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NADPH-d (dihydronicotinamide adenine dinucleotide phosphate diaphorase) activity in geniculo-tectal neurons of the rat
Neurosciem'e Letters, 167 (1994) 77-80 © 1994 Elsevier Science Ireland Ltd, All rights reserved 0304,3940/94/$ 07.00
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NSL 10207
NADPH-d (dihydronicotinamide adenine dinucleotide phosphate diaphorase) activity in geniculo-tectal neurons of the rat Tom~s Gonz/flez-Hern/mdez*, Beatriz Mantol/m-Sarmiento, Bei6n Gonz/llez-Gonz/flez, R o m u a l d o Ferres-Torres, G u n d e l a Meyer Department of Anatomy. Facuhy of Medicine, University of La Laguna. La I_,aguna. Tener(fe. Spain (Received 5 April 1993: Revised version received 29 November 1993: Accepted I December 1993)
Key words: NADPH-d: Horseradish peroxidase; Lateral geniculate complex: Superior colliculus Retrograde transport of horseradish peroxidase (HRP) and dihydronicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry were used in order to determine whether NADPH.,d-positive neurons of the ventral lateral geniculate nucleus (LGv) project to the superior colliculus (SC). Our results show that intensely stained NADPH-d neurons are restricted to the lateral half of the magnocellular division of LGv (LGv-MC), where they represent 50% of the total number of retrogradely labeled neurons. These findings indicate: (I) that LGv provides an important NADPH-d input to SC, and (2) that within the population of geniculo-tectal neurons, which constitute a morphologically well defined neuronal type, there are two different subclasses, one being NADPH-d positive and the other NADPH-d negative.
The lateral geniculate complex is the main target of retinal fibers in the thalamus [10]. In rodents it is divided into three different nuclei, the dorsal lateral geniculate nucleus (LGd), the ventral lateral geniculate nucleus (LGv), and the intergeniculate leaflet (IGL). LGd projects to the visual cortex and is involved in visual perception. LGv consists of a lateral magnocellular (LGvMC) and a medial parvocellular (LGv-PC) division [I] and is interconnected with several subcortical visual centers, but does not project to the visual cortex [16]. It is involved in visual reflexes and visuomotor integration. IGL is a narrow cellular lamina located between LGd and LGv, which on the basis of its projections to the suprachiasmatic nucleus of the hypothalamus has been related to the circadian rhythms [3]. Recent studies have shown that dihydronicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) histochemistry is a marker for nitric oxide synthase (NOS) [8], the enzyme that catalyses the synthesis of nitric oxide (NO), which is considered as an atypical messenger [2]. NADPH-d containing neurons have been described in different brain regions, e.g. in the LGv and the SC [7,13]. Recent studies suggest that the NADPH-d activity of the intermediate layers of the SC is largely dependent on afferent projections from NADPH-d containing neurons *Corresponding author. Fax: (34) (22) 655995.
S S D I 0304-3940(93)EO831.F
of mesencephalic and pontine nuclei [20,21]. in this report we present evidence that the LGv is also an important source of NADPH-d positive input to the SC. Six adult rats (Sprague-Dawley, 250-350 g) were injected in the superior colliculus with 0.1 gl 40% HRP (horseradish peroxidase, Boehringer-Mannheim, grade I). The injections were restricted to the superficial and intermediate layers. After a survival time of 48 h, the animals were deeply anesthetized with chloral hydrate and perfused transcardially with 250-300 mi of a mixture of 3% paraformaldehyde-0.5% glutaraldehyde in 0. I M phosphate buffer, pH 7.4. Following overnight immersion in 20% sucrose, brains were coronally sectioned on a freezing microtome at 60gin. For the demonstration of retrogradely labeled neurons, HRP reaction was performed using diaminobenzidine (DAB) as the chromogen. NADPH-d histochemistry was carried out according to the direct method of Sandeil [14]. Since the high concentration of paraformaldehyde in the fixative used for the NADPH-d reaction reduces the sensitivity of HRP histochemistry, three rats were injected with a retrograde fluorescent tracer, 0.1/zl of 3% Fast blue (FB) in order to establish the distribution of neurons in LGv projecting to SC. Another three rat brains were processed for NADPH-d histochemistry and counterstained with Cresyl violet. After FB injection into SC, numerous labeled neurons lie in LGv and IGL, but not in LGd (Fig. IA,C). In LGv,
78
Fig. 2. Combination of dihydronicotinamide adenine dinucleotide phosphate diaphoras¢ (NADPH-d) and horseradish peroxidasc (H R P) histea:hcmistry in the magnocellular division of the ventral lateral geniculate nucleus after HRP injection into the superior colliculus. C,D.E: double labeled neurons. F: retrogradely labeled NADPH-diaphorase negative neuron• Arrows in A and B indicate neurons of micrographs (" and E, respectively: arrowhead in B indicates neuron of micrograph F. Bar = 60 pm (A,B); bar = 20/lm (C F).
