chiasm (OC) (A: 7.4, L: 0.5, H: 10.0) according to the topographic map of Peltegrino and Cushman [ 7]. The animal was immobilized with gallamine triethiodide (40 mg/kg, i.p.) and then sustained by artificial respiration. Wound edges and pressure points were locally anesthetized with 8% lidocaine repeatedly throughout the experiment. Additional a-chloralose (40 mg/kg, i.p.) was administered when the experiment went over 4 h. Body temperature was maintained between 36.5°C and 38.0°C. A glass-insulated silver wire microelectrode with an electrical resistance of approx. 1 M~2 was inserted for recording single neuron activities in the left LC (P: 2.0, L: 1.2, H: 5.5--6.3). Stimuli composed of a square pulse with 0.05--0.1-msec duration and 5--30 V in intensity were applied to the TP, OC and SN every 1.6 sec. The responses were displayed on an oscilloscope (Nihon Kohden, VC-9) and at least 10 successive responses were photographed. After termination of each experiment, the recording sites were marked by passing an anodal current of 20--40 pA for 10--25 sec. The brain was then removed immediately and fixed in 10% formalin solution. The position of the electrode was histologically verified with thionine stain. Further experimental details are similar to those described elsewhere [4]. Out of 75 neurons tested, 45 were histologically confirmed to be located in the LC and 19 were in the subcoeruleus area. The subcoeruleus area was defined herein as the area just ventral to the LC and within 0.7 mm from the LC. The remaining 11 neurons were found in the parabrachial area which included the superior cerebellar peduncle and medial and lateral parabrachis! nuclei. Twenty-six out of 45 LC neurons, 15 out of 19 subcoeruleus neurons
TABLE I NUMBER OF NEURONS IN LC, SUBCOERULEUS AND PARABRACHIAL A R E A S IN RESPONSE TO STIMULATION OF TP, OC A N D SN Responded to stimulation o f following site(s)
TP + OC + SN
Number o f neurons LC
6
TP + SN OC + SN TP alone OC alone SN alone None Total
Subcoeruleus area
(23%)
5
(31%) 1 2 2 7 26
(27%)
(33%)
Parabrachial area
1
(20%) 4 1 0 2 15
(13%)
(9%) (27%)
1 0 0 6 11
(55%)
191
A
B
C
Fig. 1. Spikes of the same neuron in the locus coeruleus elicited by stimulation of ipsilateral TP (A) and OC (B) and contralateral SN (C). Calibration: 0.1 mV, 10 msec.
and all of 11 parabrachial neurons were serially tested as to responses to stimulation of the ipsilateral TP and OC and contralateral SN. The mean spontaneous firing rates of 17 LC, 17 subcoeruleus and 8 parabrachial neurons were 5.0 ± 1.6 (S.E.), 6.5 ± 2.1 and 5.9 + 1.6/sec, respectively. When responses to stimulation of the above-mentioned three nerves were tested on the same 26 LC neurons, 6 neurons (23%) fired spikes with a relatively consistent latency with all of these stimuli (Table I). Fig. 1 demonstrates the activity of a typical neuron in the LC elicited by stimulation of the TP, OC and SN, respectively. Eight LC neurons (31%) responded to stimulation of two of three nerves. Fig. 2 shows the latency distribution of LC neurons upon these stimulations. The spike latencies of the first spike were in the range 12.9--40.8, 6.2--58.4 and 5.4--40.5 msec in response to stimulation o f the TP, OC and SN, respectively. When the effect of stimuli to the three nerves on spontaneous firing of LC neurons was tested, there Number Mean o f neurons ± S E .
Spike latencies
TP
: •
OO oeee oeo
OC
°•
o ~ oOo •
SN
•
eooo
0
10
20
•
ee
:e
30
oe
•
•
40
50
SO
12
25.4:1=26 msec
14
225+4.4
13
23.3+2.7
7'Omsec
Fig. 2. Latency distribution of the first spike of locus coeruleus neurons (e) elicited by stimulation of ipsilateral TP, OC and SN.
