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The ventromedial nucleus as thalamic relay for fastigial projections to the cat insular cortex
Neuroscience Letters, 56 (1985) 45 49
45
Elsevier Scientific Publishers Ireland Ltd.
NSL 03267
THE V E N T R O M E D I A L N U C L E U S AS T H A L A M I C RELAY F O R F A S T I G I A L P R O J E C T I O N S TO T H E CAT I N S U L A R C O R T E X
T. NODA* and H. OKA
Department o f Physiology, Fukui Medical School, Fukui 910-11 (Japan) (Received January 12th, 1985; Revised version received February 4th, 1985; Accepted February 6th, 1985)
Key words." thalamic ventromedial nucleus - suprageniculate nucleus - fastigial nucleus - insular cortex - laminar field potential analysis - cat
Electrical stimulation of the thalamic ventromedial nucleus (VM) produced surface-negative field potentials in the insular cortex of the cat. Laminar field potential analysis revealed that the VM-evoked potentials showed the same depth profile as the potentials evoked by stimulation of the cerebellar fastigial nucleus (FN). The active synaptic site for both evoked potentials is indicated to be located in layer l of the insular cortex. These results suggest that the VM mediates the FN projections onto layer I of the insular cortex.
The insular cortex of the cat lies in the ventral bank of the anterior ectosylvian sulcus (AES) and the adjacent anterior sylvian gyrus [1, 2]. Recently, we reported electrophysiological evidence for bilateral projections from the cerebellar fastigial nucleus (FN) to layer I of the insular cortex in the cat [6]. According to morphological studies, the insular cortex receives thalamic afferent fibers from the ventromedial nucleus (VM) and the suprageniculate nucleus (SG) [1, 2, 7]. In this study, we examined the thalamocortical responses to electrical stimulation of these thalamic nuclei and compared them with the FN-evoked responses in the insular cortex, in order to determine the possible thalamic relay nucleus for the FN-insular projections. Adult cats, weighing 3.3-3.7 kg, were anesthetized with Nembutal (35 m g / k g , i.p.). Each animal was placed in a stereotaxic frame. Craniotomy was performed to expose the left cerebral cortex and the cerebellum. Concentric stimulating electrodes (outer diameter, 0.3 ram) were introduced stereotaxically into the thalamic VM (A, 10; L, 1.5-2; H, 0) [4] and the SG (A, 5; L, 5-6; H, - 1) [4] of the left side, and also into the bilateral fastigial nuclei of the cerebellum. Electrical stimulation of these sites was made with square wave pulses of 0.5 m A intensity and 0.3 ms duration at 1/s. The effects of stimulation were first explored by a silver ball *Author for correspondence.
0304-3940/85/$ 03.30 @ 1985 Elsevier Scientific Publishers Ireland Ltd.
46 electrode on the surface of the insular cortex. Then, laminar field potentials were recorded through glass microelectrodes filled with 2°7o Pontamine Sky Blue solution in 0.5 M sodium acetate (3-5 M~2). The selected recording depths were marked by iontophoretic deposition of Pontamine Sky Blue from the electrode tip (5 /~A for 5 rain). The exposed cortex usually had warm Ringer solution poured over to prevent it from cooling and drying. Following the experiment, electrolytic lesions were made through each stimulating electrode, and then the animal was perfused with 10% formol-saline containing 0.2% potassium ferrocyanide. The brain was removed, and frontal frozen sections were made, 100 txm thick, and then counterstained with neutral red. The cortical surface-potentials (S.R.) in Fig. IA were recorded with a silver ball electrode in the insular cortex close to the ventral bank of the AES (a black dot in Fig. 1B). Electrical stimulation of the VM produced surface-negative potentials in this region (S.R. in Fig. lax). in the same region, stimulation of the contralateral FN also produced surface-negative potentials (S.R. in Fig. 1A~), as previously reported [6]. The latencies of the VM- and FN-evoked potentials were 3 ms and 6 ms, respectively. On the other hand, stimulation of the SG produced surfacepositive potentials in the insular cortex (S.R. in Fig. 1A3). The SG-evoked surfacepositive potentials consisted of two components, i.e. early small positive deflection and the