The distribution of cholecystokinin-like immunoreactivity in the hippocampal formation of the guinea pig: localization in the mossy fibers

Intrinsic connections of the macaque monkey hippocampal formation: I. Dentate gyrus

We have carried out a detailed analysis of the intrinsic connectivity of the Macaca fascicularis monkey hippocampal formation. Here we report findings on the topographical organization of the major connections of the dentate gyrus. Localized anterograde tracer injections were made at various rostrocaudal levels of the dentate gyrus, and we investigated the three-dimensional organization of the mossy fibers, the associational projection, and the local projections. The mossy fibers travel throughout the transverse extent of CA3 at the level of the cells of origin. Once the mossy fibers reach the distal portion of CA3, they change course and travel for 3-5 mm rostrally. The associational projection, originating from cells in the polymorphic layer, terminates in the inner one-third of the molecular layer. The associational projection, though modest at the level of origin, travels both rostrally and caudally from the injection site for as much as 80% of the rostrocaudal extent of the dentate gyrus. The caudally directed projection is typically more extensive and denser than the rostrally directed projection. Cells in the polymorphic layer originate local projections that terminate in the outer two-thirds of the molecular layer. These projections are densest at the level of the cells of origin but also extend several millimeters rostrocaudally. Overall, the topographic organization of the intrinsic connections of the monkey dentate gyrus is largely similar to that of the rat. Such extensive longitudinal connections have the potential for integrating information across much of the rostrocaudal extent of the dentate gyrus.

Mossy fiber synaptic transmission: communication from the dentate gyrus to area CA3

Communication between the dentate gyrus (DG) and area CA3 of the hippocampus proper is transmitted via axons of granule cells--the mossy fiber (MF) pathway. In this review we discuss and compare the properties of transmitter release from the MFs onto pyramidal neurons and interneurons. An examination of the anatomical connectivity from DG to CA3 reveals a surprising interplay between excitation and inhibition for this circuit. In this respect it is particularly relevant that the major targets of the MFs are interneurons and that the consequence of MF input into CA3 may be inhibitory or excitatory, conditionally dependent on the frequency of input and modulatory regulation. This is further complicated by the properties of transmitter release from the MFs where a large number of co-localized transmitters, including GABAergic inhibitory transmitter release, and the effects of presynaptic modulation finely tune transmitter release. A picture emerges that extends beyond the hypothesis that the MFs are simply "detonators" of CA3 pyramidal neurons; the properties of synaptic information flow from the DG have more subtle and complex influences on the CA3 network.

The dentate mossy fibers: structural organization, development and plasticity

Hippocampal mossy fibers are the axons of the dentate granule cells and project to hippocampal CA3 pyramidal cells and mossy cells of the dentate hilus (CA4) as well as a number of interneurons in the two areas. Besides their role in hippocampal function, studies of which are still evolving and taking interesting turns, the mossy fibers display a number of unique features with regard to axonal projections, terminal structures and synaptic contacts, development and variations among species and strains, as well as to normal occurring and lesion-induced plasticity and neural transplantation. These features are the topic of this review, which will use the mossy fiber system of the rat as basis and reference in its aim to provide an up-to-date, yet historically based guide to students in the field.

Effects of early environment on field CA3a pyramidal neuron morphology in the guinea-pig

There is evidence that early environmental conditions have profound effects on the morphology of the dentate granule cells. The aim of the present study was to obtain information about the effects of early environment on neuron morphology in the hippocampal field CA3, a structure closely linked to the dentate gyrus. The dendritic trees and the somata of field CA3a pyramidal neurons were quantified in Golgi-stained brains of guinea-pigs of both sexes raised in either a social or an isolated environment. Two pyramidal neuron types were found in CA3a, characterized by either a long or a short shaft. Environment affected the apical tree of the long-shaft neurons only in males and that of the short-shaft neurons in both sexes. In isolated males the long-shaft neurons had a decrease in the number of dendritic intersections (62-82%), branching points (76%) and length (71%) in the middle third of the apical tree. The short-shaft neurons had a decrease in the number of intersections at two distal levels only in both isolated males (26, 83%) and females (77, 82%). The shaft spine density was affected by environment in the long-shaft neurons of males only, with a density increase (110%) in isolated males. In both sexes the basal tree of only the long-shaft neurons was affected by environment. Isolated males had a decrease in the number of dendritic intersections (65-88%), primary dendrites (80%) and dendritic length (88%) and isolated females had a decrease in the number of intersections (51-89%), branching points (77%) and dendritic length (85%). The soma major axis of only the long-shaft neurons was affected by environment with a reduction in isolated males (90%) but an increase in isolated females (111%). These results demonstrate dendritic atrophy of CA3a pyramidal neurons following early isolation and a different reactivity to environment of the two CA3a pyramidal neuron types, their apical and basal trees and the two sexes. The dendritic atrophy of CA3a neurons caused by isolation is likely to be associated with an impairment in the physiology of the hippocampal formation and in the forms of memory in which the hippocampal formation plays a major role.

