- Email: [email protected]
Catecholamine cell groups of the cat medulla oblongata
Brain Research, 192 (1980) 69-75 © Elsevier/North-Holland Biomedical Press
69
C A T E C H O L A M I N E CELL G R O U P S OF T H E CAT M E D U L L A O B L O N G A T A
W. W. BLESSING*, P. FROST and J. B. FURNESS Centre for Neuroscience, Departments of Medicine and Human Morphology, The Flinders University of South Australia, Bedford Park, S.A. 5042 (Australia)
(Accepted October 25th, 1979) Key words: medullary catecholamine cells -- cardiovascular neurons - - histofluorescence
SUMMARY The distribution of catecholamine-containing cells within the cat medulla oblongata has been studied using formaldehyde-glutaraldehyde fluorescence histochemistry. The diffuse ventrolateral cells (A 1) were scattered around but not within the lateral reticular nucleus and no ceils were found dorsal to the inferior olivary nucleus. The dorsomedial (A2) cells were scattered within the nucleus tractus solitarius with an occasional cell within the dorsal motor nucleus of the vagus. No A2 cells were found within or ventral to the hypoglossal nucleus. This description contrasts in several respects with a recently published atlas of the catecholamine-containing neurons in the cat medulla.
INTRODUCTION When Dahlstrom and Fuxe 6 described the catecholamine (CA) cell groups in the rat brain, they provided a framework for comparative descriptions in other species. There were two groups in the medulla oblongata, a ventrolateral group, designated A1 and a dorsomedial group, designated A2. Their observations in the rat have been largely confirmed20, ~6 and corresponding cell groups have been described in other mammals 1,5,s,12-14,19. Until recently, little attention has been paid to the CA cell groups in the cat medulla, possibly because an early report indicated their absence 21. Later studies coauthored by the same investigators15,17 imply that there are CA cells in this region and Poitras and Parent 22 have recently published an atlas of their distribution. When Coote and McLeod 4 studied the possible cardiovascular roles of medullary CA cells in * To whom correspondence should be addressed at: Laboratory of Neurobiology, Cornell Medical Center, 525 East 68th Street, New York, N.Y. 10021, U.S.A.
70 the cat, they first mapped the distribution of these cells and in many respects their atlas ~ contrasts with that of Poitras and Parent z2, and with descriptions of the distribution of corresponding cells in other species. Poitras and Parent found the A I cells to be within, rather than around, the lateral reticular nucleus (LRN) and some of them are described lying dorsal to the inferior olivary complex, more medial than those described by Coote and McLeod. The A2 cells extend to the level of the rostral pole of the inferior olive, much more rostral than those described by Coote and McLeod, and Poitras and Parent make the rather surprising claim that the A2 cells are found within or immediately ventral to the hypoglossal nucleus. In the cat, the authors cited all used the Falck-Hillarp fluorescence histochemical method in which freeze-dried tissue is exposed to hot formaldehyde vapour and, although CA containing cells become brightly fluorescent, the tissue is difficult to handle and anatomical relationships are difficult to define. Recently it has been found 9-11 that in vivo perfusion with buffered solutions of formaldehyde and glutaraldehyde simultaneously fixes neural tissue and converts catecholamines to fluorescent derivatives. This method is ideal for relating fluorescent and non-fluorescent structures and has been used to map the CA cells in the rabbit brain 1. In view of the number of physiological, especially cardiovascular, studies of the role of medullary CA neurons and in view of recent neuroanatomical evidence 7,J,~,1~, z3,25 suggesting that these neurons provide the major catecholaminergic innervation of the hypothalamus, it is important to re-investigate their distribution in the cat. MATERIALS AND METHODS For our study, over 200 complete transverse sections from 9 kittens and adult cats weighing between 0.9 and 3.0 kg were examined in detail. The precise location of each CA cell in each section was mapped onto white-light photographs of each section (see below). In 3 animals, pargyline (100 mg/kg intraperitoneally 2 h before perfusion) was injected to inhibit monoamine oxidase