projecting neurons lie in the entire LGv-MC, forming a continuum with those in the IGL, whereas in LGv-PC only a few, smaller neurons are retrogradely labeled. The distribution of NADPH-d containing neurons is not completely coextensive with that of neurons projecting to SC (Fig. I B,C). NADPH-d-positive cells are mainly confined to the lateral half of LGv-MC. Cresyl violet counterstained material shows that they belong to a population with relatively large (18-22 pm) somata, comprising 50-60% of the total number of neurons in this region. In the medial half of LGv-MC, there are only sparse, weakly stained small (1 0-15 pm) neurons; similar positive small somata lie scattered in LGd, LGv- PC, and in IGL. Brains processed for the colocalization of NADPH-d and HRP reveal fewer retrogradely labeled neurons than after FB injections. In the lateral half of LGv-MC. aproximately 50% of neurons retrogradely labeled with HRP are also NADPH-d positive (Fig. 2). In sum, our results indicate that intensely stained NADPH-d neurons lie in a restricted region of LGv, and that there are two different populations of geniculo-tectal neurons, one being NADPH-d positive and the other NADPH-d negative.
Geniculo-tectal neurons are a well defined cell type [I] that correspond morphologically to the intensely stained NADPH-d neurons. However, they may be NADPH-d positive or negative, which shows that they constitute a neurochemically heterogeneous population, in shortaxon neurons, NO has been considered as a retrograde messenger produced in response to activation of excitatory amino acid receptors [2,15]. NADPH-d-positive neurons may also be long projecting cells: they occur at different levels of the central nervous system, e.g. in the brainstem [21] and the subcortical white matter [12]. Since the lateral geniculate complex receives retinal [6] and cortical [4] excitatory inputs, it is possible that in LGv, which projects to several subcortical centers [! 6], diaphorase activity could be related to a neuronal subpopulation with a specific set of connections. Another interesting aspect of intensely stained NADPH-d neurons is their location in a concrete region of LGv. the lateral half of LGv-MC. Previous studies in rat [11,17] have reported that neurons of this region show no immunoreactivity for neuropeptides: only few neurons are immunoreactive for ?'-aminobutyric acid (GABA), but do not present diaphorase activity [13]. in contrast to other centers, where NADPH-d is colocalized
US~I
i-;r"-
;r!i !i pc =:
Fig. I. The lateral geniculate complex, A: Kl~iver- Barrera staining. B: distribution of dihydronicotinamideadenine dinucleotide phosphate diaphorase (NADPH-d)containing neurons. C: distribution of genicu]o-tectal neurons after Fast blue injection into the superior colliculus. IGL. intergeniculate leaflet; LGd, dorsal lateral geniculate nucleus; MC, magnocellular division of the ventral lateral geniculate nucleus: PC. parvocellular division of the ventral lateral geniculate nucleus: OT, optic tract. Bar = 300pro.