The multifarious hippocampal mossy fiber pathway: a review

The hippocampal mossy fiber pathway between the granule cells of the dentate gyrus and the pyramidal cells of area CA3 has been the target of numerous scientific studies. Initially, attention was focused on the mossy fiber to CA3 pyramidal cell synapse because it was suggested to be a model synapse for studying the basic properties of synaptic transmission in the CNS. However, the accumulated body of research suggests that the mossy fiber synapse is rather unique in that it has many distinct features not usually observed in cortical synapses. In this review, we have attempted to summarize the many unique features of this hippocampal pathway. We also have attempted to reconcile some discrepancies that exist in the literature concerning the pharmacology, physiology and plasticity of this pathway. In addition we also point out some of the experimental challenges that make electrophysiological study of this pathway so difficult.Finally, we suggest that understanding the functional role of the hippocampal mossy fiber pathway may lie in an appreciation of its variety of unique properties that make it a strong yet broadly modulated synaptic input to postsynaptic targets in the hilus of the dentate gyrus and area CA3 of the hippocampal formation.

Distribution of cholecystokinin immunoreactivity in the BALB/c mouse forebrain: an immunocytochemical study

The present study describes cholecystokinin (CCK) immunoreactivity (CCK-IR) distribution in the brains of control and colchicine-treated mice. In the brains of control mice, the CCK-IR strongly revealed numerous axons and terminals. Perikarya exhibiting a faint to moderate immunoreactivity were also observed in areas such as cortices, hippocampus, amygdala, septum, and thalamus. The colchicine treatment did not seem to notably affect the brain CCK-IR innervation, but resulted in profound changes of the perikaryal staining. Indeed, the regions, which contained numerous moderately stained perikarya in the control animals, exhibited after colchicine treatment immunoreactive perikarya intensely stained but only in moderate number. This feature obviously appeared in the cortex in which, in addition to strongly stained perikarya, colchicine induced the appearance of numerous CCK-IR hillocks. In the lateral amygdala and thalamus of colchicine-treated animals, the somatic immunoreactivity was considerably decreased. The regions, such as paraventricular hypothalamic nucleus and bed nucleus of the stria terminalis, which in the control animals did not exhibit any stained perikaryon, showed a high number of strongly stained cell bodies after colchicine treatment. This study, mapping the mouse forebrain CCK-IR, demonstrated a wide distribution of this peptide. Moreover, CCK-IR is spontaneously visible in neurons of untreated mouse in some brain areas previously shown in the rat to exhibit CCK mRNA, but no clear perikaryal CCK-IR even after colchicine treatment.

Synaptic target selectivity and input of GABAergic basket and bistratified interneurons in the CA1 area of the rat hippocampus

To assess the position of interneurons in the hippocampal network, fast spiking cells were recorded intracellularly in vitro and filled with biocytin. Sixteen non-principal cells were selected on the basis of 1) cell bodies located in the pyramidal layer and in the middle of the slice, 2) extensive labeling of their axons, and 3) a branching pattern of the axon indicating that they were not axo-axonic cells. Examination of their efferent synapses (n = 400) demonstrated that the cells made synapses on cell bodies, dendritic shafts, spines, and axon initial segments (AIS). Statistical analysis of the distribution of different postsynaptic elements, together with published data (n = 288) for 12 similar cells, showed that the interneurons were heterogeneous with regard to the frequency of synapses given to different parts of pyramidal cells. When the cells were grouped according to whether they had less or more than 40% somatic synaptic targets, each population appeared homogeneous. The population (n = 19) innervating a high proportion of somata (53 +/- 10%, SD) corresponds to basket cells. They also form synapses with proximal dendrites (44 +/- 12%) and rarely with AISs and spines. One well-filled basket cell had 8,859 boutons within the slice, covering an area of 0.331 mm2 of pyramidal layer tangentially and containing 7,150 pyramidal cells, 933 (13%) of which were calculated to be innervated, assuming that each pyramidal cell received nine to ten synapses. It was extrapolated that the intact axon probably had about 10,800 boutons innervating 1,140 pyramids. The proportion of innervated pyramidal cells decreased from 28% in the middle to 4% at the edge of the axonal field. The other group of neurons, the bistratified cells (n = 9), showed a preference for dendritic shafts (79 +/- 8%) and spines (17 +/- 8%) as synaptic targets, rarely terminating on somata (4 +/- 8%). Their axonal field was significantly larger (1,250 +/- 180 microns) in the medio-lateral direction than that of basket cells (760 +/- 130 microns). The axon terminals of bistratified cells were smaller than those of basket cells. Furthermore, in constrast to bistratified cells, basket cells had a significant proportion of dendrites in stratum lacunosum-moleculare suggesting a direct entorhinal input. The results define two distinct types of GABAergic neuron innervating pyramidal cells in a spatially segregated manner and predict different functions for the two inputs. The perisomatic termination of basket cells is suited for the synchronization of a subset of pyramidal cells that they select from the population within their axonal field, whereas the termination of bistratified cells in conjunction with Schaffer collateral/commissural terminals may govern the timing of CA3 input and/or voltage-dependent conductances in the dendrites.

Rat hippocampal mossy fibers contain cholecystokinin-like immunoreactivity

BACKGROUND

The possibility that mossy fiber endings in the rat hippocampal formation may contain cholecystokinin (CCK) was reexamined.

METHODS

For this, CCK-immunoreactivity was examined by light and electron microscopy using the avidin-biotin complex method.

