Substance P-like immunoreactive amacrine cells in the cat retina

Distribution and synaptic organization of substance P-like immunoreactive neurons in the mouse retina

Substance P (SP), a neuroprotective peptidergic neurotransmitter, is known to have immunoreactivity (IR) localized to amacrine and/or ganglion cells in a variety of species' retinas, but it has not yet been studied in the mouse retina. Thus, we investigated the distribution and synaptic organization of SP-IR by confocal and electron microscopy immunocytochemistry in the mouse retina. SP-IR was distributed in the inner nuclear layer (INL), inner plexiform layer (IPL), and ganglion cell layer (GCL). Most of the SP-IR somas belonged to amacrine cells (2.5% of all) in the INL and their processes stratified into the S1, S3, and S5 layers of the IPL, with the most intense band in the S5 layer. Some SP-IR somas can also be observed in the GCL, which were identified as displaced amacrine cells (82%, 1269/1550) and ganglion cells (18%, 281/1550) by antibodies against AP2α and RBPMS, respectively. Such SP-IR ganglion cells (1.2% of all RGCs) can be further divided into 3 subgroups expressing SP/α-Synuclein (α-Syn), SP/GAD67, and/or SP/GAD67/α-Syn. Possible physiological and pathological roles of these ganglion cells are discussed. Further, electron microscopy evidence demonstrates that SP-IR amacrine cells receive major inputs from other SP-IR amacrine cell processes (146/242 inputs) and output mostly to SP-negative amacrine cell processes (291/673 outputs), suggesting series inhibition among amacrine cells. These results reveal for the first time an explicit distribution, novel ganglion cell features, and synaptic organization of SP-IR in the mouse retina, which is important for the future use of mouse models to study the roles of SP in healthy and diseased (including Parkinson's disease) retinal states.

The Development of a Cat Model of Retinal Detachment and Re-attachment

We present an optimized surgical technique for feline retinal detachment which allows for natural re-attachment, reduces retinal scarring and vitreal bands, and allows central placement of the detachment in close proximity to the optic nerve. This enables imaging via Optical Coherence Tomography (OCT) and multifocal electroretinography (mfERG) analysis. Ideal detachment conditions involve a lensectomy followed by a three-port pars plana vitrectomy. A 16-20 % retinal detachment is induced by injecting 8 % C3F8 gas into the subretinal space in the central retina with a 42G cannula. The retinal detachment resolves approximately 6 weeks post-surgery. Imaging is enhanced by using a 7.5 and 20 diopter lens for OCT and mfERG fundus imaging, respectively, to compensate for the removed lens.

Neurokinin A and neurokinin B in the human retina

Very recently, the authors found levels of neurokinin (NK) A-like immunoreactivities in the human retina which were more than five times higher than those of substance P (SP). The present study aimed to find out how many of these immunoreactivities can be attributed to NKA and NKB and then the exact distribution pattern of both NKA and NKB was evaluated in the human retina and compared with that of SP. For this purpose, NKA-like immunoreactivities were characterized in the human retina by reversed phase HPLC followed by radioimmunoassay using the K12 antibody which recognizes both NKA and NKB. Furthermore, the retinae from both a 22- and 70-year-old donor were processed for double-immunofluorescence NKA/SP and NKB/SP. The results showed that NKA contributes to approximately two thirds and NKB to approximately one third of the immunoreactivities measured with the K12 antibody. NKA was found to be localized in sparse amacrine cells in the proximal inner nuclear layer, in displaced amacrine cells in the ganglion cell layer with processes ramifying in stratum 3 of the inner plexiform layer and also in sparse ganglion cells. By contrast, staining for NKB was only observed in ganglion cells and in the nerve fiber layer. Double-immunofluorescence revealed cellular colocalization of NKA with SP and also of NKB with SP. Thus, the levels of NKA and NKB are more than three and two times higher than those of SP, respectively. Whereas the distribution pattern of NKA is typical for neuropeptides, the localization of NKB exclusively in ganglion cells is atypical and unique.