192
were no significant reductions in the firing rate in any of 26 LC neurons, within 90 msec after each stimulation. Five (33%) out of 15 subcoeruleus neurons were activated by all stimuli given to the TP, OC and SN and 3 neurons (20%) fired spikes with stimulation of two of three nerves (Table I). In the parabrachial area, 6 (55%) out of 11 neurons were n o t affected by any of the three nerve stimulations. The present results suggest that most of LC neurons have no specific modality from the peripheral nerves, being parallel with those obtained by Nakamura [6] who reported that all LC neurons examined were excited by electrical stimulation of the skin around the elbow and knee joints and the optic nerve. The spike latencies of LC neurons with stimulation of the TP, OC and SN were widely distributed. Since the direct connections of the LC from the spinal trigeminal nucleus and dorsal horn of the spinal cord have been histologically traced in the rat [2], the short latency of the spike generation upon TC and SN stimulation could be due to direct transmission to the LC from the respective primary sensory nuclei. As discussed in our previous paper [4], the long latency is probably due to a multisynaptic delay in the respective relay nuclei such as the trigeminal sensory nuclei, lateral geniculate body and spinal dorsal horn. The extremely long latency may be attributed to a delay in the reticular formation, since impulses from the peripheral nerves are transmitted to the reticular formation. This possibility is supported by histological findings that there is a direct afferent projection from the reticular formation to the LC [2]. Inhibition and inhibition-excitation sequence of LC neurons with stimulation of the vagus nerve have been reported by Takigawa and Mogenson [ 14]. In the present study, however, the inhibition of spontaneous firing was not observed with stimulation of the TP, OC and SN. Similarly, most of the subcoeruleus neurons responded to stimulation of at least one nerve tested and convergence of sensory input from the peripheral nerves was obtained in the subcoeruleus neurons. In contrast to LC and subcoeruleus neurons, most of the parabrachial neurons apparently do not receive convergence of input from the TP, OC and SN. Since most of cells in the LC and subcoeruleus area of rats contain noradrenaline, the present results suggest that input from several peripheral nerves converge onto the same noradrenaline-containing neurons of LC as well as subcoeruleus area, but not onto the neurons in the parabrachial area. In conclusion, sensory input from the TP, OC and SN activates most of the LC and subcoeruleus neurons and converges on more than half the number of these neurons. ACKNOWLEDGEMENTS
The authors are grateful to Miss M. Ohara for preparing this manuscript and to Miss E. Ikeda for technical assistance.
193
REFERENCES
1 Austin, J.H. and Takaori, S., Studies of connections between locus coeruleus and cerebral cortex, Japan. J. Pharmacol., 26 (1976) 145--160. 2 Cedarbaum, J.M. and Aghajanian, G.K., Afferent projections to the rat locus coeruleus as determined by a retrograde tracing technique, J. comp. Neurol., 178 (1978) 1--16. 3 Hoffer, B.J., Siggins, G.R., Oliver, A.P. and Bloom, F.E., Activation of the pathway from locus coeruleus to rat cerebellar Purkinje neurons: Pharmacological evidence of noradrenergic central inhibition, J. Pharmacol. exp. Ther., 184 (1973) 553--569. 4 Igarashi, S., Sasa, M. and Takaori, S., Feedback loop between locus coeruleus and spinal trigeminal nucleus neurons responding to tooth pulp stimulation in the rat, Brain Res. Bull, 4 (1979) in press. 5 Korp, J., Bunney, B.S. and Aghajanian, G.K., Noradrenergic neurons: Morphine inhibition of spontaneous activity, Europ. J. Pharmacol., 25 (1974) 165--169. 6 Nakamura, S., Some electrophysiological properties of neurones of rat locus coeruleus, J. Physiol. (Lond.), 267 (1977) 641--658. 7 Pellegrino, L.J. and Cushman, A.J., A Stereotaxic Atlas of the Rat Brain, Meredith Publishing Co., New York, 1967. 8 Philis, J.W. and Kostopoulos, G.K., Activation of a noradrenergic pathway from the brain stem to rat cerebral cortex, Gen. Pharmacol., 8 (1977) 207--211. 9 Sasa, M., Munekiyo, K., Ikeda, H. and Takaori, S., Noradrenaline-mediated inhibition by locus coemleus of spinal trigeminal neurons, Brain Res., 80 (1974) 443--460. 10 Sasa, M. and Takaori, S., Influence of the locus coeruleus on transmission in the spinal trigeminal nucleus neurons, Brain Res., 55 (1973) 203--208. 11 Segal, M. and Bloom, F.E., The action of norepinephrine in the rat hippocampus. II. Activation of the input pathway, Brain Res., 72 (1974) 99--114. 12 Swanson, L.W., The locus coeruleus: A cytoarchitectonic, Golgi and immunohistochemical study in the albino rat,Brain Res., ii0 (1976) 39--56. 13 Takemoto, I.,Sam, M. and Takaori, S., Role of the locus coeruleus in transmission onto anteriorcolliculusneurons, Brain Res., 158 (1978) 269-278. 14 Takigawa, M. and Mogenson, G.J., A study of inputs to antidromically identified neurons of the locus coeruleus, Brain Res., 135 (1977) 217--230.
