A comparative Golgi study of chicken (Gallus domesticus) and homing pigeon (Columba livia) hippocampus

Neurons and fibres in the chick and homing pigeon hippocampus were described following Golgi impregnation. Two principal classes of neurons were distinguished: projection neurons with distant projecting axons and spiny dendrites, and local circuit neurons. In the homing pigeon and chicken hippocampus there are three types of projection neurons: pyramidal, pyramidal-like and multipolar. The pyramidal and pyramidal-like neurons are only found in the central ’pyramidal’ layer of the hippocampus whereas multipolar neurons are present in the suprapyramidal, pyramidal and infrapyramidal layers. The axon of projection neurons typically emits several varicose collaterals from the initial section. Most of these collaterals extend along the infrapyramidal layer of the hippocampus, while others ascend to the pyramidal and suprapyramidal layers where they branch. The number of impregnated axon collaterals was higher in the homing pigeon than in the chick hippocampus. A variety of multiangular/ovoid local circuit neurons ranging from small to large size are found in the homing pigeon and chick hippocampus. Their axons develop local arborisation of varicose branches, the extent of which varies with the type of local circuit neurons. The density of GABA immunopositive local circuit neurons was found to be greater in the homing pigeon than in the chick. The profuse arborisation of projection neuron axon collaterals and the higher density of GABA-immunopositive local circuit neurons in the homing pigeon hippocampus may underlie the differences in hippocampal function between the homing pigeon and chick, and this complex local connectivity may contribute to the ability of spatial orientation and memory. Accepted: 16 July 1999     

A comparative Golgi study of chicken (Gallus domesticus) and homing pigeon (Columba livia) hippocampus

Neurons and fibres in the chick and homing pigeon hippocampus were described following Golgi impregnation. Two principal classes of neurons were distinguished: projection neurons with distant projecting axons and spiny dendrites, and local circuit neurons. In the homing pigeon and chicken hippocampus there are three types of projection neurons: pyramidal, pyramidal-like and multipolar. The pyramidal and pyramidal-like neurons are only found in the central 'pyramidal' layer of the hippocampus whereas multipolar neurons are present in the suprapyramidal, pyramidal and infrapyramidal layers. The axon of projection neurons typically emits several varicose collaterals from the initial section. Most of these collaterals extend along the infrapyramidal layer of the hippocampus, while others ascend to the pyramidal and suprapyramidal layers where they branch. The number of impregnated axon collaterals was higher in the homing pigeon than in the chick hippocampus. A variety of multi-angular/ovoid local circuit neurons ranging from small to large size are found in the homing pigeon and chick hippocampus. Their axons develop local arborization of varicose branches, the extent of which varies with the type of local circuit neurons. The density of GABA immunopositive local circuit neurons was found to be greater in the homing pigeon than in the chick. The profuse arborization of projection neuron axon collaterals and the higher density of GABA-immunopositive local circuit neurons in the homing pigeon hippocampus may underlie the differences in hippocampal function between the homing pigeon and chick, and this complex local connectivity may contribute to the ability of spatial orientation and memory.     

The homing pigeon hippocampus and the development of landmark navigation

The role of the homing pigeon hippocampal formation was examined in the development of loft fidelity and landmark navigation. During the course of five summers, different groups of young pigeons (hippocampal-lesioned, control-lesioned, and unoperated controls) were given free flight experience followed by short distance training and experimental releases. In Experiment 1, a census of which loft each pigeon entered revealed that hippocampal lesioned pigeons displayed less loft fidelity than controls. In Experiment 2 and 3, the percent of young birds lost during their first summer of training and their first experimental release was examined. Despite displaying similarly good homeward-oriented vanishing bearings, significantly more hippocampal lesioned pigeons were lost compared to control groups. The results support the hypothesis that the homing pigeon hippocampal formation participates in the learning/operation of a spatial representation of local landmarks near the loft that can be used for loft recognition and navigation. © 1998 John Wiley & Sons, Inc. Dev Psychobiol 33: 305–315, 1998     

Postnatal development of nonpyramidal neurons in the rat hippocampus (areas CA1 and CA3): a combined Golgi/electron microscope study