following large positive one; the latencies were 3 ms and 10 ms, respectively. Laminar field potentials (the records below S.R. in Fig. 1At on stimulation of the contralateral FN (Fig. 1AI), the ipsilateral VM (Fig. 1A2) and SG (Fig. IA3) were recorded through one and the same microelectrode penetration in the insular cortex. The insertion point of this track on the cortical surface corresponds to a black dot in Fig. lB. In Fig. 1At, A2, the FN- (Fig. 1All and VM-evoked potentials (Fig. 1A2) showed almost the same depth profile. They consisted of negative waves at the recording depths of 0-50 btm, turned flat at 150/tm and then reversed polarity at deeper depths down to 2750/zm. The recording depths marked with blue dye spots were 150 p.m and 2750 #m. In Fig. IC, these two dye spots can be seen on the frontal section of the insular cortex (A15). The dye spot at 150/,m was located in the upper half of layer 1 and the dye spot at 2750/,m lies in layer VI. The direction of the track (an arrow in Fig. IC) was almost perpendicular to the cortical surface. In the same track, the SG-evoked potentials consisted of two consecutive positive waves al recording depths of 0-250/,nl. At 500/ml, only their late component reversed polarity. Since their early component also reversed polarity at 1250 /,m, fused negative potentials were seen at deeper depths down to 2750/,m. Fig. 2 shows the histological locations of electrolytic lesions through the stimulating electrode tips for the VM (an arrow in Fig. 2a) and the SG (an arrow in Fig. 2b) in the same animal as that of Fig. 1. Our results indicate that both VM and FN stimulation produce surface-negative potentials in the insular cortex. Laminar field potential analysis showed that the FNand VM-evoked potentials shared the same depth profile. The isoelectric points of
47
A
,
3
s .-
10.2m
50 150 0~m~m~lm
!~uL,pi~,
250 ' ~ m ~ "
500
13
750
1000 1250
1750
2250
2750
_Jo.smsmV
Fig. 1. A: laminar field potentials recorded through one and the same microelectrode penetration in the insular cortex on stimulation of the contralateral FN (AL) and the ipsilateral VM (A2) and the SG (A3). Cortical surface-potentials are shown in the uppermost row (S.R.). The polarity of all the potentials is upward-negative. Each trace is the superimposition of about 5 sweeps. B and C: histological localization of the surface-recording and microelectrode-recording sites in A. B: a black dot on the surface of the insular cortex indicates the recording site with a silver ball electrode as well as the insertion point of the microelectrode track in A. C: an arrow indicates the direction of the track. Two dye spots marked at the recording depths of 150 #m and 2750 ~m in A were located in cortical layers 1 and VI, respectively. AES, anterior ectosylvian sulcus; ARS, anterior rhinal sutcus; CI, claustrum; Pu, putamen. Scale bar= 2 mm.
b o t h e v o k e d p o t e n t i a l s w e r e l o c a t e d in l a y e r I o f t h e i n s u l a r c o r t e x . T h e s e f i n d i n g s s u g g e s t t h a t b o t h t h e F N - a n d V M - e v o k e d p o t e n t i a l s o r i g i n a t e f r o m e x c i t a t o r y inp u t s t o l a y e r I o f t h a t c o r t e x . M o r p h o l o g i c a l l y , it h a s b e e n r e p o r t e d t h a t m a n y F N f i b e r s t e r m i n a t e in t h e V M [8]. T h e d i f f e r e n c e o f 3 m s b e t w e e n t h e l a t e n c i e s o f t h e F N - a n d V M - e v o k e d p o t e n t i a l s in o u r s t u d y s e e m s t o a g r e e w i t h t h e l a t e n c y o f t h e
48
Fig. 2. Histological localization of lhe stimulating electrode lips by electrolytic lesions. Arrows indicate lhe locations of the stimulating electrode tips for the VM (a) and the SG (b) on frontal sections at A I0 and A5, respectively, in the same animal as that of Fig. 1. CeM, central medial nucleus; CL, central lateral nucleus; LD, lateral dorsal nucleus; LG, laleral geniculate complex; LP, lateral poslerior nucleus; MD, mediodorsal nucleus; MG, medial geniculate complex; ML, medial lemniscus; MTT, mare millothalamic tract; Pc, paracentral nu,:lens; Pt, preteclum; RN, red nucleus; SG, suprageniculate nucleus; SN, substantia nigra; VB, ventrobasa] complex: VI, ventrolateral nucleus; VM, ventromedial nucleus. Scale bar 2 ram.
