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Presynaptic dendrites and serial synapses in the intermediate and deep layers of the cat superior colliculus
Neuroscitnce Letters, 11 (1979) 1C1--164 © Ekevie~/North-Holland Scientific Publishers Ltd.
161
PRES~~IC DENDR~ES AND SERIAL SYNAPSES IN THE ~~D~i~DiDEEPLAYERS OF THE CAT SUPERIOR •
:
MASAO NORITA and MASAAKI 8UGIYAMA DePartment of Anatomy, School of Medicine, lwate M,edieal University, Morio~a 020 (Japan.) (Receivedjuly 31St; 19781) (Revised version received November 8th, 1978) (Accepted November 9th, 1978) _ , , ,
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SUMMARY
Presynaptic dendarites (PSDs) which participate in the serial synapses have frequently been found in the intermediate and deep layers of the c~t superior Colliculus. The PSDs are presynaptic to small dendritic shafts or spines with symmetrical membrane thickening, and postsynaptic to axon terrr~inals with asymmetrical synapfic contact. Two types of the axon terminals are obsen, ed, both of which contain pleomorphic vesicles. Presynaptic dendrites (PSDs), which contain pleomorphic synal~tic vesicles and participate in axodendrodendritic serial synapses, have been described in several structures in the central nervous system, e.g., the lab~ral geniculate body [8,13], the medial geniculate body [4,5], the ventral thalamic nuclei [11] and the red nucleus [6]. Furthermore, it has been shown that the PSDs belong to Golgi type II neurons or intemeurons [ 4,8,11] in cats and monkeys. In the present study, the PSDs and the serial synapses were observed in the intermediate and deep layers of the cat superior colliculus. Under Nembutal anesthesia, animals were transcardially perfused with Karlsson~chultz buffer (pH 7.3) [3] cent ning 3.7% paraformaldehyde, 1% glutaraldehyde and 2% sucrose. Brains were dissected f ~ e and cut coronally in thick slices (1--2 mm) which contain the colliculus. They were postosmicated, dehydt:ated and e m ~ d d e d ~ e p o x y resin, as described previously [7 ]. Ultrathin sections were ~ ~ ,;Wi~uranYl acetate and lead citrate [12], and they were examined with a Hitachi HU.I!A electron microscope. From profiles of serial synapses, the synaptic vesicles in the PSDs and the axon terminals were measured. In addition, the occurrence ratio of the spheri,=al and flattened vesicles an~ the ellipticity of the latter vesicles (ratio of the ~ortest to the longest length of the vesicle)were calculated. ThePSDS~o~rved in the intermediate and deep layers of the colliculus, w e ~ f r o m m a l l t0 medium sized (leps than 2.5 #m in diameter) and contained granular endoP!R~ic reticulum and' free ribosomes (Fig. 1). 32% of the
162
Fig. 1. A vesicle-containing dendrite (PSD) with ribosomes (r) and microtubules (m), postsynaptic to an axon terminal (At) with pleomorphic vesicles. Arrows indicate sites of asymmetrical synapses. s y n a p t i c vesicles were spherical and 68% were flattened. Diameters of the spherical vesicles were 3 2 - - 5 5 n m (mean, 41 nm) and t h e mean ellipticity o f t h e flattened vesicles was 1 : 1.5, t h e majority being I : 1.2--1 : 1.7.
163
Fig. 2A and B show examples of the axodendrodendritic serial synapses. Within the serial synapses, the PSDs display paler aspect than the axon terminals. The PSDs were seen to make symmetrical synapses with a small dendrite (Fig. 2A) or a spine (Fig. 2B), and postsynaptic to axon terminals with asymmetrical membrane thickening (Figs. 2A and B). T w o types of the axon terminals were observed. The first type of axon, 1--3 ~m in diameter, was frequently observed which contained spherical (57%) and flattened (43%) vesicles (Fig. 1). Diameters of the spherical vesicles were 35---56 nm (average, 43 nm), and the majority of the flattened vesicles showed an ellipticity of 1 : 1.2--1 : 1.5. A number of neurofilaments and some mitochondria were found in the central portion of axoplasm, which appeared to represent boutons en passant. The second t y p e of axon (Figs. 2A and B), 0.5--1.5 ~m in diameter, contained approximately 85% of spherical vesicles in
Fig. 2A and B. Examples of axodendrodendritic serial synapses. Axon terminals (At) with many spherical vesicles are seen as forming asymmetrical synaptic contacts (arrows) with presynaptic dendrites ( P S r which are presynaptic to a dendritic shaft (D in Fig. 2A) or a dendritic spine (asterisk in Fig. 2B). The dendrodendritic synapses show symmetrical membrane thickening (ringed arrows). Arrow heads indicate ribosomes.
