- Email: [email protected]
Basal forebrain projections to the lower brain stem in the rat
EXPERIMENTAL
NEUROLOGY
106.316-319
(1989)
BRIEF COMMUNICATION Basal Forebrain Projections to the Lower Brain Stem in the Rat A. DINOPOULOS,*
G. C. PAPADOPOULOS,*
J. G. PARNAVELAS,~
J. ANTONOPOULOS,*
AND A. N. KARAMANLIDIS*
*Department of Anatomy, School of Veterinary Medicine, University of Thessaloniki, 54006 Thessaloniki, Greece; and TDepartment of Anatomy and Developmental Biology, University College London, London, United Kingdom
The projections of the magnocellular nuclei of the basal forebrain to the lower brain stem were studied using the WGA-HRP method. Of these nuclei, the nucleus of the vertical and the nucleus of the horizontal limb of the diagonal band of Broca, the magnocellular preoptic nucleus, and the substantia innominata were found to project bilaterally to the caudal midbrain, pons, and medulla. Labeled cells in the medial septal nucleus and in the nucleus basalis were found ipsilaterally only when injections stained the caudal part of the interpeduncular nucleus. The present findings together with other recent reports reveal a more extensive distribution of basal forebrain efferents than was previously 0 1989 Academic Press, Inc. thought.
The basal forebrain contains many large neurons, most of which are cholinergic, located in the medial septal nucleus (MS), the nuclei of the diagonal band of Broca, the magnocellular preoptic nucleus (MgPO), the nucleus basalis (NB), and the substantia innominata (SI) (15). Many of these neurons have been found to project to a wide variety of structures, such as the cerebral cortex, the amygdala, the hippocampus, and the olfactory bulb (4, 11, 1519, 21, 28). However, accumulating data show that basal forebrain efferents are more extensively distributed than was previously believed. For example, it has been recently shown that in the rat, basal forebrain neurons project to the interpeduncular nucleus (IP) (8, 24, 29) and the contralateral basal forebrain (22). In addition, the mediodorsal and the reticular nucleus of the thalamus, in both cats and primates, receive inputs from the nuclei of the diagonal band and the SI (25). It has also been reported that HRP injections in the midbrain and pons labeled cells in the basal forebrain of the rat (7). However, these injections were made in only two rats and were very large, extending bilaterally in both the midbrain and the pons. The aim of the present investigation was to examine the descending efferents of the basal forebrain by placing more restricted wheat germ agglutinin-horseradish peroxidase 0014-4866/89 $3.00 Copyright 0 1989 by Academic Press, All rights of reproduction in any form
(WGA-HRP) injections in the lower brain stem and the spinal cord. A total of 16 Wistar albino rats received injections of a 4% WGA-HRP (Sigma) solution in sterile water. Twelve animals each received 0.1~1 WGA-HRP at various levels of the caudal midbrain, pons, and medulla. All injections were placed unilaterally (Fig. 2a). In addition, two rats received a unilateral injection (0.1~1) in the first cervical segment of the spinal cord and another two rats injections (0.3 ~1) in the vermis and the right hemisphere of the cerebellum. The cerebellar injections were made to examine the possibility of direct basal forebrain projections to the cerebellum, since in all animals the injections in the brain stem were made by lowering the needle through the cerebellum. All injections were made under pentobarbital anaesthesia (47 mg/kg, ip), over a period of 10 min using a l-p1 Hamilton microsyringe. In each case, the injection needle was left in place 10 min both before and after the injection. For injection coordinates the atlas of Paxinos and Watson (17) was consulted. Animals were allowed to survive for 2 days and were perfused, under deep anaesthesia, with saline followed by a mixture of 1% paraformaldehyde and 1.25% glutaraldehyde in 0.1 M phosphate buffer (pH 7.4). The brains were removed and immersed in fixative containing 5% sucrose for 12 h and then placed into 30% sucrose in phosphate buffer until they sank, all at 4°C. Serial frozen sections were cut in the transverse plane at 40 pm. Every second section was collected in cold phosphate buffer and was processed with tetramethyl benzidine according to the procedure of Mesulam (13). The sections were subsequently counterstained with neutral red, while adjacent sections were stained with toluidine blue. The distributions of WGA-HRP-positive cells in the basal forebrain were plotted with the aid of a drawing tube attached to a microscope. In four rats WGA-HRP injections in the brain stem resulted in intense staining of the caudal midbrain and the pons. Staining was also observed in the caudal part of the IP. Following these injections, retrogradely labeled neurons were found bilaterally, but mainly ipsilaterally, throughout the basal forebrain, with the excep-