F N - e v o k e d o r t h o d r o m i c spikes o f n e u r o n s in the VM [5]. H e r k e n h a m [3] r e p o r t e d hat the VM-cortical p r o j e c t i o n is d i s t r i b u t e d in layer I o f the entire ipsilateral n e o c o r t e x o f the rat. All o f these findings m a y s u p p o r t the possibility that the F N e v o k e d s u r f a c e - n e g a t i v e potentials in the insular cortex are m e d i a t e d by the VM. O n the o t h e r h a n d , the S G - e v o k e d p o t e n t i a l s in the insular cortex are surfacepositive, a n d their d e p t h profile is quite different f r o m that o f the VM- or F N e v o k e d p o t e n t i a l s . W h e n the r e c o r d i n g depths at which the late c o m p o n e n t o f the S G - e v o k e d p o t e n t i a l s reversed p o l a r i t y , as the p o t e n t i a l s at 500/xm in Fig. 1A3, were m a r k e d with dye spots in a d i f f e r e n t a n i m a l , these dye spots were located in the upper part o f layer III o f the insular cortex (not shown). The early c o m p o n e n t o f the S G - e v o k e d p o t e n t i a l s reverses p o l a r i t y at still d e e p e r depths, as the potentials at 1250 #m in Fig. 1A3, t h a n their late c o m p o n e n t . In Fig. 1C, the r e c o r d i n g d e p t h o f 1250 #m can be e s t i m a t e d to c o r r e s p o n d a p p r o x i m a t e l y to the cortical d e p t h a r o u n d the b o r d e r between layers 11I a n d IV. These results suggest that the S G - e v o k e d p o t e n t i a l s in the insular cortex o r i g i n a t e f r o m e x c i t a t o r y t h a l a m o c o r t i c a l inputs to d e e p e r layers, p r o b a b l y layers l l I a n d IV. W e are grateful to Mr. H. Y o s h i k a w a for assistance in the e x p e r i m e n t s .
49 1 Burton, H. and Kopf, E.M., Connections between the thalamus and the somatosensory areas of the anterior ectosylvian gyrus in the cat, J. Comp. Neurol., 224 (1984) 173-205. 2 Guldin, W.O. and Markowitsch, H.J., Cortical and thalamic afferent connections of the insular and adjacent cortex of the cat, J. Comp. Neurol., 229 (1984) 393-418. 3 Herkenham, M., The afferent and efferent connections of the ventromedial thalamic nucleus in the rat, J. Comp. Neurol., 183 (1979) 487-518. 4 Jasper, H.H. and Ajmone-Marsan, C., A Stereotaxic Atlas of the Diencephalon of the Cat, National Research Council of Canada, Ottawa, 1954. 5 Nakamura, M. and Matsuda, Y., Re-evaluation of cortical and thalamic responses evoked by stimulation of the cerebellar fastigial nucleus in the cat, Jpn. J. Physiol., 33 (1983) 215-226. 6 Noda, T. and Oka, H., Fastigial inputs to the insular cortex in the cat: field potential analysis, Neurosci. Lett., 53 (1985) 331-336. 7 Roda, J.M. and Reinoso-Su~trez, F., Topographical organization of the thalamic projections to the cortex of the anterior ectosylvian sulcus in the cat, Exp. Brain Res., 49 (1983) 131-139. 8 Sugimoto, T., Mizuno, N. and Itoh, K., An autoradiographic study on the terminal distribution of cerebellothalamic fibers in the cat, Brain Res., 215 (1981) 29-47.