RESULTS

At the light level, the topographical distribution of perikarya and processes with CCK-like immunoreactivity (CCK-LI) was similar to that previously described by others. Ultrastructural analysis of the dentate gyrus and CA3 region of the hippocampus revealed that some mossy fiber terminals contained CCK-LI most often affiliated with large, dense-core vesicles (DCV). Quantitative analysis revealed that 4-8% of the mossy terminal profiles examined (n = 350) contained CCK-labeled DCVs, which corresponded to 0.03-0.2 labeled DCVs per 100 microns2 of neuropil.

CONCLUSIONS

The presence of CCK-LI within mossy fibers in the rat suggests that there is less species variability in peptide expression in this pathway than formerly believed.

Connection matrix of the hippocampal formation: I. The dentate gyrus

The hippocampal formation presents a special opportunity for realistic neural modeling since its structure, connectivity, and physiology are better understood than that of other cortical components. A review of the quantitative neuroanatomy of the rodent dentate gyrus (DG) is presented in the context of the development of a computational model of its connectivity. The DG is a three-layered folded sheet of neural tissue. This sheet is represented as a rectangle, having a surface area of 37 mm2 and a septotemporal length of 12 mm. Points, representing cell somata, are distributed in the model rectangle in a roughly uniform fashion. Synaptic connectivity is generated by assigning each presynaptic cell a spatial zone representing its axonal arbor. For each postsynaptic cell, a list of potential presynaptic cells is compiled, based on which arbor zones the given postsynaptic cell falls within. An appropriate number of presynaptic inputs are then selected at random. The principal cells of the DG, the granule cells, are represented in the model, as are non-principal cells, including basket cells, chandelier cells, mossy cells, and GABAergic peptidergic polymorphic (GPP) cells. The neurons of layer II of the entorhinal cortex are included also. The DG receives its main extrinsic input from these cells via the perforant path. The basket cells, chandelier cells, and GPP cells receive perforant path and granule cell input and exert both feedforward and feedback inhibition onto the granule cells. Mossy cells receive converging input from granule cells and send their output back primarily to distant septotemporal levels, where they contact both granule cells and non-principal cells. To permit numerical simulations, the model must be scaled down while preserving its anatomical structure. A variety of methods for doing this exist. Hippocampal allometry provides valuable clues in this regard.

Localization of cholecystokinin binding sites in the adult and developing Brazilian opossum brain

Cholecystokinin (CCK) is now recognized as one of the most abundant peptides in the mammalian central nervous system. We have previously used immunohistochemistry to localize CCK in the adult and developing Brazilian opossum brain. However, little is known about the distribution of CCK binding sites in the developing mammalian brain. Therefore, to further our knowledge of the sites of action for CCK during development, we initiated a series of studies to localize CCK binding sites in the adult and developing Brazilian opossum. This species was chosen because pups are born in a fetus-like state. Receptor autoradiography was performed on coronally sectioned brains of 1 to 60 day postnatal (PN) animals and adults with 125I-Bolton Hunter-CCK-8 as the radioligand. Binding is evident in the 1PN opossum brainstem and is observed in the developing forebrain by 5PN. Region-specific binding increases during development, and binding in the 35PN brain resembles the adult pattern. Binding is evident prior to the detection of CCK-like immunoreactivity in many areas. The facial motor nucleus is identifiable and exhibits high levels of binding in Brazilian opossum pups of 10 to 35 days of age. However, binding is undetectable in the facial motor nucleus of 45 and 60PN pups. In general, the binding patterns for CCK in the adult opossum resemble those of other mammals and likely mediate similar physiological functions. However, some cholecystokininergic pathways appear to be unique to neonatal mammals.

Cholecystokinin-, enkephalin-, and substance P-like immunoreactivity in the dentate area, hippocampus, and subiculum of the domestic pig

The distribution of cholecystokinin-like, enkephalin-like, and substance P-like immunoreactivities is described in the dentate area, hippocampus, and subiculum of the domestic pig (Sus scrofa domesticus) as a baseline for future experimental studies. The distributions in the pig are compared with previous observations in other species. Cholecystokinin-like immunoreactive nerve cell bodies were intensely stained and present in large numbers in all subfields studied. Cholecystokinin-like immunoreactive terminals appeared as stained puncta, whereas fibers were only rarely encountered. The puncta were mainly seen in the dentate molecular layer and dentate granule cell layer, the pyramidal cell layer of the hippocampal regio inferior, stratum moleculare of the hippocampal regio superior, and in the subiculum. Enkephalin-like immunoreactive nerve cell bodies were faintly stained and generally present in very small numbers, except for some pyramidal cells in the subicular cell layer. Enkephalin-like immunoreactive fibers were few in number, whereas stained puncta appeared with variable densities. Puncta of particularly high densities were found in the dentate molecular layer, whereas they appeared of moderate density in the dentate hilus, stratum moleculare of the hippocampal regio superior, and in the subiculum. Substance P-like immunoreactive nerve cell bodies were few and very faintly stained. They primarily occurred in the dentate hilus, stratum oriens of the hippocampus, and in the subicular cell layer. Stained fibers were few in number, whereas stained puncta were present in abundant numbers corresponding to the mossy fiber projection in the dentate hilus and the layer of mossy fibers of the hippocampal regio inferior, and in moderate numbers in stratum moleculare of the hippocampal regio superior and in the subiculum. For all three neuropeptides there were consistent and very characteristic variations in the distribution of immunoreactivity along the septotemporal axis of the hippocampus. When viewed in a comparative perspective the distribution of enkephalin-like and substance P-like terminals in the domestic pig displayed striking differences from the basic pattern observed in other species. This contrasted with the distribution of cholecystokinin-like neurons and terminals, which resembled more closely these species.