316 Inc. reserved.
BRIEF
COMMUNICATION
FIG. 1. Drawings of transverse sections showing the distribution of WGA-HRP-labeled cells in the basal forebrain of two rats, following an injection that stained the caudal midbrain, including the caudal part of the IP, and the pons (A) and following an injection in the cauda1 midbrain and the pons (B). The top drawings depict the injection sites. Each dot represents one labeled cell. Scale bar, 1 mm. Abbreviations used in this and the following figures: ac, anterior commissure; CG, central gray; CPU, caudate/putamen; GP, globus pallidus; lfp, longitudinal fascicle of pons; MgPO, magnocellular preoptic nucleus; LH, lateral hypothalamic area; mlf, medial longitudinal fascicle; MPO, medial preoptic area; MS, medial septum; NB, nucleus basalis; NHL, nucleus of the horizontal limb of the diagonal band of Broca; NVL, nucleus of the vertical limb of the diagonal band of Broca; Pn, pontine nuclei; PnO, oral pontine reticular nucleus; scp, superior cerebellar peduncle; SI, substantia innominata; VLL, ventral nucleus of the lateral lemniscus.
tion of the NB in which labeled cells were present only in the ipsilateral side (Fig. 1A). More specifically, labeled cells were found in the nucleus of the vertical limb (NVL) and the nucleus of the horizontal limb (NHL) of the diagonal band of Broca, the MgPO, MS, and NB. Fewer labeled cells were also found in the SI. In three rats injections stained the caudal midbrain and the pons without any diffusion in the IP. In these cases no labeled cells were observed in the MS and NB but they were present, although fewer, in the NVL, NHL, MgPO, and SI of both hemispheres (Figs. lB, 2b, 2~). Injections confined to the pons of three rats resulted in labeling of even
317
fewer cells in the NVL, NHL, MgPO, and SI of both sides. Moreover, injections in the medulla of two rats labeled a sparse population of cells in the basal forebrain. These cells were found in all of the above nuclei with the exception of the MS and NB. Finally, injections of WGA-HRP in the first cervical segment of the spinal cord or in the cerebellar cortex resulted in no cell labeling in any of the basal forebrain nuclei. It is now well documented with both retrograde (24, 29) and anterograde (8) tracing studies that the nuclei of the diagonal band of Broca project to the IP. Woolf and Butcher (29) also found a minor projection to the IP from the MS and NB. Divac (7) found retrogradely labeled cells in the nuclei of the diagonal band, MgPO, and NB after placing large HRP injections in the midbrain and pons which presumably also stained the IP. Our findings, although indirect, are in favor of a NB projection to the IP. In addition, they clearly show that projections to other caudal midbrain structures, pons, and medulla arise bilaterally, only from the nuclei of the diagonal band and the MgPO, as well as fewer from the SI. These projections are more numerous in the midbrain and pons than in the medulla. It should be noted that it cannot be ascertained from these results whether these projections are collaterals of the ascending basal forebrain fibres. However, recent double-labeling experiments (16) have shown that in squirrel monkeys descending basal forebrain projections to the brain stem peribrachial area are not collaterals of the ascending projections to the cerebral cortex. Tract tracing studies have revealed that the basal forebrain receives afferents from a large number of neurons located in the brain stem reticular formation (9,23, 26). Some of these neurons have been found to contain acetylcholine or monoamines and other unknown neurotransmitters and to influence the activity of neurons in the basal forebrain (9,23,26). It is reasonable to hypothesize that basal forebrain neurons projecting to the brain stem may be reciprocally connected with at least some of these neurons and thus modulate their activity. The neurotransmitter(s) used by the basal forebrain neurons that project to the brain stem has not yet been identified. However, most cells in the basal forebrain are known to contain acetylcholine (15), with smaller populations containing GABA (5), or one of a number of identified peptides (3, 10, 12, 27). Ascending fibers arising from cholinergic neurons of the basal forebrain innervate all neocortical areas. This cholinergic system has been suggested to be involved in behavioral tasks related to learning and memory (20) and in Alzheimer’s disease (1,2). The fact that neurons in the basal forebrain exhibit common morphological features with the so-called “isodendritic or generalized neurons” of the reticular formation (6, 14, 18) as well as other data (see Refs. (9, 14)) has led authors to suggest that cells in the basal forebrain may constitute a telencephalic extension of the
BRIEF
FIG. 2. (a) Example cells are seen in the NVL
of a WGA-HRP (c) and MgPO
injection (b) following
COMMUNICATION
site in the pons. X23.5. (b, c) Photomicrographs of transverse an injection of WGA-HRP into the caudal midbrain and pons.