Morphologic maturation of tachykinin peptide-expressing cells in the postnatal rabbit retina

Tachykinin (TK) peptides, which include substance P, neurokinin A, two neurokinin A-related peptides and neurokinin B, are widely present in the nervous system, including the retina, where they act as neurotransmitters/modulators as well as growth factors. In the present study, we investigated the maturation of TK-immunoreactive (IR) cells in the rabbit retina with the aim of further contributing to the knowledge of the development of transmitter-identified retinal cell populations. In the adult retina, the pattern of TK immunostaining is consistent with the presence of TK peptides in amacrine, displaced amacrine, interplexiform and ganglion cells. In the newborn retina, intensely immunostained TK-IR somata are located in the ganglion cell layer (GCL) and in the inner nuclear layer (INL) adjacent to the inner plexiform layer (IPL). They are characterized by an oval-shaped cell body originating a single process without ramifications. TK-IR processes are occasionally observed in the IPL and in the outer plexiform layer (OPL). Long TK-IR fiber bundles are observed in the ganglion cell axon layer. TK-IR profiles resembling small somata are rarely observed in the INL adjacent to the OPL. At postnatal day (PND) 2, some TK-IR cells display more complex morphologic features, including processes with secondary ramifications. Long TK-IR processes in the IPL are often seen to terminate with growth cones. Between PND 6 and PND 11 (eye opening), there is a dramatic increase in the number of immunolabeled processes with growth cones both in the IPL and in the OPL and the mature lamination of TK-IR fibers in laminae 1, 3 and 5 of the IPL is established. TK-IR cells attain mature morphological characteristics and the rare, putative TK-IR somata in the distal INL are no longer observed. After eye opening, growth cones are not present and the pattern typical of the adult is reached. These observations indicate that the development of TK-IR cells can be divided into an early phase (from birth to PND 6) in which these cells establish their morphological characteristics, and a later phase (from PND 6 to eye opening) in which they are involved in active growth of their processes and likely in synapse formation. Since TK peptides are thought to play neurotrophic actions in the developing nervous system and they are consistently present in the retina throughout postnatal development, they may also act as growth factors during retinal maturation.

Light- and electron-microscopic study of substance P-immunoreactive neurons in the guinea pig retina

Substance P (SP) immunoreactivity in the guinea pig retina was studied by light and electron microscopy. The morphology and distribution of SP-immunoreactive neurons was defined by light microscopy. The SP-immunoreactive neurons formed one population of amacrine cells whose cell bodies were located in the proximal row of the inner nuclear layer. A single dendrite emerged from each soma and descended through the inner plexiform layer toward the ganglion cell layer. SP-immunoreactive processes ramified mainly in strata 4 and 5 of the inner plexiform layer. SP-immunoreactive amacrine cells were present at a higher density in the central region around the optic nerve head and at a lower density in the peripheral region of the retina. The synaptic connectivity of SP-immunoreactive amacrine cells was identified by electron microscopy. SP-labeled amacrine cell processes received synaptic inputs from other amacrine cell processes in all strata of the inner plexiform layer and from bipolar cell axon terminals in sublamina b of the same layer. The most frequent postsynaptic targets of SP-immunoreactive amacrine cells were the somata of ganglion cells and their dendrites in sublamina b of the inner plexiform layer. Amacrine cell processes were also postsynaptic to SP-immunoreactive neurons in this sublamina. No synaptic outputs onto the bipolar cells were observed.