Differential release of amino acids, neuropeptides, and catecholamines from isolated nerve terminals

We have investigated transmitter release from small and large dense-core vesicles in nerve terminals isolated from guinea pig hippocampus. Small vesicles are found in clusters near the active zone, and large dense-core vesicles are located at ectopic sites. The abilities of Ca2+ channel activation and uniform elevation of Ca2+ concentration (with ionophores) to evoke secretion of representative amino acids, catecholamines, and neuropeptides were compared. For a given increase in Ca2+ concentration, ionophore was less effective than Ca2+ channel activation in releasing amino acids, but not in releasing cholecystokinin-8. Titration of the average Ca2+ concentration showed that the Ca2+ affinity for cholecystokinin-8 secretion was higher than that for amino acids. Catecholamine release showed intermediate behavior. It is concluded that neuropeptide release is triggered by small elevations in the Ca2+ concentration in the bulk cytoplasm, whereas secretion of amino acids requires higher elevations, as produced in the vicinity of Ca2+ channels.

Distribution of cells containing mRNA encoding cholecystokinin in the rat central nervous system

The distribution of cells containing mRNA encoding cholecystokinin was studied in the rat central nervous system by in situ hybridization histochemistry. Cholecystokinin mRNA containing neurons were considerably more numerous than the cholecystokinin-like immunoreactive neurons detected by immunocytochemistry even after colchicine pretreatment and appeared to be heavily, moderately, or lightly labeled. Such neurons were present in the olfactory bulb, olfactory nuclei, layers II-III and V-VI of the cerebral cortex, amygdaloid nuclei, subiculum, hippocampus, claustrum, endopiriform nucleus, several hypothalamic nuclei, most of the thalamic nuclei, ventral tegmental area, substantia nigra, interfascicularis nucleus, linearis rostralis, central gray, Edinger-Westphal nucleus, superior and inferior colliculi, parabrachial nucleus, reticular formation, raphe nuclei, and spinal trigeminal nucleus. This distribution partly confirmed and partly extended the previous immunohistochemical descriptions. Several brain areas such as the thalamus and the colliculi contain cholecystokinin mRNA but are devoid of perikarya exhibiting cholecystokinin-like immunoreactivity. The cerebral cortex and the hippocampus present a far higher density of cholecystokinin mRNA containing cells, including pyramidal neurons, than of perikarya containing cholecystokinin-like immunoreactivity. These results suggest that cholecystokinin or cholecystokinin-related peptides could have a functional role in numerous cerebral pathways including long projections such as cortical or thalamic projections.

Distribution of cholecystokinin-like-immunoreactive neurons in the guinea pig forebrain

The distribution of cholecystokinin (CCK)-immunoreactive nerve fibers and cell bodies was studied in the forebrain of control and colchicine-treated guinea pigs by using an antiserum directed against the carboxyterminus of CCK octapeptide (CCK-8) in the indirect immunoperoxidase technique. Virtually all forebrain areas examined contained immunoreactive nerve fibers. A dense innervation was visualized in; neocortical layers II-III, piriform cortex, the medial amygdala, the medial preoptic area, a circumventricular organ-like structure located at the top of the third ventricle in the preoptic area, the subfornical organ, the posterior bed nucleus of the stria terminalis, the posterior globus pallidus (containing labeled woolly fiber-like profiles), the ventromedial hypothalamus, the median eminence, and the premammillary nucleus. A moderately dense innervation was visualized elsewhere excepted in the septum and thalamus where labeled axons were comparatively few. Immunoreactive perikarya were abundant in: neocortex (especially layers II-III), piriform cortex, amygdala, the median preoptic nucleus, the bed nucleus of the stria terminalis, the hypothalamic paraventricular (parvicellular part), arcuate, and dorsomedial (pars compacta) nuclei, the dorsal and perifornical hypothalamic areas, and throughout the thalamus. Areas also containing a moderate number of labeled cell bodies were the medial preoptic area, the globus pallidus, the caudate-putamen, and the periventromedial area in the hypothalamus. Immunostained perikarya were absent or only occasionally observed in the septum, the suprachiasmatic nucleus, the magnocellular hypothalamoneurohypophyseal nuclei, and the ventral mesencephalon. In the adenohypophysis, corticomelanotrophs were labeled in both males and females, and thyrotrophs were labeled in females only. This distribution pattern of CCK-8 immunoreactivity is compared to those previously recorded in other mammals. This shows that very few features are peculiar to the the guinea pig. It is discussed whether some interspecific differences in immunostaining are real rather than methodological.

Immunohistochemical localization of cholecystokinin in the medial preoptic area and anterior hypothalamus of the Brazilian gray short-tailed opossum: a sex difference

We have studied the anatomical localization of cholecystokinin-like immunoreactivity (CCK IR) in somata and fibers in the medial preoptic area (MPA) and anterior hypothalamus (AH) of the Brazilian gray short-tailed opossum, (Monodelphis domestica). With the aid of an avidin-biotin, nickel-enhanced, immunohistochemical technique, CCK IR neuronal elements were found within the MPA and AH. A large number of CCK IR cell bodies were located in the MPA of colchicine-treated opossums. The MPA also contained a CCK IR fiber plexus. Quantitative image analysis revealed that the periventricular preoptic area of noncolchicine-treated male opossums had a significantly higher percent of blocked light measurements than that of the noncolchicine-treated females, indicating a higher density of CCK IR neuronal elements in the males. Neuronal fibers and somata containing CCK IR were also found within the periventricular hypothalamic nucleus (Pe), and the suprachiasmatic nucleus (SCh). These results show that CCK IR neuronal elements are found within the MPA and AH of the Brazilian short-tailed opossum. Furthermore, there is a sexually dimorphic distribution of CCK IR elements within the MPA of this small marsupial.

