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Heterogeneous distribution of benzodiazepine receptors in the human striatum: a quantitative autoradiographic study comparing the pattern of receptor labelling with the distribution of acetylcholinesterase staining
Brain Research, 381 (1986) 153-158 Elsevier
153
BRE 21722
Heterogeneous distribution of benzodiazepine receptors in the human striatum: a quantitative autoradiographic study comparing the pattern of receptor labelling with the distribution of acetylcholinesterase staining R.L.M. FAULL and J.W. VILLIGER Departmentof Anatomy, School of Medicine, Universityof Auckland, Auckland (New Zealand) (Accepted May 6th, 1986) Key words: [3H]flunitrazepam - - benzodiazepine receptor - - acetylcholinesterase - - striosome - - striatum - - human
The distribution of benzodiazepine receptors in the human striatum was studied by quantitative autoradiography following in vitro labelling of cryostat sections with [3H]flunitrazepam, and the pattern of receptor-labelling was compared to the distribution of acetylcholinesterase (ACHE) staining in adjacent sections. A heterogeneous pattern of benzodiazepine receptors was found in all regions of the striatum. The highest densities of receptors were seen in the ventral striatum (nucleus accumbens and olfactory tubercle), where very dense receptor patches aligned with both AChE-poor and AChE-rich regions. The dorsal striatum (caudate nucleus and putamen) contained lower concentrations of benzodiazepine receptors, but dense receptor patches were still evident (especially in the caudate nucleus) and these aligned with AChE-poor striosomes.
Recent studies have demonstrated that the seemingly homogeneous mammalian striatum is, in fact, organized in a heterogeneous compartmental fashion with respect to cytoarchitecture, i n p u t - o u t p u t relations and chemoarchitecture (see reviews by GraybieP '5 and Graybiel and Ragsdale9,1°). In particular, in the dorsal striatum major units of this compartmental organization are the so-called 'striosomes' or striatal bodies which were first identified by Graybiel and Ragsdale 7-9 in the cat, monkey and human with acetylcholinesterase (ACHE) histochemistry as A C h E - p o o r regions in an otherwise darkly staining striatal neuropil. It has now been shown that the striosomes are also characterised by high or low densities of neurochemical markers for several putative neurotransmitters. For example, the striosomes are characterized by: high concentrations of opiate peptides H and receptors 14, neurotensin-like immunoreactivity 3 and glutamic acid decarboxylase-like immunoreactivity 6, low somatostatin-like immunoreactivity 5, and high or low substance P-like immunoreactivity 11. In the present study we have used quantitative
autoradiographic methods in the human striatum to analyse the distribution of benzodiazepine receptors, a neurochemical marker for ),-aminobutyric acid ( G A B A ) receptorsl3,18, and compared the pattern of receptor labelling to the distribution of A C h E staining in adjacent sections. Postmortem human brains were obtained from 4 subjects (two females and two males) aged 4, 33, 43 and 53 years (average age 33 years) who died immediately following myocardial infarction or asphyxiation. All subjects had previously been in good health with no known history of neurological disease or drug treatment and all had died suddenly without the opportunity of receiving any form of medical treatment. Immediately following death, the bodies were removed to the University of Auckland Medical School mortuary and stored at 4 °C until autopsy. The interval between death and autopsy (i.e. the postmortem delay) ranged from 5 to 18 h (average delay of 13.5 h). At autopsy the brain was carefully removed and blocks were immediately selected from various regions of the striatum and frozen onto cryostat chucks
Correspondence: R.L.M. Faull, Department of Anatomy, School of Medicine, University of Auckland, Private Bag, Auckland, Ncw Zealand. 0006-8993/86/$03.50© 1986Elsevier Science PublishersB.V (Biomedical Division)
155 using dry ice. They were then sectioned transversely
for acetylcholinesterase (ACHE) histochemistry 2 in
at 16 ~tm using a cryostat and thaw-mounted onto ge-
the presence of the pseudocholinesterase inhibitor,
latine/chrome alum-coated slides. One series of slide-mounted sections was immediately processed
ethopropazine, and this staining was enhanced by silver intensification12 (see Fig. 1B). As detailed below,
B striatum) indicate benzodiazepine patches in A which align with AChE-poor striosomes in B. In the ventral striatum, the large arrows indicate benzodiazepinc patches which align mainly with AChE-poor zones (with some overlap into adjacent AChE-rich regions) in B, and the small arrows indicate receptor patches in A, which align with AChE-rich regions in B. The distance between sections A and B is 16urn. A and B have the same magnification; bar, 5 mm.
