The substance P innervation of the rat hippocampal region

Intrinsic organization of the corpus callosum

The corpus callosum-the largest commissural fiber system connecting the two cerebral hemispheres-is considered essential for bilateral sensory integration and higher cognitive functions. Most studies exploring the corpus callosum have examined either the anatomical, physiological, and neurochemical organization of callosal projections or the functional and/or behavioral aspects of the callosal connections after complete/partial callosotomy or callosal lesion. There are no works that address the intrinsic organization of the corpus callosum. We review the existing information on the activities that take place in the commissure in three sections: I) the topographical and neurochemical organization of the intracallosal fibers, II) the role of glia in the corpus callosum, and III) the role of the intracallosal neurons.

Substance P Regulation in Epilepsy

Background:

Epilepsy is a common neurological disease characterized by abnormal temporary discharge of neurons in the central nervous system. In recent years, studies have revealed the localization and changes in the density of neuropeptides, such as substance P (SP) in the pathogenesis of epilepsy. This review is a concise overview of SP and their physiologic and pathologic functions on regulating epilepsy, and the underline mechanisms.

Methods:

We research and collect relative online content for reviewing the effects of SP in Epilepsy.

Results:

The SP/NK-1 receptor system may induce seizures and play an important role in status epilepticus and in experimental animal models of epilepsy. Newest studies show that several mechanisms may explain the excitatory effects of the SP/NK-1 receptor signaling pathway in epilepsy. By binding to the NK-1 receptor, NK-1 receptor antagonists may block the pathophysiological effects of SP, and further studies are needed to confirm the possible anti-epileptic activity of NK-1 receptor antagonists.

Conclusion:

SP plays crucial roles on through binding with NK-1 receptor during epilepsy pathologic processing, and the NK-1 receptor is receiving a great attention as a therapeutic target for treating epilepsy. Thus, the use of NK-1 receptor antagonists for the treatment of epilepsy should be investigated in further studies.

Immunohistochemical characterization of substance P receptor (NK(1)R)-expressing interneurons in the entorhinal cortex

It has been reported that application of substance P (SP) to the medial portion of the entorhinal cortex (EC) induces a powerful antiepileptic effect (Maubach et al. [1998] Neuroscience 83:1047-1062). This effect is presumably mediated via inhibitory interneurons expressing the neurokinin-1 receptor (NK(1)R), but the existence of NK(1)R-expressing inhibitory interneurons in the EC has not yet been reported. The present immunohistochemical study was performed in the rat to examine the existence and distribution of NK(1)R-expressing neurons in the EC as well as any co-expression of other neurotransmitters/neuromodulators known to be associated with inhibitory interneurons: gamma-aminobutyric acid (GABA), parvalbumin (PARV), calretinin (CT), calbindin (CB), somatostatin (SST), and neuropeptide Y (NPY). Our results indicated that NK(1)R-positive neurons were distributed rather sparsely (especially in the medial EC), primarily in layers II, V, and VI. The results of our double-immunohistochemical staining indicated that the vast majority of NK(1)R-expressing neurons also expressed GABA, SST, and NPY. In addition, CT was co-expressed in a weakly stained subgroup of NK(1)R-expressing neurons, and CB was co-expressed very rarely in the lateral EC, but not in the medial EC. In contrast, SP-immunopositive axons with fine varicosities were distributed diffusely throughout all layers of the EC, appearing to radiate from the angular bundle. SP may be released in a paracrine manner to activate a group of NK(1)R-expressing entorhinal neurons that co-express GABA, SST, and NPY, exerting a profound inhibitory influence on synchronized network activity in the EC.

Morphology and synaptic input of substance P receptor-immunoreactive interneurons in control and epileptic human hippocampus

Substance P (SP) is known to be a peptide that facilitates epileptic activity of principal cells in the hippocampus. Paradoxically, in other models, it was found to be protective against seizures by activating substance P receptor (SPR)-expressing interneurons. Thus, these cells appear to play an important role in the generation and regulation of epileptic seizures. The number, distribution, morphological features and input characteristics of SPR-immunoreactive cells were analyzed in surgically removed hippocampi of 28 temporal lobe epileptic patients and eight control hippocampi in order to examine their changes in epileptic tissues. SPR is expressed in a subset of inhibitory cells in the control human hippocampus, they are multipolar interneurons with smooth dendrites, present in all hippocampal subfields. This cell population is considerably different from SPR-positive cells of the rat hippocampus. The CA1 (cornu Ammonis subfield 1) region was chosen for the detailed morphological analysis of the SPR-immunoreactive cells because of its extreme vulnerability in epilepsy. The presence of various neurochemical markers identifies functionally distinct interneuron types, such as those responsible for perisomatic, dendritic or interneuron-selective inhibition. We found considerable colocalization of SPR with calbindin but not with parvalbumin, calretinin, cholecystokinin and somatostatin, therefore we suppose that SPR-positive cells participate mainly in dendritic inhibition. In the non-sclerotic CA1 region they are mainly preserved, whereas their number is decreased in the sclerotic cases. In the epileptic samples their morphology is considerably altered, they possessed more dendritic branches, which often became beaded. Analyses of synaptic coverage revealed that the ratio of symmetric synaptic input of SPR-immunoreactive cells has increased in epileptic samples. Our results suggest that SPR-positive cells are preserved while principal cells are present in the CA1 region, but show reactive changes in epilepsy including intense branching and growth of their dendritic arborization.