Seizures, neuropeptide regulation, and mRNA expression in the hippocampus

Recent studies have demonstrated that the regulation of neuropeptide expression in forebrain neurons is responsive to external influences including changes in physiological activity. This has been demonstrated most clearly in studies of hippocampus where the synthesis and resting levels of several neuropeptides, localized within well-characterized components of hippocampal circuitry, have been shown to be selectively influenced by seizure activity. In studies described here, we examined the influence of recurrent limbic seizures on the expression of enkephalin, dynorphin, cholecystokinin, and neuropeptide Y (NPY) in rat and mouse hippocampus using immunohistochemical, in situ hybridization and blot hybridization techniques. The data demonstrate that seizures differentially influence the expression of each peptide as a part of a broader cascade of changes in genomic expression within individual hippocampal neurons. In particular, seizures increase preproenkephalin mRNA and enkephalin peptide but decrease dynorphin peptide in the dentate gyrus granule cell/mossy fiber system. Seizure-induced decreases in the concentration of preprodynorphin mRNA in the granule cells have been reported by others. Immunoreactivity for CCK, which is codistributed with the opioid peptides in the mossy fiber system of mouse, is also dramatically reduced in the granule cell axons by seizure. Recurrent seizures induce two temporally distinct changes in NPY expression in hippocampus. First, there is an increase in hybridization to preproNPY mRNA within scattered, probable local circuit neurons in all subfields. This is followed by the seemingly novel appearance of preproNPY mRNA within the dentate gyrus granule cells and pyramidal cells of field CA1. Clues about mechanisms of neuropeptide regulation have come from observations of other, more rapid, transcriptional events induced by seizure. Most notably, our results and those of others demonstrate that seizures increase the expression of messenger RNAs from immediate-early genes (c-fos, c-jun, and NGFI-A) which encode proteins that may mediate neuropeptide gene regulation. In addition, mRNA for nerve growth factor is dramatically increased in the dentate gyrus granule cells by seizure; increased production of this trophic factor might mediate the more delayed changes in genomic expression and growth responses observed to occur in hippocampus and other forebrain areas following seizure activity.

Neuronal localization of cholecystokinin mRNA in the rat brain by using in situ hybridization histochemistry

The distribution of cholecystokinin (CCK) mRNA in the rat brain was determined by means of in situ hybridization histochemistry. Our results demonstrate a widespread distribution of neurons containing CCK mRNA throughout the rat brain. Hybridization-positive neurons were distributed throughout the neocortex, olfactory bulb, claustrum, amygdala, the dentate gyrus and hippocampus proper, and several subnuclei of the thalamus and the hypothalamus. The most abundant and most heavily labeled neurons were found in the endopiriform/piriform cortex, tenia tecta, and the ventral tegmental area. The distribution of neurons positive for CCK mRNA paralleled that of CCK-like immunoreactive neurons. These results detail the distribution of CCK mRNA and clearly identify the existence of CCK-synthesizing neurons in regions such as the paraventricular and supraoptic nuclei of the hypothalamus, where the presence of CCK cell bodies was previously uncertain.

Ultrastructural localization of tyrosine hydroxylase-like immunoreactivity in the rat hippocampal formation

The light and electron microscopic localization of antigenic sites for a polyclonal antiserum directed against the catecholamine synthesizing enzyme, tyrosine hydroxylase (TH), was examined in the hippocampal formation of the rat brain with a double-bridged peroxidase-antiperoxidase method. By light microscopy, the majority of varicose processes with intense TH-like immunoreactivity (LI) were contained in the hilus of the dentate gyrus (DG) and strata radiatum and lacunosum-moleculare of the CA3 region of the hippocampus. Only a few immunoreactive fibers were observed in the molecular and granule cell layers of the DG, in strata oriens and pyramidale of CA3, and in all layers of CA1. Electron microscopy confirmed that these labeled processes were primarily axons and axon terminals. Terminals with TH-LI were 0.4-1.1 micron in diameter and contained many small clear vesicles and from 0 to 3 larger dense-core vesicles. The number and types of associations formed by terminals with TH-LI were remarkably similar in the DG and hippocampus proper despite known differences in intrinsic cells and function. In both regions, the majority of terminals with TH-LI formed junctions on small (distal dendrites (52% of 112 in the DG; 67% of 116 in CA3) and dendritic spines (30% in the DG; 18% in CA3) that were both asymmetric and symmetric. In the DG, axosomatic junctions (2% of 112) were symmetric and occurred exclusively on the perikarya of granule cells, whereas junctions on large (proximal) dendrites were more numerous (16%), exhibited symmetric as well as asymmetric membrane specializations, and were of both granule (molecular layer) and nongranule (hilus) cell origin. In CA3, synaptic contacts on perikarya (5% of 116) and large (proximal) dendrites (10%) of both pyramidal cell and nonpyramidal cell origin were few and all symmetric. The distribution and types of synaptic associations formed by terminals with TH-LI in the CA1 region paralleled that seen in the CA3 region. In both the dentate and hippocampus proper, 10% of the terminals with TH-LI were observed closely apposed to unlabeled terminals that formed asymmetric synapses with dendrites and dendritic spines. In rare instances, TH-immunoreactive terminals were found in close association with the basement membrane of blood vessels, astrocytic processes, or with other unlabeled terminals not forming recognizable junctions. In addition TH-LI was occasionally detected within the cytoplasm of a minority of astrocytes.(ABSTRACT TRUNCATED AT 400 WORDS)