with the intention of increasing amine levels in the cells. The cats were anaesthetized with pentobarbital (35 mg/kg, intraperitoneal) and perfused via a catheter inserted retrogradely into the abdominal aorta, with the cut right atrium acting as an outlet. A sphygmomanometer bulb and gauge were used to maintain and monitor pressure as described previously 11. The blood was flushed out by an initial perfusion with a solution of 1 ~o sodium nitrite in 0.01 M phosphate buffer pH 7.0, to which 500 I.U. heparin/100 ml was added. Perfusion was then continued with 1500 ml of 4~o formaldehyde plus 0.5~o glutaraldehyde in 0.1 M phosphate buffer, pH 7.0. Transverse sections (25-50 #m) of the medulla were cut on a vibratome at room temperature and transferred to perfusion solution. Wet sections were photographed at low power using a Zeiss Tessovar microscope and then the same sections were dried and mounted on chrome-alum coated slides. The distribution of catecholamine cells was examined with a Leitz Ortholux fluorescence microscope. The positions of the fluorescent cells were marked on the low power Tessovar micrographs. After the fluorescence of the catecholamine neurons had been examined, the sections were
A
[3
C
Fig. 1. Photographs of representative transverse sections through the cat medulla. The catecholamine cell bodies are indicated by filled circles. Abbreviations: ap, area postrema; c, central canal; cn, cuneate nucleus; gn, gracile nucleus; io, inferior olive; lrn, lateral reticular nucleus; lrn st, lateral reticular nucleus, subtrigeminal portion; ha, nucleus ambiguus; nts, nucleus tractus solitarius; nXII, hypoglossal nerve, p, pyramidal tract; sV, spinal tract of trigeminal nerve; ts, tractus solitarius; X, dorsal motor nucleus of vagus; XII, hypoglossal nucleus.
72 r e h y d r a t e d a n d stained with neutral red or cresyl fast violet and then r e - e x a m i n e d to confirm the relationship between the positions or the c a t e c h o l a m i n e cells and m e d u l l a r y nuclei. RESULTS AND DISCUSSION The d i s t r i b u t i o n of C A cells in representative transverse sections f r o m different levels o f the m e d u l l a is shown in Fig. 1. There is a ventrolateral g r o u p (A1) and a d o r s o m e d i a l g r o u p (A2) with cells occasionally f o u n d between these two groups. In the area p o s t r e m a there are some small fluorescent cells. P r e t r e a t m e n t with pargyline did n o t reveal any a d d i t i o n a l groups. The A1 g r o u p extended f r o m the p y r a m i d a l decussation to the rostral-third o f the inferior olivary complex. A t the caudal extreme (Fig. 1A) the cells were f o u n d in the lateral reticular f o r m a t i o n with occasional cells between the fibre bundles o f the corticospinal tract. In m o r e rostral sections (Fig. 1B), the C A cells were scattered a r o u n d but not within the L R N . In a 30 # m transverse section an average o f a b o u t 8 fluorescent cells were f o u n d on the dorsal b o r d e r o f this nucleus with occasional a d d i t i o n a l cells wedged between the nucleus a n d the v e n t r o l a t e r a l surface o f the medulla. After Nissl staining, the A1 cells were seen to be scattered a m o n g s t other similar cells which showed no histochemical reaction for catecholamines (Fig. 3a-c). The smaller spindle-shaped A1 cells c o n t r a s t e d with the p r o m i n e n t m o r e regular cells o f the L R N (Fig. 3c). In the open m e d u l l a (Fig. 1C) the m a j o r i t y o f the C A cells were f o u n d d o r s a l to the principal p o r t i o n of the L R N , j u s t ventrolateral to the cells o f the nucleus ambiguus. A t levels rostral to the L R N the C A cells were f o u n d closer to the ventral surface o f the medulla. N e a r l y all the A2 C A cells were scattered within the N T S with an occasional cell within the dorsal m o t o r nucleus o f the vagus. A t the caudal level (Fig. 1A), where the c o m m i s s u r a l p o r t i o n o f the N T S a p p e a r s compressed by the gracile and cuneate nuclei, and at the level o f the obex (Fig. 1B), the C A cells were f o u n d in b o t h the medial a n d lateral p o r t i o n s of the c o m m i s s u r a l nucleus of the N T S b u t they were rarely f o u n d b e y o n d the rostral extent o f the a r e a p o s t r e m a . The A2 cells were interspersed a m o n g s t the non-fluorescent cells (Fig. 2a-c).