brain stem reticular formation. The described ascending projections from parts of the brain stem reticular formation to the basal forebrain and the present finding of a possible descending basal forebrain projection to at least parts of this structure further support this view. ACKNOWLEDGMENTS The authors thank Messrs. Zlatis for technical assistance, help. The work was supported
2.
3.
4.
A. Christodoulou, C. Drossos, and T. and Mrs. A. Tsipinia for secretarial by Wellcome Trust. 5.
REFERENCES 1.
ARENDASH, G. W., W. J. MILLARD, A. J. DUNN, AND E. M. MEYER. 1987. Long-term neuropathological and neurochemical
6.
sections X450.
in which
labeled
effects of nucleus basalis lesions in the rat. Science 238: 952956. BARTUS, R. T., R. L. DEAN III, B. BEER, AND A. S. LIPPA. 1982. Cholinergic hypothesis of geriatric memory dysfunction. Science 217: 408-41’7. BENNETT-CLARKE, C., M. A. ROMAGNANO, AND S. A. JOSEPH. 1980. Distribution of somatostatin in the rat brain: Telencephalon and diencephalon. Bruin Res. 188: 473-486. BIGL, V., N. J. WOOLF, AND L. L. BUTCHER. 1982. Cholinergic projections from the basal forebrain to frontal, parietal, temporal, occipital, and cingulate cortices: A combined fluorescent tracer and acetylcholinesterase analysis. Bruin Res. Bull. 8: 727749. BRASHEAR, H. R., L. ZABORSZKY, AND L. HEIMER. 1986. Distribution of GABAergic and choline@ neurons in the rat diagonal band. Neuroscience 17: 439-451. DINOPOULOS, A., J. G. PARNAVELAS, H. B. M. UYLINGS, AND C. G. VAN EDEN. 1988. Morphology of neurons in the basal fore-
BRIEF brain
nuclei
of the rat: A Golgi
study.
J. Comp.
Neural.
272:
319
COMMUNICATION 461-
17. PAXINOS,
474. 18.
G., AND C. WATSON. 1982. The Rat Brain in Stereotaxic Coordinates. Academic Press, New York/Sydney. RAM~N-MOLINER, E., AND W. J. H. NAUTA. 1966. The isodendritic core of the brain stem. J. Comp. Neural. 126: 311-336. RYE, D. B., B. H. WAINER, M.-M. MESULAM, E. J. MUFSON, AND C. B. SAPER. 1984. Cortical projections arising from the basal forebrain: A study of cholinergic and noncholinergic components employing combined retrograde tracing and immunohistochemical localization of choline acetyltransferase. Neuroscience 13:
7.
DIVAC, I. 1975. Magnocellular nuclei of the basal forebrain project to neocortex, brain stem, and olfactory bulb. Review of some functional correlates. Brain Res. 93: 385-398.
a.
HAMILL, G. S., AND B. FASS. 1984. Differential distribution diagonal band afferents to subnuclei of the interpeduncular cleus in rats. Neurosci. Lett. 48: 43-48.
9.