189
© Elsevier/North-HoUand Scientific Publishers Ltd.
CONVERGENCE OF SENSORY INPUT F R O M T O O T H PULP, OPTIC CHIASM AND SCIATIC NERVE ONTO LOCUS C O E R U L E U S N E U R O N S IN THE RAT
SEISHI IGARASHI, M A S A S H I S A S A and SHUJI T A K A O R I
Department of Pharmacology, Faculty of Medicine, Kyoto University, Kyoto 606 (Japan) (Received December 18th, 1978) (Revised versionreceived February 12th, 1979) (Accepted February 14th, 1979)
SUMMARY Electrophysiological studies using rats were performed to determine whether or n o t neurons in the locus coeruleus (LC), subcoeruleus and parabrachial areas receive convergence of sensory input from t o o t h pulp (TP), optic chiasm (OC) and sciatic nerve (SN). Convergence of input from these nerves was observed in 23% and 33% of LC and subcoeruleus neurons, respectively, and from t w o nerves in 31% and 20% of LC and subcoeruleus neurons, respectively, while convergence was rarely detected in parabrachial neurons. These results suggest that there is a convergence of peripheral sensory input onto more than half the noradrenergic coerulear neurons.
It has been d o c u m e n t e d that activation of noradrenaline-containing neurons originating in the locus coeruleus (LC) produces an inhibition of neuronal activity in the cerebral and cerebellar cortices, hippocampus, spinal trigeminal nucleus and superior colliculus [1,3,8--11,13]. Furthermore, stimulation of the peripheral nerves and skin transiently inhibits or accelerates the firing of LC neurons [ 5,6,14] ;however, these observations have been mainly based on the spontaneous firing discharge of LC neurons. We recently reported that more than 70% of LC neurons fired spikes upon ipsilateral t o o t h pulp (TP) stimulation [4]. The unilateral LC of rats contains approx. 1500 cells, which number is small from the standpoint of input from various areas of the peripheral and central nervous system. Therefore, the present study was an a t t e m p t to elucidate that different sensory input may converge onto the same neurons in the LC and subcoeruteus area. Male Wistar rats weighing 280--320 g were anesthetized with a-chloralose (70 mg/kg, i.p.). A bipolar stainless steel electrode with a tip diameter of 0.1 mm was inserted into the pulp of left lower incisor and fixed with dental
190 cement. A pair of platinum wire electrodes was twined round the right sciatic nerve (SN) exposed in the gluteal muscle. The skull was partially removed and a bipolar stimulating electrode was introduced stereotaxically into the optic chiasm (OC) (A: 7.4, L: 0.5, H: 10.0) according to the topographic map of Peltegrino and Cushman [ 7]. The animal was immobilized with gallamine triethiodide (40 mg/kg, i.p.) and then sustained by artificial respiration. Wound edges and pressure points were locally anesthetized with 8% lidocaine repeatedly throughout the experiment. Additional a-chloralose (40 mg/kg, i.p.) was administered when the experiment went over 4 h. Body temperature was maintained between 36.5°C and 38.0°C. A glass-insulated silver wire microelectrode with an electrical resistance of approx. 