156 an adjacent series of sections was processed for the autoradiographic localization of benzodiazepine receptors using [3H]flunitrazepam ([3H]FNZ) I. Following storage at 4 °C for 1-7 days, slidemounted sections were incubated in 250 ml 50 mM Tris-HCl (pH 7.4) containing 1 nM [3H]FNZ (84 Ci/mmol, Amersham Radiochemical Centre) for l h. They were then washed (2 x 1 min in Tris-HC1 buffer, dipped in distilled water) and dried under a stream of cold air. All the above steps were performed at 4 °C. Non-specific control [3HJFNZ binding was determined by incubation of slides in the presence of 1 ,um cionazepam. Once dry, slides were brought to room-temperature and together with slide-mounted tritium micro-scale standards (RPA.501 and RPA.505, Amersham) they were taped into X-ray cassettes, apposed with [3H]sensitive Ultrofilm (LKB, Bromma, Sweden) and exposed in the dark at 4 °C for 6-10 weeks. The exposed films were developed in Kodak D19 for 4 min at 15 °C, washed and fixed. The Ultrofilm autoradiograms were subsequently printed using standard photographic procedures to yield 'darkfield' type autoradiograms where the autoradiographic labelled receptors appear as white dots on a black background (see Fig. 1A). The optical densities of the autoradiographic labelling in the various regions of the striatum were determined directly from the Ultrofilm autoradiograms using a spot densitometer designed to sample 75 1~m spots on the autoradiogram ~. These optical density values were then converted to nCi tritium bound/mg tissue using a standard curve derived from the optical density readings of the autoradiographic standards in which log nCi/mg was plotted against log optical density. These values were then converted to femtomol [3H]FNZ bound/mg tissue using the known specific activity of the labelled ligand j9 (Table I). In all cases, the autoradiograms demonstrated that benzodiazepine receptors were distributed in a heterogeneous fashion throughout all subdivisions of the human striatum which comprised the ventral striatum (nucleus accumbens and olfactory tubercle) and dorsal striatum (caudate nucleus and putamen). The heterogeneous pattern was present in the form of irregularly shaped high density patches of benzodiazepine receptors dispersed against a background of lower receptor densities (Fig. 1A, Table 1). As shown
in Fig. I A, the benzodiazepine patches were especially prominent in the ventral striatum, where they varied from large irregularly shaped patches (large arrows, Fig. IA) to small, discrete round and ova! patches (small arrows, Fig. IAI. Fhe density oi receptors in these patches was more than 5()(?~ greater than the receptor densities m t.he dorsal striatal patches (Table l). In the dorsal striatum the patches were best seen in the caudate nucleus where they ',tppeared as small circular (0.5 mm diameter) or elongated (1.6-3.0 mm long) patches, in the putamen the patches were not so easily distinguished: here, the patches appeared as variably shaped dense regions of receptors which merged imperceptively with the surrounding background region of lmver receptor densities. Quantitative analysis of the autoradiograms (Table 1) revealed that the caudate and putamen patches contained similar receptor densities, but the concentration of receptors in the non-patch regions was lower in the caudate nucleus: these findings explain why the caudate patches are more easily distinguished than the putamen patches in the autoradiograms. Comparison of the heterogeneous distribution of benzodiazepine receptors m the striatum (Fig. 1A) with the pattern of AChE staining (Fig. IB) shows that the patches in the dorsal striatum (caudate nucleus and putamen) correspond with the AChE-poor striosomes (large arrows, Fig. 1). The correspondence is best seen in the caudate nucleus where the benzodiazepine patches and striosomes are more clearly delineated. A careful comparison of the sizes of the patches and striosomes in the dorsal striatum
TABLE I The density of /~H]flunitrazeparn binding m the patch and nonpatch regions of the human striatum
The densities are expressed as means _+ standard deviations of femtomol of [-~H]FNZ bound per milligram Of tissue. The values given were determined from optical densitometric readings obtained from 15 sections sampled from two cases and convetted into fmol/mg tissue using tritium standards (see text for details).
