Distribution and spatial geometry of dopamine interplexiform cells in the rat retina: I. Developing retina

The morphology and distribution of dopaminergic interplexiform cells were analyzed in 9-day-old rat retinas processed as wholemounts for tyrosine hydroxylase immunohistochemistry. The mean number of dopaminergic interplexiform cells was estimated as about half of the total number of dopaminergic neurons in the immature retina, with a higher density in the temporal retina. Four interplexiform cells were individually analyzed and reconstructed with a computer system. Their arborizations could be divided into three different regions based on both their morphological features and their position within the retinal layers: (1) an internal arborization, spreading at the margin between the inner nuclear layer and the inner plexiform layer, composed of long, thick, somatofugal dendrites branching at acute angles, (2) an external arborization in the middle of the inner nuclear layer, formed by short, thin, varicose, recurved, axon-like processes branching at right angles, (3) and one or more scleral process(es), originating either from the cell body or from the internal arborization, running toward the outermost cell row of the INL, some of which reached the outer plexiform layer. Finally, analysis of the arborization network by computer simulations based on the 4 digitalized cells was compared with a nearest-neighbour analysis of cell body distribution. It showed that cell bodies are almost randomly distributed--at least in the inferior retina--but that an adjustment of dendritic growth and orientation probably occurs to ensure a homogeneous coverage of the retina with a constant degree of overlap in the adult. This report represents the first three-dimensional computer reconstruction of chemically identified neurons in the retina.     

So-called interplexiform cells immunoreactive to tyrosine hydroxylase or somatostatin in rat retina

The morphology of so-called interplexiform (IP) cells immunoreactive to tyrosine hydroxylase (TH) or somatostatin (SOM) in the rat retina was described in comparison with those in the carp retina. In frozen cross-sections of the rat retina, many processes of TH-like immunoreactive cells were found to extend toward the outer plexiform layer (OPL), forming a thin layer of network fibers. A few of them further extended into the photoreceptor cell layer; such fibers were never found in the carp retina. Some processes of SOM-like immunoreactive cells in the rat retina were found to travel across the inner nuclear layer and appeared to poorly develop a network at the OPL. In the carp retina, on the other hand, only one exceptional cross-section contained such an ascending process.     

Tyrosine hydroxylase immunohistochemistry fails to demonstrate dopaminergic interplexiform cells in the turtle retina

A number of catecholaminergic, presumably dopaminergic, cells could be observed in the turtle retina, because of their tyrosine hydroxylase immunoreactivity. They were amacrine cells with a pear-shaped soma and dendrites distributed in 3 sublayers within the inner plexiform layer. Neither sclerally directed TH-positive processes nor terminals in the outer plexiform layer were observed, suggesting that dopaminergic interplexiform cells do not exist in the turtle retina.     

Distribution and synaptic connectivity of neuropeptide Y-immunoreactive amacrine cells in the rat retina

Neuropeptide Y (NPY) is a potent bioactive peptide that is widely expressed in the nervous system, including the retina. Here we show that specific NPY immunoreactivity was localized to amacrine and displaced amacrine cells in the rat retina. Immunoreactive cells had a regular distribution across the retina and an overall cell density of 280 cells/mm(2) in the inner nuclear layer (INL) and 90 cells/mm(2) in the ganglion cell layer (GCL). In the INL, most immunoreactive cells were characterized by small cell bodies and fine processes that appeared to ramify primarily in stratum 1 of the inner plexiform layer (IPL). A few cells in the INL also ramified in stratum 3 of the IPL. In the GCL, small to medium immunoreactive cells appeared to ramify primarily in stratum 5 of the IPL. A few immunoreactive processes, originating from somata in the INL and processes in the IPL, ramified in the OPL. NPY-immunoreactive cells contained GABA immunoreactivity, and some amacrine cells also contained tyrosine hydroxylase immunoreactivity. NPY-immunostained processes were most frequently presynaptic to nonimmunostained amacrine and ganglion cell processes and postsynaptic to nonimmunostained amacrine cell processes and cone bipolar cell axonal terminals. These findings indicate that NPY immunoreactivity is present in two populations of amacrine cells, one located in the INL and the other in the GCL, and that these cells mainly form synaptic contacts with other amacrine cells. These observations suggest that NPY-immunoreactive cells participate in multiple circuits mediating visual information processing in the inner retina.     