Fig. 2. Three views of the same tissue section, localizing A2 catecholamine-containing cells by the formaldehyde-glutaraldehyde fluorescence technique, a: photograph of a transverse section through the dorsomedial medulla at the level of the obex; cc, central canal; cn, cuneate nucleus; gn, gracile nucleus ; ts, tractus solitarius, XII, hypoglossal nucleus. Bar - 0.5 ram. b: fluorescence photomicrograph of the portion of the NTS indicated by the rectangle in Fig. 2a. Bar -- 50 f~m. c : Nissl stain of the same NTS area. Some corresponding cells are indicated by arrows. Bar --- 50 l~m. Fig. 3. Three views of the same tissue section, localizing A1 catecholamine-containing cells by the formaldehyde glutaraldehyde fluorescence technique, a : photograph of a transverse section through the ventrolateral medulla at the level of the obex. A small area on the dorsal border of the lrn is indicated by a rectangle. Bar 0.5 ram. b: fluorescence photomicrograph showing 3 CA cells in the dorsal portion of the area indicated in Fig. 3a. Bar 50/~m.c: N issl stain of the area indicated by the rectangle. The cells arrowed correspond to the fluorescent cells seen in Fig. 3b. In the lower portion of Fig. 3c there are 3 cells from the dorsal part of the lrn. v, blood vessel; io, inferior olive; lrn, lateral reticular nucleus. Bar - 50 l~m.
[
~P
74 O u r description o f the cat m e d u l l a r y C A cells contrasts in several respects with t h a t o f Poitras a n d Parent2L N o A2 cells were f o u n d within or ventral to the hypoglossal nucleus and they d i d n o t extend far into the open medulla. N o AI cells were f o u n d dorsal to the inferior olivary complex nor were they f o u n d within the L R N . This p o i n t should be e m p h a s i z e d since A I cells have been described within the L R N o f the r a ¢ , 2° a n d in biochemical studies it is c o m m o n (e.g. ref. 24) to p u n c h out the L R N as a sample o f the A1 group. However, our findings in the cat and studies in other species1,5,13, including a recent review o f the rat d a t a is, m a k e it unlikely t h a t the A1 cells are p a r t o f the L R N . This nucleus projects mainly to the cerebellum :3 in c o n t r a s t to the A1 cells which project to the spinal cord and the h y p o t h a l a m u s 6,7. In the r a b b i t the A1 cells are m o r e c o m p a c t l y a r r a n g e d ~ a n d lesions of this g r o u p o f cells have resulted in hypertension and p u l m o n a r y e d e m a '). Because the cat A 1 cells tend to be diffusely scattered a r o u n d the L R N it will be m o r e difficult to selectively lesion these n e u r o n s in studies o f their function. ACKNOWLEDGEMENTS W . W . B . is a Research F e l l o w o f the Life Insurance M e d i c a l Research F u n d o f A u s t r a l i a a n d New Zealand. P . F . was s u p p o r t e d by a grant f r o m the N a t i o n a l H e a r t F o u n d a t i o n o f Australia.
REFERENCES l Blessing, W. W., Chalmers, J. P. and Howe, P. R. C., Distribution of catecholamine-containing cell bodies in the rabbit central nervous system, J. comp. Neurol., 179 (1978) 407-424. 2 Blessing, W. W., West, M. J. and Chalmers, J. P., Hypertension and pulmonary edema following lesions of catecholamine neurons (A1) in the ventrolateral medulla oblongata of the rabbit, Proc. Austr. Physiol. Pharmacol. Soc., 10 (1979) 272P. 3 Brodal, A., The Reticular Formation of the Brain Stem. Anatomical Aspects and Functional Considerations, Oliver and Boyd, Edinburgh and London, 1957, p. 14. 4 Coote, J. H. and McLeod, V. H., The influence of bulbospinal monoaminergic pathways on sympathetic nerve activity, J. Physiol. (Lond.), 241 (1974) 453475. 5 Crutcher, K. A. and Humbertson, A. O., The organization of monoamine neurons within the brainstem of the North American opossum (Didelphis virginiana), J. comp. Neurol., 179 (1978) 195-222. 6 Dahlstrom, A. and Fuxe, K., Evidence for the existence of monoamine-containing neurons in the central nervous system. I. Demonstration of monoamines in the cell bodies of brain stem neurons, Aetaphysiol. scand., 62, Suppl. 232: (1964) 1-55. 7 Day, T. A., Blessing, W. W. and Willoughby, J. O., Catecholaminergic afferents to the preoptic area of the rat, Proc. Austr. Physiol. Pharmacol. Soc., 10 (1979) 273P. 8 Felten, D. L., Laties, A. M. and Carpenter, M. B., Monoamine-containing cell bodies in the squirrel monkey brain, Amer. J. Anat., 139 (1974) 153-165. 9 Furness, J. B., Costa, M. and Blessing, W. W., Simultaneous fixation and production of catecholamine fluorescence in central nervous tissue by perfusion with aldehydes, Histochem. J., 9 (1977) 745-750. 10 Furness, J. B., Costa, M. and Wilson, A., Water-stable fluorophores, produced by reaction with aldehyde solutions, for the histochemical localization of catechol- and indolethylamines, Histochemistry, 52 (1977) 159-170. 11 Furness, J. B., Heath, J. W. and Costa, M., Aqueous aldehyde (Faglu) methods for the fluorescence histochemicallocalizationof catecholamines and for ultrastructural studies of central nervous tissue, Histochemistry, 57 (1978) 285-295.