Caudate nucleus Putamen Ventral striatum
Patch r e g i o n
Non-patch region
34.77 _+ 1.35 35.55 _+2.35 54.95 _+5.11
24.33 _+2.22 27.84 _+2.5t 25.46 _+5.99
157 shows that the b e n z o d i a z e p i n e patches are slightly smaller than their corresponding A C h E - p o o r striosome. In contrast, the patches in the ventral striatum overlap with both A C h E - p o o r and A C h E - r i c h regions. For example, the large irregularly shaped benzodiazepine patches in the medial (nucleus accumbens) and lateral (olfactory tubercle) regions of the ventral striatum (large arrows, Fig. 1A) align with A C h E - p o o r regions (large arrows, Fig. 1B), although there is considerable overlap into adjacent A C h E - r i c h zones. On the other hand the smaller benzodiazepine patches in the central region of the ventral striatum (small arrows, Fig. 1A) align with A C h E - r i c h zones (small arrows, Fig. 1B). These results provide further evidence for a compartmental organization of the m a m m a l i a n striatum. In particular, they d e m o n s t r a t e for the first time that benzodiazepine receptors in the human striatum are distributed in a heterogeneous fashion. Furthermore, since recent studies have shown that the benzodiazepine receptor is a subunit of the G A B A receptor complex 13"Is, then it follows that G A B A receptors may also be distributed in a similar heterogeneous fashion within the m a m m a l i a n striatum. Indeed, immunohistochemical studies in the caudate nucleus of the cat on the distribution of the G A B A synthetic enzyme glutamic acid decarboxylase ( G A D ) ~', have shown that G A D - l i k e immunoreactivitv is distributed in a heterogeneous fashion similar to our findings on benzodiazepine receptors in the human caudate nucleus; that is, the striatal neuropil was G A D - p o s i t i v e and there were patches of very intense G A D - l i k e immunoreactivity which aligned with the A C h E - p o o r striosomes.
1 Faull, R.L.M. and Villiger, J.W., Benzodiazepine receptors in the human spinal cord: a detailed anatomical and pharmacological study, Neuroscience, 17 (1986) 791-802. 2 Gcncscr-Jensen, F.A. and Blackstad, T.W., Distribution ot acetyl cholinesterase in the hippocampal region of the guinea pig. 1. Entorhinal area, parasubiculum, and presubiculum. Z. Zellfi)rsch. Mikrosk. Anat., 114 (1971) 460-481. 3 Goedert, M., Mantyh, P.W., Hunt, S.P. and Emson, P.C., Mosaic distribution of neurotensin-like immunoreactivity in the cat striatum, Brain Research, 274 (1983) 176-179. 4 Graybiel, A.M., Compartmental organization of the mammalian striatum, Prog. Brain Res., 58 (1983) 247-256. 5 Graybicl, A.M., Neurochemically specified subsystems in the basal ganglia. In Functions of the Basal Ganglia, Ciba Foundation symposium 1(}7, Pitman, London, 1984, pp. 114-149.