Summary This study describes the morphological differentiation of nonpyramidal neurons in areas CA1 and CA3 of the rat hippocampus as seen after Golgi-impregnation. Representative neurons were gold-toned and processed for an electron microscopic study of identified cells. We analyzed the postnatal stages P0 (day of birth), P5, P10 and P20. The results can be summarized as follows: 1. On the day of birth nonpyramidal neurons display relatively large cell bodies with short, clumsy dendrites. Great variability of the shape of the cell body and of the orientation of dendrites was observed when compared with the more stereotyped pyramidal neurons. Electron microscopy of identified nonpyramidal neurons revealed small infoldings of the nuclear membrane and immature synapses on the short dendritic shafts of these cells. 2. Developing nonpyramidal neurons from P0 and P5 display growth cones, filopodia, preterminal growth buds, and irregular varicose swellings along the dendrites. 3. Further postnatal development of nonpyramidal neurons is mainly characterized by an increase in dendritic length, paralled by a decrease in growth cones and preterminal growth buds. By means of the electron microscope an increase in the number of mature input synapses on the gold-toned dendritic shafts of identified nonpyramidal neurons was observed. 4. There is a significant developmental difference between nonpyramidal neurons in CA1 and CA3 that was most obvious on P5. Nonpyramidal neurons in CA3 appear more mature, displaying longer dendrites that sometimes traverse through several hippocampal layers. In contrast, the dendrites of nonpyramidal neurons in CA1 are still restricted to the layer of the parent cell body. The earlier differentiation of nonpyramidal neurons in CA3 may result from the earlier formation of neurons in CA3 than in CA1. Longer dendrites of nonpyramidal neurons in CA3, together with an earlier arrival of afferent fibers in this region, suggest that nonpyramidal neurons in CA3 are integrated into inhibitory hippocampal circuits earlier than their counterparts in CA1. 5. On P20, hippocampal nonpyramidal neurons showed all structural characteristics as observed in adult animals both at light and electron microscopic levels. It is concluded that the structural maturation of hippocampal nonpyramidal cells is completed by that postnatal age.In partial fulfilment of the requirements for the degree of Dr. med. at the University of Frankfurt/Main     

Local circuit neurons in the rat ventrobasal thalamus--a GABA immunocytochemical study

The ventrobasal thalamus of seven rats was processed for immunocytochemistry using antisera to glutamate decarboxylase or gamma-aminobutyrate (GABA). Glutamate decarboxylase-stained sections showed a network of stained fibers and terminals but no stained cell bodies. GABA-stained sections had fewer stained fibers and terminals but did show a few stained cell bodies. Cell bodies were especially apparent when carbazole was used for a chromogen for the peroxidase-antiperoxidase visualization. The GABA-stained cells were found to be distributed throughout the ventrobasal complex, to have smaller soma cross-sectional areas than most other cells (81 +/- 34 microns vs 105 +/- 36 microns for all cells) and to make up 0.4 +/- 0.3% of the neuronal population of the ventrobasal complex. Injections of horseradish peroxidase into the somatosensory cortex (SI) retrogradely filled many neurons in the ventrobasal thalamus, but none of these labeled neurons were double labeled with GABA. These results indicate that the GABA-labeled cells probably represent a small population of local circuit neurons in the rat ventrobasal thalamus.     

The avian hippocampus: evidence for a role in the development of the homing pigeon navigational map

Young homing pigeons were subjected to hippocampal lesion before being placed in their permanent loft to examine what effect such treatment may have on the development of their navigational map, which supports homing from distant unfamiliar locations. When later released from 3 distant unfamiliar locations, the hippocampal-lesioned pigeons were impaired in taking up a homeward bearing. The results identify a deficit in the acquisition of navigational ability after hippocampal ablation in homing pigeons. The results strongly suggest a deficit in navigational map acquisition, but alternative interpretations cannot be excluded. The findings offer the first insight into the central neural structures involved in the acquisition of the pigeon navigational map. Further, the results identify the hippocampus as a structure critical for the regulation of navigational behavior that manifests itself in a natural setting.     