80
with different neuroactive substances [I 9-2 I], in the lateral half of LGv-MC it is the only neurochemical marker. Therefore, we can consider NADPH-d histochemistry as a possible criterion for establishing subdivisions in the lateral geniculate complex. NADPH-d activity in the neuropil of the intermediate layers of SC represents the terminal distribution of afferent fibers from mainly cholinergic mesencephalic and pontine nuclei [20], where cholinergic cells contain NADPH-d [20,21]. The intermediate and superficial layers of SC receive afferents from other centers, including the LGv [5,18] which, as shown here, also contains NADPH-d-positive neurons. In addition, in a previous paper [7], we reported an intense NADPH-d activity in all types of short-axon neurons in the superficial layers of SC. Therefore, NADPH-d activity in SC is the result of the interaction between extrinsic input from different centers, and NADPH-d-positive intrinsic collicular neurons. Geniculo-tectal neurons provide a neurochemically mixed visual input to the SC: some of them contribute to the NADPH-d innervation, while others are NADPH-d negative. This work was supported by a grant from the DGICYT, Ministerio de Educaci6n y Ciencia (PM900081), and a grant from the Consejeria de Educacibn, Gohierno Aut6nomo de Canarias (91/246). I Brauer, K., Schober, W., Leibnitz, L., Werner, L., Lfith, H.-J. and Winkelmann, E., The ventral lateral geniculate nucleus of the albino rat morphological and histochemical observations, J. Hirnforsch., 25 (1984) 205-236. 2 Bredt, D.S., Hwang, P.M. and Snyder, S.H., Localization of nitric oxide synthase indicating a neural role for nitric oxide, Nature, 347 (I 990) 768-770. 3 Card, J.P. and Moore, R.Y., Ventral lateral 8eniculate nucleus efferents to the rat suprachiasmatic nucleus exhibit avian pancreatic polypeptide-like immunoreactivity, J. Comp. Neurol.. 206 (1982) 390-396. 4 Dori, I., Dinopoulos, A., Cavanagh, M.E. and Parnavelas, J.G.. Proportion of glutamate- and aspartate-immunoreactive neurons in the efferent pathways of the rat visual cortex varies according to the target, J. Comp. Neurol., 319 (1992) 191-204. 5 Edwards, S.R, Ginsbusgh, Ch.L., Henkel, C.K. and Stein, B.E., Sources of subcortical projections to the superior collicuhis in the cat, J. Comp. Neurol., 184 (1979) 309-330. 6 Funke, K., Eysel, U.T. and FitzGibbon, T., Retinogeniculate transmission by NMDA and non-NMDA receptors in the cat, Brain Res., 547 (1991) 229-238.
7 Gonz~iez-Herndndez, T., Conde-Sendin, M. and Meyer, G.. Laminar distribution and morphology of NADPH-diaphorase containing neurons in the superior colliculus and underlying periaqucductal gray of the rat, Anat Embryol., 186 (1992) 245-250. 8 Hope, B.T., Michael, G.J., Knigge, K.M. and Vincent, S.R., Neuronal NADPH diaphorase is a nitric oxide synthase, Proc. Natl. Acad. Sci. USA, 88 0991) 2811-2814. 9 Kiedrowski, L,, Costa, E. and Wroblewski, J.T., Glutamate receptor agonists stimulate nitric oxide synthase in primary cultures of cerebellar granule cells,J. Neurochem., 58 (1992) 335. 341. I0 Laties. A.M. and Sprague, J.M., The projection of optic fibers to the visual centers in the cat, J. Comp. Neurof., 127 (1966) 35--70. I I Mantyh, P.W. and Kemp, J.A., The distribution of putative neurotransmitters in the lateral geniculate nucleus of the rat, Brain Res., 288 (1983) 344-348. 