Substance P-immunoreactive neurons in the human retina

Substance P (SP) is a neuropeptide that acts as a neurotransmitter or a neuromodulator in the retina. The aim of this study was to identify the type(s) and the distribution of the SP-immunoreactive (SP-IR) cells in the human retina. We have used an antiserum to SP to immunostain neurons in postmortem human retinae. Immunostained retinae were processed with the avidin-biotin complex (ABC) to visualize the cells either whole mounted in glycerol or embedded in plastic. Some retinae were also sectioned at 20 microns in order to obtain radial views of stained cells. SP-IR amacrine cells stain intensely and appear to be of a single type in the human retina. They are large-field cells with large cell bodies (16 microns diameter) lying in normal or displaced positions on either side of the inner plexiform layer (IPL). Their sturdy, spiny, and appendage-bearing dendrites stratify in stratum 3 (S3) of the IPL, where many overlapping, fine dendrites intermingle to form a plexus of stained processes. Either cell bodies or primary dendrites emit an "axon-like" process that, typically, divides into two long, fine processes, which run in opposite directions for hundreds of micrometers in S5 and S3 before disappearing as distinct entities in the stained plexus in S3. Long, fine dendrites also pass from the dendritic plexus to run in S5 and down to the nerve fiber layer to end as large varicosities at blood vessel walls. In addition, fine processes are emitted from the dendritic plexus that runs in S1, and some pass up to the outer plexiform layer (OPL) to run therein for short distances. The SP-IR amacrine cell has many similarities to the thorny, type 2 amacrine cells described from Golgi studies. In addition to the SP-IR amacrine cells, a presumed ganglion cell type is faintly immunoreactive. Its 20-22 microns cell body gives rise to a radiate, sparsely branched, wide-spreading dendritic tree running in S3. Its dendrites and cell body become enveloped by the more intensely SP-IR processes and boutons from the SP-IR amacrine cell type. The SP-IR ganglion cell type most resembles G21 from a Golgi study.

Neuropeptide Y immunoreactivity identifies a regularly arrayed group of amacrine cells within the cat retina

Retinal amacrine cells can be divided into subgroups on the basis of morphological properties and chemical content. It is likely that these subgroups have specific connections and serve unique functional roles within the inner plexiform layer. In the present study we show that immunoreactivity to neuropeptide Y (NPY) identifies a group of amacrine cells (165,000-170,000) within the adult cat retina. This is the largest group of peptide-containing amacrine cells identified to date in the cat retina. These neurons have small cell bodies and are regularly spaced at all retinal eccentricities examined. The density of NPY-immunoreactive cells, as well as their regular spacing, suggests that these neurons form a specific subgroup of the amacrine cell class and are likely to serve a unique role in the transfer of visual information through the inner plexiform layer.

Projections of tachykinin- and glutaminase-containing rat retinal ganglion cells

Glutamate (Glu) and the tachykinin substance P (SP) have been proposed as neurotransmitters or neuromodulators of the retinal projection to the brain. In the present study, we demonstrate that tachykinin-like (TK) immunoreactivity (IR) accumulates in rat retinal axons following electrical lesions to the optic tract, indicating that SP is conveyed in the optic nerve to its central targets. In addition, we show that eye enucleation causes a dramatic decrease in TK-IR fibers in the pretectal olivary nucleus (PON), but not in other retinorecipient nuclei of the thalamus and the midbrain, and that Fluorogold injected into the pretectum is retrogradely transported to the somata of TK-IR retinal ganglion cells (RGCs), indicating an important projection of TK-IR RGCs to the PON. We also show that most rat RGCs are labeled with antibodies against phosphate-activated glutaminase, an enzyme considered to generate the transmitter pool of glutamate. Unlike TK-IR fibers, phosphate-activated glutaminase-IR structures disappear in most retinorecipient nuclei following eye enucleation. The present results give neuroanatomical support to the idea that glutamate is a neurotransmitter in the retinal projection and suggest an important role for TK-IR RGCs in the relay of visual information to the PON.

Acetylcholinesterase and choline acetyltransferase localization patterns do correspond in cat and rat retinas

Is acetylcholinesterase (AChE) a reliable marker for cholinergic activity in the cat and rat retinas? To evaluate this question, radial sections, labeled for AChE, have been compared to sections labeled for choline acetyltransferase (ChAT). Within the inner plexiform layer (IPL) of each species, two lightly-stained AChE bands are revealed which correspond to the depths of ChAT immunoreactivity. Although retinal AChE is not limited exclusively to sites where ChAT is present, AChE and ChAT activity do occur in the same IPL sublaminae. Used with proper caution, AChE is a reliable secondary indicator of cholinergic activity.