New aspects of dopaminergic interplexiform cell organization in the goldfish retina

Dopaminergic interplexiform cells (DA-IPCs) in the goldfish retina have been reexamined by light and electron microscopic immunocytochemistry with antisera against dopamine (DA) or tyrosine hydroxylase (TH). Successful immunostaining with a specific anti-DA antiserum offers further direct support for DA-IPCs. Anti-DA immunocytochemistry in combination with [³H]-DA autoradiography shows 92% colocalization of the two markers, indicating that [³H]-DA autoradiography is a reliable technique for identification of DA-IPCs. Incubations with anti-TH antiserum show that immunoreactive DA-IPCs have a homogeneous distribution, with an average frequency of 71 ± 8 cells/mm² in retinas of 14–15 cm long goldfish. Their arrangement is distinctly nonrandom. Electron microscopy of TH-immunoreactive cell processes confirms that horizontal cell axons synapse onto DA-IPCs and adds the following junctional arrangements to the circuit diagram of the DA-IPC: (1) adjacent serial synapses between DA-IPCs, external horizontal cells, and putative glycinergic interplexiform cells, (2) junctional appositions between DA-IPCs and photoreceptor cells, (3) junctional appositions between neighbouring DA-IPCs, and (4) the “gap junctional complex”, typically consisting of a DA-IPC process juxtaposed with a gap junction between horizontal cell axons. The gap junction is flanked by clusters of small, round vesicles and groups of electron-dense structures resembling intermediate filaments. These morphological results support the functional involvement of DA-IPCs in adaptive retinomotor movements and in horizontal cell gap junction modulation and/or dynamics. They also suggest particular interaction between the dopaminergic and the glycinergic IPC system in the outer plexiform layer of goldfish retina. © 1993 Wiley-Liss, Inc.     

Amacrine cells of the rhesus monkey retina

Amacrine cells of the rhesus monkey, Macaca mulatta, were studied in 38 retinas Golgi-impregnated as whole, flat preparations. By using criteria of dendritic morphology, span of arborization, and level of arborization in the inner plexiform layer, 26 types of amacrine cell ranging in size of dendritic span from 30 microns to 2 mm were identified and listed in increasing size of dendritic span. In some instances, different cell types could be grouped together due to similar morphological features. For example, 1 group, "knotty amacrine cells," has small cell bodies and a profusion of small, varicose, intertwined processes that span up to 30 microns and are essentially monostratified, but each of the 3 types ends in different strata. Another group is 2 types with about 20 fine radiating processes spanning 1 mm that possess some prominent varicosities. One of these has all of its processes terminating in the innermost stratum of the inner plexiform layer ("spidery"-type 2 amacrine cells). The other with predominantly similarly ending processes has some that also terminate in the outermost stratum ("spidery"-type 1 amacrines). These 2 cell types likely correspond to the type 1 and type 2 indolamine-accumulating amacrine cells in rabbit retina. Other types are individuals which cannot be grouped together but resemble familiar types in cat retina (AII and A13). Other types can be correlated with their putative neurotransmitter (type 1 CA-dopamine) or transmitter/drug receptor ("spiny"-benzodiazepine receptor) phenotype. Many types as yet have no known correlate from other Golgi studies or clues as to transmitter or receptor phenotype. This study provides evidence for an unprecedented number of amacrine cell types in the primate retina. The similar morphologies of different types of amacrine cell types within a group suggest other common features within these groups such as neurotransmitter phenotype.     