Recent
studies
on
benzodiazepine
receptor
changes in H u n t i n g t o n ' s disease 2° suggest the presence of two types of benzodiazepine receptors (Type I and II) in the normal human striatum, and that it is the p r e d o m i n a n t Type II receptor which is reduced in Huntington's disease. In the light of these results it would be interesting to determine whether the patches d e m o n s t r a t e d in the present study are comprised of one or both types of benzodiazepine receptor and whether the depletion of benzodiazepine receptors in Huntington's disease results from a loss of receptors in the patches and/or b a c k g r o u n d regions of the striatum. The finding that the benzodiazepine patches in the dorsal striatum align with A C h E - p o o r striosomes, whereas patches in the ventral striatum are in register with both A C h E - p o o r and A C h E - r i c h zones, suggest that different principles may apply to the alignment of benzodiazepine receptors and A C h E in the dorsal and ventral divisions of the striatum. Furthermore, our studies have also shown that the highest densities of benzodiazepine receptors were found in the ventral striatum, suggesting a m a j o r role for these receptors in ventral striatal ftmetions. These considerations are especially interesting since it is well established that the ventral striatum has particularly extensive connectional affiliations with the limbic system ~'~5"1~, and it is thought that anti-anxiety drugs such as the benzodiazepines r exert their effects, at least in part, via the limbic system. This research was supported by the New Z e a l a n d Medical Research Council and the New Z e a l a n d Neurological Foundation.
6 Graybiel, A.M., Chessetet, M.-F., Wu, J.-Y., Eckenstein, F. and Joh, T.E., The relation of striosomes in the caudate nucleus of the cat to the organization of early-developing dopaminergic fibers, GAD-positive ncuropil, and CATpositive neurons, Neurosci. Abstr., 9 (1983) 14. 7 Graybiel, A.M. and Ragsdale, C.W., Striosomal organization of the caudate nucleus. 1. Acetylcholinesterase histochemistry of the striatum in the cat, rhesus monkey and human being, Neurosci. Abstr., 4 (1978) 44. 8 Graybiel, A.M. and Ragsdale. C.W., Histochemically distinct compartments in the striatum of human, monkey and cat demonstrated by acetylthiocholinestcrase staining, Proc. Natl. Acad. Sci. U.S.A., 75 (1978) 5723-5726. 9 Graybiel, A.M. and Ragsdale, C.W., Fiber connections of the basal ganglia. In M. Cuenod, G.W. Kreutzberg and F.E. Bloom (Eds.), Development and Chemical Specificity
158 of neurons, Progress in Brain Research, Vol. 51, Elsevier.
10
11
12
13
14
15
Amsterdam, 1979, pp. 239-283. Graybiel, A.M. and Ragsdale, C.W., Biochemical anatomy of the striatum. In Emson P.C. (Ed.), Chemical Neuroanatomy, Raven Press, New York, 1983, pp. 427-504. Graybiel, A.M., Ragsdale, C.W., Yoneoka, E.S. and Elde, R.P., An immunohistochemical study of enkephalins and other neuropeptides in the striatum of the cat with evidence that the opiate peptides are arranged to form mosaic patterns in register with the striosomal compartments visible by acetylcholinesterase staining, Neuroscience, 6 (1981) 377-397. Hardy, H., Heimer, L., Switzer, R. and