164
which the diameter measured 3 0 - 5 2 n m (average, 40 n m ) and no neurofilaments could be observed. T h e PSDs observed in the present s t u d y were identified as a dendrite b y t h e presence o f ribosomes and granular endoplasmic retictflum in thv cytoplasm (cf. Peters et al. [9] ). In addition, we have frequently observed m u c t u r e s which were loaded b y pleomorphic vesicles and postsynsptic to the s x o n terminals o f t h e same features which constitute t h e serial synapses. Thus, t h e y contained almost t h e same population o f vesicles as seen in t h e PSDs described above. It is likely, therefore, t h a t these structures with pleomorphic vesicles represent the PSDs, even though no characteristic signs o f dendrites could be obtained. Ir. the se,iculate bodies and the ventral thalamic nuclei, there is anatomical evidence that the PSDs are derived from interneurons (see above), and, it is considered t h a t the interneurons would account for inhibitory nab~re in some brahl structures [ 1 ~ , 8 , 1 0 ] . Although the PSDs have n o t been traced to their p a r e n t somata, it is likely t h a t some of the PSDs observed in t h e pre~ent study belong to t h e intemeurons. Thus, some neurons in t h e intermediate and deep layers o f t h e cat superior colliculus may well be o f inhibitory nature. REFERENCES
I Aitkin, L.M. and Dunlop, C.W., Inhibition in ~'.hemedial ganleulate body of the cat, Exp. Brain Res., 7 (1969)68--88. 2 Eccles, J.C., LIiuas, R. and 8a~tkj, K., The inJtibitory Jntemeurona within the eerebeltsr cortex, Exp. Brain Rse., 1 (1966) 1--16. 3 Karlsson, U. and Sehultz, R.L., Fixation of the central nervous system for electron microscopy by aldehyde perfuslon, J. Ultrutrue. Res., 12 (1965) 160-186. 4 Majorossy, K. and Kiss, A., 8p~ific patterns ¢4 neuron arranfpment and of synsptie articulation in the medial 8eniculate body, Exp. Brain RN., 26 (1976) 1--17. 5 Morest, D.K., Dendrodendritie synapses of ceils that have axons: the fine structure of the Goigi type II cell in the med~d pniculate body of the eat, Z. Auat. Entwiekl.Gesch., 133 (1971) 216--246. 6 Nakamura, Y., An ~lectron microscope study of the red nucleus in the eat, with special reference to the quantitative anelysk of the ~toeomatie synal~es, BrahJ ~ s . , 94 (19"75) I--17. 7 Norits, M. and Hirata, Y., 8ome electron micm~seope findinp of the elaustrum of the cat, Arch. histol, jap., 39 (1976) $$-49. 8 Pasik, P., Pasik, T. and H/mori, J., ~qynapsesbetween intemeurons in the latend geniculate nucleus of monkeys, Exp. Brain Res., 25 (1976) 1--13. 9 Peters, A., Palay, 8.L. and Webster, H. de H., The fine structure of the nervous system: the neurons and supporting ceils, SannderL, ]Philadelphia, 19"76, 406 pp. 10 Ralston. H.J. IH~, Evidence for presynaptic dendrites ~nd a proposal for their mechanism of action, Nature (Lond.), 230 (19"71) 585--$87. 11 Rinvik, E. and Grofov/, I., L~ht and electron microscopical studies of the normal nuclei ventr~Its lat~:ralis and ventralis anterior thalami in the eat, Anat. Embwol., 146 (!974) 5"7---93. 12 Venable, J.H. and CosgeshalI, R., A simplified lead citrate stain for use in electron microscopy, J. CeLlBiol., 25 (1965) 407--408. 13 Wong-Riley, M.T.T., Neuronal and synaptie organization of the normal dorsal lateral geniculate nucleus of the squirrel monkey, saimiri seiureus, J. eGmp. Neurol., 144 (1972) ~5-6o.