A combined Golgi-electron microscopic study of non-pyramidal neurons in the CA 1 area of the hippocampus

Summary Non-pyramidal neurons of the CA 1 area of the rat hippocampus were identified with a combined Golgi-electron microscopic method. They were observed to have distinctive light and electron microscopic characteristics that are different from those of pyramidal cells. These features included smooth dendrites, locally arborizing axons, infolded cell nuclei with intranuclear rods or sheets, and a well-developed perikaryal cytoplasm with many organelles. In addition, the axon terminals that contact the somata and dendrites of local circuit neurons may form asymmetric as well as symmetric synapses. The axons of these cells form symmetric synapses with dendrites and somata of pyramidal cells. Some of these features were utilized to identify non-pyramidal neurons of the CA 1 area for studies of connectivity. Degenerating commissural terminals were found to form synapses with the dendrites and somata of non-pyramidal neurons. These results indicate that these neurons are a significant population of hippocampal neurons that may provide feed-forward inhibition of pyramidal neurons.     

Fine structure of the optic fibre termination layers in the pigeon optic tectum: A golgi and electron microscope study

This paper describes the fine structure of the optic fibre termination layers (Cajal's layers 2–7) of the pigeon optic tectum. The results indicate that a large proportion of the cellular population is composed of interneurones. The large area of the neuropil occupied by synaptic knobs of local origin contrasts with the relatively discrete retinotectal contribution. The neuropil of the tectal superficial layers is made up of small nervous elements, among which four types of vesicle-bearing profiles have been distinguished. Quantitative analysis revealed the numerical preponderance of two types of vesicle-containing varicosities : (i) Small varicosities with rounded vesicles, corresponding to the terminals of retinotectal fibres. They represent a little less than one fourth of all the vesicle-bearing profiles of the pigeon supercial tectum. (ii) Small varicosities with pleiomorphic vesicles, which can be found postsynaptic to other terminals. They represent over 60% of the vesicle-containing profiles. Similar varicosities are classically assigned to vesicle-bearing dendrites.A survey of the literature shows major similarities between the tectal synaptic circuitry in the pigeon with that in other vertebrates, ranging from fishes to mammals. However, there are quantitative differences. Thus, the proportion of visual boutons is the same in the pigeon tectum as it is in the superior colliculus of lower mammals, but it is significantly lower than in primates. Conversely, the ratio of vesicle-bearing dendrites is much higher in the pigeon than in primates. Optic fibre termination layers are far more extensive in birds than they are in mammals, in particular primates. We consider that the differences in the relative proportions of the types of vesicle-containing profiles are in keeping with the differences in gross anatomy and that they indicate that the tectal internuncial network is much less developed in higher mammals than it is in the pigeon. The possible functional implications of these comparisons are considered.     

The axon arbourisation of nuclei isthmi neurons in the optic tectum of the chick and pigeon. A Golgi and anterograde tracer-study

The optic tectum is reciprocally connected to the nuclei isthmi pars magnocellularis (Imc) and pars parvocellularis (Ipc), which have different modulatory effects on optic transmission. We studied the axon arbourisation of these isthmic nuclei in the optic tectum in order to differentiate between them using Golgi-impregnated preparations both in chickens and pigeons. In addition, sections from animals injected with the anterograde tracer biotinylated dextran-amine (BDA) into the Imc were examined in the bright-field and electron microscope to identify the axon arbourisations and terminals. Also, GABA immunogold stained sections were examined in the electron microscope. In Golgi preparations, slab-like (or poplar tree-like) axon terminal arbourisations of both magnocellular and parvocellular isthmic nuclei neurons were found extending to the tectal surface, with similar branching patterns, but different lengths. The axon arbourisations extending from layer 5 of the optic tectum to the surface were termed type 1, whereas those extending from the internal (12–11) layers to the tectal surface were termed type 2. Type 2 arbourisations very closely matched arbourisations observed in BDA injected material, indicating that Imc neurons gave rise to type 2 arbourisations. The two kinds of axon arbourisation in the external tectal layers were alike in both types of bird, except for the width, which was about 10 m larger in the type 2 axon arbour. Controlling for size, there was no significant difference between chicks and pigeons. The significance of these afferents in the optic tectum is discussed.     