Watkins, D2, Simultaneous demonstration of horseradish peroxidase and acetylcholinesterase, Neurosci. Lett., 3 (1976) 1-5. Haring, P., Stahli, C., Schoch, P., Takacs, B., Staehelin, T. and Mohler, H., Monoclonal antibodies reveal structural homogeneity of ~,-aminobutyric acid/benzodiazepine receptors in different brain areas, Proc. Natl. Acad. Sci. U.S.A., 82 (1985) 4837-4841. Herkenham, M. and Pert, C.B., Mosaic distribution of opiate receptors, parafascicular projections and acetylcholinesterase in rat striatum, Nature (London), 291 (1981) 415-418. Kelley, A.E. and Domesick, V.B., The distribution of the projection from the hippocampal formation to the nucleus
accumbens in the rat: an anterograde- and retrogradehorseradish peroxidase study, Neuroscience. 7 [1982) 2321-2335. 16 Kelley, A.E.. Domesick. V.B. and Nauta, W.J.H.. The amygdalostriatal projection in the rat --- an anatomical study by anterograde and retrograde tracing methods. Neuroscience. 7 (1982) 615-630. 17 Niehoff. D.L. and Whitehouse. P.J.. Multiple benzodiazepme receptors: autoradiographic localization in normal human amygdala. Brain Research. 276t t983) 237-245 18 Schoch. P.. Richards. J.G.. Haring, P.. Takacs. B.. Stahli. C.. Staehelin. T,. Haefety, W. and Mohler. H. Co-localization of GABA A receptors and benzodiazepine receptors in the brain shown by monoclonal antibodies. Nature (Londonj 314 (19851 168-171. 19 Unnerstall, J.R., Niehoff. D.L.. Kuhar, M.J and Palacios. J.M., Quantitative receptor autoradiography using [3H]UItrofilm: application to multiple benzodiazepine receptors. J. Neurosci. Meth . 6 ( 1982159-73. 20 Whitehouse. P.J.. Trifiletti. R.R.. Jones. B.E.. Folstcin, S.. Price. D,L.. Snyder. S.H. and Kuhar. M.J.. Neurotransmitter receptor alterations m fluntington's disease: autoradiographic and homogenate studies with special reference to benzodiazepine receptor complexes. Ann. Neurol. 18[19851202-210.
153
BRE 21722
Heterogeneous distribution of benzodiazepine receptors in the human striatum: a quantitative autoradiographic study comparing the pattern of receptor labelling with the distribution of acetylcholinesterase staining R.L.M. FAULL and J.W. VILLIGER Departmentof Anatomy, School of Medicine, Universityof Auckland, Auckland (New Zealand) (Accepted May 6th, 1986) Key words: [3H]flunitrazepam - - benzodiazepine receptor - - acetylcholinesterase - - striosome - - striatum - - human
The distribution of benzodiazepine receptors in the human striatum was studied by quantitative autoradiography following in vitro labelling of cryostat sections with [3H]flunitrazepam, and the pattern of receptor-labelling was compared to the distribution of acetylcholinesterase (ACHE) staining in adjacent sections. A heterogeneous pattern of benzodiazepine receptors was found in all regions of the striatum. The highest densities of receptors were seen in the ventral striatum (nucleus accumbens and olfactory tubercle), where very dense receptor patches aligned with both AChE-poor and AChE-rich regions. The dorsal striatum (caudate nucleus and putamen) contained lower concentrations of benzodiazepine receptors, but dense receptor patches were still evident (especially in the caudate nucleus) and these aligned with AChE-poor striosomes.