Differential staining of neurons in the human retina with antibodies to protein kinase C isozymes

Monoclonal antibodies to the three isozymes of protein kinase C (PKC) (alpha, beta, and gamma) were applied to postmortem human retina. Immunostaining was done on wholemount, or cryostat-sectioned retina, and visualized after ABC/DAB procedures by light (LM) and electron (EM) microscopy. The PCK-alpha antibody stained rod bipolar cells throughout the retina. EM analysis confirmed they were PKC-alpha-immunoreactive (IR) on their characteristic dendritic and axonal synaptology. Putative blue cone bipolar cells with wide-field axon terminals, stratifying in s5 of the inner plexiform layer (IPL), were also PKC-alpha-IR, and EM showed them to engage in narrow-cleft ribbon junctions in blue cone pedicles. The PKC-beta antibody stained cone bipolar cells, many amacrine cells, and most ganglion cells. Cone bipolar cells were stained all the way into the foveal center: both midget and diffuse varieties were included. The IPL was densely PKC-IR and individual neurons could not be identified on stratification patterns. EM of the outer plexiform layer (OPL) revealed that both flat and invaginating cone bipolar types were IR and that IR axon terminals were presynaptic in all strata of the IPL. The occurrence of PKC-beta-IR bipolar axons in stratum 2 of the IPL suggests that OFF-center as well as ON-center types were included. The PKC-gamma antibody gave inferior staining compared with results from the other two antibodies; however, two varieties of wide-field monostratified amacrine cell and a large-bodied ganglion cell type were discernible. PKC in one form or another appears to be a second messenger used in neurotransmission by both rod and cone systems and ON- and OFF-center systems in the human retina.

Substance-P-like immunoreactive amacrine cells in the adult and the developing rat retina

Substance-P-like immunoreactivity (SP-LI) cells in the Long-Evans rat retina were investigated by combining immunohistochemistry with [3H]thymidine autoradiography. Two subpopulations of SP-LI amacrine cells, with cell bodies in either the proximal portion of the inner nuclear layer (INL) or the ganglion cell layer (GCL), were identified based on morphology, pattern of distribution and development. In the INL, SP-LI cells were found scattered throughout the retina. However, in the GCL, they were limited to the superio-temporal region. Such a contrast in distribution specific to nuclear layers was present upon first detection of SP-LI amacrine cells and persisted throughout development. Birthdating revealed a temporal lag in the histogenesis of SP-LI cells situated in the GCL relative to that in the INL, suggesting that the two subpopulations developed separately. Overall, unique anatomical features of the SP-LI amacrine cells in the rat retina were observed which could only have been uncovered through detailed analyses in the adult as well as during postnatal development.