JONES, B. E., AND T.-Z. YANG. 1985. The efferent projections from the reticular formation and the locus coeruleus studied by anterograde and retrograde axonal transport in the rat. J. Comp. Neurol. 242: 56-92.
627-643. 20. SALAMONE,
LJUNGDAHL, A., T. HBKFELT, AND G. NILSSON. 1978. Distribution of substance P-like immunoreactivity in the central nervous system of the rat. I. Cell bodies and nerve terminals. Neurosci-
21.
10.
11.
12.
19.
of nu-
J. D. 1986. Behavioural functions of nucleus basalis magnocellularis and its relationship to dementia. Trends Neurosci. 9: 256-258. SAPER, C. B. 1984. Organization of cerebral cortical afferent systems in the rat. II. Magnocellular basal nucleus. J. Comp. Neural.
ence3:861-943.
222:313-342. 22. SEMBA, K., P. B. REINER,
MCKINNEY, M., J. T. COYLE, AND J. C. HEDREEN. 1983. Topographic analysis of the innervation of the rat neocortex and hippocampus by the basal forebrain cholinergic system. J. Comp. Neurol. 217: 103-121.
23.
MELANDER, T., T. HBKFELT, AND A. RBKAEUS. 1986. Distribution of galaninlike immunoreactivity in the rat central nervous system. J. Comp. Neural. 248: 475-517.
24.
13. MESULAM,
M.-M. 1978. Tetramethyl benzidine for horseradish peroxidase neurohistochemistry: A non-carcinogenic blue reaction product with superior sensitivity for visualizing neural afferents and efferents. J. Histochem. Cytochem. 26: 106-117.
14. MESULAM,
M.-M., E. J. MUFSON, A. I. LEVEY, AND B. H. WAINER. 1983. Cholinergic innervation of cortex by the basal forebrain: Cytochemistry and cortical connections of the septal area, diagonal band nuclei, nucleus basalis (substantia innominata), and hypothalamus in the rhesus monkey. J. Comp. Neural. 214: 170-197.
15. MESULAM,
M.-M., E. J. MUFSON, B. H. LEVEY. 1983. Central cholinergic pathways view based on an alternative nomenclature science 10: 118551201.
WAINER, AND A. I. in the rat: An over(Chl-Ch6). Neuro-
272-284. 25. STERIADE,
M., A. PARENT, D. PARE, AND Y. SMITH. 1987. Cholinergic and non-cholinergic neurons of cat basal forebrain project to reticular and mediodorsal thalamic nuclei. Brain Res.
408:372-376. 26. 27. 28.
16. PARENT,
A., D. PAR& Y. SMITH, AND M. STERIADE. 1988. Basal forebrain cholinergic and noncholinergic projections to the thalamus and brainstem in cats and monkeys. J. Comp. Neural. 277: 281-301.
E. G. MCGEER, AND H. C. FIBIGER. 1988. Non-cholinergic basal forebrain neurons project to the contralateral basal forebrain in the rat. Neurosci. Lett. 84: 23-28. SEMBA, K., P. B. REINER, E. G. MCGEER, AND H. C. FIBIGER. 1988. Brainstem afferents to the magnocellular basal forebrain studied by axonal transport, immunohistochemistry, and electrophysiology in the rat. J. Comp. Neural. 267: 433-453. SHIBATA, H., T. SUZUKI, AND M. MATSUSHITA. 1986. Afferent projections to the interpeduncular nucleus in the rat, as studied by retrograde and anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. J. Camp. Neural. 248:
29.
VERTES, R. P. 1988. Brainstem afferents to the basal forebrain in the rat. Neuroscience 24: 907-935. WAMSLEY, J. K., W. S. YOUNG III, AND M. J. KUHAR. 1980. Immunohistochemical localization of enkephalin in rat forebrain. BrainRes. 190:153-174. WOOLF, N. J., AND L. L. BUTCHER. 1982. Cholinergic projections to the basolateral amygdala: A combined Evans Blue and acetylcholinesterase analysis. Brain Res. Bull. 8: 751-763. WOOLF, N. J., AND L. L. BUTCHER. 1985. Cholinergic systems in the rat brain: II. Projections to the interpeduncular nucleus. Brain Res. Bull. 14: 63-83.