Quantitative autoradiographic localization of cholecystokinin receptors in rat and guinea pig brain using 125I-Bolton-Hunter-CCK8

The autoradiographic localization of receptors for the brain-gut peptide cholecystokinin (CCK) has shown differences in receptor distribution between rat and guinea pig brain. However the full anatomical extent of the differences has not been determined quantitatively. In the present study, 125I-Bolton-Hunter-CCK8 (125I-BH-CCK8) was employed in a comparative quantitative autoradiographic analysis of the distribution of CCK receptors in these two species. The pharmacological profile of 125I-BH-CCK8 binding in guinea pig forebrain sections was comparable to those previously reported for rat and human. Statistically significant differences in receptor binding between rat and guinea pig occurred in olfactory bulb, caudate-putamen, amygdala, several cortical areas, ventromedial hypothalamus, cerebellum, and a number of midbrain and brainstem nuclei. The results of this study confirm the presence of extensive species-specific variation in the distribution of CCK receptors, suggesting possible differences in the physiological roles of this peptide in different mammalian species.

High concentration of cholecystokinin neurons in the newborn human entorhinal cortex

Numerous cholecystokinin (CCK)-immunoreactive cells are detected in the newborn human entorhinal cortex. They are located essentially in layer II and in the superficial part of layer III. Their shape and size indicate that they are interneurons. Most of them are vertically oriented and have beaded processes reaching layer I and the deep part of layer III. The cell type most frequently observed are bipolar cells with an ovoid cell body measuring 8-10 microns across and 15 microns in length. No CCK immunoreactivity is seen in the large stellate and pyramidal cells.

Distribution of immunoreactive cholecystokinin in the human hippocampus

The distribution of cholecystokinin immunoreactive (CCK-IR) nerve cell bodies and processes is reported in the human hippocampus by using the peroxidase-antiperoxidase technique of Sternberger. The CCK-immunoreactivity occurs in three major classes of interneurons: small (10-20 microns) horizontal multipolar neurons of the alveus and stratum oriens; small vertically oriented bipolar or multi-polar neurons in the stratum oriens and stratum pyramidale of Ammon's horn, layers II and III of the subicular system and the entorhinal area; large (20-35 microns) bipolar neurons in the hilus. Each region of the hippocampus is distinct in its CCK-IR nerve fibers content. Those fibers are particularly abundant around pyramidal cells of the CA2 and CA3 subfields of the Ammon's horn and around granular cells suggesting synaptic interaction between the CCK nerve terminals and glutamate neurons of these two regions. No CCK-IR fiber is detected in the fimbria and only a few number of CCK-IR beaded fibers are seen in the angular bundle. These anatomical data suggest that CCK interacts in the functional circuitry of the human hippocampus.

Inhibition of synaptic transmission in the hippocampus by cholecystokinin (CCK) and its antagonism by a CCK analog (CCK27-33)

The actions of CCK-8 and putative CCK-8 antagonists were examined on synaptic transmission in the hippocampal slice preparation. CCK-8 (10(-7) M) caused a reversible depression of postsynaptic responses of the Schaffer collateral-CA1 synapse. CCK-mediated depression was unaffected by proglumide (10(-3) M) but was antagonized by a CCK analog (CCK27-33). The CCK analog alone had an excitatory effect on synaptic transmission. These results suggest that CCK has an inhibitory action on synaptic transmission.

Localization of cholecystokinin in the dentate commissural-associational system of the mouse and rat

Cholecystokinin immunoreactivity (CI) was demonstrated in the inner one third of the molecular layer of area dentata in the rat and 3 strains of mice. This part of the molecular layer coincides with the terminal field of the commissural-associational system (C/A-system). In rats there is also CI in the middle third of this layer where the medial perforant path terminates, but there is no CI in this area in any of the 3 strains of mice. Different selective lesions except those involving the hilus, did not change this staining pattern. Electrolytic lesions of the hilus removed the CI in the terminal field of the C/A-system. Similarly, after kainic acid injections, the CI in the C/A-zone is reduced to a degree that is proportional to the amount of damage of the hilus. In the rat these lesions produced virtually no change in the CI of the medial perforant path terminal zone. The predominant type of cell within the hilus is the mossy cell and the cells of this type contain CI. The mossy cells have both commissural and ipsilateral projections that terminate in the inner one third of the molecular layer. Other cell types within the hilus contain CI, such as basket cells, oviform-like and fusiform-like cells. However, there was no evidence that any of these cells had commissural projections. Apart from the mossy cells there are other cells with commissural projections such as those in regio inferior. However, there was no evidence that any of them contained CI or also gave rise to an associational projection to the inner one third of the molecular layer. Moreover, there was a difference in the distribution of commissurally projecting cells that contained CI in the rat as compared to the mouse brain. This difference is the same as that occurring in the distribution of mossy cells where in the rat cells are found throughout the hilus, with most close to, but never inside the granule cell layer as compared to the mouse where virtually all are at a central part of the hilus. Thus these results are consistent with the hypothesis that all mossy cells contain CI and are the sole source of the C/A-system. After X-ray irradiation of the neonatal rat it is known that only part of the infrapyramidal blade of the granule cell layer is formed.(ABSTRACT TRUNCATED AT 400 WORDS)

