Biomedical subjects

B Dreher

Publications and source records attributed to B Dreher.

At least 55 records · Page 3Linked to original sources

PubMed1988

Peak density and distribution of ganglion cells in the retinae of microchiropteran bats: implications for visual acuity.

We have estimated the total number, distribution and peak density of retinal ganglion cells (RGCs) in retinal wholemounts of several species of microchiropteran (echolocating) bats. The estimates are based on counts of Nissl-stained, presumed RGCs. The total number of presumed RGCs varies among the species: from about 4,500 in Rhinolophus rouxi to about 120,000 in Macroderma gigas. In addition, in two species (Nyctophilus gouldi and M. gigas), the estimates are based on counts of positively identified RGCs retrogradely labelled with the enzyme horseradish peroxidase injected into the retinorecipient nuclei. In these two species, the numbers and distributions of retrogradely labelled RGCs and Nissl-stained presumed RGCs are very similar. In all six species studied, the peak-density regions of presumed (or positively identified) RGCs are located in the inferotemporal retinae, and the RGC isodensity lines tend to be horizontally elongated. However, the RGC densities in the high-density regions are only 2-4 times greater than those in the low-density regions in the superior retinae. The somal sizes of RGCs vary from 5 to 16 micron in diameter and are unimodally distributed. There is no indication of the existence of distinct morphological classes of RGCs. The axial lengths of microchiropteran eyes vary from 1.8 mm in R. rouxi to 7.0 mm in M. gigas. For all species the posterior nodal distance (PND) was assumed to be 0.52 of the axial length of the eye. This assumption is based on the analysis of published data concerning schematic eyes of nocturnal vertebrates. These derived values of the PNDs allowed us to calculate the retinal magnification factors and the number of RGCs per degree of visual angle. From these, the upper limits of visual acuity were derived on the basis of the assumptions of the sampling theorem. The estimated upper limits of visual acuity of the six species of echolocating bats vary from about 0.35 cycles/degree in R. rouxi to about 2 cycles/degree in M. gigas. This range is quite similar to the range of visual acuities in murid rodents.

Animals↗

PubMed1988

Development of the retinofugal pathway in birds and mammals: evidence for a common 'timetable'.

We have compared changes in axon numbers in the developing optic nerves of eight homeotherms (seven mammals and one bird) using data from the available literature and our own material. The proportion of axons lost during development is smaller in the chick (35%) than in mammals (54-74%). The relative magnitude of this loss does not correlate with the extent of the binocular visual field or the size of the retinofugal ipsilateral projection. The timing of developmental events in the retinofugal pathway was compared as a proportion of the period between conception and eye opening (percentage of the 'caecal period', CP). In eutherian mammals, retinal ganglion cells and their target neurons are generated between 30 and 49% of CP (a duration of 19% of CP). In homeotherms, a phase of rapid axon generation begins around 38% of CP and the peak number of axons is reached at about 56% of CP (a duration of 18% of CP). A phase of rapid axon loss begins thereafter, and in most species it ends at about 74% of CP (a duration of 18% of CP), the rate of rapid axons loss being about half the rate of rapid axon generation. The similarity in relative timing (homochrony), like the similarity in the relative magnitude of the axon loss, suggests that cell generation and loss in the retinofugal pathway are influenced by a mechanism common to all homeotherms. We propose that in homeotherms each cohort of retinal ganglion cells is numerically matched with a group of target cells that is at an appropriate stage of maturation ('temporal matching' hypothesis). About twice as many ganglion cells are produced in each cohort than are needed, and their survival is determined by natural selection.

Animals↗

PubMed1987

Parallel processing of binocular disparity in the cat's retinogeniculocortical pathways.