45
Elsevier Scientific Publishers Ireland Ltd.
NSL 03267
THE V E N T R O M E D I A L N U C L E U S AS T H A L A M I C RELAY F O R F A S T I G I A L P R O J E C T I O N S TO T H E CAT I N S U L A R C O R T E X
T. NODA* and H. OKA
Department o f Physiology, Fukui Medical School, Fukui 910-11 (Japan) (Received January 12th, 1985; Revised version received February 4th, 1985; Accepted February 6th, 1985)
Key words." thalamic ventromedial nucleus - suprageniculate nucleus - fastigial nucleus - insular cortex - laminar field potential analysis - cat
Electrical stimulation of the thalamic ventromedial nucleus (VM) produced surface-negative field potentials in the insular cortex of the cat. Laminar field potential analysis revealed that the VM-evoked potentials showed the same depth profile as the potentials evoked by stimulation of the cerebellar fastigial nucleus (FN). The active synaptic site for both evoked potentials is indicated to be located in layer l of the insular cortex. These results suggest that the VM mediates the FN projections onto layer I of the insular cortex.
The insular cortex of the cat lies in the ventral bank of the anterior ectosylvian sulcus (AES) and the adjacent anterior sylvian gyrus [1, 2]. Recently, we reported electrophysiological evidence for bilateral projections from the cerebellar fastigial nucleus (FN) to layer I of the insular cortex in the cat [6]. According to morphological studies, the insular cortex receives thalamic afferent fibers from the ventromedial nucleus (VM) and the suprageniculate nucleus (SG) [1, 2, 7]. In this study, we examined the thalamocortical responses to electrical stimulation of these thalamic nuclei and compared them with the FN-evoked responses in the insular cortex, in order to determine the possible thalamic relay nucleus for the FN-insular projections. Adult cats, weighing 3.3-3.7 kg, were anesthetized with Nembutal (35 m g / k g , i.p.). Each animal was placed in a stereotaxic frame. Craniotomy was performed to expose the left cerebral cortex and the cerebellum. Concentric stimulating electrodes (outer diameter, 0.3 ram) were introduced stereotaxically into the thalamic VM (A, 10; L, 1.5-2; H, 0) [4] and the SG (A, 5; L, 5-6; H, - 1) [4] of the left side, and also into the bilateral fastigial nuclei of the cerebellum. Electrical stimulation of these sites was made with square wave pulses of 0.5 m A intensity and 0.3 ms duration at 1/s. The effects of stimulation were first explored by a silver ball *Author for correspondence.
0304-3940/85/$ 03.30 @ 1985 Elsevier Scientific Publishers Ireland Ltd.
46 electrode on the surface of the insular cortex. Then, laminar field potentials were recorded through glass microelectrodes filled with 2°7o Pontamine Sky Blue solution in 0.5 M sodium acetate (3-5 M~2). The selected recording depths were marked by iontophoretic deposition of Pontamine Sky Blue from the electrode tip (5 /~A for 5 rain). The exposed cortex usually had warm Ringer solution poured over to prevent it from cooling and drying. Following the experiment, electrolytic lesions were made through each stimulating electrode, and then the animal was perfused with 10% formol-saline containing 0.2% potassium ferrocyanide. The brain was removed, and frontal frozen sections were made, 100 txm thick, and then counterstained with neutral red. The cortical surface-potentials (S.R.) in Fig. IA were recorded with a silver ball electrode in the insular cortex close to the ventral bank of the AES (a black dot in Fig. 1B). Electrical stimulation of the VM produced surface-negative potentials in this region (S.R. in Fig. lax). in the same region, stimulation of the contralateral FN also produced surface-negative potentials (S.R. in Fig. 1A~), as previously reported [6]. The latencies of the VM- and FN-evoked potentials were 3 ms and 6 ms, respectively. On the other hand, stimulation of the SG produced surfacepositive potentials in the insular cortex (S.R. in Fig. 1A3). The SG-evoked surfacepositive potentials consisted of two components, i.e. early small positive deflection and the following large positive one; the latencies were 3 ms and 10 ms, respectively. Laminar field