1 M~2 was inserted for recording single neuron activities in the left LC (P: 2.0, L: 1.2, H: 5.5--6.3). Stimuli composed of a square pulse with 0.05--0.1-msec duration and 5--30 V in intensity were applied to the TP, OC and SN every 1.6 sec. The responses were displayed on an oscilloscope (Nihon Kohden, VC-9) and at least 10 successive responses were photographed. After termination of each experiment, the recording sites were marked by passing an anodal current of 20--40 pA for 10--25 sec. The brain was then removed immediately and fixed in 10% formalin solution. The position of the electrode was histologically verified with thionine stain. Further experimental details are similar to those described elsewhere [4]. Out of 75 neurons tested, 45 were histologically confirmed to be located in the LC and 19 were in the subcoeruleus area. The subcoeruleus area was defined herein as the area just ventral to the LC and within 0.7 mm from the LC. The remaining 11 neurons were found in the parabrachial area which included the superior cerebellar peduncle and medial and lateral parabrachis! nuclei. Twenty-six out of 45 LC neurons, 15 out of 19 subcoeruleus neurons
TABLE I NUMBER OF NEURONS IN LC, SUBCOERULEUS AND PARABRACHIAL A R E A S IN RESPONSE TO STIMULATION OF TP, OC A N D SN Responded to stimulation o f following site(s)
TP + OC + SN
Number o f neurons LC
6
TP + SN OC + SN TP alone OC alone SN alone None Total
Subcoeruleus area
(23%)
5
(31%) 1 2 2 7 26
(27%)
(33%)
Parabrachial area
1
(20%) 4 1 0 2 15
(13%)
(9%) (27%)
1 0 0 6 11
(55%)
191
A
B
C
Fig. 1. Spikes of the same neuron in the locus coeruleus elicited by stimulation of ipsilateral TP (A) and OC (B) and contralateral SN (C). Calibration: 0.1 mV, 10 msec.
and all of 11 parabrachial neurons were serially tested as to responses to stimulation of the ipsilateral TP and OC and contralateral SN. The mean spontaneous firing rates of 17 LC, 17 subcoeruleus and 8 parabrachial neurons were 5.0 ± 1.6 (S.E.), 6.5 ± 2.1 and 5.9 + 1.6/sec, respectively. When responses to stimulation of the above-mentioned three nerves were tested on the same 26 LC neurons, 6 neurons (23%) fired spikes with a relatively consistent latency with all of these stimuli (Table I). Fig. 1 demonstrates the activity of a typical neuron in the LC elicited by stimulation of the TP, OC and SN, respectively. Eight LC neurons (31%) responded to stimulation of two of three nerves. Fig. 2 shows the latency distribution of LC neurons upon these stimulations. The spike latencies of the first spike were in the range 12.9--40.8, 6.2--58.4 and 5.4--40.5 msec in response to stimulation o f the TP, OC and SN, respectively. When the effect of stimuli to the three nerves on spontaneous firing of LC neurons was tested, there Number Mean o f neurons ± S E .
Spike latencies
TP
: •
OO oeee oeo
OC
°•
o ~ oOo •
SN
•
eooo
0
10
20
•
ee
:e
30
oe
•
•
40
50
SO
12
25.4:1=26 msec
14
225+4.4
13
23.3+2.7
7'Omsec
Fig. 2. Latency distribution of the first spike of locus coeruleus neurons (e) elicited by stimulation of ipsilateral TP, OC and SN.