Recent studies have demonstrated that the seemingly homogeneous mammalian striatum is, in fact, organized in a heterogeneous compartmental fashion with respect to cytoarchitecture, i n p u t - o u t p u t relations and chemoarchitecture (see reviews by GraybieP '5 and Graybiel and Ragsdale9,1°). In particular, in the dorsal striatum major units of this compartmental organization are the so-called 'striosomes' or striatal bodies which were first identified by Graybiel and Ragsdale 7-9 in the cat, monkey and human with acetylcholinesterase (ACHE) histochemistry as A C h E - p o o r regions in an otherwise darkly staining striatal neuropil. It has now been shown that the striosomes are also characterised by high or low densities of neurochemical markers for several putative neurotransmitters. For example, the striosomes are characterized by: high concentrations of opiate peptides H and receptors 14, neurotensin-like immunoreactivity 3 and glutamic acid decarboxylase-like immunoreactivity 6, low somatostatin-like immunoreactivity 5, and high or low substance P-like immunoreactivity 11. In the present study we have used quantitative
autoradiographic methods in the human striatum to analyse the distribution of benzodiazepine receptors, a neurochemical marker for ),-aminobutyric acid ( G A B A ) receptorsl3,18, and compared the pattern of receptor labelling to the distribution of A C h E staining in adjacent sections. Postmortem human brains were obtained from 4 subjects (two females and two males) aged 4, 33, 43 and 53 years (average age 33 years) who died immediately following myocardial infarction or asphyxiation. All subjects had previously been in good health with no known history of neurological disease or drug treatment and all had died suddenly without the opportunity of receiving any form of medical treatment. Immediately following death, the bodies were removed to the University of Auckland Medical School mortuary and stored at 4 °C until autopsy. The interval between death and autopsy (i.e. the postmortem delay) ranged from 5 to 18 h (average delay of 13.5 h). At autopsy the brain was carefully removed and blocks were immediately selected from various regions of the striatum and frozen onto cryostat chucks
Correspondence: R.L.M. Faull, Department of Anatomy, School of Medicine, University of Auckland, Private Bag, Auckland, Ncw Zealand. 0006-8993/86/$03.50© 1986Elsevier Science PublishersB.V (Biomedical Division)
155 using dry ice. They were then sectioned transversely
for acetylcholinesterase (ACHE) histochemistry 2 in
at 16 ~tm using a cryostat and thaw-mounted onto ge-
the presence of the pseudocholinesterase inhibitor,
latine/chrome alum-coated slides. One series of slide-mounted sections was immediately processed
ethopropazine, and this staining was enhanced by silver intensification12 (see Fig. 1B). As detailed below,
B striatum) indicate benzodiazepine patches in A which align with AChE-poor striosomes in B. In the ventral striatum, the large arrows indicate benzodiazepinc patches which align mainly with AChE-poor zones (with some overlap into adjacent AChE-rich regions) in B, and the small arrows indicate receptor patches in A, which align with AChE-rich regions in B. The distance between sections A and B is 16urn. A and B have the same magnification; bar, 5 mm.
156 an adjacent series of sections was processed for the autoradiographic localization of benzodiazepine receptors using [3H]flunitrazepam ([3H]FNZ) I. Following storage at 4 °C for 1-7 days, slidemounted sections were incubated in 250 ml 50 mM Tris-HCl (pH 7.4) containing 1 nM [3H]FNZ (84 Ci/mmol, Amersham Radiochemical Centre) for l h. They were then washed (2 x 1 min in Tris-HC1 buffer, dipped in distilled water) and dried under a stream of cold air. All the above steps were performed at 4 °C. Non-specific control [3HJFNZ binding was determined by incubation of slides in the presence of 1 ,um cionazepam. Once dry, slides were brought to room-temperature and together with slide-mounted tritium micro-scale standards (RPA.501 and RPA.505, Amersham) they were taped into X-ray cassettes, apposed with [3H]sensitive Ultrofilm (LKB, Bromma, Sweden) and exposed in the dark at 4 °C for 6-10 weeks. The exposed films were developed in Kodak D19 for 4 min at 15 °C, washed and fixed. The Ultrofilm autoradiograms were subsequently printed using standard photographic procedures to yield 'darkfield' type autoradiograms where the autoradiographic labelled receptors appear as white dots on a black background (see Fig. 1A). The optical densities of the autoradiographic labelling in the various regions of the striatum were determined directly from the Ultrofilm autoradiograms using a spot densitometer designed to sample 75 1~m spots on the autoradiogram ~. These optical density values were then converted to nCi