potentials (the records below S.R. in Fig. 1At on stimulation of the contralateral FN (Fig. 1AI), the ipsilateral VM (Fig. 1A2) and SG (Fig. IA3) were recorded through one and the same microelectrode penetration in the insular cortex. The insertion point of this track on the cortical surface corresponds to a black dot in Fig. lB. In Fig. 1At, A2, the FN- (Fig. 1All and VM-evoked potentials (Fig. 1A2) showed almost the same depth profile. They consisted of negative waves at the recording depths of 0-50 btm, turned flat at 150/tm and then reversed polarity at deeper depths down to 2750/zm. The recording depths marked with blue dye spots were 150 p.m and 2750 #m. In Fig. IC, these two dye spots can be seen on the frontal section of the insular cortex (A15). The dye spot at 150/,m was located in the upper half of layer 1 and the dye spot at 2750/,m lies in layer VI. The direction of the track (an arrow in Fig. IC) was almost perpendicular to the cortical surface. In the same track, the SG-evoked potentials consisted of two consecutive positive waves al recording depths of 0-250/,nl. At 500/ml, only their late component reversed polarity. Since their early component also reversed polarity at 1250 /,m, fused negative potentials were seen at deeper depths down to 2750/,m. Fig. 2 shows the histological locations of electrolytic lesions through the stimulating electrode tips for the VM (an arrow in Fig. 2a) and the SG (an arrow in Fig. 2b) in the same animal as that of Fig. 1. Our results indicate that both VM and FN stimulation produce surface-negative potentials in the insular cortex. Laminar field potential analysis showed that the FNand VM-evoked potentials shared the same depth profile. The isoelectric points of
47
A
,
3
s .-
10.2m
50 150 0~m~m~lm
!~uL,pi~,
250 ' ~ m ~ "
500
13
750
1000 1250
1750
2250
2750
_Jo.smsmV
Fig. 1. A: laminar field potentials recorded through one and the same microelectrode penetration in the insular cortex on stimulation of the contralateral FN (AL) and the ipsilateral VM (A2) and the SG (A3). Cortical surface-potentials are shown in the uppermost row (S.R.). The polarity of all the potentials is upward-negative. Each trace is the superimposition of about 5 sweeps. B and C: histological localization of the surface-recording and microelectrode-recording sites in A. B: a black dot on the surface of the insular cortex indicates the recording site with a silver ball electrode as well as the insertion point of the microelectrode track in A. C: an arrow indicates the direction of the track. Two dye spots marked at the recording depths of 150 #m and 2750 ~m in A were located in cortical layers 1 and VI, respectively. AES, anterior ectosylvian sulcus; ARS, anterior rhinal sutcus; CI, claustrum; Pu, putamen. Scale bar= 2 mm.
b o t h e v o k e d p o t e n t i a l s w e r e l o c a t e d in l a y e r I o f t h e i n s u l a r c o r t e x . T h e s e f i n d i n g s s u g g e s t t h a t b o t h t h e F N - a n d V M - e v o k e d p o t e n t i a l s o r i g i n a t e f r o m e x c i t a t o r y inp u t s t o l a y e r I o f t h a t c o r t e x . M o r p h o l o g i c a l l y , it h a s b e e n r e p o r t e d t h a t m a n y F N f i b e r s t e r m i n a t e in t h e V M [8]. T h e d i f f e r e n c e o f 3 m s b e t w e e n t h e l a t e n c i e s o f t h e F N - a n d V M - e v o k e d p o t e n t i a l s in o u r s t u d y s e e m s t o a g r e e w i t h t h e l a t e n c y o f t h e
48
Fig. 2. Histological localization of lhe stimulating electrode lips by electrolytic lesions. Arrows indicate lhe locations of the stimulating electrode tips for the VM (a) and the SG (b) on frontal sections at A I0 and A5, respectively, in the same animal as that of Fig. 1. CeM, central medial nucleus; CL, central lateral nucleus; LD, lateral dorsal nucleus; LG, laleral geniculate complex; LP, lateral poslerior nucleus; MD, mediodorsal nucleus; MG, medial geniculate complex; ML, medial lemniscus; MTT, mare millothalamic tract; Pc, paracentral nu,:lens; Pt, preteclum; RN, red nucleus; SG, suprageniculate nucleus; SN, substantia nigra; VB, ventrobasa] complex: VI, ventrolateral nucleus; VM, ventromedial nucleus. Scale bar 2 ram.