Cholinergic neurons in the hippocampus. A combined light- and electron-microscopic immunocytochemical study in the rat

We report here on cholinergic neurons in the rat hippocampal formation that were identified by immunocytochemistry employing a monoclonal antibody against choline acetyltransferase (ChAT), the acetylcholine-synthesizing enzyme. In general, ChAT-immunoreactive cells were rare, but were observed in all layers of the hippocampus proper and fascia dentata with a preponderance in zones adjacent to the hippocampal fissure and in the part of CA1 bordering the subiculum. All immunoreactive cells found were non-pyramidal neurons. They were relatively small with round or ovoid perikarya, which gave rise to thin spine-free dendrites. These hippocampal neurons were very similar to ChAT-immunoreactive cells in the neocortex of the same animals but were quite different from cholinergic neurons in the basal forebrain, medial septal nucleus, and neostriatum, which were larger and more intensely immunostained. Electron-microscopic analysis of ChAT-immunoreactive cells in the hippocampus and fascia dentata revealed synaptic contacts, mainly of the asymmetric type, on cell bodies and smooth proximal dendrites. The nuclei of the immunoreactive cells exhibited deep indentations, which are characteristic for non-pyramidal neurons. Our results provide evidence for an intrinsic source of the hippocampal cholinergic innervation in addition to the well-established septo-hippocampal cholinergic projection.

Cholecystokinin-immunoreactive boutons in synaptic contact with hippocampal pyramidal neurons that project to the nucleus accumbens

Neurons in the hippocampal formation of the rat that project to the medial nucleus accumbens were identified following the retrograde transport of a conjugate of horseradish peroxidase with wheat germ agglutinin. The great majority of such projecting neurons were located in the ventral subiculum and were pyramidal in shape; the pyramidal nature of 25 such retrogradely labelled neurons was established by Golgi impregnation. In material processed to reveal both retrogradely labelled cells and cholecystokinin-immunoreactivity, no immunoreactive projecting neurons were found. However, 48 identified projecting neurons, probably pyramidal, were found to receive input from cholecystokinin-immunoreactive boutons that formed symmetrical synaptic contacts with the soma or proximal dendrites. It is suggested that one function of cholecystokinin-immunoreactive neurons in the hippocampal formation might be to influence the output of the pyramidal neurons that project to the nucleus accumbens. Since this pathway is one of the main links between the limbic system and the basal ganglia, it is conceivable that changes in the cholecystokinin levels in the hippocampus, as found in schizophrenia, might influence behaviour through the pathway connecting the hippocampus with the nucleus accumbens.

A light and electron microscopic analysis of the mossy fibers of the rat dentate gyrus

The axon collaterals of dentate granule cells have been analyzed with the aid of a computerized microscope, following intracellular injections of horseradish peroxidase in hippocampal slice preparations. The axon of each granule cell gives rise to approximately seven primary collaterals; these collaterals usually divide into secondary and tertiary branches, which form an extensive plexus within the hilar region of the dentate gyrus. Individual axon collaterals vary greatly in length, but most have been found to be between 100 and 300 microns long. On average, the summed lengths of the collaterals (exclusive of the parent mossy fiber) are approximately 2,300 microns. Except for an occasional collateral that is given off by a mossy fiber in the proximal part of field CA3 of the hippocampus, the collaterals of the granule cell axons are confined to the hilar region; they are rarely seen in the granule cell layer itself and have never been observed in the molecular layer. In the longitudinal dimension of the dentate gyrus, most of the collaterals are contained within a zone about 400 microns wide. The distribution of the collaterals within the hilar region is correlated with the location of the granule cell body. Those that arise from cells near the tip of the suprapyramidal blade tend to be confined to the region above field CA3; those from cells nearer the crest and from the infrapyramidal blade ramify widely throughout the hilus. Two types of varicosities are present on the collaterals. Numerous small (approximately 2 microns), round varicosities are distributed unevenly along the collaterals; in electron micrographs these varicosities can be seen to make asymmetric synaptic contacts with dendritic shafts. On average, each granule cell collateral plexus has about 160 of these varicosities. The second type of varicosity is irregular in shape and ranges from 2 to 4 microns in diameter; there is usually only one such varicosity per collateral. In all respects except size, these varicosities resemble the expansions found on the parent mossy fibers. Mossy fiber trajectories in the proximal part of field CA3 were studied after extracellular injections of HRP into localized regions of the granule cell layer. Granule cells at different locations around the blade send their mossy fibers to different depths within the pyramidal cell layer in the proximal part of field CA3. However, further distally, mossy fibers from all parts of the granule cell layer contribute to the suprapyramidal bundle that occupies the stratum lucidum.