Catecholaminergic and cholinergic neurons in the developing retina of the rat

We have examined the development of catecholaminergic and cholinergic neurons in the retina of the rat by using antibodies against the enzymes tyrosine hydroxylase (TH) and choline acetyl transferase (ChAT), respectively. TH-immunoreactivity was first detected at P (postnatal day) 3 in somata located in the inner part of the cytoblast layer (CBL) and in fine dendrites extending toward the middle of the inner plexiform layer (IPL). These cells were similar in shape and soma size to the class 2 TH-immunoreactive (TH-IR) cells of the adult rat. At P6, TH-immunoreactivity was expressed by a second population of cells. Their somata were in the inner part of the inner nuclear layer (INL), but were distinctly larger, with short thick dendrites extending into the outer and/or middle parts of the IPL. Over subsequent days, the dendrites of these larger cells spread profusely in the outer part of the IPL, making it likely that they are the class 1 TH-IR cells of the adult. ChAT-immunoreactive (ChAT-IR) cells were not detected until P15, when ChAT-IR somata were observed in the ganglion cell layer (GCL) and INL, and their dendrites were observed already segregated into the distinct strata of the IPL in which they are found in the adult. The subsequent growth of TH-IR somata of both classes was uneven, persisting longer in temporal than in nasal retina. This extended growth of temporal cells establishes the marked nasotemporal differences in soma diameter apparent among TH-IR cells in the adult (Mitrofanis and Stone, '86; Mitrofanis et al., '88b). The growth and adult size of ChAT-IR somata, on the other hand, did not vary with retinal position; their diameters were similar to those of the adult cells from the time they first appeared. The distribution of ChAT-IR cells at P15 shared several features of the distribution of ganglion cells. The density of ChAT-IR cells was greatest at the area of peak ganglion cell density and declined toward the periphery. In contrast, TH-IR cells concentrated from the time they first appeared at the superior temporal margin, peripheral to the area of peak density of ganglion and ChAT-IR cells.     

Alpha and delta ganglion cells in the rat retina

In the rat retina a distinctive class of large ganglion cell was demonstrated by intracellular staining with Lucifer Yellow and with reduced silver staining. They are referred to as alpha cells because they resemble the alpha cells of other mammalian retinae. A second class, called delta cells, is also described. Both classes belong to the type I group defined by Perry (Proc. R. Soc. Lond. [Biol.] 204:363-375, '79). The dendritic trees of both classes stratify in either an inner or outer lamina of the inner plexiform layer which presumably corresponds to an on/off dichotomy in the response to light. Rat alpha cells constitute 2-4% of all ganglion cells, and their density, size, and detailed morphological appearance change with retinal location. Inner and outer stratifying alpha cells of the rat show significant differences compared to those of other mammals. In central retina (at the large cell density maximum) the densities and dendritic field sizes of inner and outer alpha cells are approximately equal. However, in peripheral retina outer alpha cells are up to three times more numerous and have dendritic field areas only one-third the size of those of the inner alpha cells. The maximal density is about 110 alpha cells/mm2; peripheral densities are about 30/mm2. The smallest central dendritic field diameters are 220 microns. Peripheral dendritic field diameters are 350-550 microns for outer and 570-790 microns for inner alpha cells. Each subpopulation is distributed in a regular mosaic, and the territorial arrangement of the dendritic fields provides a homogeneous coverage of the retina. The dendritic coverage is three- to 3.6-fold for each subpopulation, irrespective of their other quantitative differences. Eccentricity-dependent receptive field sizes of the alpha cells are predicted from the morphological data.     

Antibody to calretinin stains AII amacrine cells in the rabbit retina: Double-label and confocal analyses