F N - e v o k e d o r t h o d r o m i c spikes o f n e u r o n s in the VM [5]. H e r k e n h a m [3] r e p o r t e d hat the VM-cortical p r o j e c t i o n is d i s t r i b u t e d in layer I o f the entire ipsilateral n e o c o r t e x o f the rat. All o f these findings m a y s u p p o r t the possibility that the F N e v o k e d s u r f a c e - n e g a t i v e potentials in the insular cortex are m e d i a t e d by the VM. O n the o t h e r h a n d , the S G - e v o k e d p o t e n t i a l s in the insular cortex are surfacepositive, a n d their d e p t h profile is quite different f r o m that o f the VM- or F N e v o k e d p o t e n t i a l s . W h e n the r e c o r d i n g depths at which the late c o m p o n e n t o f the S G - e v o k e d p o t e n t i a l s reversed p o l a r i t y , as the p o t e n t i a l s at 500/xm in Fig. 1A3, were m a r k e d with dye spots in a d i f f e r e n t a n i m a l , these dye spots were located in the upper part o f layer III o f the insular cortex (not shown). The early c o m p o n e n t o f the S G - e v o k e d p o t e n t i a l s reverses p o l a r i t y at still d e e p e r depths, as the potentials at 1250 #m in Fig. 1A3, t h a n their late c o m p o n e n t . In Fig. 1C, the r e c o r d i n g d e p t h o f 1250 #m can be e s t i m a t e d to c o r r e s p o n d a p p r o x i m a t e l y to the cortical d e p t h a r o u n d the b o r d e r between layers 11I a n d IV. These results suggest that the S G - e v o k e d p o t e n t i a l s in the insular cortex o r i g i n a t e f r o m e x c i t a t o r y t h a l a m o c o r t i c a l inputs to d e e p e r layers, p r o b a b l y layers l l I a n d IV. W e are grateful to Mr. H. Y o s h i k a w a for assistance in the e x p e r i m e n t s .
49 1 Burton, H. and Kopf, E.M., Connections between the thalamus and the somatosensory areas of the anterior ectosylvian gyrus in the cat, J. Comp. Neurol., 224 (1984) 173-205. 2 Guldin, W.O. and Markowitsch, H.J., Cortical and thalamic afferent connections of the insular and adjacent cortex of the cat, J. Comp. Neurol., 229 (1984) 393-418. 3 Herkenham, M., The afferent and efferent connections of the ventromedial thalamic nucleus in the rat, J. Comp. Neurol., 183 (1979) 487-518. 4 Jasper, H.H. and Ajmone-Marsan, C., A Stereotaxic Atlas of the Diencephalon of the Cat, National Research Council of Canada, Ottawa, 1954. 5 Nakamura, M. and Matsuda, Y., Re-evaluation of cortical and thalamic responses evoked by stimulation of the cerebellar fastigial nucleus in the cat, Jpn. J. Physiol., 33 (1983) 215-226. 6 Noda, T. and Oka, H., Fastigial inputs to the insular cortex in the cat: field potential analysis, Neurosci. Lett., 53 (1985) 331-336. 7 Roda, J.M. and Reinoso-Su~trez, F., Topographical organization of the thalamic projections to the cortex of the anterior ectosylvian sulcus in the cat, Exp. Brain Res., 49 (1983) 131-139. 8 Sugimoto, T., Mizuno, N. and Itoh, K., An autoradiographic study on the terminal distribution of cerebellothalamic fibers in the cat, Brain Res., 215 (1981) 29-47.