192
were no significant reductions in the firing rate in any of 26 LC neurons, within 90 msec after each stimulation. Five (33%) out of 15 subcoeruleus neurons were activated by all stimuli given to the TP, OC and SN and 3 neurons (20%) fired spikes with stimulation of two of three nerves (Table I). In the parabrachial area, 6 (55%) out of 11 neurons were n o t affected by any of the three nerve stimulations. The present results suggest that most of LC neurons have no specific modality from the peripheral nerves, being parallel with those obtained by Nakamura [6] who reported that all LC neurons examined were excited by electrical stimulation of the skin around the elbow and knee joints and the optic nerve. The spike latencies of LC neurons with stimulation of the TP, OC and SN were widely distributed. Since the direct connections of the LC from the spinal trigeminal nucleus and dorsal horn of the spinal cord have been histologically traced in the rat [2], the short latency of the spike generation upon TC and SN stimulation could be due to direct transmission to the LC from the respective primary sensory nuclei. As discussed in our previous paper [4], the long latency is probably due to a multisynaptic delay in the respective relay nuclei such as the trigeminal sensory nuclei, lateral geniculate body and spinal dorsal horn. The extremely long latency may be attributed to a delay in the reticular formation, since impulses from the peripheral nerves are transmitted to the reticular formation. This possibility is supported by histological findings that there is a direct afferent projection from the reticular formation to the LC [2]. Inhibition and inhibition-excitation sequence of LC neurons with stimulation of the vagus nerve have been reported by Takigawa and Mogenson [ 14]. In the present study, however, the inhibition of spontaneous firing was not observed with stimulation of the TP, OC and SN. Similarly, most of the subcoeruleus neurons responded to stimulation of at least one nerve tested and convergence of sensory input from the peripheral nerves was obtained in the subcoeruleus neurons. In contrast to LC and subcoeruleus neurons, most of the parabrachial neurons apparently do not receive convergence of input from the TP, OC and SN. Since most of cells in the LC and subcoeruleus area of rats contain noradrenaline, the present results suggest that input from several peripheral nerves converge onto the same noradrenaline-containing neurons of LC as well as subcoeruleus area, but not onto the neurons in the parabrachial area. In conclusion, sensory input from the TP, OC and SN activates most of the LC and subcoeruleus neurons and converges on more than half the number of these neurons. ACKNOWLEDGEMENTS
The authors are grateful to Miss M. Ohara for preparing this manuscript and to Miss E. Ikeda for technical assistance.
193
REFERENCES
1 Austin, J.H. and Takaori, S., Studies of connections between locus coeruleus and cerebral cortex, Japan. J. Pharmacol., 26 (1976) 145--160. 2 Cedarbaum, J.M. and Aghajanian, G.K., Afferent projections to the rat locus coeruleus as determined by a retrograde tracing technique, J. comp. Neurol., 178 (1978) 1--16. 3 Hoffer, B.J., Siggins, G.R., Oliver, A.P. and Bloom, F.E., Activation of the pathway from locus coeruleus to rat cerebellar Purkinje neurons: Pharmacological evidence of noradrenergic central inhibition, J. Pharmacol. exp. Ther., 184 (1973) 553--569. 4 Igarashi, S., Sasa, M. and Takaori, S., Feedback loop between locus coeruleus and spinal trigeminal nucleus neurons responding to tooth pulp stimulation in the rat, Brain Res. Bull, 4 (1979) in press. 5 Korp, J., Bunney, B.S. and Aghajanian, G.K., Noradrenergic neurons: Morphine inhibition of spontaneous activity, Europ. J. Pharmacol., 25 (1974) 165--169. 6 Nakamura, S., Some electrophysiological properties of neurones of rat locus coeruleus, J. Physiol. (Lond.), 267 (1977) 641--658. 7 Pellegrino, L.J. and Cushman, A.J., A Stereotaxic Atlas of the Rat Brain, Meredith Publishing Co., New York, 1967. 8 Philis, J.W. and Kostopoulos, G.K., Activation of a noradrenergic pathway from the brain stem to rat cerebral cortex, Gen. Pharmacol., 8 (1977) 207--211. 9 Sasa, M., Munekiyo, K., Ikeda, H. and Takaori, S., Noradrenaline-mediated inhibition by locus coemleus of spinal trigeminal neurons, Brain Res., 80 (1974) 443--460. 10 Sasa, M. and Takaori, S., Influence of the locus coeruleus on transmission in the spinal trigeminal nucleus neurons, Brain Res., 55 (1973) 203--208. 11 Segal, M. and Bloom, F.E., The action of norepinephrine in the rat hippocampus. II. Activation of the input pathway, Brain Res., 72 (1974) 99--114. 12 Swanson, L.W., The locus coeruleus: A cytoarchitectonic, Golgi and immunohistochemical study in the albino rat,Brain Res., ii0 (1976) 39--56. 13 Takemoto, I.,Sam, M. and Takaori, S., Role of the locus coeruleus in transmission onto anteriorcolliculusneurons, Brain Res., 158 (1978) 269-278. 14 Takigawa, M. and Mogenson, G.J., A study of inputs to antidromically identified neurons of the locus coeruleus, Brain Res., 135 (1977) 217--230.