75 12 Garver, D. L. and Sladek, J. R., Monoamine distribution in primate brain. I. Catecholamine-containing perikarya in the brain stem of Macaca speciosa, J. comp. Neurol., 159 (1975) 289-304. 13 Hubbard, J. E. and DiCarlo, V., Fluorescence histochemistry of monoamine-containing cell bodies in the brain stem of the squirrel monkey (Saimiri sciureus), II. Catecholamine-containing groups, J. comp. Neurol., 153 (1974) 369-384. 14 Jacobowitz, D. M. and MacLean, P. D., A brain stem atlas of catecholaminergic neurons and serotonergic perikarya in a primate (Cebeulla pygmaea), J. comp. Net~roL, 177 (1978) 397-416. 15 Jones, B. A., Halaris, A. E. and Freedman, D. X., Innervation of forebrain regions by medullary noradrenaline neurons, a biochemical study in cats with central tegmental lesions, Neurosci. Lett., 10 (1978) 251-258. 16 Loewy, A. D. and Burton, H., Nuclei of the solitary tract: efferent projections to the lower brain stem and spinal cord of the cat, J. comp. Neural., 181 (1978) 421-450. 17 Maeda, T., Pin, C., Salvert, D., Ligier, M. and Jouvet, M., Les neurones contenant des catecholamines du tegmentum poutique et leurs voies de projection chez le chat, Brain Research, 57 (1973) 119-152. 18 Moore, R. Y. and Bloom, F. E., Central catecholamine neuron systems : anatomy and physiology of the norepinephrine and epinephrine systems, Ann. Rev. Neurosci., 2 (1979) 113-168. 19 Nobin, A. and Bjorklund, A., Topography of the monoamine neuron systems in the human brain as revealed in fetuses, ActaphysioL scand., Suppl., 388 (1973) 1-40. 20 Palkovits, M. and Jacobowitz, D. M., Topographic atlas ofcatecholamine and acetylcholinesterasecontaining neurons in the rat brain, II. Hindbrain (mesencephalon, rhombencephalon), J. comp. Neurol., 157 (1974) 29-42. 21 Pin, C., Jones, B. and Jouvet, M., Topographie des neurones monoaminergiques du tronc cerebral du chat: etude par histofluorescence, C.R. Soc. Biol. (Paris), 162 (1968) 2136-2141. 22 Poitras, D. and Parent, A., Atlas of the distribution of monoamine-containing nerve cell bodies in the brain stem of the cat, J. comp. Neurol., 179 (1978) 699-718. 23 Ricardo, J. A. and Koh, E. T., Anatomical evidence of direct projections from the nucleus of the solitary tract to the hypothalamus, amygdala, and other forebrain structures in the rat, Brain Research, 153 (1978) 1-26. 24 Saavedra, J. M., Kvetnansky, R. and Kopin, I. J., Adrenaline, noradrenaline and dopamine levels in specific brain stem areas of acutely immobilized rats, Brain Research, 160 (1979) 271-280. 25 Sakumoto, T., Tohyama, M., Satoh, K., Kimoto, Y., Kinugasa, T., Tanizawa, O., Kurachi, K. and Shimizu, N., Afferent connections from lower brain stem to hypothalamus studied by the horseradish peroxidase method with special reference to noradrenaline innervation, Exp. Brain Res., 31 (1978) 81-94. 26 Swanson, L. W. and Hartman, B. K., The central adrenergic system. An immunofluorescence study of the location of cell bodies and their efferent connections in the rat utilizing dopamine-fl-hydroxylase as a marker, J. comp. NeuroL, 163 (1975) 467-505.