Hippocampal fields in the hedgehog tenrec. Their architecture and major intrinsic connections

The Madagascan lesser hedgehog tenrec was investigated to get insight into the areal evolution of the hippocampal formation in mammals with poorly differentiated brains. The hippocampal subdivisions were analyzed using cyto- and chemoarchitectural criteria; long associational and commissural connections were demonstrated with tracer techniques. The hedgehog tenrec shows a well differentiated dentate gyrus, CA3 and CA1. Their major intrinsic connections lie within the band of variations known from other species. The dentate hilar region shows calretinin-positive mossy cells with extensive projections to the molecular layer. The calbindin- and enkephalin-positive granule mossy fibers form a distinct endbulb and do not invade the CA1 as reported in the erinaceous hedgehog. Isolated granule cells with basal dendrites were also noted. A CA2 region is hard to identify architecturally; its presence is suggested due to its contralateral connections. Subicular and perisubicular regions are clearly present along the dorsal aspects of the hemisphere, but we failed to identify them unequivocally along the caudal and ventral tip of the hippocampus. A temporal portion of the subiculum, if present, differs in its chemoarchitecture from its dorsal counterpart. The perisubicular region, located medially adjacent to the dorsal subiculum may be equivalent to the rat's presubiculum; evidence for the presence of a parasubiculum was rather weak.

Patterns of status epilepticus-induced substance P expression during development

Substance P, which modulates synaptic excitability, can be induced by a variety of stimuli. We studied the expression of hippocampal substance P in rats in using lithium-pilocarpine model of status epilepticus during development. Status epilepticus resulted in an age-specific manner of substance P expression that was anatomically distinctive in hippocampal subfields. Maximal induction of substance P immunoreactivity was seen in the CA1 region of the two-week-old rats, and progressively decreased in the three-, four-week-old rats and adults. Meanwhile, the number of substance P-immunoreactive neurons in the CA3 region and dentate granule cell layer was minimal in the two-week-old animals, but approximated the adult level in the three- and four-week-old rats. No substance P-immunoreactive axon terminals were seen in the strata pyramidale and lucidum in the CA3 region of the two-week-old rats, but they were found to progressively increase in the three-, four-week-old rats and adults. To confirm substance P expression after status epilepticus, we studied the expression of preprotachykinin-A mRNA in the hippocampus of the three-week-old rats by in situ hybridization. Two hours following injection of lithium-pilocarpine, preprotachykinin-A mRNA dramatically increased in the granule cells, as well as in the CA3 and CA1 pyramidal cell layers of the hippocampus. To evaluate the relationship between behavioral seizures and substance P induction, we used the NMDA receptor antagonist MK-801. Injection of MK-801 completely blocked lithium-pilocarpine-induced behavioral seizures and SP induction in the two-week-old rats. These results indicate that seizure activity selectively evokes age-dependent and region-selective expression of substance P.

Facilitation of cholinergic transmission by substance P methyl ester in the mouse hippocampal slice preparation

Using sharp microelectrode recording from CA1 pyramidal neurons of the adult mouse hippocampal slice preparation, we studied the modulatory action of the selective neurokinin 1 (NK1) receptor agonist substance P methyl ester (SPME), a peptidase-resistant analogue of the peptide substance P (SP), on cholinergic responses. While SPME (0.1-1 microM) had only slight effects on membrane potential and input resistance of CA1 neurons, it largely and reversibly enhanced the membrane depolarization and oscillatory activity induced by the cholinergic agonist carbachol (CCh; 0.1-100 microM). This effect of SPME was prevented by the selective NK1 receptor antagonist SR 140333 (4 microM). In about half of the tested neurons the action of SPME was preserved in tetrodotoxin (TTX) solution, suggesting that it partly occurred at the level of pyramidal cells. Cholinergic slow excitatory postsynaptic potentials (sEPSPs) were reversibly enhanced by SPME which increased their amplitude and prolonged any associated bursting activity. This action was also blocked by SR 140333. The present results suggest that SPME largely enhances cholinergic activity in the mouse hippocampus, an effect which can help to explain, in this brain area, the recently reported facilitation of seizures by SP.