NEUROLOGY
106.316-319
(1989)
BRIEF COMMUNICATION Basal Forebrain Projections to the Lower Brain Stem in the Rat A. DINOPOULOS,*
G. C. PAPADOPOULOS,*
J. G. PARNAVELAS,~
J. ANTONOPOULOS,*
AND A. N. KARAMANLIDIS*
*Department of Anatomy, School of Veterinary Medicine, University of Thessaloniki, 54006 Thessaloniki, Greece; and TDepartment of Anatomy and Developmental Biology, University College London, London, United Kingdom
The projections of the magnocellular nuclei of the basal forebrain to the lower brain stem were studied using the WGA-HRP method. Of these nuclei, the nucleus of the vertical and the nucleus of the horizontal limb of the diagonal band of Broca, the magnocellular preoptic nucleus, and the substantia innominata were found to project bilaterally to the caudal midbrain, pons, and medulla. Labeled cells in the medial septal nucleus and in the nucleus basalis were found ipsilaterally only when injections stained the caudal part of the interpeduncular nucleus. The present findings together with other recent reports reveal a more extensive distribution of basal forebrain efferents than was previously 0 1989 Academic Press, Inc. thought.
The basal forebrain contains many large neurons, most of which are cholinergic, located in the medial septal nucleus (MS), the nuclei of the diagonal band of Broca, the magnocellular preoptic nucleus (MgPO), the nucleus basalis (NB), and the substantia innominata (SI) (15). Many of these neurons have been found to project to a wide variety of structures, such as the cerebral cortex, the amygdala, the hippocampus, and the olfactory bulb (4, 11, 1519, 21, 28). However, accumulating data show that basal forebrain efferents are more extensively distributed than was previously believed. For example, it has been recently shown that in the rat, basal forebrain neurons project to the interpeduncular nucleus (IP) (8, 24, 29) and the contralateral basal forebrain (22). In addition, the mediodorsal and the reticular nucleus of the thalamus, in both cats and primates, receive inputs from the nuclei of the diagonal band and the SI (25). It has also been reported that HRP injections in the midbrain and pons labeled cells in the basal forebrain of the rat (7). However, these injections were made in only two rats and were very large, extending bilaterally in both the midbrain and the pons. The aim of the present investigation was to examine the descending efferents of the basal forebrain by placing more restricted wheat germ agglutinin-horseradish peroxidase 0014-4866/89 $3.00 Copyright 0 1989 by Academic Press, All rights of reproduction in any form
(WGA-HRP) injections in the lower brain stem and the spinal cord. A total of 16 Wistar albino rats received injections of a 4% WGA-HRP (Sigma) solution in sterile water. Twelve animals each received 0.1~1 WGA-HRP at various levels of the caudal midbrain, pons, and medulla. All injections were placed unilaterally (Fig. 2a). In addition, two rats received a unilateral injection (0.1~1) in the first cervical segment of the spinal cord and another two rats injections (0.3 ~1) in the vermis and the right hemisphere of the cerebellum. The cerebellar injections were made to examine the possibility of direct basal forebrain projections to the cerebellum, since in all animals the injections in the brain stem were made by lowering the needle through the cerebellum. All injections were made under pentobarbital anaesthesia (47 mg/kg, ip), over a period of 10 min using a l-p1 Hamilton microsyringe. In each case, the injection needle was left in place 10 min both before and after the injection. For injection coordinates the atlas of Paxinos and Watson (17) was consulted. Animals were allowed to survive for 2 days and were perfused, under deep anaesthesia, with saline followed by a mixture of 1% paraformaldehyde and 1.25% glutaraldehyde in 0.1 M phosphate buffer (pH 7.4). The brains were removed and immersed in fixative containing 5% sucrose for 12 h and then placed into 30% sucrose in phosphate buffer until they sank, all at 4°C. Serial frozen sections were cut in the transverse plane at 40 pm. Every second section was collected in cold phosphate buffer and was processed with tetramethyl benzidine according to the procedure of Mesulam (13). The sections were subsequently counterstained with neutral red, while adjacent sections were stained with toluidine blue. The distributions of WGA-HRP-positive cells in the basal forebrain were plotted with the aid of a drawing tube attached to a microscope. In four rats WGA-HRP injections in the brain stem resulted in intense staining of the caudal midbrain and the pons. Staining was also observed in the caudal part of the IP. Following these injections, retrogradely labeled neurons were found bilaterally, but mainly ipsilaterally, throughout the basal forebrain, with the excep-