In the cat, parallel streams of information processing have been traced from X-, Y- and W-type retinal ganglion cells to visual cortical areas 17 (X-, Y- and W-type), 18 (Y-type) and 19 (W-type). In the present study we have examined, in the anaesthetized and paralysed adult cat, the role played by X-, Y- and W-subsystems, projecting to areas 17 and 19, in the processing of binocular retinal disparity. The tapetal reflection technique was used to monitor residual eye movements and to provide a map, for each eye, of the retinal blood vessels which could later be compared with retinal wholemounts stained with cresyl violet to reveal the area centralis. The receptive-field disparities of cells recorded from areas 17 and 19 were compared with each other and with reference to the visual axes defined by the area centralis of each eye. Cells of area 19 (receiving W-type input) had horizontal receptive-field disparities that were significantly more divergent than those of the cells in area 17 and 17-18 'border region'. Referred to the area centralis, the mean horizontal receptive-field disparity in area 19 was -0.5 degrees (+/- 0.8 degrees). The mean horizontal receptive-field disparity of area 17 (receiving X-, Y- and W-type input) was convergent with respect to the visual axis at +2 degrees (+/- 0.5 degrees). Finally, the mean horizontal receptive-field disparity of the cells in the 17-18 border region (which receive mainly Y-type input) was even more convergent (2.6 degrees +/- 1.5 degrees) than that of area 17. Binocular interactions of cortical neurons were tested with the Risley biprism technique. Area 19 cells had maximal responses to binocular stimulation when the receptive-field disparities were either close to zero or slightly divergent. In contrast, area 17 cells tended to respond optimally to disparities that were either slightly or strongly convergent. At the level of the lateral geniculate nucleus there were significant differences between the receptive-field disparities inferred from the comparison of receptive-field positions of adjacent neurons recorded on either side of the border between the A and A1 geniculate laminae and those inferred from a similar comparison at the C1-C2 border. The mean horizontal disparities inferred from the interlaminar comparison at the A-A1 border were +2.1 degrees (+/- 0.3 degrees); those inferred from the interlaminar comparison at the C1-C2 border -0.2 (+/- 0.2 degrees) were more divergent.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1987

The development of the corticotectal pathway in the albino rat: transient projections from the visual and motor cortices.

In rats ranging in age from the second postnatal day (23rd postconceptional day-23 PCD) to adulthood, we have studied the distribution of corticotectal terminals labelled anterogradely by unilateral injections of horseradish peroxidase (conjugated with wheat germ agglutinin) into the visual or motor cortices. No projection to the contralateral superior colliculus (SC) was observed. The earliest age at which the labelled axons and/or terminals from the visual cortex were observed in the ipsilateral SC was 25 PCD. At this stage the projection only involves the optic layer. From 28 to 34 PCD, the projection involves the optic layer, the intermediate layers and the deep part of superficial gray layer. Between 34 and 40 PCD the projection becomes restricted to the superficial laminae (i.e. adultlike). On the 23 PCD (the earliest age examined) we observed a projection from the motor cortex to the intermediate laminae and to a lesser extent the optic layer of the ipsilateral SC. By 34 PCD only the adult-like projection extending from the brachium to the periaqueductal gray (PAG) is apparent. The disappearance of the transient projections to the intermediate collicular laminae may be the result of withdrawal of 'misprojecting' axonal collaterals.

Animals↗

PubMed1987

Differential retinal growth appears to be the primary factor producing the ganglion cell density gradient in the rat.

We have studied the distribution of retinal ganglion cells (RGCs) that had been retrogradely labelled from bilateral injections of horseradish peroxidase into the retino-recipient nuclei of albino rats aged from the 22nd postconceptional day (22PCD-day of birth) to adulthood. During the period in which most (85%) of the naturally occurring RGC loss takes place (22-26 PCD) the distribution of RGCs remains almost uniform. Between the 26 and 32PCD (11th postnatal day), the peak RGC density decreases by only 20% while the RGC density at the superior retinal periphery decreases by 80%. In the same period a centro-peripheral RGC density difference of 4:1 becomes apparent. We have interpreted these changes to be due to a phase of rapid differential retinal growth (with more growth occurring at the retinal periphery). Thereafter the reduction in RGC density (and presumably retinal growth) is more uniform resulting by adulthood in a centro-peripheral RGC density ratio of 5:1.

Aging↗

PubMed1987

Changes in the numbers of retinal ganglion cells and optic nerve axons in the developing albino rabbit.