The AII or rod amacrine cell is a critical interneuron in the rod pathway of mammalian retinae. In this report, it is shown that commercially available antibodies to the calcium binding protein calretinin may be used to label the population of AII amacrine cells selectively. Calretinin-positive amacrine cells had the morphological attributes of AII amacrine cells. Double-labeling procedures showed that calretinin-positive somata were surrounded by dopaminergic varicosities and that calretinin-positive dendrites enclosed rod bipolar terminals, both as previously described for AII amacrine cells. By analyzing the surrounding kernel for each labeled pixel in the rod bipolar image, it is shown here that AII processes are adjacent to rod bipolar terminals at a level that far exceeds the random overlap present in images in which one label was rotated out of phase. Such a spatial relationship is indicative of synaptic connections, as well described for rod bipolar input to AII amacrine cells. AII amacrine cells also were double-labeled for calretinin and parvalbumin; however, a scattergram analysis of red versus green intensity showed that the parvalbumin antibody stained additional unidentified amacrine cells. In conclusion, at the appropriate dilution, calretinin antibodies are a useful marker for AII amacrine cells in the rabbit retina. J. Comp. Neurol. 411:3–18, 1999. © 1999 Wiley-Liss, Inc.     

The dopamine D2 receptor subfamily in rat retina: ultrastructural immunogold and in situ hybridization studies

Dopamine, a major neurotransmitter in the vertebrate retina, is released from interplexiform cells and a restricted subset of amacrine cells. Dopamine effects vary between different retinal cell types, most likely due to differences in cell-specific receptor subtype expression. Identification of cells expressing receptors of the D2-subfamily (D2R, D3R, D4R) on a light microscopical level has rendered equivocal results, and no information is as yet available concerning the subcellular distribution of receptor protein. In the present study, D2R and D2/3R subtype-specific antisera, and D2R-, D3R- and D4R-specific oligonucleotide probes were used for ultrastructural and in situ hybridization analyses of the receptor subtype distribution in the rat retina. Light and electron microscopy showed that in addition to the known localization of intense D2R-immunoreactivity in all dopaminergic cells immunoreactive for tyrosine hydroxylase (TH), homogeneous, less intense D2R-immunoreactivity was also seen throughout the inner plexiform layer (IPL). Ultrastructurally, many additional amacrine cell processes devoid of TH-immunoreactivity at all levels of the inner plexiform layer were immunoreactive. D2R-immunoreactivity was found mainly on intracellular vesicles, and immunoreactivity associated with the plasma membrane was always extrasynaptic. No D2R-immunoreactivity was found in amacrine cell somata postsynaptic to the so-called dopaminergic 'ring endings'. Many D2R-mRNA reactive cells were observed throughout the inner nuclear layer. Morphologically, labelled cells resemble amacrines and bipolars but not horizontal cells. Reactivity with splice variant-specific oligonucleotide probes suggested that the D2LR variant is the predominant if not the only D2R isoform in the rat retina. D2R-mRNA reactivity was not observed in other retinal layers, in particular not in photoreceptor inner segments, which displayed D4R-mRNA reactivity. D3R-mRNA reactivity was not detected. The results indicate that D2-like responses are mediated through the D2R subtype, by an autoreceptor mechanism in dopaminergic cells, and by volume transmission in non-dopaminergic cells of the inner retina. D2-like responses in photoreceptors probably represent D4R activation.     

Modulation of cone horizontal cell activity in the teleost fish retina. II. Role of interplexiform cells and dopamine in regulating light responsiveness

Following the destruction of the terminals of the dopaminergic interplexiform cells by intraocular injections of 6-hydroxydopamine (6-OHDA), cone horizontal cells exhibited high light responsiveness in prolonged darkness and their responses to moderate and bright full-field flashes were as large as 60 mV. Furthermore, the light responsiveness of these cells in the 6-OHDA-treated retinas was not enhanced by background illumination. The application of dopamine (50 microM) by superfusion to 6-OHDA-treated retinas resulted in a decrease in light responsiveness and changes in response waveform of the cone horizontal cells. Twenty minutes following dopamine application the responses of the cone horizontal cells closely resembled the response of cells recorded in prolonged dark-adapted retinas. Dopamine caused similar changes in cone horizontal cells recorded in light-exposed retinas, but had no obvious effects on rod horizontal cells. The selective dopamine D1 receptor antagonist, Sch 23390, enhanced cone horizontal cell responsiveness when applied to prolonged dark-adapted retinas, mimicking background illumination. The light responsiveness of cone horizontal cells recorded after application of Sch 23390 was less than that for cells in retinas that had been exposed to background lights, but light responsiveness could not be further enhanced by background illumination. Another dopamine antagonist, (+)-butaclamol, was found to have effects similar to Sch 23390 on cone horizontal cells, but (-)-butaclamol, the inactive enantiomer, did not enhance the light responsiveness of these cells. The results suggest that the dopaminergic interplexiform cells play a crucial role in the regulation of cone horizontal cell responsiveness by prolonged darkness and background illumination. These cells may release dopamine tonically in the dark, which suppresses cone horizontal cell responsiveness. Background illumination may decrease dopamine release and liberate cone horizontal cells from the suppression.     