A light and electron microscopic study of betaine/GABA transporter distribution in the monkey cerebral neocortex and hippocampus

The present study aimed to elucidate the distribution of betaine/gamma-aminobutyric acid (GABA) transporter-1 (BGT-1) in the normal monkey cerebral neocortex and hippocampus by immunoperoxidase and Immunogold labelling. BGT-1 was observed in pyramidal neurons in the cerebral neocortex and the CA fields of the hippocampus. Large numbers of small diameter dendrites or dendritic spines were observed in the neuropil. These made asymmetrical synaptic contacts with unlabelled axon terminals containing small round vesicles, characteristic of glutamatergic terminals. BGT-1 label was observed in an extra-perisynaptic region, away from the post-synaptic density. Immunoreactivity was not observed in portions of dendrites that formed symmetrical synapses, axon terminals, or glial cells. The distribution of BGT-1 on dendritic spines, rather than at GABAergic axon terminals, suggests that the transporter is unlikely to play a major role in terminating the action of GABA at a synapse. Instead, the osmolyte betaine is more likely to be the physiological substrate of BGT-1 in the brain, and the presence of the transporter in pyramidal neurons suggests that these neurons utilize betaine to maintain osmolarity.     

A selective serotonin reuptake inhibitor reduces REM sleep in the homing pigeon

Avian and mammalian 'rapid eye movement' sleep (REM sleep) resemble each other in several aspects. However, the question of whether REM sleep has a shared evolutionary ancestry in birds and mammals has yet to be thoroughly explored. The brain regions and neurotransmitter systems involved in the generation of mammalian REM sleep are phylogenetically ancient, and are also found in extant birds and reptiles. Several pharmacological experiments in birds indicate that similar neural substrates are involved in the regulation of avian and mammalian sleep. However, because the drugs used in these studies generally resulted in non-specific sleep loss, the neurochemical regulation of avian REM sleep in particular remains uncertain. The selective serotonin reuptake inhibitor (SSRI) zimelidine is known to reduce REM sleep in mammals. If avian REM sleep is similarly regulated by serotonin, it would be expected that an acute dose of a SSRI should also reduce avian REM sleep. To investigate a putative role of serotonin in the regulation of avian REM sleep, changes in sleep electroencephalogram (EEG) and behavior were recorded in five pigeons (Columba livia) after the administration of an acute dose of zimelidine. Our results demonstrate that the effects of zimelidine on avian REM sleep are comparable to those observed in mammals, indicating that serotonin may serve a similar function in the control of avian and mammalian REM sleep.     

A Golgi study of neurons in the camel cerebellum (Camelus dromedarius)

Neurons in the cerebellar cortex of camels were studied using modified Golgi impregnation methods. Neurons were classified according to their position, morphology of their soma, density and distribution of dendrites, and the course of their axons. Accordingly, eight types of neurons were identified. Three types were found in the molecular layer: upper and lower stellate cells and basket cells, and four types were found in the granular layer: granule cells, Golgi Type II cells, Lugaro cells, and unipolar brush cells. Only the somata of Purkinje cells were found in the Purkinje cell layer. The molecular layer is characterized by the presence of more dendrites, dendritic spines, and transverse fibers. Golgi cells also show extensive dendritic branching and spines. The results illustrate the neuronal features of the camel cerebellum as a large mammal living in harsh environmental conditions. These findings should contribute to advancing our understanding of species-comparative anatomy in achieving better coordination of motor activity.     

GABA down-regulates the GABA/benzodiazepine receptor complex in developing cerebral neurons

Neuronal cultures of the chick embryo cerebrum were used to study the chronic effects of gamma-aminobutyric acid (GABA) on the expression of the GABA/benzodiazepine receptor complex. A 7 day exposure of developing neurons to 100 microM GABA produced a 70% reduction in the level of [3H]flunitrazepam binding to intact cells, when compared to untreated controls. The reduction was due to a decrease in receptor density (Bmax) rather than the affinity. The same treatment also caused a 75% reduction in the rates of GABA-gated 36Cl- uptake by intact cells, without an effect on the basal (GABA-independent) flux. Eight days after removal of GABA from the medium of treated cultures, the neurons recovered [3H]flunitrazepam binding to levels corresponding to 74% of unexposed, age-matched controls. The results are consistent with a GABA-induced down-regulation of the GABA/benzodiazepine receptor.     