Neurons of the human retina: a Golgi study

Golgi techniques have been applied to post mortem specimens of human retina. Analysis was possible on 150 human retinas processed and viewed by light microscopy as wholemounts. Camera lucida drawings and photography were used to classify the impregnated neurons into 3 types of horizontal cell, 9 types of bipolar cell, 24 basic types of amacrine cell, a single type of interplexiform cell, and 18 types of ganglion cell. We have distinguished two types of midget bipolar cell: fmB (flat) and imB (invaginating). In central retina, both types are typically single-headed, each clearly contacting a single cone. Peripherally, they may be two- or even three-headed, obviously contacting more than one cone. Two types of small-field diffuse cone bipolars occurring as flat and invaginating varieties are found across the entire retina from fovea to far periphery. The single rod bipolar type appears about 1 mm from the fovea and increases in dendritic tree diameter from there into the far periphery. The putative "ON-center" blue cone bipolar and the giant bistratified bipolar first described by Mariani are also present in human retina and we add two previously undescribed bipolar cell types: a putative giant diffuse invaginating and a candidate "OFF-center" blue cone bipolar. Taking into account the variation of cell size with eccentricity at all points on the retina, we observed three distinct varieties of horizontal cell. The HI is the well known, long-axon-bearing cell of Polyak. HII is the more recently described multibranched, wavy-axoned horizontal cell. The third variety, HIII, introduced here, has been separated from the HI type on morphological criteria of having a larger, more asymmetrical dendritic field and in contacting 30% more cones than the HI at any point on the retina. Amacrine cells proved to be most diverse in morphology. Many of the amacrine cell types that have been described in cat retina (Kolb et al., '81: Vision Res. 21; 1081-1114) were seen in this study. Where there are no equivalent cells in cat, we have adopted the descriptive terminology used by Mariani in monkey retina. Thus eight varieties of small-field amacrines (under 100 microns dendritic trees), eight varieties of medium-field cells (100-500 microns dendritic span), and eight large-field varieties (over 500 microns dendritic trees) have been classified. Often a broadly described variety of amacrine cell can be subdivided into as many as three subtypes dependent on stratification levels of their dendrites in the inner plexiform layer.(ABSTRACT TRUNCATED AT 400 WORDS)

Hydrolysis of substance P in the rabbit retina: I. Involvement of acetylcholine and acetylcholinesterase. An in vivo study

The laminar patterns of acetylcholinesterase (AChE) activity and substance P (SP) immunoreactivity within the inner plexiform layer (IPL) of the rabbit retina show striking similarities. Discrete bands of SP-immunoreactivity were seen at 1-7%, 40-48% and 85-95% depth of IPL. AChE activity was present throughout the entire thickness of the IPL with moderately stained bands in each sublamina (3-24% in sublamina a and 62-89% in sublamina b depth IPL). These bands were bordered on both sides by bands of even greater density (in sublamina a 0-3% and 24-34% and in sublamina b 55-62% and 89-100% depth IPL). Cell processes staining for choline acetyltransferase (ChAT) have previously been shown to ramify at 19-24% and 63-79% depth levels. Thus, SP- and ChAT-immunoreactive bands are located in both sublaminae, positioned within regions of moderate AChE activity and flanked by bands with greater AChE activity. This strong morphological correspondence and reported interactions between acetylcholine (ACh), AChE and SP in vitro provide the basis for the present study to determine whether such interactions can be demonstrated in vivo. Retinas infused with ACh showed a 60% average increase in SP-IR as compared with untreated retinas from the same animals. Treatment with diisopropylfluorophosphate (DFP) also resulted in a 56% increase in SP-IR. The ability of ACh to induce increased levels of SP was not inhibited by CoCl2, atropine or mecamylamine, ruling out the possibilities of polysynaptic transmission or involvement of muscarinic or nicotinic receptors. Infusion of ACh did not increase the levels of preprotachykinin-mRNA indicating that the increase in SP-IR is not due to de novo synthesis but rather to inhibition of the enzyme(s) responsible for SP degradation. Whether AChE functions alone or in concert with other enzymes to hydrolyze SP cannot be determined from these experiments but is addressed in a separate study.