Morphology and distribution of catecholaminergic amacrine cells in the cone-dominated tree shrew retina.

The tree shrew (Tupaia belangeri) has a cone-dominated retina with a rod proportion of only 5%. This is in contrast to the usual mammalian pattern of rod-dominated retinae. Rod bipolar cells are present at relatively low densities in the tree shrew retina, suggesting that a reduced, but normal, rod pathway might be preserved. The present study investigated another common constituent of the rod pathway, the dopaminergic amacrine cells, and analysed their morphology and distribution by light and electron microscopy. Catecholaminergic (presumed dopaminergic) amacrine cells were labelled with an antibody against tyrosine hydroxylase (TH). Intense TH-immunoreactivity was found in perikarya and dendrites of a uniform amacrine cell population. TH-immunoreactive amacrine cell density varies across the retina from 10 cells/mm2 in the periphery to 40 cells/mm2 in more central regions (mean cell density about 25 cells/mm2). The relatively large cell bodies are located exclusively in the innermost part of the inner nuclear layer. The dendrites form a dense plexus at the border between the inner plexiform layer and the inner nuclear layer. The finer dendritic processes contain many varicosities and form characteristic dendritic "rings" like those seen in other mammals. TH-immunoreactive processes also run between cell bodies in the vitread inner nuclear layer; a few extend into the sclerad inner nuclear layer and occasionally reach the outer plexiform layer (possible interplexiform cells). A few TH-immunoreactive processes are seen in the middle of the inner plexiform layer. Electron microscopy of TH-immunoreactive processes revealed conventional synapses onto somata and processes of unlabelled amacrine cells.     

Development of A9/A10 dopamine neurons during the second and third trimesters in the African green monkey

Disruption in the development of dopamine-containing neurons has been postulated to underlie several CNS disorders. However, there have been no quantitative studies on the normal development of primate dopamine neurons. Thus, the fetal maturation of primate midbrain dopamine neurons was examined to establish changes that occur in the A9/A10 groups during the second and third trimesters. Eleven fetal African green monkey midbrains were immunostained for tyrosine hydroxylase (TH-ir) as a marker for dopamine neurons and quantified using stereological techniques (nucleator method). The number and size of defined dopamine neurons and the volume occupied by A9/A10 neurons increased in near linear fashion throughout the term. The estimated number of defined dopamine neurons in each hemisphere rose from approximately 50,000 at embryonic day (E) 70 to 225,000 at birth (E165), similar to the adult population. The size and the area occupied by them at birth were, however, well below the estimated adult levels. Additionally, the younger fetal midbrains had far less diversity in dopamine cell volumes compared with older fetuses and adult brains. Until midway through gestation (E81), clusters of apparently immature midbrain TH-ir cells were observed, but could not be counted. Even though the majority of cells destined to become dopamine neurons are generated in the first trimester, phenotypical maturation of A9 and A10 cell bodies continues steadily throughout gestation and extends well into the postnatal period. These data have relevance to transplantation studies that employ fetal dopaminergic grafts, and to disorders hypothesized to result from damage to developing midbrain dopamine neurons.     