316 Inc. reserved.
BRIEF
COMMUNICATION
FIG. 1. Drawings of transverse sections showing the distribution of WGA-HRP-labeled cells in the basal forebrain of two rats, following an injection that stained the caudal midbrain, including the caudal part of the IP, and the pons (A) and following an injection in the cauda1 midbrain and the pons (B). The top drawings depict the injection sites. Each dot represents one labeled cell. Scale bar, 1 mm. Abbreviations used in this and the following figures: ac, anterior commissure; CG, central gray; CPU, caudate/putamen; GP, globus pallidus; lfp, longitudinal fascicle of pons; MgPO, magnocellular preoptic nucleus; LH, lateral hypothalamic area; mlf, medial longitudinal fascicle; MPO, medial preoptic area; MS, medial septum; NB, nucleus basalis; NHL, nucleus of the horizontal limb of the diagonal band of Broca; NVL, nucleus of the vertical limb of the diagonal band of Broca; Pn, pontine nuclei; PnO, oral pontine reticular nucleus; scp, superior cerebellar peduncle; SI, substantia innominata; VLL, ventral nucleus of the lateral lemniscus.
tion of the NB in which labeled cells were present only in the ipsilateral side (Fig. 1A). More specifically, labeled cells were found in the nucleus of the vertical limb (NVL) and the nucleus of the horizontal limb (NHL) of the diagonal band of Broca, the MgPO, MS, and NB. Fewer labeled cells were also found in the SI. In three rats injections stained the caudal midbrain and the pons without any diffusion in the IP. In these cases no labeled cells were observed in the MS and NB but they were present, although fewer, in the NVL, NHL, MgPO, and SI of both hemispheres (Figs. lB, 2b, 2~). Injections confined to the pons of three rats resulted in labeling of even
317
fewer cells in the NVL, NHL, MgPO, and SI of both sides. Moreover, injections in the medulla of two rats labeled a sparse population of cells in the basal forebrain. These cells were found in all of the above nuclei with the exception of the MS and NB. Finally, injections of WGA-HRP in the first cervical segment of the spinal cord or in the cerebellar cortex resulted in no cell labeling in any of the basal forebrain nuclei. It is now well documented with both retrograde (24, 29) and anterograde (8) tracing studies that the nuclei of the diagonal band of Broca project to the IP. Woolf and Butcher (29) also found a minor projection to the IP from the MS and NB. Divac (7) found retrogradely labeled cells in the nuclei of the diagonal band, MgPO, and NB after placing large HRP injections in the midbrain and pons which presumably also stained the IP. Our findings, although indirect, are in favor of a NB projection to the IP. In addition, they clearly show that projections to other caudal midbrain structures, pons, and medulla arise bilaterally, only from the nuclei of the diagonal band and the MgPO, as well as fewer from the SI. These projections are more numerous in the midbrain and pons than in the medulla. It should be noted that it cannot be ascertained from these results whether these projections are collaterals of the ascending basal forebrain fibres. However, recent double-labeling experiments (16) have shown that in squirrel monkeys descending basal forebrain projections to the brain stem peribrachial area are not collaterals of the ascending projections to the cerebral cortex. Tract tracing studies have revealed that the basal forebrain receives afferents from a large number of neurons located in the brain stem reticular formation (9,23, 26). Some of these neurons have been found to contain acetylcholine or monoamines and other unknown neurotransmitters and to influence the activity of neurons in the basal forebrain (9,23,26). It is reasonable to hypothesize that basal forebrain neurons projecting to the brain stem may be reciprocally connected with at least some of these neurons and thus modulate their activity. The neurotransmitter(s) used by the basal forebrain neurons that project to the brain stem has not yet been identified. However, most cells in the basal forebrain are known to contain acetylcholine (15), with smaller populations containing GABA (5), or one of a number of identified peptides (3, 10, 12, 27). Ascending fibers arising from cholinergic neurons of the basal forebrain innervate all neocortical areas. This cholinergic system has been suggested to be involved in behavioral tasks related to learning and memory (20) and in Alzheimer’s disease (1,2). The fact that neurons in the basal forebrain exhibit common morphological features with the so-called “isodendritic or generalized neurons” of the reticular formation (6, 14, 18) as well as other data (see Refs. (9, 14)) has led authors to suggest that cells in the basal forebrain may constitute a telencephalic extension of the
BRIEF
FIG. 2. (a) Example cells are seen in the NVL
of a WGA-HRP (c) and MgPO
injection (b) following
COMMUNICATION
site in the pons. X23.5. (b, c) Photomicrographs of transverse an injection of WGA-HRP into the caudal midbrain and pons.