The mode of migration of neurons to the hippocampus: a Golgi and electron microscopic analysis in foetal rhesus monkey

Summary The mode of neuron migration from the site of their origin in the ventricular zone to area CA1 of the hippocampus was analysed with Golgi and electron microscopic methods during the first half of gestation in the foetal rhesus monkey. In the inner portion of the intermediate zone, the migrating cells have a bipolar form with one, or occasionally two, leading processes which do not reach the ammonic plate and with a single trailing process which usually ends within the intermediate zone. Both the nucleus and the cytoplasm of the migrating cells are relatively electron-dense and the latter contains organelles typical of young neurons as described in other brain regions. Analysis of electron micrographs from serial sections reveals that the length of the somata and of the leading and trailing processes of the migrating neurons is apposed to fascicles of radially oriented, electron-lucent, microtubule-filled fibres which are ultrastructurally similar to the radial glial fibres of the neocortex and to the Bergmann glial fibres of the cerebellum. The close (20 nm) apposition between the membranes of the migrating cell and the radial fibre is maintained even in areas where the fibres bend or curve tortuously. Migrating neurons situated at progressively more superficial levels of the intermediate zone become progressively more differentiated and complex. Thus, in the outer portion of the intermediate zone, the migrating cells acquire several additional cytoplasmic processes and occasionally a long thin axon-like process which courses into the incipient alveus. These cells have somewhat larger somata and less electron-dense nuclei and cytoplasm than the migrating neurons still situated in the inner part of the intermediate zone. Cells close to the ammonic plate usually have one to three cytoplasmic processes that enter the ammonic plate and terminate near their presumed final position. Migrating neurons situated at the lower border of the ammonic plate have a single large apical process which intermingles with neurons already in their final position and which sometimes traverses the ammonic plate. The apposition of the migrating neurons to the radial glial processes becomes less explicit as the cell soma enters the ammonic plate, reflecting the more complex three-dimensional intercellular relationships. However, the present analysis indicates that during the middle and late stages of neuronal migration to the hippocampus radial glial fibres may guide postmitotic young neurons across the intermediate zone to the ammonic plate in the same way that they guide neurons migrating to the superficial and middle layers of the neocortical plate.The recommendations of the Boulder Committee (Anatomical Record 166, 257–61, 1970) have been followed for the nomenclature of the cardinal embryonic zones.     

Cell types within the medial forebrain bundle: A golgi study of preoptic and hypothalamic neurons in the rat

The morphology of lateral preoptic (POL) and lateral hypothalamic (HLA) neurons was studied in 14- to 200-day-old rats with the chlorate-formaldehyde modification of the Golgi method. Drawings of 91 POL and HLA neurons revealed three distinct neuronal types within the MFB based on somatic size and shape and dendritic morphology. Class I neurons, which accounted for 75–80% of the neurons in the MFB, had fusiform or multipolar somata averaging 21 × 14 μm and 2–5 sparsely branched dendrites with a moderate number of sticklike spines. The extensive dendritic domains of Class I neurons ranged from 700 to 1,500 μm and were usually oriented perpendicular to the longitudinal fibers of the MFB. Both nonoriented and oriented Class I neurons were encountered. Nonoriented Class I neurons had expansive dendritic arbors which reached nearly all regions of the MFB in the coronal plane. Oriented Class I neurons had dendritic domains which were confined to specific regions (e.g., ventral-lateral) of the MFB. Class II neurons, which made up approximately 10% of the MFB neurons, had large multipolar somata averaging 30 × 17 μm and 2–5 stout dendrites which were densely covered with hairlike spines. Class II neurons also exhibited spines on their somata and proximal dendritic trunks and had dendritic domains of 700–1,000 μm. Class III neurons had small somata averaging 15 × 12 μm and restricted dendritic arbors of 500–700 μm in diameter. Class III neurons exhibited both spiny and spine-free dendrites and made up 10% of MFB neurons. Because of the parcellation of chemically coded fiber systems within the MFB, individual POL and HLA neurons may not be homogeneous in the type of afferents they receive from other brain areas.     