161
PRES~~IC DENDR~ES AND SERIAL SYNAPSES IN THE ~~D~i~DiDEEPLAYERS OF THE CAT SUPERIOR •
:
MASAO NORITA and MASAAKI 8UGIYAMA DePartment of Anatomy, School of Medicine, lwate M,edieal University, Morio~a 020 (Japan.) (Receivedjuly 31St; 19781) (Revised version received November 8th, 1978) (Accepted November 9th, 1978) _ , , ,
,
,,
.
, .
,
.
.
.
.
.
_
.
.
.
.
.
.
.
•
- - -
,
.
.
.
.
.
.
.
.
.
.
=
-
,
-
_
SUMMARY
Presynaptic dendarites (PSDs) which participate in the serial synapses have frequently been found in the intermediate and deep layers of the c~t superior Colliculus. The PSDs are presynaptic to small dendritic shafts or spines with symmetrical membrane thickening, and postsynaptic to axon terrr~inals with asymmetrical synapfic contact. Two types of the axon terminals are obsen, ed, both of which contain pleomorphic vesicles. Presynaptic dendrites (PSDs), which contain pleomorphic synal~tic vesicles and participate in axodendrodendritic serial synapses, have been described in several structures in the central nervous system, e.g., the lab~ral geniculate body [8,13], the medial geniculate body [4,5], the ventral thalamic nuclei [11] and the red nucleus [6]. Furthermore, it has been shown that the PSDs belong to Golgi type II neurons or intemeurons [ 4,8,11] in cats and monkeys. In the present study, the PSDs and the serial synapses were observed in the intermediate and deep layers of the cat superior colliculus. Under Nembutal anesthesia, animals were transcardially perfused with Karlsson~chultz buffer (pH 7.3) [3] cent ning 3.7% paraformaldehyde, 1% glutaraldehyde and 2% sucrose. Brains were dissected f ~ e and cut coronally in thick slices (1--2 mm) which contain the colliculus. They were postosmicated, dehydt:ated and e m ~ d d e d ~ e p o x y resin, as described previously [7 ]. Ultrathin sections were ~ ~ ,;Wi~uranYl acetate and lead citrate [12], and they were examined with a Hitachi HU.I!A electron microscope. From profiles of serial synapses, the synaptic vesicles in the PSDs and the axon terminals were measured. In addition, the occurrence ratio of the spheri,=al and flattened vesicles an~ the ellipticity of the latter vesicles (ratio of the ~ortest to the longest length of the vesicle)were calculated. ThePSDS~o~rved in the intermediate and deep layers of the colliculus, w e ~ f r o m m a l l t0 medium sized (leps than 2.5 #m in diameter) and contained granular endoP!R~ic reticulum and' free ribosomes (Fig. 1). 32% of the
162
Fig. 1. A vesicle-containing dendrite (PSD) with ribosomes (r) and microtubules (m), postsynaptic to an axon terminal (At) with pleomorphic vesicles. Arrows indicate sites of asymmetrical synapses. s y n a p t i c vesicles were spherical and 68% were flattened. Diameters of the spherical vesicles were 3 2 - - 5 5 n m (mean, 41 nm) and t h e mean ellipticity o f t h e flattened vesicles was 1 : 1.5, t h e majority being I : 1.2--1 : 1.7.
163
Fig. 2A and B show examples of the axodendrodendritic serial synapses. Within the serial synapses, the PSDs display paler aspect than the axon terminals. The PSDs were seen to make symmetrical synapses with a small dendrite (Fig. 2A) or a spine (Fig. 2B), and postsynaptic to axon terminals with asymmetrical membrane thickening (Figs. 2A and B). T w o types of the axon terminals were observed. The first type of axon, 1--3 ~m in diameter, was frequently observed which contained spherical (57%) and flattened (43%) vesicles (Fig. 1). Diameters of the spherical vesicles were 35---56 nm (average, 43 nm), and the majority of the flattened vesicles showed an ellipticity of 1 : 1.2--1 : 1.5. A number of neurofilaments and some mitochondria were found in the central portion of axoplasm, which appeared to represent boutons en passant. The second t y p e of axon (Figs. 2A and B), 0.5--1.5 ~m in diameter, contained approximately 85% of spherical vesicles in
Fig. 2A and B. Examples of axodendrodendritic serial synapses. Axon terminals (At) with many spherical vesicles are seen as forming asymmetrical synaptic contacts (arrows) with presynaptic dendrites ( P S r which are presynaptic to a dendritic shaft (D in Fig. 2A) or a dendritic spine (asterisk in Fig. 2B). The dendrodendritic synapses show symmetrical membrane thickening (ringed arrows). Arrow heads indicate ribosomes.