brain stem reticular formation. The described ascending projections from parts of the brain stem reticular formation to the basal forebrain and the present finding of a possible descending basal forebrain projection to at least parts of this structure further support this view. ACKNOWLEDGMENTS The authors thank Messrs. Zlatis for technical assistance, help. The work was supported
2.
3.
4.
A. Christodoulou, C. Drossos, and T. and Mrs. A. Tsipinia for secretarial by Wellcome Trust. 5.
REFERENCES 1.
ARENDASH, G. W., W. J. MILLARD, A. J. DUNN, AND E. M. MEYER. 1987. Long-term neuropathological and neurochemical
6.
sections X450.
in which
labeled
effects of nucleus basalis lesions in the rat. Science 238: 952956. BARTUS, R. T., R. L. DEAN III, B. BEER, AND A. S. LIPPA. 1982. Cholinergic hypothesis of geriatric memory dysfunction. Science 217: 408-41’7. BENNETT-CLARKE, C., M. A. ROMAGNANO, AND S. A. JOSEPH. 1980. Distribution of somatostatin in the rat brain: Telencephalon and diencephalon. Bruin Res. 188: 473-486. BIGL, V., N. J. WOOLF, AND L. L. BUTCHER. 1982. Cholinergic projections from the basal forebrain to frontal, parietal, temporal, occipital, and cingulate cortices: A combined fluorescent tracer and acetylcholinesterase analysis. Bruin Res. Bull. 8: 727749. BRASHEAR, H. R., L. ZABORSZKY, AND L. HEIMER. 1986. Distribution of GABAergic and choline@ neurons in the rat diagonal band. Neuroscience 17: 439-451. DINOPOULOS, A., J. G. PARNAVELAS, H. B. M. UYLINGS, AND C. G. VAN EDEN. 1988. Morphology of neurons in the basal fore-
BRIEF brain
nuclei
of the rat: A Golgi
study.
J. Comp.
Neural.
272:
319
COMMUNICATION 461-
17. PAXINOS,
474. 18.
G., AND C. WATSON. 1982. The Rat Brain in Stereotaxic Coordinates. Academic Press, New York/Sydney. RAM~N-MOLINER, E., AND W. J. H. NAUTA. 1966. The isodendritic core of the brain stem. J. Comp. Neural. 126: 311-336. RYE, D. B., B. H. WAINER, M.-M. MESULAM, E. J. MUFSON, AND C. B. SAPER. 1984. Cortical projections arising from the basal forebrain: A study of cholinergic and noncholinergic components employing combined retrograde tracing and immunohistochemical localization of choline acetyltransferase. Neuroscience 13:
7.
DIVAC, I. 1975. Magnocellular nuclei of the basal forebrain project to neocortex, brain stem, and olfactory bulb. Review of some functional correlates. Brain Res. 93: 385-398.
a.
HAMILL, G. S., AND B. FASS. 1984. Differential distribution diagonal band afferents to subnuclei of the interpeduncular cleus in rats. Neurosci. Lett. 48: 43-48.
9.
JONES, B. E., AND T.-Z. YANG. 1985. The efferent projections from the reticular formation and the locus coeruleus studied by anterograde and retrograde axonal transport in the rat. J. Comp. Neurol. 242: 56-92.