69
C A T E C H O L A M I N E CELL G R O U P S OF T H E CAT M E D U L L A O B L O N G A T A
W. W. BLESSING*, P. FROST and J. B. FURNESS Centre for Neuroscience, Departments of Medicine and Human Morphology, The Flinders University of South Australia, Bedford Park, S.A. 5042 (Australia)
(Accepted October 25th, 1979) Key words: medullary catecholamine cells -- cardiovascular neurons - - histofluorescence
SUMMARY The distribution of catecholamine-containing cells within the cat medulla oblongata has been studied using formaldehyde-glutaraldehyde fluorescence histochemistry. The diffuse ventrolateral cells (A 1) were scattered around but not within the lateral reticular nucleus and no ceils were found dorsal to the inferior olivary nucleus. The dorsomedial (A2) cells were scattered within the nucleus tractus solitarius with an occasional cell within the dorsal motor nucleus of the vagus. No A2 cells were found within or ventral to the hypoglossal nucleus. This description contrasts in several respects with a recently published atlas of the catecholamine-containing neurons in the cat medulla.
INTRODUCTION When Dahlstrom and Fuxe 6 described the catecholamine (CA) cell groups in the rat brain, they provided a framework for comparative descriptions in other species. There were two groups in the medulla oblongata, a ventrolateral group, designated A1 and a dorsomedial group, designated A2. Their observations in the rat have been largely confirmed20, ~6 and corresponding cell groups have been described in other mammals 1,5,s,12-14,19. Until recently, little attention has been paid to the CA cell groups in the cat medulla, possibly because an early report indicated their absence 21. Later studies coauthored by the same investigators15,17 imply that there are CA cells in this region and Poitras and Parent 22 have recently published an atlas of their distribution. When Coote and McLeod 4 studied the possible cardiovascular roles of medullary CA cells in * To whom correspondence should be addressed at: Laboratory of Neurobiology, Cornell Medical Center, 525 East 68th Street, New York, N.Y. 10021, U.S.A.
70 the cat, they first mapped the distribution of these cells and in many respects their atlas ~ contrasts with that of Poitras and Parent z2, and with descriptions of the distribution of corresponding cells in other species. Poitras and Parent found the A I cells to be within, rather than around, the lateral reticular nucleus (LRN) and some of them are described lying dorsal to the inferior olivary complex, more medial than those described by Coote and McLeod. The A2 cells extend to the level of the rostral pole of the inferior olive, much more rostral than those described by Coote and McLeod, and Poitras and Parent make the rather surprising claim that the A2 cells are found within or immediately ventral to the hypoglossal nucleus. In the cat, the authors cited all used the Falck-Hillarp fluorescence histochemical method in which freeze-dried tissue is exposed to hot formaldehyde vapour and, although CA containing cells become brightly fluorescent, the tissue is difficult to handle and anatomical relationships are difficult to define. Recently it has been found 9-11 that in vivo perfusion with buffered solutions of formaldehyde and glutaraldehyde simultaneously fixes neural tissue and converts catecholamines to fluorescent derivatives. This method is ideal for relating fluorescent and non-fluorescent structures and has been used to map the CA cells in the rabbit brain 1. In view of the number of physiological, especially cardiovascular, studies of the role of medullary CA neurons and in view of recent neuroanatomical evidence 7,J,~,1~, z3,25 suggesting that these neurons provide the major catecholaminergic innervation of the hypothalamus, it is important to re-investigate their distribution in the cat. MATERIALS AND METHODS For our study, over 200 complete transverse sections from 9 kittens and adult cats weighing between 0.9 and 3.0 kg were examined in detail. The precise location of each CA cell in each section was mapped onto white-light photographs of each section (see below). In 3 animals, pargyline (100 mg/kg intraperitoneally 2 h before perfusion) was injected to inhibit monoamine oxidase with the intention of increasing amine levels in the cells. The cats were