Evidence for coexistence of GABA and dopamine in neurons of the rat olfactory bulb

Immunoreactivities for gamma-aminobutyric acid (GABA) and the dopamine-synthesizing enzyme tyrosine hydroxylase (TH) were localized ultrastructurally and colocalized at the light microscopic level in neurons of the rat main olfactory bulb. By means of a simultaneous indirect immunofluorescence technique, GABA and TH immunoreactivities were found to coexist in a large number of neurons in the glomerular and external plexiform layers. Virtually all the TH-immunoreactive periglomerular neurons also contained GABA immunoreactivity (GABA-I) while there was an additional number of GABA-immunoreactive periglomerular cells (27%) which did not contain TH immunoreactivity (TH-I). In contrast, the numerous tufted-type neurons in the glomerular and superficial external plexiform layers which contained TH-I did not contain GABA-I. In the external plexiform layer (EPL), 41% of the immunoreactive neurons contained GABA-I alone, 24% contained TH-I alone, and 35% contained both. EPL neurons containing GABA-I only or both GABA-I and TH-I never exhibited tufted cell morphological characteristics and were generally of the short-axon type. Electron microscopic examination of GABA-I and TH-I elements in the glomerular layer detected morphologically similar periglomerular perikarya and intraglomerular processes immunoreactive for each substance and other neurons and processes of the same type containing neither GABA-I or TH-I. These data indicate that the classical neurotransmitters GABA and dopamine coexist in large numbers of neurons in the rat main olfactory bulb including characteristic periglomerular cells and certain other local-circuit neuronal types.     

Shapes and distributions of the catecholamine-accumulating neurons in the rabbit retina

Rabbit retinas were fixed with mixed aldehydes and examined for the fluorescence of catecholamines. Labeled cell bodies were present in the layer of the amacrine cells. A band of fluorescent processes was present in layer 1 of the inner plexiform layer. Weaker labeling was present in two deeper strata, one near the middle of the inner plexiform layer (presumably layer 3) and one at the juction of layers 4 and 5. Immunohistochemistry showed tyrosine hydroxylase (TH) to be present in the same cells and the same strata of the inner plexiform layer as the endogenous catecholamines. Exposing the retina to exogenous dopamine or norepinephrine resulted in stronger labeling in the middle and deep levels of the inner plexiform layer. At the same time a second population of amacrine cell bodies became visible. Catecholamine fluorescence contained in the amacrine cell bodies was used as a guide to their injection with Lucifer yellow CH. The filled dendritic arbors revealed two main types of cells. The type 1 cells are monostratified at the most distal level of the inner plexiform layer. They have relatively uncomplicated, radially branching dendritic trees. They are the cells densely stained by immunohistochemistry with antibodies against. TH. The type 2 cells are tristratified, with minor branching in layer 1 of the inner plexiform layer and major branching in the two deeper sublayers. The descending dendrites follow a complicated course, and it is not uncommon for intermediate dendrites to cross between strata more than once. The relationship of the cells to their dendritic plexuses was further studied in retinas in which the aldehyde-induced fluorescence of catecholamines was photoconverted to a diaminobenzidine product. The type 1 cells were found to dominate the plexus of dendrites in layer 1 of the inner plexiform layer. The catecholaminergic plexuses in the middle and deep levels of the inner plexiform layer are formedf by dendrites of the type 2 cells. The position of every type 1 cell was mapped in retinas stained with antibodies directed against TH. In one retina we counted 5,613 type 1 cells, distributed evenly across the retina. In another retina, all of the catecholamine-accumulating cells were counted. There were 9,058 with a distribution that peaks in the visual streak. The type 1 cells appear to be the dopaminergic cells previously studied by others and thought to regulate the flow of information from rod bipolar cells to ganglion cells. The low density and wide spread of type 2 cells suggests that they, too, perform a generalized control function, presumably a novel one that dictates their intricate, tristratified shape.     

Displaced ganglion cells in the retina of the rat

The distribution, laterality of projection, and perikaryal sizes of displaced ganglion cells (DGCs) were examined in whole-mounted retinae after massive unilateral injections of horseradish peroxidase along the optic tract in pigmented rats. The DGCs were found predominantly in the lower temporal periphery of the retina. Nearly all DGCs labeled had contralaterally projecting axons. The sizes of the labeled DGCs spanned the range of ordinary ganglion cells, but few middle-sized DGCs were labeled. The results support the hypothesis that displaced ganglion cells are late-developing neurons that do not complete their migration toward the ganglion cell layer during retinal histogenesis.     