In albino rabbits aged from the 16th postconceptional day (16PCD) to adulthood, the number of axons in the optic nerves were estimated from sample areas totalling 1-12% of the cross-sectional area of the nerve. On the 16PCD there are about 20,000 axons in the optic stalk. The number of axons in the retrobulbar part of the optic nerve reaches a peak value of 766,000 on the 23PCD, and then decreases to about 350,000 by the 32PCD (the day of birth). The number of axons does not change between the 32PCD and 50PCD, but thereafter it slowly decreases, reaching the adult number (294,000) by the 84PCD. A similar trend is apparent in pigmented animals. Thus, on the 25PCD there are 736,000 axons in the retrobulbar part of the optic nerve and the number decreases to 428,000 by the 31PCD. In the adult pigmented rabbit there are 280,000 axons in the optic nerve. In animals younger than the 32PCD, growth cones are present, and the number of axons in the prechiasmal part of the optic nerve was 8-22% lower than in the retrobulbar part of the same nerve. These observations suggest that there is a continued outgrowth of axons from the eye towards the target nuclei. By the 32PCD, the numbers of axons in the retrobulbar and prechiasmal parts of the nerve were very similar, suggesting that by this age all axons had reached the chiasm. The numbers of retinal ganglion cells (RGCs) labelled by massive injections of horseradish peroxidase into the retino-recipient nuclei were estimated in albino rabbits aged from the 24PCD to adulthood. RGCs were counted in evenly spaced sample areas totalling 4-11% of the retinal area. On the 24PCD, the number of labelled RGCs (500,000) was lower than the number of axons in the optic nerve (probably because not all RGC axons had reached their target nuclei by this age). However, by the 27PCD the number of labelled RGCs (550,000) was very similar to the number of prechiasmal axons (568,000). At all ages thereafter, the numbers of both RGCs and axons were very similar, with adult RGC numbers (about 291,000) being reached by the 85PCD. We conclude that axon loss in the rabbit optic nerve after the 27PCD is almost certainly due to the elimination (presumably death) of the parent RGCs, and we suggest that RGC death is also the most likely cause of axon loss prior to the 27PCD.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗

PubMed1986

Role of target tissue in regulating the development of retinal ganglion cells in the albino rat: effects of kainate lesions in the superior colliculus.

Kainic acid or ibotenic acid was injected unilaterally into the major target regions of the axons of retinal ganglion cells--the superior colliculus (SC) or dorsal lateral geniculate nucleus (DLG)--of rat pups ranging in age from postnatal day 0 to postnatal day 10 (P0 - P10). While the collicular or geniculate neurons within the injection site died within 48 hours of the injection, damage to axons and terminals of extrinsic origin within the injected region was not apparent. The neuronal degeneration induced by the neurotoxins, observed at both the light and electron microscopic levels, resembled the neuronal degeneration that occurs in the colliculus during normal development. Macrophages were identified in the regions containing degenerating cells. Two to three weeks after the injections of neurotoxin, massive injections of the enzyme, horseradish peroxidase (HRP), were made into the retinorecipient nuclei. After about 24-hour survival time the numbers of retinal ganglion cells were estimated by counting the number of neurons containing HRP reaction products in sample areas distributed in a regular rectangular array across the entire retinal surface. In the animals in which the neurotoxin was injected into the SC during the first 4 postnatal days, there was a substantial reduction (on average 41.5%; the range: 27.5-65.5%) in the normal number (mean value of 113,000--Potts et al.: Dev. Brain Res. 3:481-486, '82) of retinal ganglion cells surviving the period of "naturally occurring ganglion cell death" in the retinae contralateral to the injected SC. By contrast, injections of neurotoxins into the DLG and/or the optic tract of newborn rats did not result in a significant reduction in the numbers of retinal ganglion cells surviving the period of naturally occurring ganglion cell death. The period of sensitivity of retinal ganglion cells to the injection of neurotoxin into the colliculi extends from birth to about the end of the first postnatal week; the greatest sensitivity seems to be restricted to the first 3-4 postnatal days. In the retinae in which the total number (and density) of ganglion cells was substantially reduced by the selective destruction of their target cells, the centro-peripheral difference in the somal diameters of the ganglion cells (apparent in normal animals) was abolished, both amongst the whole population of ganglion cells and amongst the ganglion cells with the largest somata, relatively thick axons, and large-gauge primary dendrites (Class I cells). The number and distribution of the Class I cells in the depleted retinae were, however, unaltered.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗

PubMed1986

The development of the corticotectal pathway in the albino rat.

To study the development of the corticotectal pathway, the enzyme horseradish peroxidase (HRP) was injected electrophoretically into the superior colliculus (SC) of rats ranging in age from newborn to adult. In animals younger than postnatal day 3 (P3), collicular injections did not label any cells in the cortex while in animals injected at P3-P4, only a few cortical cells were retrogradely labeled. In contrast, injections made at P5 or later resulted in the labeling of a substantial proportion of lamina V cells in a number of cortical areas ipsilateral to the injected colliculus. Although at P5-P7 the bulk of labeled cells was located in the visual cortices (both striate and extrastriate), a substantial proportion of the labeled cells was located in the somatosensory, motor and association cortices. On the other hand, in animals injected at P12 (or later), the labeled cells were largely restricted to the visual cortices with relatively few corticotectal cells located in somatosensory area I. At all ages studied, labeled cortical cells were confined to lamina V and had clear-cut apical dendrites (pyramidal cells). The dendritic morphologies and somal sizes of the corticotectal cells indicate that in animals younger than P12 these cells are immature. These observations suggest that the axons of cortical cells do not reach the SC before P3 and that these early corticotectal projections (P3-P12) are established by immature cells. Furthermore, although the corticotectal projection exhibits, from its onset, a high degree of specificity in terms of the laminar distribution of its cells of origin, its areal distribution is 'exuberant'. The 'exuberant' projections originating from non-visual cortical areas disappear by P12-P14, that is at the time when young rats open their eyes for the first time.