anaesthetized with pentobarbital (35 mg/kg, intraperitoneal) and perfused via a catheter inserted retrogradely into the abdominal aorta, with the cut right atrium acting as an outlet. A sphygmomanometer bulb and gauge were used to maintain and monitor pressure as described previously 11. The blood was flushed out by an initial perfusion with a solution of 1 ~o sodium nitrite in 0.01 M phosphate buffer pH 7.0, to which 500 I.U. heparin/100 ml was added. Perfusion was then continued with 1500 ml of 4~o formaldehyde plus 0.5~o glutaraldehyde in 0.1 M phosphate buffer, pH 7.0. Transverse sections (25-50 #m) of the medulla were cut on a vibratome at room temperature and transferred to perfusion solution. Wet sections were photographed at low power using a Zeiss Tessovar microscope and then the same sections were dried and mounted on chrome-alum coated slides. The distribution of catecholamine cells was examined with a Leitz Ortholux fluorescence microscope. The positions of the fluorescent cells were marked on the low power Tessovar micrographs. After the fluorescence of the catecholamine neurons had been examined, the sections were
A
[3
C
Fig. 1. Photographs of representative transverse sections through the cat medulla. The catecholamine cell bodies are indicated by filled circles. Abbreviations: ap, area postrema; c, central canal; cn, cuneate nucleus; gn, gracile nucleus; io, inferior olive; lrn, lateral reticular nucleus; lrn st, lateral reticular nucleus, subtrigeminal portion; ha, nucleus ambiguus; nts, nucleus tractus solitarius; nXII, hypoglossal nerve, p, pyramidal tract; sV, spinal tract of trigeminal nerve; ts, tractus solitarius; X, dorsal motor nucleus of vagus; XII, hypoglossal nucleus.
72 r e h y d r a t e d a n d stained with neutral red or cresyl fast violet and then r e - e x a m i n e d to confirm the relationship between the positions or the c a t e c h o l a m i n e cells and m e d u l l a r y nuclei. RESULTS AND DISCUSSION The d i s t r i b u t i o n of C A cells in representative transverse sections f r o m different levels o f the m e d u l l a is shown in Fig. 1. There is a ventrolateral g r o u p (A1) and a d o r s o m e d i a l g r o u p (A2) with cells occasionally f o u n d between these two groups. In the area p o s t r e m a there are some small fluorescent cells. P r e t r e a t m e n t with pargyline did n o t reveal any a d d i t i o n a l groups. The A1 g r o u p extended f r o m the p y r a m i d a l decussation to the rostral-third o f the inferior olivary complex. A t the caudal extreme (Fig. 1A) the cells were f o u n d in the lateral reticular f o r m a t i o n with occasional cells between the fibre bundles o f the corticospinal tract. In m o r e rostral sections (Fig. 1B), the C A cells were scattered a r o u n d but not within the L R N . In a 30 # m transverse section an average o f a b o u t 8 fluorescent cells were f o u n d on the dorsal b o r d e r o f this nucleus with occasional a d d i t i o n a l cells wedged between the nucleus a n d the v e n t r o l a t e r a l surface o f the medulla. After Nissl staining, the A1 cells were seen to be scattered a m o n g s t other similar cells which showed no histochemical reaction for catecholamines (Fig. 3a-c). The smaller spindle-shaped A1 cells c o n t r a s t e d with the p r o m i n e n t m o r e regular cells o f the L R N (Fig. 3c). In the open m e d u l l a (Fig. 1C) the m a j o r i t y o f the C A cells were f o u n d d o r s a l to the principal p o r t i o n of the L R N , j u s t ventrolateral to the cells o f the nucleus ambiguus. A t levels rostral to the L R N the C A cells were f o u n d closer to the ventral surface o f the medulla. N e a r l y all the A2 C A cells were scattered within the N T S with an occasional cell within the dorsal m o t o r nucleus o f the vagus. A t the caudal level (Fig. 1A), where the c o m m i s s u r a l p o r t i o n o f the N T S a p p e a r s compressed by the gracile and cuneate nuclei, and at the level o f the obex (Fig. 1B), the C A cells were f o u n d in b o t h the medial a n d lateral p o r t i o n s of the c o m m i s s u r a l nucleus of the N T S b u t they were rarely f o u n d b e y o n d the rostral extent o f the a r e a p o s t r e m a . The A2 cells were interspersed a m o n g s t the non-fluorescent cells (Fig. 2a-c).