Synaptic inputs to physiologically identified retinal X-cells in the cat

The cat retina contains a number of different classes of ganglion cells, each of which has a unique set of receptive field properties. The mechanisms that underlie the functional differences among classes, however, are not well understood. All of the afferent input to retinal ganglion cells are from bipolar and amacrine cell terminals in the inner plexiform layer, suggesting that the physiological differences among cat retinal ganglion cells might be due to differences in the proportion of input that they receive from these cell types. In this study, we have combined in vivo intracellular recording and labeling with subsequent ultrastructural analysis to determine directly the patterns of synaptic input to physiologically identified X-cells in the cat retina. Our primary aim in these analyses was to determine whether retinal X-cells receive a characteristic pattern of bipolar and amacrine cell input, and further, whether the functional properties of this cell type can be related to identifiable patterns of synaptic input in the inner plexiform layer. We reconstructed the entire dendritic arbor of an OFF-center X-cell and greater than 75% of the dendritic tree of an ON-center X-cell and found that 1) both ON- and OFF-center X-cells are contacted with approximately the same frequency by bipolar and amacrine cell terminals, 2) each of these input types is distributed widely over their dendritic fields, and 3) there is no significant difference in the pattern of distribution of bipolar and amacrine cell synapses onto the dendrites of either cell type. Comparisons of the inputs to the ON- and the OFF-center cell, however, did reveal differences in the complexity of the synaptic arrangements found in association with the two neurons; a number of complex synaptic arrangements, including serial amacrine cell synapses, were found exclusively in association with the dendrites of the OFF-center X-cell. Most models of retinal X-cell receptive fields, because their visual responses share a number of features with those of bipolar cells, have attributed X-cell receptive field properties to their bipolar cell inputs. The data presented here, the first obtained from analyzing the inputs to the entire dendritic arbors of retinal X-cells, demonstrate that these retinal ganglion cells receive nearly one-half of their input from amacrine cells. These results clearly indicate that further data concerning the functional consequences of amacrine cell input are needed to understand more fully visual processing in the X-cell pathway.

Angiotensin-like immunoreactive cells in the chicken retina

The cellular distribution of Angiotensin II (ANGII) in the chicken retina was studied by immunocytochemical methods. Three different antibodies directed against ANGII revealed a distinct subpopulation of ANGII-positive amacrine cells. Their cell bodies were located in the innermost rows of the inner nuclear layer (INL). ANGII-positive cell bodies also were found in the ganglion cell layer (GCL). Faint labelling in the centre of the INL was visible, probably related to Müller cell bodies. Single ANGII-positive fibres, each arising from an amacrine cell body, ran to sublayer 3 or 5 of the INL, forming narrow plexi. In addition, small fibres connecting sublayer 3 with sublayer 5 could be observed. ANGII-positive fibres could neither be detected in the optic nerve nor in the outer parts of the retina. Incubation of the tissue in ANGII or angiotensin I (ANGI) dissolved in Ringer solution prior to fixation, increased number and intensity of labelled cells and resulted in better labelling of sublayers 3 and 5 of the inner plexiform layer (IPL). Blockage of the conversion of ANGI to ANGII by adding captopril to the ANGI containing pre-incubation medium reduced the ANGII induced staining enhancement. All three ANGII-antibodies showed corresponding results. These results indicate that a subpopulation of amacrine cells contains angiotensin II in chicken retina. This subpopulation is apparently able to take up ANGII and ANGI, to convert ANGI to ANGII and to store ANGII.

A subpopulation of displaced ganglion cells of the pigeon retina exhibits substance P-like immunoreactivity

Immunohistochemical and retrograde tracing techniques were combined to demonstrate the occurrence of displaced ganglion cells (DGCs) exhibiting substance P-like immunoreactivity (SP-LI) in the pigeon retina. Following injections of rhodamine-labeled latex microspheres into the nucleus of the basal optic root (accessory optic system), about 5200 DGCs were observed to contain rhodamine fluorescence in the contralateral retina. Approximately 26% of the retrogradely labeled DGCs also contained SP-LI. The soma sizes of the doubly labeled DGCs ranged from 12 to 24 microns, and their distribution mirrored the overall distribution of DGCs projecting to the nucleus of the basal optic root. The density of doubly labeled DGCs ranged from 2 to 15 cells/mm2, with density peaks occurring in the superior-nasal and inferior-temporal retinal quadrants. Larger DGCs projecting to the nBOR (25-32 microns) were never seen to contain SP-LI. Together with previous results of enucleation experiments, these data indicate the existence of a subpopulation of SP-LI DGCs which are connected with the accessory optic system in the pigeon. The present results also contribute information on the heterogeneity of retinal ganglion cells transmitters and modulators.