Non-pyramidal neurons in the guinea pig hippocampus. A combined Golgi-electron microscope study

Morphological characteristics of non-pyramidal neurons in the guinea pig hippocampus (regions CA1 and CA3) were analyzed by a correlated light and electron microscopic approach. Following Golgi impregnation, the cells were first studied under the light microscope and classified according to the location of their cell bodies and the distribution of their dendrites in the different hippocampal layers. Next, the Golgi impregnated non-pyramidal neurons were gold-toned and deimpregnated, allowing an electron microscopic analysis of the identified structures. With regard to cell body location and dendritic pattern, non-pyramidal cells are a rather heterogeneous group of neurons. Their perikarya were found in all hippocampal layers and their dendrites had a less regular orientation when compared to pyramidal neurons and granule cells. Two basic types, i.e., "vertical" and "horizontal" non-pyramidal neurons are described. Many cells were of an intermediate type with dendrites extending in all directions. Non-pyramidal cell dendrites were mostly devoid of spines but exhibited numerous varicosities. Non-pyramidal cell axons could sometimes be seen extending towards the pyramidal cell layer. A surprising uniformity was observed when the impregnated, identified non-pyramidal neurons were studied in the electron microscope. Their perikarya exhibited a well-developed endoplasmic reticulum and indented nuclei. Both the cell bodies and the varicose dendrites were densely covered with synaptic boutons which mainly formed asymmetric synaptic contacts. Only occasionally were symmetric synaptic contacts observed. Non-pyramidal cell dendrites extending into the stratum lucidum of CA3 were found to be contacted by the giant boutons of mossy fiber axons. In addition to synaptic contacts, the dendrites of gold-toned non-pyramidal neurons formed gap junctions with neighboring dendrites. The results are discussed in relation to recent immunocytochemical studies which have shown non-pyramidal neurons in the hippocampus to contain gamma-aminobutyric acid and/or various neuropeptides.

GABAergic neurons containing CCK-8-like and/or VIP-like immunoreactivities in the rat hippocampus and dentate gyrus

The coexistence of cholecystokinin-octapeptide-like (CCK-L) and/or vasoactive-intestinal-polypeptide-like immunoreactive (VIP-LI) materials and glutamate decarboxylase (GAD) was studied in the rat hippocampus and dentate gyrus by means of immunohistochemistry. Consecutive 40-micron-thick sections were incubated in different antisera and those cells which were bisected by the plane of sectioning so as to be included at the paired surfaces of two adjacent sections were identified. The coexistence of the immunoreactivities for these peptides and GAD in the same cell could thus be determined by observing the immunoreactivity of the two halves of the cell, incubated in two different antisera. Almost all of the CCK-LI neurons were also GAD immunoreactive, whereas only about 10% of the GAD-immunoreactive neurons were CCK-LI. The percentages of GAD-immunoreactive neurons which were also immunoreactive for CCK were dependent on the laminar area in which they were found: i.e., 15-20% in the stratum radiatum of the hippocampus, about 10% in the stratum pyramidale, and about 6% in the stratum oriens. In contrast to the CCK-LI neurons, only about 40% of the VIP-LI neurons were identified to be also GAD immunoreactive, which might correspond to only part of the GAD-immunoreactive neurons. Furthermore the coexistence of VIP-LI and CCK-LI materials was recognized in about 10% of the CCK-LI neurons or about 35% of the VIP-LI neurons, indicating that some GABAergic neurons (presumably about 1%) in the rat hippocampus and dentate gyrus may contain both CCK-LI and VIP-LI materials.

Morphology of synapses formed by cholecystokinin-immunoreactive axon terminals in regio superior of rat hippocampus

Immunocytochemical and electron microscopic methods were used to examine neurons in regio superior of rat hippocampus displaying cholecystokinin octapeptide-like immunoreactivity. Cholecystokinin-immunoreactive synaptic terminals and somata are found in all layers of regio superior but are most numerous in stratum pyramidale. The vast majority of terminals form symmetric synaptic contacts onto the somata and proximal dendrites of hippocampal pyramidal cells and onto smaller dendrites which may also arise from pyramidal cells. A very small number of cholecystokinin-immunoreactive terminals form synapses that appear asymmetric and contact dendritic shafts or spines. The somata of some pyramidal cells receive symmetric synapses from cholecystokinin-immunoreactive terminals that are joined by cytoplasmic bridges to form parts of pericellular baskets. These and adjacent pyramidal cell somata are also contacted by terminals that are not immunoreactive for cholecystokinin. No cholecystokinin-positive terminals contacted the initial segments of pyramidal cell axons. Cholecystokinin-immunoreactive cells are found in all layers of regio superior. Their somata receive a few symmetric synapses, most of which are formed by terminals not immunoreactive for cholecystokinin. Their dendrites receive a greater number of both symmetric and asymmetric contacts, some of which are immunoreactive for cholecystokinin. We conclude the following: The localization of cholecystokinin immunoreactivity in synaptic terminals contacting the somata and dendrites of hippocampal pyramidal cells is consistent with the suggestion that cholecystokinin acts as a neurotransmitter at these sites and at sites in other parts of the cerebral cortex. Results from the present and previous studies suggest that cholecystokinin-like immunoreactivity may co-exist with gamma-aminobutyrate in some non-pyramidal neurons of regio superior. Cholecystokinin-immunoreactive terminals arise mainly from non-pyramidal cells intrinsic to the hippocampus, one class of which appears to be a type of basket cell.