Fig. 2. Three views of the same tissue section, localizing A2 catecholamine-containing cells by the formaldehyde-glutaraldehyde fluorescence technique, a: photograph of a transverse section through the dorsomedial medulla at the level of the obex; cc, central canal; cn, cuneate nucleus; gn, gracile nucleus ; ts, tractus solitarius, XII, hypoglossal nucleus. Bar - 0.5 ram. b: fluorescence photomicrograph of the portion of the NTS indicated by the rectangle in Fig. 2a. Bar -- 50 f~m. c : Nissl stain of the same NTS area. Some corresponding cells are indicated by arrows. Bar --- 50 l~m. Fig. 3. Three views of the same tissue section, localizing A1 catecholamine-containing cells by the formaldehyde glutaraldehyde fluorescence technique, a : photograph of a transverse section through the ventrolateral medulla at the level of the obex. A small area on the dorsal border of the lrn is indicated by a rectangle. Bar 0.5 ram. b: fluorescence photomicrograph showing 3 CA cells in the dorsal portion of the area indicated in Fig. 3a. Bar 50/~m.c: N issl stain of the area indicated by the rectangle. The cells arrowed correspond to the fluorescent cells seen in Fig. 3b. In the lower portion of Fig. 3c there are 3 cells from the dorsal part of the lrn. v, blood vessel; io, inferior olive; lrn, lateral reticular nucleus. Bar - 50 l~m.
[
~P
74 O u r description o f the cat m e d u l l a r y C A cells contrasts in several respects with t h a t o f Poitras a n d Parent2L N o A2 cells were f o u n d within or ventral to the hypoglossal nucleus and they d i d n o t extend far into the open medulla. N o AI cells were f o u n d dorsal to the inferior olivary complex nor were they f o u n d within the L R N . This p o i n t should be e m p h a s i z e d since A I cells have been described within the L R N o f the r a ¢ , 2° a n d in biochemical studies it is c o m m o n (e.g. ref. 24) to p u n c h out the L R N as a sample o f the A1 group. However, our findings in the cat and studies in other species1,5,13, including a recent review o f the rat d a t a is, m a k e it unlikely t h a t the A1 cells are p a r t o f the L R N . This nucleus projects mainly to the cerebellum :3 in c o n t r a s t to the A1 cells which project to the spinal cord and the h y p o t h a l a m u s 6,7. In the r a b b i t the A1 cells are m o r e c o m p a c t l y a r r a n g e d ~ a n d lesions of this g r o u p o f cells have resulted in hypertension and p u l m o n a r y e d e m a '). Because the cat A 1 cells tend to be diffusely scattered a r o u n d the L R N it will be m o r e difficult to selectively lesion these n e u r o n s in studies o f their function. ACKNOWLEDGEMENTS W . W . B . is a Research F e l l o w o f the Life Insurance M e d i c a l Research F u n d o f A u s t r a l i a a n d New Zealand. P . F . was s u p p o r t e d by a grant f r o m the N a t i o n a l H e a r t F o u n d a t i o n o f Australia.
REFERENCES l Blessing, W. W., Chalmers, J. P. and Howe, P. R. C., Distribution of catecholamine-containing cell bodies in the rabbit central nervous system, J. comp. Neurol., 179 (1978) 407-424. 2 Blessing, W. W., West, M. J. and Chalmers, J. P., Hypertension and pulmonary edema following lesions of catecholamine neurons (A1) in the ventrolateral medulla oblongata of the rabbit, Proc. Austr. Physiol. Pharmacol. Soc., 10 (1979) 272P. 3 Brodal, A., The Reticular Formation of the Brain Stem. Anatomical Aspects and Functional Considerations, Oliver and Boyd, Edinburgh and London, 1957, p. 14. 4 Coote, J. H. and McLeod, V. H., The influence of bulbospinal monoaminergic pathways on sympathetic nerve activity, J. Physiol. (Lond.), 241 (1974) 453475. 5 Crutcher, K. A. and Humbertson, A. O., The organization of monoamine neurons within the brainstem of the North American opossum (Didelphis virginiana), J. comp. Neurol., 179 (1978) 195-222. 6 Dahlstrom, A. and Fuxe, K., Evidence for the existence of monoamine-containing neurons in the central nervous system. I. Demonstration of monoamines in the cell bodies of brain stem neurons, Aetaphysiol. scand., 62, Suppl. 232: (1964) 1-55. 7 Day, T. A., Blessing, W. W. and Willoughby, J. O., Catecholaminergic afferents to the preoptic area of the rat, Proc. Austr. Physiol. Pharmacol. Soc., 10 (1979) 273P. 8 Felten, D. L., Laties, A. M. and Carpenter, M. B., Monoamine-containing cell bodies in the squirrel monkey brain, Amer. J. Anat., 139 (1974) 153-165. 9 Furness, J. B., Costa, M. and Blessing, W. W., Simultaneous fixation and production of catecholamine fluorescence in central nervous tissue by perfusion with aldehydes, Histochem. J., 9 (1977) 745-750. 10 Furness, J. B., Costa, M. and Wilson, A., Water-stable fluorophores, produced by reaction with aldehyde solutions, for the histochemical localization of catechol- and indolethylamines, Histochemistry, 52 (1977) 159-170. 11 Furness, J. B., Heath, J. W. and Costa, M., Aqueous aldehyde (Faglu) methods for the fluorescence histochemicallocalizationof catecholamines and for ultrastructural studies of central nervous tissue, Histochemistry, 57 (1978) 285-295.