Aging↗

PubMed1985

Central projections of cat retinal ganglion cells.

The central projections of different groups of cat retinal ganglion cells were studied following small iontophoretic injections of horseradish peroxidase (HRP) into physiologically characterized sites. Analysis was restricted to labeled cells in the upper periphery of the nasal retina, contralateral to the injection site. Injections were made to the A lamina and C lamina of the dorsal lateral geniculate nucleus (LGNd-A,C), the geniculate wing (LGNd-W), the ventral lateral geniculate nucleus (LGNv), the pretectum (PT), and the superior colliculus (SC). The dendritic fields of alpha, beta, and epsilon cells were well labeled by the procedures we employed. A group, termed "g1," had somal sizes within the range of the smaller beta and epsilon cells, but dendritic morphologies distinct from either class. The g1 group may consist of a number of types, but our material provided no basis for further distinguishing them. Many cells were observed that had smaller somas; all had thin axons, and few had dendritic fields that labeled to any significant extent. We were not able to further distinguish these cells, and refer to this group, which may include a number of types, as "g2" cells. From the peripheral nasal retina, alpha cells project to LGNd-A, LGNd-C, PT, and SC. Beta cells project to LGNd-A, LGNd-C, and PT. Epsilon and g1 cells project to the LGNd-C, LGNd-W, LGNv, PT, and SC. We determined the total spatial density of cells in the region of the retina analyzed, using a Nissl-stained preparation. We then estimated the relative fraction of cells in each of the above groupings by injecting HRP throughout a cross section of the optic tract. Multiplying this relative fraction by the total spatial density gave an estimate of the spatial density of each of these groupings. From the spatial density of cells labeled from the injection site, we were able to estimate the fraction of cells of each retinal grouping that project to each of the zones investigated. By these calculations, almost all alpha cells from the upper nasal retina project to LGNd-A and LGNd-C; most project to SC, and about a third to PT. Beta cells, by contrast, project almost exclusively to LGNd-A, with about 10% going to LGNd-C, and about 1% to the PT. The great majority of epsilon cells, if not all, project to LGNd-W, and up to half of this population also project to the other zones noted above.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1985

Afferents to a midbrain periaqueductal grey region involved in the 'defence reaction' in the cat as revealed by horseradish peroxidase. I. The telencephalon.

Horseradish peroxidase injections were made at sites, within the midcollicular portion of the midbrain periaqueductal grey region (PAG), at which both electrical stimulation and subsequent microinjections of excitatory amino acids elicited defensive behaviour. Since excitatory amino acids depolarize cell bodies and dendrites located in the vicinity of the injection site but not axons of passage, the injections were centred within a PAG region known to contain neurones whose excitation elicited defensive behaviour. The telencephalic afferents to these sites were then determined. Sixty percent of the labelled telencephalic neurones were found in the frontal cortex, specifically in the medial frontal cortex along the banks of the rostral two-thirds of the cruciate sulcus, primarily area 6 and area 4, and the medial frontal cortex ventral to area 6 (area 32). Twenty-five percent of the labelled telencephalic neurones were found in the orbito-insular cortex while 8% were found in the parietal cortex surrounding the anterior ectosylvian sulcus. Although the functional significance of these projections remains to be established, available data suggest that these projections to the PAG arise from frontal 'oculomotor' and motor cortices, a polysensory insular cortical region and somatosensory, visual and auditory parietal cortical areas.

Aggression↗

PubMed1985

Development of cortical afferents and cortico-tectal efferents of the mammalian (rat) primary visual cortex.