Colocalization of substance P and GABA in retinal ganglion cells: a computer-assisted visualization

Ganglion cells in the albino rat retina were retrogradely labeled with the fluorescent dye, diamindino-yellow, from the superior colliculus. Preembedding and postembedding immunocytochemical techniques were employed in conjunction with computer-assisted image processing to visualize SP- and GABA-immunoreactivity. Examination of flatmount and sectioned retinas revealed that approximately 3% of the ganglion cells projecting to the contralateral superior colliculus exhibit SP-immunoreactivity. Moreover, these cells were found to comprise a subpopulation of the GABA-immunoreactive cells projecting to the rat tectum.

Somatostatin-immunoreactive cells in the adult cat retina

Peptides have been found in the retinas of all mammalian species studied to date, but little is known about their localization and function in the cat. Using two mouse monoclonal antibodies directed to somatostatin 14, we have observed two sparse groups of somatostatin-immunoreactive neurons in the cat, both distributed preferentially in the inferior retina. The more numerous cell type is characterized by a small- to medium-sized soma (mean diameter = 16.3 +/- 9.0 microns; n = 186) with sparsely branching, far-reaching varicose processes that ramify mainly in the inner plexiform layer. The majority of these cells are located in the ganglion cell layer, with the remainder in the proximal inner nuclear layer and the inner plexiform layer. They are in especially high density at the retinal margin. In morphology and soma size, these cells resemble wide-field amacrine cells. The second cell type has a large, granular-staining soma (mean diameter = 29.7 +/- 14.8 microns; n = 145) with poorly stained primary processes and is found only in the ganglion cell layer. Cells of this type are most similar in their size and morphology to alpha ganglion cells. In contrast to the location of somatostatin-immunoreactive somata, a dense meshwork of immunoreactive processes was observed at all eccentricities within the inner plexiform layer, adjacent to the inner nuclear layer and to the ganglion cell layer. Labeled processes arising from the inner plexiform layer were also occasionally detected in the outer plexiform layer and the nerve fiber layer. Additional processes of unknown origin were observed in the nerve fiber layer and the optic nerve head. The extensive distribution of immunoreactive processes suggests that somatostatin-immunoreactive somata located preferentially in the inferior half of the retina have a widespread influence on neural activity.

Morphology and distribution of neurons immunoreactive for substance P in the turtle retina

Immunocytochemical staining procedures with the HRP-complexed antibody to substance P have been carried out on the turtle retina. Examination by light microscopy of wholemount retinas has allowed us to evaluate the morphology and distribution of the substance P immunoreactive cell types. Two amacrine cell types and two or more ganglion cell types are stained in our hands. Type A amacrines are tri-stratified wide-field amacrines. They have their major dendrites in S1 and S3 of the inner plexiform layer and they emit fine dendrites from the major dendrites that end in varicose boutons in S5 on and around cell bodies in the ganglion cell layer. Some of the dendrites in S1 radiate out in axon-like fashion for 1 mm across the retina. The type B amacrine cells are small to medium-field in dendritic extent. They have smaller cell bodies than type A and a single or, at most, two primary dendrites that pass directly to S3 before branching profusely into an intricate net-like dendritic field. The ganglion cells that are stained with substance P antibodies appear to be of several types but their exact morphologies are in doubt because only portions of their major dendrites are stained. Substance P immunoreactive axons are clearly seen to project from the cell bodies to the optic nerve head and axons are stained in the optic nerve itself. The substance P-stained ganglion cells occur in an irregular distribution that reaches a peak density in an elongated band parallel to and 1 mm below the visual streak. The type B amacrine cells reach a maximum density in the visual streak and are distributed in a highly regular mosaic decreasing in density in elliptical isodensity contours from the visual streak. In contrast the type A amacrine cells are rare or absent in the streak, being located in an irregular mosaic in peripheral retina.