164
which the diameter measured 3 0 - 5 2 n m (average, 40 n m ) and no neurofilaments could be observed. T h e PSDs observed in the present s t u d y were identified as a dendrite b y t h e presence o f ribosomes and granular endoplasmic retictflum in thv cytoplasm (cf. Peters et al. [9] ). In addition, we have frequently observed m u c t u r e s which were loaded b y pleomorphic vesicles and postsynsptic to the s x o n terminals o f t h e same features which constitute t h e serial synapses. Thus, t h e y contained almost t h e same population o f vesicles as seen in t h e PSDs described above. It is likely, therefore, t h a t these structures with pleomorphic vesicles represent the PSDs, even though no characteristic signs o f dendrites could be obtained. Ir. the se,iculate bodies and the ventral thalamic nuclei, there is anatomical evidence that the PSDs are derived from interneurons (see above), and, it is considered t h a t the interneurons would account for inhibitory nab~re in some brahl structures [ 1 ~ , 8 , 1 0 ] . Although the PSDs have n o t been traced to their p a r e n t somata, it is likely t h a t some of the PSDs observed in t h e pre~ent study belong to t h e intemeurons. Thus, some neurons in t h e intermediate and deep layers o f t h e cat superior colliculus may well be o f inhibitory nature. REFERENCES
I Aitkin, L.M. and Dunlop, C.W., Inhibition in ~'.hemedial ganleulate body of the cat, Exp. Brain Res., 7 (1969)68--88. 2 Eccles, J.C., LIiuas, R. and 8a~tkj, K., The inJtibitory Jntemeurona within the eerebeltsr cortex, Exp. Brain Rse., 1 (1966) 1--16. 3 Karlsson, U. and Sehultz, R.L., Fixation of the central nervous system for electron microscopy by aldehyde perfuslon, J. Ultrutrue. Res., 12 (1965) 160-186. 4 Majorossy, K. and Kiss, A., 8p~ific patterns ¢4 neuron arranfpment and of synsptie articulation in the medial 8eniculate body, Exp. Brain RN., 26 (1976) 1--17. 5 Morest, D.K., Dendrodendritie synapses of ceils that have axons: the fine structure of the Goigi type II cell in the med~d pniculate body of the eat, Z. Auat. Entwiekl.Gesch., 133 (1971) 216--246. 6 Nakamura, Y., An ~lectron microscope study of the red nucleus in the eat, with special reference to the quantitative anelysk of the ~toeomatie synal~es, BrahJ ~ s . , 94 (19"75) I--17. 7 Norits, M. and Hirata, Y., 8ome electron micm~seope findinp of the elaustrum of the cat, Arch. histol, jap., 39 (1976) $$-49. 8 Pasik, P., Pasik, T. and H/mori, J., ~qynapsesbetween intemeurons in the latend geniculate nucleus of monkeys, Exp. Brain Res., 25 (1976) 1--13. 9 Peters, A., Palay, 8.L. and Webster, H. de H., The fine structure of the nervous system: the neurons and supporting ceils, SannderL, ]Philadelphia, 19"76, 406 pp. 10 Ralston. H.J. IH~, Evidence for presynaptic dendrites ~nd a proposal for their mechanism of action, Nature (Lond.), 230 (19"71) 585--$87. 11 Rinvik, E. and Grofov/, I., L~ht and electron microscopical studies of the normal nuclei ventr~Its lat~:ralis and ventralis anterior thalami in the eat, Anat. Embwol., 146 (!974) 5"7---93. 12 Venable, J.H. and CosgeshalI, R., A simplified lead citrate stain for use in electron microscopy, J. CeLlBiol., 25 (1965) 407--408. 13 Wong-Riley, M.T.T., Neuronal and synaptie organization of the normal dorsal lateral geniculate nucleus of the squirrel monkey, saimiri seiureus, J. eGmp. Neurol., 144 (1972) ~5-6o.