12 Meyer, G.. Gonz~lez-Hern:mdez, T., Galindo-Mireles, D., Castafieyra-Perdomo, A. and Ferres-Torres, R., The efferent projections of neurons in the white matter of different cortical areas of the adult rat, Anat. Embryol., 184 (1991) 99-102. 13 Mitrofanis, J., NADPH-diaphorase reactivity in the ventral and dorsal lateral geniculate nuclei of the rat, Vis. Neurosci., 9 0992) 211-216. 14 Sandell, J.H., NADPH diaphorase histochemislry in the macaque striate cortex, J. Comp. Neurol., 251 (1986) 388-397. 15 Schuman, E.M. and Madison, E.V., A requierement for the intercellular messenger nitric oxide in the long-term potentiation, Science, 254 (1991) 1503-1506. 16 Swanson, L.W., Cowan, W.M. and Jones, E.G., An autoradiographic study of the efferent connections of the ventral lateral geniculate nucleus in the albino rat and the cat, J. Comp. Neurol., 156 (1974) 143.164. i 7 Takatsuji, K. and Tohyama, M., The organization of the rat lateral geniculate body by immunohistochemical analysis of neuroactive substances, Brain Res., 480 (1989) 198-209. 18 Taylor, A.M., Jeffery, G. and Lieberman, A.R., Subcortical afferent and efferent connections of the superior colliculus in the rat and comparisons between albino and pigmented strains, Exp. Brain Res., 62 (1986) 131-142. 19 Vincent, S.R., Johansson, O., H6kfelt, T., Skirboll, L., EIde, R.P.. Terenius, L., Kimmel, J. and Goldstein, M., NAPDH-diaphorase: a selective histucbemical marker for striatal neurons containing both somatostatin- and avian pancreatic polypeptid¢ (APP)-Iike immunoreactivities, J. Comp. Neurol., 217 (1983) 252- 263. 20 Vincent, S.R., Satoh, K., Amstrong, D.M. and Fibiger, H.C.. NADPH-diaphorase: a selective histochemical marker for the cholinergic neurons of the pontine reticular formation, Neurosci. Lett., 43 0983) 31-36. 21 Wallace. M.N. and Fredens, K., Relationship of afferent inputs to the lattice of high NADPH-diaphorase activity in the mouse superior colliculus, Exp. Brain Res., 78 0989) 435--445.
77
NSL 10207
NADPH-d (dihydronicotinamide adenine dinucleotide phosphate diaphorase) activity in geniculo-tectal neurons of the rat Tom~s Gonz/flez-Hern/mdez*, Beatriz Mantol/m-Sarmiento, Bei6n Gonz/llez-Gonz/flez, R o m u a l d o Ferres-Torres, G u n d e l a Meyer Department of Anatomy. Facuhy of Medicine, University of La Laguna. La I_,aguna. Tener(fe. Spain (Received 5 April 1993: Revised version received 29 November 1993: Accepted I December 1993)
Key words: NADPH-d: Horseradish peroxidase; Lateral geniculate complex: Superior colliculus Retrograde transport of horseradish peroxidase (HRP) and dihydronicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry were used in order to determine whether NADPH.,d-positive neurons of the ventral lateral geniculate nucleus (LGv) project to the superior colliculus (SC). Our results show that intensely stained NADPH-d neurons are restricted to the lateral half of the magnocellular division of LGv (LGv-MC), where they represent 50% of the total number of retrogradely labeled neurons. These findings indicate: (I) that LGv provides an important NADPH-d input to SC, and (2) that within the population of geniculo-tectal neurons, which constitute a morphologically well defined neuronal type, there are two different subclasses, one being NADPH-d positive and the other NADPH-d negative.