75 12 Garver, D. L. and Sladek, J. R., Monoamine distribution in primate brain. I. Catecholamine-containing perikarya in the brain stem of Macaca speciosa, J. comp. Neurol., 159 (1975) 289-304. 13 Hubbard, J. E. and DiCarlo, V., Fluorescence histochemistry of monoamine-containing cell bodies in the brain stem of the squirrel monkey (Saimiri sciureus), II. Catecholamine-containing groups, J. comp. Neurol., 153 (1974) 369-384. 14 Jacobowitz, D. M. and MacLean, P. D., A brain stem atlas of catecholaminergic neurons and serotonergic perikarya in a primate (Cebeulla pygmaea), J. comp. Net~roL, 177 (1978) 397-416. 15 Jones, B. A., Halaris, A. E. and Freedman, D. X., Innervation of forebrain regions by medullary noradrenaline neurons, a biochemical study in cats with central tegmental lesions, Neurosci. Lett., 10 (1978) 251-258. 16 Loewy, A. D. and Burton, H., Nuclei of the solitary tract: efferent projections to the lower brain stem and spinal cord of the cat, J. comp. Neural., 181 (1978) 421-450. 17 Maeda, T., Pin, C., Salvert, D., Ligier, M. and Jouvet, M., Les neurones contenant des catecholamines du tegmentum poutique et leurs voies de projection chez le chat, Brain Research, 57 (1973) 119-152. 18 Moore, R. Y. and Bloom, F. E., Central catecholamine neuron systems : anatomy and physiology of the norepinephrine and epinephrine systems, Ann. Rev. Neurosci., 2 (1979) 113-168. 19 Nobin, A. and Bjorklund, A., Topography of the monoamine neuron systems in the human brain as revealed in fetuses, ActaphysioL scand., Suppl., 388 (1973) 1-40. 20 Palkovits, M. and Jacobowitz, D. M., Topographic atlas ofcatecholamine and acetylcholinesterasecontaining neurons in the rat brain, II. Hindbrain (mesencephalon, rhombencephalon), J. comp. Neurol., 157 (1974) 29-42. 21 Pin, C., Jones, B. and Jouvet, M., Topographie des neurones monoaminergiques du tronc cerebral du chat: etude par histofluorescence, C.R. Soc. Biol. (Paris), 162 (1968) 2136-2141. 22 Poitras, D. and Parent, A., Atlas of the distribution of monoamine-containing nerve cell bodies in the brain stem of the cat, J. comp. Neurol., 179 (1978) 699-718. 23 Ricardo, J. A. and Koh, E. T., Anatomical evidence of direct projections from the nucleus of the solitary tract to the hypothalamus, amygdala, and other forebrain structures in the rat, Brain Research, 153 (1978) 1-26. 24 Saavedra, J. M., Kvetnansky, R. and Kopin, I. J., Adrenaline, noradrenaline and dopamine levels in specific brain stem areas of acutely immobilized rats, Brain Research, 160 (1979) 271-280. 25 Sakumoto, T., Tohyama, M., Satoh, K., Kimoto, Y., Kinugasa, T., Tanizawa, O., Kurachi, K. and Shimizu, N., Afferent connections from lower brain stem to hypothalamus studied by the horseradish peroxidase method with special reference to noradrenaline innervation, Exp. Brain Res., 31 (1978) 81-94. 26 Swanson, L. W. and Hartman, B. K., The central adrenergic system. An immunofluorescence study of the location of cell bodies and their efferent connections in the rat utilizing dopamine-fl-hydroxylase as a marker, J. comp. NeuroL, 163 (1975) 467-505.