Prenatal ontogenetic history of the principal neurons of the neocortex of the cat (Felis domestica) a golgi study

Summary The individual prenatal ontogenetic history of the horizontal neurons (the Cajal-Retzius cells) of layer I, the Martinotti neurons of layer VI, the pyramid-like neurons (the polymorphous or spindle cells) of layer VI, and the pyramidal neurons of layer V of the cat neocortex have been investigated. These neurons undergo, in the course of prenatal ontogenesis, a series of significant changes in their dendritic and axonic arborizations resulting in their complete structural transformation. Some of these changes have led to the appearance of new types of neurons quite different from the original in their morphological features as wells as in the territory of distribution of their axons. The horizontal neurons of layer I (superficial plexiform layer) come to assume the morphological characteristics of Cajal-Retzius cells late in prenatal ontogenesis. Also, the pyramid-like neurons of layer VI (deep plexiform layer) acquire the features of polymorphous (spindle) neurons of layer VI late in prenatal neocortical ontogenesis.Certainly, the resulting functional transformations that these neuronal changes cause are important and of great significance in the understanding of the organization of the mammalian neocortex. In the course of prenatal ontogenesis the following occur: the horizontal neurons of layer I lose their axonic connections with layer VI and acquire an increasing relevance in the structural organization of layer I; the pyramid-like neurons of layer VI lose their axonic and dendritic connections with layer I and undergo pronounced regressive changes in their dendritic and axonic arborizations; and the Martinotti neurons lose their axonic connections with layer I and also undergo regressive changes in their dendritic arborizations. In addition, the structural-functional interrelationships among these three neurons, which are quite prominent during early neocortical ontogenesis, fade away in the course of late prenatal ontogenesis and possibly disappear altogether by the time of birth in the cat. These three neurons are the basic neuronal elements of the early, precallosal organization (the primordial neocortical organization) of the mammalian neocortex. Phylogenetically, these three types of neurons are very old ones and have been described in the cerebral cortices of amphibians and reptiles. Therefore, it is not surprising that the early, precallosal organization of the mammalian neocortex should resemble the structural organization of the reptilian (general cortex) neocortex.It is postulated in this communication that these neuronal transformations are the result of a restructuring in the organization of the mammalian neocortex which follows the arrival of the callosal fibers and of a new type of corticipetal fibers at the pyramidal plate. this restructuring represents a transformation of the fibrillary-neuronal structure of the mammalian neocortex from its early, precallosal (reptilian) organization into a more distinctly mammalian one. The mammalian neocortical organization is characterized by the sequential maturation of several strata of true pyramidal neuronal systems. In the course of prenatal ontogenesis the fibrillar and neuronal elements of the early, precallosal neocortical organization lose progressively their relevance in the structural organization of the mammalian neocortex while the new pyramidal neuronal systems acquire an increasing relevance in it.Supported by Grant HD-03298 and by General Research Support Grant FR-05392 from the General Research Branch, National Institutes of Health.     

Types of neurons and some dendritic patterns of basolateral amygdala in humans--a golgi study.

Classification of the neurons in the human basolateral amygdala is performed on preparations impregnated by the Golgi technique. Three different neuronal types are found in the nuclei of the basolateral amygdala: Type I--Pyramidal cells, with numerous dendritic spines and two subtypes (slender and squat); Type II--Modified pyramidal cells, sparsely spinous with rare dendritic spines and two subtypes (single apical and double apical) and; Type III--Non-pyramidal cells, with few dendritic spines and three subtypes (bipolar, multipolar and gliaform). The analysis of the primary dendritic branches pointed out the occasional presence of dendritic bundles (fascicular dendritic arrangement) with their predomination in the parvicellular division of the basal nucleus and paralaminar nucleus. Additionally, the presence of dendrodendritic contacts, indicated by light microscopy, was also found in the parvicellular division of the basal nucleus and especially in the paralaminar nucleus.