The lateral geniculate complex is the main target of retinal fibers in the thalamus [10]. In rodents it is divided into three different nuclei, the dorsal lateral geniculate nucleus (LGd), the ventral lateral geniculate nucleus (LGv), and the intergeniculate leaflet (IGL). LGd projects to the visual cortex and is involved in visual perception. LGv consists of a lateral magnocellular (LGvMC) and a medial parvocellular (LGv-PC) division [I] and is interconnected with several subcortical visual centers, but does not project to the visual cortex [16]. It is involved in visual reflexes and visuomotor integration. IGL is a narrow cellular lamina located between LGd and LGv, which on the basis of its projections to the suprachiasmatic nucleus of the hypothalamus has been related to the circadian rhythms [3]. Recent studies have shown that dihydronicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) histochemistry is a marker for nitric oxide synthase (NOS) [8], the enzyme that catalyses the synthesis of nitric oxide (NO), which is considered as an atypical messenger [2]. NADPH-d containing neurons have been described in different brain regions, e.g. in the LGv and the SC [7,13]. Recent studies suggest that the NADPH-d activity of the intermediate layers of the SC is largely dependent on afferent projections from NADPH-d containing neurons *Corresponding author. Fax: (34) (22) 655995.
S S D I 0304-3940(93)EO831.F
of mesencephalic and pontine nuclei [20,21]. in this report we present evidence that the LGv is also an important source of NADPH-d positive input to the SC. Six adult rats (Sprague-Dawley, 250-350 g) were injected in the superior colliculus with 0.1 gl 40% HRP (horseradish peroxidase, Boehringer-Mannheim, grade I). The injections were restricted to the superficial and intermediate layers. After a survival time of 48 h, the animals were deeply anesthetized with chloral hydrate and perfused transcardially with 250-300 mi of a mixture of 3% paraformaldehyde-0.5% glutaraldehyde in 0. I M phosphate buffer, pH 7.4. Following overnight immersion in 20% sucrose, brains were coronally sectioned on a freezing microtome at 60gin. For the demonstration of retrogradely labeled neurons, HRP reaction was performed using diaminobenzidine (DAB) as the chromogen. NADPH-d histochemistry was carried out according to the direct method of Sandeil [14]. Since the high concentration of paraformaldehyde in the fixative used for the NADPH-d reaction reduces the sensitivity of HRP histochemistry, three rats were injected with a retrograde fluorescent tracer, 0.1/zl of 3% Fast blue (FB) in order to establish the distribution of neurons in LGv projecting to SC. Another three rat brains were processed for NADPH-d histochemistry and counterstained with Cresyl violet. After FB injection into SC, numerous labeled neurons lie in LGv and IGL, but not in LGd (Fig. IA,C). In LGv,
78
Fig. 2. Combination of dihydronicotinamide adenine dinucleotide phosphate diaphoras¢ (NADPH-d) and horseradish peroxidasc (H R P) histea:hcmistry in the magnocellular division of the ventral lateral geniculate nucleus after HRP injection into the superior colliculus. C,D.E: double labeled neurons. F: retrogradely labeled NADPH-diaphorase negative neuron• Arrows in A and B indicate neurons of micrographs (" and E, respectively: arrowhead in B indicates neuron of micrograph F. Bar = 60 pm (A,B); bar = 20/lm (C F).
projecting neurons lie in the entire LGv-MC, forming a continuum with those in the IGL, whereas in LGv-PC only a few, smaller neurons are retrogradely labeled. The distribution of NADPH-d containing neurons is not completely coextensive with that of neurons projecting to SC (Fig. I B,C). NADPH-d-positive cells are mainly confined to the lateral half of LGv-MC. Cresyl violet counterstained material shows that they belong to a population with relatively large (18-22 pm) somata, comprising 50-60% of the total number of neurons in this region. In the medial half of LGv-MC, there are only sparse, weakly stained small (1 0-15 pm) neurons; similar positive small somata lie scattered in LGd, LGv- PC, and in IGL. Brains processed for the colocalization of NADPH-d and HRP reveal fewer retrogradely labeled neurons than after FB injections. In the lateral half of LGv-MC. aproximately 50% of neurons retrogradely labeled with HRP are also NADPH-d positive (Fig. 2). In sum, our results indicate that intensely stained NADPH-d neurons lie in a restricted region of LGv, and that there are two different populations of geniculo-tectal neurons, one being NADPH-d positive and the other NADPH-d negative.