Postnatal development of tyrosine hydroxylase immunoreactive amacrine cells in the rabbit retina: II. Quantitative analysis.

Tyrosine hydroxylase (TH)-immunoreactive (IR) amacrine cells of the rabbit retina mature during the first four postnatal weeks, and their cellular development is described in the preceding paper (Casini, G., and N.C. Brecha, J. Comp. Neurol. 326:283-301, 1992). The present investigation is a quantitative analysis of the postnatal development of the TH-IR amacrine cell population. TH-IR amacrine cells gradually increase in size from birth (soma area of 44.7 +/- 12.4 microns2, mean +/- standard deviation) to adulthood (144.2 +/- 28.0 microns2). Cell density slightly increases from postnatal day (PND) 0 (41.9 +/- 9.5 cells/mm2) to PND 6 (47.2 +/- 7.2 cells/mm2), then markedly decreases from PND 6 to adulthood (17.8 +/- 5.3 cells/mm2) as a consequence of retinal growth. TH-IR cell number almost doubles from PND 0 (about 4,100 cells/retina) to adulthood (about 7,850 cells/retina). The increase in the total number of TH-IR amacrine cells can be explained by the generation of new TH-IR cells in the inner nuclear layer, a delay in the expression of the TH phenotype after neurogenesis by cells committed to be dopaminergic, or the acquisition of this dopaminergic phenotype by uncommitted cells. The development of the TH-IR amacrine cell mosaic was assessed by an evaluation of the distribution of nearest neighbor distances of TH-IR cells. There is a poor correlation between this distribution and a theoretical nonrandom distribution before PND 12. After this age, the nearest neighbor distance distribution shifts towards a nonrandom distribution, and is similar to that of the TH-IR amacrine cell population in the adult retina. The establishment of the TH-IR amacrine cell population mosaic is likely to be achieved through different interacting events, including intrinsic (e.g., genetic) factors, environmental influences, and nonuniform retinal growth. Overall, the population parameters analyzed in the present study approach adult values about the time of eye opening (PND 12) and they reach adult values by PND 26.     

Postnatal development of striatal neurotensin immunoreactivity in relation to clusters of substance P immunoreactive neurons and the "dopamine islands" in the rat.

Conventional immunoperoxidase preparations of the coronally sectioned brains of rats killed at various times during the early postnatal period revealed the distributions of tyrosine hydroxylase, substance P, and neurotensin immunoreactivities. At birth, patches of dense tyrosine hydroxylase immunoreactivity were present across the breadth of the rostral striatum, whereas patches displaying substance P immunoreactivity were present only in its lateral half, appearing in its medial half by about postnatal day 3. Neuronal neurotensin immunoreactivity was absent in the rostral striatum at birth, although some neurotensin immunoreactive cells were present in the tail of the caudate-putamen. Rostrally, neurotensin immunoreactive cells appeared first along the lateral margin of the caudate-putamen on postnatal day 3, became numerous there about day 5, spread medially into the striatum by day 7, and achieved their medialmost distribution by about day 10. Their numbers and those of substance P immunoreactive neurons diminished thereafter. Substance P immunoreactive patches, which contained numerous labeled neurons and "puncta," shared coextensive distributions with patches of dense tyrosine hydroxylase immunoreactivity, but interdigitated with neurotensin immunoreactive cell clusters. The neurotensin immunoreactive cell clusters lacked puncta, the light microscopic representation of axon terminals, or swellings. It is concluded that the patchy infrastructure of the striatum, which is established prior to birth, is substrate for the progression of separate "waves" of elevated neuronal peptide content, one reflecting substance P and a later one reflecting neurotensin. These proceed along rostromedialward trajectories to involve interdigitating neuronal domains.