tritium bound/mg tissue using a standard curve derived from the optical density readings of the autoradiographic standards in which log nCi/mg was plotted against log optical density. These values were then converted to femtomol [3H]FNZ bound/mg tissue using the known specific activity of the labelled ligand j9 (Table I). In all cases, the autoradiograms demonstrated that benzodiazepine receptors were distributed in a heterogeneous fashion throughout all subdivisions of the human striatum which comprised the ventral striatum (nucleus accumbens and olfactory tubercle) and dorsal striatum (caudate nucleus and putamen). The heterogeneous pattern was present in the form of irregularly shaped high density patches of benzodiazepine receptors dispersed against a background of lower receptor densities (Fig. 1A, Table 1). As shown
in Fig. I A, the benzodiazepine patches were especially prominent in the ventral striatum, where they varied from large irregularly shaped patches (large arrows, Fig. IA) to small, discrete round and ova! patches (small arrows, Fig. IAI. Fhe density oi receptors in these patches was more than 5()(?~ greater than the receptor densities m t.he dorsal striatal patches (Table l). In the dorsal striatum the patches were best seen in the caudate nucleus where they ',tppeared as small circular (0.5 mm diameter) or elongated (1.6-3.0 mm long) patches, in the putamen the patches were not so easily distinguished: here, the patches appeared as variably shaped dense regions of receptors which merged imperceptively with the surrounding background region of lmver receptor densities. Quantitative analysis of the autoradiograms (Table 1) revealed that the caudate and putamen patches contained similar receptor densities, but the concentration of receptors in the non-patch regions was lower in the caudate nucleus: these findings explain why the caudate patches are more easily distinguished than the putamen patches in the autoradiograms. Comparison of the heterogeneous distribution of benzodiazepine receptors m the striatum (Fig. 1A) with the pattern of AChE staining (Fig. IB) shows that the patches in the dorsal striatum (caudate nucleus and putamen) correspond with the AChE-poor striosomes (large arrows, Fig. 1). The correspondence is best seen in the caudate nucleus where the benzodiazepine patches and striosomes are more clearly delineated. A careful comparison of the sizes of the patches and striosomes in the dorsal striatum
TABLE I The density of /~H]flunitrazeparn binding m the patch and nonpatch regions of the human striatum
The densities are expressed as means _+ standard deviations of femtomol of [-~H]FNZ bound per milligram Of tissue. The values given were determined from optical densitometric readings obtained from 15 sections sampled from two cases and convetted into fmol/mg tissue using tritium standards (see text for details).
Caudate nucleus Putamen Ventral striatum
Patch r e g i o n
Non-patch region
34.77 _+ 1.35 35.55 _+2.35 54.95 _+5.11
24.33 _+2.22 27.84 _+2.5t 25.46 _+5.99
157 shows that the b e n z o d i a z e p i n e patches are slightly smaller than their corresponding A C h E - p o o r striosome. In contrast, the patches in the ventral striatum overlap with both A C h E - p o o r and A C h E - r i c h regions. For example, the large irregularly shaped benzodiazepine patches in the medial (nucleus accumbens) and lateral (olfactory tubercle) regions of the ventral striatum (large arrows, Fig. 1A) align with A C h E - p o o r regions (large arrows, Fig. 1B), although there is considerable overlap into adjacent A C h E - r i c h zones. On the other hand the smaller benzodiazepine patches in the central region of the ventral striatum (small arrows, Fig. 1A) align with A C h E - r i c h zones (small arrows, Fig. 1B). These results provide further evidence for a compartmental organization of the m a m m a l i a n striatum. In particular, they d e m o n s t r a t e for the first time that benzodiazepine receptors in the human striatum are distributed in a heterogeneous fashion. Furthermore, since recent studies have shown that the benzodiazepine receptor is a subunit of the G A B A receptor complex 13"Is, then it follows that G A B A receptors may also be distributed in a similar heterogeneous fashion within the m a m m a l i a n striatum. Indeed, immunohistochemical studies in the caudate nucleus of the cat on the distribution of the G A B A synthetic enzyme glutamic acid decarboxylase ( G A D ) ~', have shown that G A D - l i k e immunoreactivitv is distributed in a heterogeneous fashion similar to our findings on benzodiazepine receptors in the human caudate nucleus; that is, the striatal neuropil was G A D - p o s i t i v e and there were patches of very intense G A D - l i k e immunoreactivity which aligned with the A C h E - p o o r striosomes.