Geniculo-tectal neurons are a well defined cell type [I] that correspond morphologically to the intensely stained NADPH-d neurons. However, they may be NADPH-d positive or negative, which shows that they constitute a neurochemically heterogeneous population, in shortaxon neurons, NO has been considered as a retrograde messenger produced in response to activation of excitatory amino acid receptors [2,15]. NADPH-d-positive neurons may also be long projecting cells: they occur at different levels of the central nervous system, e.g. in the brainstem [21] and the subcortical white matter [12]. Since the lateral geniculate complex receives retinal [6] and cortical [4] excitatory inputs, it is possible that in LGv, which projects to several subcortical centers [! 6], diaphorase activity could be related to a neuronal subpopulation with a specific set of connections. Another interesting aspect of intensely stained NADPH-d neurons is their location in a concrete region of LGv. the lateral half of LGv-MC. Previous studies in rat [11,17] have reported that neurons of this region show no immunoreactivity for neuropeptides: only few neurons are immunoreactive for ?'-aminobutyric acid (GABA), but do not present diaphorase activity [13]. in contrast to other centers, where NADPH-d is colocalized
US~I
i-;r"-
;r!i !i pc =:
Fig. I. The lateral geniculate complex, A: Kl~iver- Barrera staining. B: distribution of dihydronicotinamideadenine dinucleotide phosphate diaphorase (NADPH-d)containing neurons. C: distribution of genicu]o-tectal neurons after Fast blue injection into the superior colliculus. IGL. intergeniculate leaflet; LGd, dorsal lateral geniculate nucleus; MC, magnocellular division of the ventral lateral geniculate nucleus: PC. parvocellular division of the ventral lateral geniculate nucleus: OT, optic tract. Bar = 300pro.
80
with different neuroactive substances [I 9-2 I], in the lateral half of LGv-MC it is the only neurochemical marker. Therefore, we can consider NADPH-d histochemistry as a possible criterion for establishing subdivisions in the lateral geniculate complex. NADPH-d activity in the neuropil of the intermediate layers of SC represents the terminal distribution of afferent fibers from mainly cholinergic mesencephalic and pontine nuclei [20], where cholinergic cells contain NADPH-d [20,21]. The intermediate and superficial layers of SC receive afferents from other centers, including the LGv [5,18] which, as shown here, also contains NADPH-d-positive neurons. In addition, in a previous paper [7], we reported an intense NADPH-d activity in all types of short-axon neurons in the superficial layers of SC. Therefore, NADPH-d activity in SC is the result of the interaction between extrinsic input from different centers, and NADPH-d-positive intrinsic collicular neurons. Geniculo-tectal neurons provide a neurochemically mixed visual input to the SC: some of them contribute to the NADPH-d innervation, while others are NADPH-d negative. This work was supported by a grant from the DGICYT, Ministerio de Educaci6n y Ciencia (PM900081), and a grant from the Consejeria de Educacibn, Gohierno Aut6nomo de Canarias (91/246). I Brauer, K., Schober, W., Leibnitz, L., Werner, L., Lfith, H.-J. and Winkelmann, E., The ventral lateral geniculate nucleus of the albino rat morphological and histochemical observations, J. Hirnforsch., 25 (1984) 205-236. 2 Bredt, D.S., Hwang, P.M. and Snyder, S.H., Localization of nitric oxide synthase indicating a neural role for nitric oxide, Nature, 347 (I 990) 768-770. 3 Card, J.P. and Moore, R.Y., Ventral lateral 8eniculate nucleus efferents to the rat suprachiasmatic nucleus exhibit avian pancreatic polypeptide-like immunoreactivity, J. Comp. Neurol.. 206 (1982) 390-396. 4 Dori, I., Dinopoulos, A., Cavanagh, M.E. and Parnavelas, J.G.. Proportion of glutamate- and aspartate-immunoreactive neurons in the efferent pathways of the rat visual cortex varies according to the target, J. Comp. Neurol., 319 (1992) 191-204. 5 Edwards, S.R, Ginsbusgh, Ch.L., Henkel, C.K. and Stein, B.E., Sources of subcortical projections to the superior collicuhis in the cat, J. Comp. Neurol., 184 (1979) 309-330. 6 Funke, K., Eysel, U.T. and FitzGibbon, T., Retinogeniculate transmission by NMDA and non-NMDA receptors in the cat, Brain Res., 547 (1991) 229-238.