627-643. 20. SALAMONE,
LJUNGDAHL, A., T. HBKFELT, AND G. NILSSON. 1978. Distribution of substance P-like immunoreactivity in the central nervous system of the rat. I. Cell bodies and nerve terminals. Neurosci-
21.
10.
11.
12.
19.
of nu-
J. D. 1986. Behavioural functions of nucleus basalis magnocellularis and its relationship to dementia. Trends Neurosci. 9: 256-258. SAPER, C. B. 1984. Organization of cerebral cortical afferent systems in the rat. II. Magnocellular basal nucleus. J. Comp. Neural.
ence3:861-943.
222:313-342. 22. SEMBA, K., P. B. REINER,
MCKINNEY, M., J. T. COYLE, AND J. C. HEDREEN. 1983. Topographic analysis of the innervation of the rat neocortex and hippocampus by the basal forebrain cholinergic system. J. Comp. Neurol. 217: 103-121.
23.
MELANDER, T., T. HBKFELT, AND A. RBKAEUS. 1986. Distribution of galaninlike immunoreactivity in the rat central nervous system. J. Comp. Neural. 248: 475-517.
24.
13. MESULAM,
M.-M. 1978. Tetramethyl benzidine for horseradish peroxidase neurohistochemistry: A non-carcinogenic blue reaction product with superior sensitivity for visualizing neural afferents and efferents. J. Histochem. Cytochem. 26: 106-117.
14. MESULAM,
M.-M., E. J. MUFSON, A. I. LEVEY, AND B. H. WAINER. 1983. Cholinergic innervation of cortex by the basal forebrain: Cytochemistry and cortical connections of the septal area, diagonal band nuclei, nucleus basalis (substantia innominata), and hypothalamus in the rhesus monkey. J. Comp. Neural. 214: 170-197.
15. MESULAM,
M.-M., E. J. MUFSON, B. H. LEVEY. 1983. Central cholinergic pathways view based on an alternative nomenclature science 10: 118551201.
WAINER, AND A. I. in the rat: An over(Chl-Ch6). Neuro-
272-284. 25. STERIADE,
M., A. PARENT, D. PARE, AND Y. SMITH. 1987. Cholinergic and non-cholinergic neurons of cat basal forebrain project to reticular and mediodorsal thalamic nuclei. Brain Res.
408:372-376. 26. 27. 28.
16. PARENT,
A., D. PAR& Y. SMITH, AND M. STERIADE. 1988. Basal forebrain cholinergic and noncholinergic projections to the thalamus and brainstem in cats and monkeys. J. Comp. Neural. 277: 281-301.
E. G. MCGEER, AND H. C. FIBIGER. 1988. Non-cholinergic basal forebrain neurons project to the contralateral basal forebrain in the rat. Neurosci. Lett. 84: 23-28. SEMBA, K., P. B. REINER, E. G. MCGEER, AND H. C. FIBIGER. 1988. Brainstem afferents to the magnocellular basal forebrain studied by axonal transport, immunohistochemistry, and electrophysiology in the rat. J. Comp. Neural. 267: 433-453. SHIBATA, H., T. SUZUKI, AND M. MATSUSHITA. 1986. Afferent projections to the interpeduncular nucleus in the rat, as studied by retrograde and anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase. J. Camp. Neural. 248:
29.
VERTES, R. P. 1988. Brainstem afferents to the basal forebrain in the rat. Neuroscience 24: 907-935. WAMSLEY, J. K., W. S. YOUNG III, AND M. J. KUHAR. 1980. Immunohistochemical localization of enkephalin in rat forebrain. BrainRes. 190:153-174. WOOLF, N. J., AND L. L. BUTCHER. 1982. Cholinergic projections to the basolateral amygdala: A combined Evans Blue and acetylcholinesterase analysis. Brain Res. Bull. 8: 751-763. WOOLF, N. J., AND L. L. BUTCHER. 1985. Cholinergic systems in the rat brain: II. Projections to the interpeduncular nucleus. Brain Res. Bull. 14: 63-83.