At the time when the fibres from the striate cortex (area 17) begin to innervate the superficial layers of the superior colliculus of the young rat (postnatal days 4 and 5) a high degree of specificity in the organization of this newly formed cortico-tectal projection is already apparent. Thus, in young rats, as in adult mammals of virtually all species studied so far, the somata of cortico-tectal neurones are confined to lamina V of the ipsilateral cortex. However, this high degree of laminar (radial) specificity in young animals is accompanied by a substantial degree of exuberance as indicated by a tangential distribution of the cortico-tectal cells which is wider than that in the adult. The exuberant projections are pruned during the second postnatal week. The cortico-cortical associational and commissural fibres start to enter the grey matter of the rat striate cortex after postnatal day 7. Again a high degree of specificity in the laminar distribution of those newly established projections is apparent. However, the cortico-cortical projection, at the time when cortico-cortical fibres enter the cortical laminae, is clearly exuberant since the tangential spread of cortical cells projecting to the striate cortex is wider than that in the adult. Pruning of these excessive projections takes place some time after postnatal day 14. It is believed that understanding the mechanism(s) underlying the development of connections of the rat visual cortex might be of general importance in understanding developmental abnormalities in the pattern of interconnections of the visual cortices of other mammalian orders.

Afferent Pathways↗

PubMed1985

The morphology, number, distribution and central projections of Class I retinal ganglion cells in albino and hooded rats.

Class I retinal ganglion cells have been identified in wholemounts of rat retinae following injections of horseradish peroxidase (HRP) into retino-recipient nuclei. Class I cells are characterized by relatively large somata, 3-7 fairly frequently branching large-gauge primary dendrites and relatively thick axons. Cells with a very similar morphology have been visualized in the ganglion cell layer of retinal wholemounts using a neurofibrillar stain. The size of the somata and dendritic trees of Class I cells is affected by the density of all classes of ganglion cells: both somata and dendritic trees of Class I cells located in the region of peak density are smaller than those located in medium- and low-density ganglion cell regions. The mean numbers of Class I ganglion cells labelled following massive injections of HRP into retino-recipient nuclei were 876 (in albino rats) and 944 (in hooded rats), while the mean number of cells stained with the neurofibrillar method in albino retinae was 791. Thus, with the total number of positively identified retinal ganglion cells being 110,000-115,000 [Potts et al., 1982; Perry et al., 1983], Class I cells in both strains of rat constitute less than 1% of all retinal ganglion cells. Nevertheless the dendritic fields of Class I cells cover the entire retina. Although Class I cells are distributed relatively evenly across the retina, the density is slightly greater in the lower temporal retina where the bulk of the ipsilaterally projecting fibres originates. While Class I cells represent up to 10% of ipsilaterally projecting retinal ganglion cells in both strains of rat, fewer Class I cells project ipsilaterally in albinos than in hooded rats. All contralaterally projecting Class I cells appear to send branching axons to the superior colliculus and dorsal lateral geniculate nucleus. Class I cells represent a larger proportion of the ganglion cells projecting to the dorsal lateral geniculate nucleus (4-5%) than that of ganglion cells projecting to the superior colliculus (about 1%). The morphology, numbers, distribution and the pattern of the central projections of Class I retinal ganglion cells in rats suggest that they are likely to be homologues of the alpha-type ganglion cells distinguished in carnivores.

Animals↗

PubMed1984

Claustral afferents to the rat's visual cortex.

Horseradish peroxidase (HRP) was injected electrophoretically into the rat's primary visual cortex (V1), and three other retinotopically organized cortical areas, anterior medial visual area (AM), posterior medial visual area (PM) and anterior lateral area (AL). While the HRP injections into V1 labelled many neurons in the ipsilateral claustrum, the injections in any of the three other visual areas labelled very few claustral neurons.

Afferent Pathways↗

PubMed1983

The retinal location and fate of ganglion cells which project to the ipsilateral superior colliculus in neonatal albino and hooded rats.

We have studied the organization of the ipsilateral retinocollicular pathway in neonatal rats by injecting the enzyme horseradish peroxidase (HRP) into the superior colliculus within 24 h of birth and later examining the location of labelled cells in the contralateral and ipsilateral retinae. One day after HRP injection, regardless of the location of the injection site in the superior colliculus, the great majority (over 80%) of ipsilaterally projecting cells was located in the lower peripheral retina. Five days after injection into the posterior pole of the superior colliculus (which in adult animals does not receive input from the ipsilateral retina), there were very few labelled cells in the ipsilateral retina, but labelled cells were quite numerous in the appropriate part of the contralateral retina. These results suggest that in the neonatal rat the great majority of ipsilaterally projecting retinal ganglion cells lie in the same part of the retina as do ipsilaterally projecting cells in the adult, but that many of those cells which project to inappropriate parts of the superior colliculus die by the fifth postnatal day.