7 Gonz~iez-Herndndez, T., Conde-Sendin, M. and Meyer, G.. Laminar distribution and morphology of NADPH-diaphorase containing neurons in the superior colliculus and underlying periaqucductal gray of the rat, Anat Embryol., 186 (1992) 245-250. 8 Hope, B.T., Michael, G.J., Knigge, K.M. and Vincent, S.R., Neuronal NADPH diaphorase is a nitric oxide synthase, Proc. Natl. Acad. Sci. USA, 88 0991) 2811-2814. 9 Kiedrowski, L,, Costa, E. and Wroblewski, J.T., Glutamate receptor agonists stimulate nitric oxide synthase in primary cultures of cerebellar granule cells,J. Neurochem., 58 (1992) 335. 341. I0 Laties. A.M. and Sprague, J.M., The projection of optic fibers to the visual centers in the cat, J. Comp. Neurof., 127 (1966) 35--70. I I Mantyh, P.W. and Kemp, J.A., The distribution of putative neurotransmitters in the lateral geniculate nucleus of the rat, Brain Res., 288 (1983) 344-348. 12 Meyer, G.. Gonz~lez-Hern:mdez, T., Galindo-Mireles, D., Castafieyra-Perdomo, A. and Ferres-Torres, R., The efferent projections of neurons in the white matter of different cortical areas of the adult rat, Anat. Embryol., 184 (1991) 99-102. 13 Mitrofanis, J., NADPH-diaphorase reactivity in the ventral and dorsal lateral geniculate nuclei of the rat, Vis. Neurosci., 9 0992) 211-216. 14 Sandell, J.H., NADPH diaphorase histochemislry in the macaque striate cortex, J. Comp. Neurol., 251 (1986) 388-397. 15 Schuman, E.M. and Madison, E.V., A requierement for the intercellular messenger nitric oxide in the long-term potentiation, Science, 254 (1991) 1503-1506. 16 Swanson, L.W., Cowan, W.M. and Jones, E.G., An autoradiographic study of the efferent connections of the ventral lateral geniculate nucleus in the albino rat and the cat, J. Comp. Neurol., 156 (1974) 143.164. i 7 Takatsuji, K. and Tohyama, M., The organization of the rat lateral geniculate body by immunohistochemical analysis of neuroactive substances, Brain Res., 480 (1989) 198-209. 18 Taylor, A.M., Jeffery, G. and Lieberman, A.R., Subcortical afferent and efferent connections of the superior colliculus in the rat and comparisons between albino and pigmented strains, Exp. Brain Res., 62 (1986) 131-142. 19 Vincent, S.R., Johansson, O., H6kfelt, T., Skirboll, L., EIde, R.P.. Terenius, L., Kimmel, J. and Goldstein, M., NAPDH-diaphorase: a selective histucbemical marker for striatal neurons containing both somatostatin- and avian pancreatic polypeptid¢ (APP)-Iike immunoreactivities, J. Comp. Neurol., 217 (1983) 252- 263. 20 Vincent, S.R., Satoh, K., Amstrong, D.M. and Fibiger, H.C.. NADPH-diaphorase: a selective histochemical marker for the cholinergic neurons of the pontine reticular formation, Neurosci. Lett., 43 0983) 31-36. 21 Wallace. M.N. and Fredens, K., Relationship of afferent inputs to the lattice of high NADPH-diaphorase activity in the mouse superior colliculus, Exp. Brain Res., 78 0989) 435--445.