1 Faull, R.L.M. and Villiger, J.W., Benzodiazepine receptors in the human spinal cord: a detailed anatomical and pharmacological study, Neuroscience, 17 (1986) 791-802. 2 Gcncscr-Jensen, F.A. and Blackstad, T.W., Distribution ot acetyl cholinesterase in the hippocampal region of the guinea pig. 1. Entorhinal area, parasubiculum, and presubiculum. Z. Zellfi)rsch. Mikrosk. Anat., 114 (1971) 460-481. 3 Goedert, M., Mantyh, P.W., Hunt, S.P. and Emson, P.C., Mosaic distribution of neurotensin-like immunoreactivity in the cat striatum, Brain Research, 274 (1983) 176-179. 4 Graybiel, A.M., Compartmental organization of the mammalian striatum, Prog. Brain Res., 58 (1983) 247-256. 5 Graybicl, A.M., Neurochemically specified subsystems in the basal ganglia. In Functions of the Basal Ganglia, Ciba Foundation symposium 1(}7, Pitman, London, 1984, pp. 114-149.
Recent
studies
on
benzodiazepine
receptor
changes in H u n t i n g t o n ' s disease 2° suggest the presence of two types of benzodiazepine receptors (Type I and II) in the normal human striatum, and that it is the p r e d o m i n a n t Type II receptor which is reduced in Huntington's disease. In the light of these results it would be interesting to determine whether the patches d e m o n s t r a t e d in the present study are comprised of one or both types of benzodiazepine receptor and whether the depletion of benzodiazepine receptors in Huntington's disease results from a loss of receptors in the patches and/or b a c k g r o u n d regions of the striatum. The finding that the benzodiazepine patches in the dorsal striatum align with A C h E - p o o r striosomes, whereas patches in the ventral striatum are in register with both A C h E - p o o r and A C h E - r i c h zones, suggest that different principles may apply to the alignment of benzodiazepine receptors and A C h E in the dorsal and ventral divisions of the striatum. Furthermore, our studies have also shown that the highest densities of benzodiazepine receptors were found in the ventral striatum, suggesting a m a j o r role for these receptors in ventral striatal ftmetions. These considerations are especially interesting since it is well established that the ventral striatum has particularly extensive connectional affiliations with the limbic system ~'~5"1~, and it is thought that anti-anxiety drugs such as the benzodiazepines r exert their effects, at least in part, via the limbic system. This research was supported by the New Z e a l a n d Medical Research Council and the New Z e a l a n d Neurological Foundation.
6 Graybiel, A.M., Chessetet, M.-F., Wu, J.-Y., Eckenstein, F. and Joh, T.E., The relation of striosomes in the caudate nucleus of the cat to the organization of early-developing dopaminergic fibers, GAD-positive ncuropil, and CATpositive neurons, Neurosci. Abstr., 9 (1983) 14. 7 Graybiel, A.M. and Ragsdale, C.W., Striosomal organization of the caudate nucleus. 1. Acetylcholinesterase histochemistry of the striatum in the cat, rhesus monkey and human being, Neurosci. Abstr., 4 (1978) 44. 8 Graybiel, A.M. and Ragsdale. C.W., Histochemically distinct compartments in the striatum of human, monkey and cat demonstrated by acetylthiocholinestcrase staining, Proc. Natl. Acad. Sci. U.S.A., 75 (1978) 5723-5726. 9 Graybiel, A.M. and Ragsdale, C.W., Fiber connections of the basal ganglia. In M. Cuenod, G.W. Kreutzberg and F.E. Bloom (Eds.), Development and Chemical Specificity
158 of neurons, Progress in Brain Research, Vol. 51, Elsevier.
10
11
12
13
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