Animals↗

PubMed1983

Evidence that the early postnatal reduction in the number of rat retinal ganglion cells is due to a wave of ganglion cell death.

Horseradish peroxidase (HRP) was injected into the retino-recipient nuclei of each hemisphere in newborn rats. The animals were perfused 3--9 days after the injections; the number of retinal ganglion cells in retinal wholemounts was estimated by counting cells containing granules of HRP reaction product. The mean number (150,500) of labelled cells in 3-day-old rats was significantly higher than those in older animals (117,000, 121,000, 113,000 respectively on 6th, 8th and 9th postnatal days). However, in animals of any of the ages studied, the estimated numbers of ganglion cells were virtually the same as those in the animals of the same age but injected with HRP only 15--20 h before the perfusion. Thus, the reduction in the number of retinal cells projecting to the central visual nuclei observed during the first few postnatal days is due to a wave of retinal ganglion cell death; ganglion cell death induced by the neonatal removal of the contralateral superior colliculus has a similar time course.

Animals↗

PubMed1982

Lack of binocularity in cells of area 19 of cat visual cortex following monocular deprivation.

We have studied the visual receptive field properties of neurons in cortical area 19 of monocularly deprived cats. Almost all visually responsive units responded to stimulation of the non-deprived eye only. Receptive field properties assessed through the non-deprived eye were found to be normal. Monocular deprivation appears thus to have sharply reduced the normal binocularity of neurons in area 19. Since the W-cell component of the visual pathways provide the predominant input to area 19, our results suggest that W-cells are vulnerable to environmental manipulation.

Animals↗

PubMed1982

Retinal W-cell projections to the medial interlaminar nucleus in the cat: implications for ganglion cell classification.

The perikaryal sizes and retinal distribution of ganglion cells labeled after small iontophoretic injections of horseradish peroxidase (HRP) into the medial interlaminar nucleus (MIN) were studied. Injections were also made into the LGNv and the C-laminae of the dorsal lateral geniculate nucleus (LGNd) for comparison. The results are consistent with suggestions that the MIN contains three approximately vertically oriented laminae which, from medial to lateral, receive their input from, respectively, contralateral nasal, ipsilateral temporal, and contralateral temporal retina. Each MIN lamina receives afferents from two distinct groups of retinal ganglion cells (1) cells with large somas (over 25 micron), coarse primary dendrites, large dendritic trees (500-900 micron in diameter), and coarse axons; (2) cells with medium-sized somas (14-20 micron), medium-caliber primary dendrites, large dendritic trees (350-700 micron), and fine axons. The large cells are clearly Y-cells or alpha cells, and they provide approximately 50% of the retinal input to all layers of the MIN. The medium-sized cells, which provide the remaining 50% of the retinal output in the MIN, are, we argue, W-cells, since they do not differ in soma size, dendritic morphology, axon caliber, or receptive field properties from medium-sized W-cells which project to other thalamic or midbrain structures. These results suggest two phylogenetic trends within the W-cell group: (1) the differentiation of thalamic and midbrain components; and (2) the further differentiation of ipsilateral and contralateral projections within the midbrain component. This latter division corresponds to the distinction between W1 and W2 cells described previously (Rowe and Stone, '77, '80).

Animals↗

PubMed1982

The survival of neonatal rat retinal ganglion cells in vitro is enhanced in the presence of appropriate parts of the brain.

The enzyme horseradish peroxidase (HRP) was injected into the visual centres of the brains of neonatal rats. Following dissociation of retinae into tissue culture, the ganglion cells could be identified by appropriate histochemical staining for HRP reaction product. Cultures were prepared of dissociated retinae from rats aged 2-6 days postnatal. After 3 h the cultures were fixed, and HRP-labelled cells visualized and counted. Estimates were made of the number of ganglion cells per retina at each age. Results indicated a loss of ganglion cells during the first few postnatal days. This loss paralleled that observed in vivo. It was further found the retinal ganglion cells died rapidly in vitro when cultured in a minimal medium. Only 50% of ganglion cells originally plated remained viable after 24 h. However, the survival rate could be increased to 100% by co-culturing the cells with diencephalon and mesencephalon; these contain the retinorecipient nuclei. Co-culturing with cerebellum did not result in such an enhanced survival rate. Ganglion cells could be maintained over longer periods of time by reinoculating the cultures with additional tissue containing diencephalon and mesencephalon. These results support the hypothesis that developing neurons require trophic factors from their target tissues in order to survive.

Animals↗