Substance P is expressed in hippocampal principal neurons during status epilepticus and plays a critical role in the maintenance of status epilepticus

Substance P (SP), a member of the tachykinin family, is widely distributed in the central nervous system and is involved in a variety of physiological processes including cardiovascular function, inflammatory responses, and nociception. We show here that intrahippocampal administration of SP triggers self-sustaining status epilepticus (SSSE) in response to stimulation of the perforant path for periods too brief to have any effect in control rats, and this SSSE generates a pattern of acute hippocampal damage resembling that known to occur in human epilepsy. The SP receptor (SPR) antagonists, spantide II and RP-67,580, block both the initiation of SSSE and SSSE-induced hippocampal damage and terminate established anticonvulsant-resistant SSSE. SSSE results in a rapid and dramatic increase in the expression of preprotachykinin A (a precursor of SP) mRNA and SP in principal neurons in CA3, CA1, and the dentate gyrus as well as in hippocampal mossy fibers. SP also increases glutamate release from hippocampal slices. Enhanced expression of SP during SSSE may modulate hippocampal excitability and contribute to the maintenance of SSSE. Thus, SPR antagonists may constitute a novel category of drugs in antiepileptic therapy.

Modulation by substance P of synaptic transmission in the mouse hippocampal slice

The modulatory action of substance P on synaptic transmission of CA1 neurons was studied using intra- or extracellular recording from the mouse hippocampal slice preparation. Bath-applied substance P (2-4 microM) or the selective NK1 receptor agonist substance P methylester (SPME, 10 nM-5 microM) depressed field potentials (recorded from stratum pyramidale) evoked by focal stimulation of Schaffer collaterals. This effect was apparently mediated via NK1 receptors since it was completely blocked by the selective NK1 antagonist SR 140333. The field potential depression by SPME was significantly reduced in the presence of bicuculline. Intracellular recording from CA1 pyramidal neurons showed that evoked excitatory postsynaptic potentials (EPSPs) and evoked inhibitory postsynaptic potentials (IPSPs) were similarly depressed by SPME, which at the same time increased the frequency of spontaneous GABAergic events and reduced that of spontaneous glutamatergic events. The effects of SPME on spontaneous and evoked IPSPs were prevented by the ionotropic glutamate receptor blocker kynurenic acid. In tetrodotoxin (TTX) solution, no change in either the frequency of spontaneous GABAergic and glutamatergic events or in the amplitude of responses of pyramidal neurons to 4 microM alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) or 10 microM N-methyl-D-aspartate (NMDA) was observed. On the same cells, SPME produced minimal changes in passive membrane properties unable to account for the main effects on synaptic transmission. The present data indicate that SPME exerted its action on CA1 pyramidal neurons via a complex network mechanism, which is hypothesized to involve facilitation of a subset of GABAergic neurons with widely distributed connections to excitatory and inhibitory cells in the CA1 area.

Distribution of substance P-immunoreactive neurons and fibers in the monkey hippocampal formation

Substance P containing neurons was visualized by immunocytochemistry in the monkey hippocampus, subicular complex, and entorhinal cortex. Immunoreactive neurons were found solely in the hilar region of the dentate gyrus, and in strata oriens and pyramidale of Ammon's horn. In the subicular complex, immunoreactive neurons were located in those layers which were close to the alveus, whereas in the entorhinal cortex most of the substance P-positive neurons appeared in the second and third layers above the lamina dissecans. The majority of substance P-containing neurons were large multipolar cells, but small bipolar and multipolar cells also occurred in Ammon's horn, subiculum and entorhinal cortex. Dendrites of immunoreactive cells were smooth and displayed a few small, faintly stained spines which were hard to identify in the light microscopic preparations, but were visible with electron microscopy. Substance P-positive dendrites were exclusively found in the hilar region and never observed in the upper two-thirds of the molecular layer of the dentate gyrus. Moreover, immunoreactive dendrites rarely penetrated the stratum lacunosum-moleculare of Ammon's horn. In the electron microscopic preparations, somal and dendritic features of substance P-positive neurons were similar to those observed for GABAergic local circuit neurons. Axons of the substance P-immunoreactive local circuit neurons were thin and richly arborized in the upper two-thirds of the molecular layer of the dentate gyrus, in the stratum lacunosum-moleculare of Ammon's horn as well as in the subpial layers of the subicular complex and entorhinal cortex. Their terminals formed exclusively symmetric synapses with dendrites and spines. However, substance P-immunoreactive boutons were not found to make symmetric, axosomatic synapses on the granule cells of the dentate gyrus and very few were present on the pyramidal neurons of Ammon's horn, subicular complex, and entorhinal cortex. Hippocampal neurons, which were immunoreactive for substance P, also contained the neuropeptide somatostatin. However, not all of the somatostatin-containing neurons were substance P-immunoreactive. Thus, substance P-positive neurons are a subpopulation of somatostatin immunoreactive, GABAergic neurons. In conclusion, substance P-immunoreactive neurons are ideally suited for feed-back dendritic inhibition which may control the effectiveness of the main excitatory cortical input to the granule cells of the dentate gyrus and pyramidal neurons of the Ammon's horn.

Effects of chronic substance P treatment and intracranial fetal grafts on learning after hippocampal kainic acid lesions

The purpose of this experiment was to investigate whether the neurokinin substance P (SP) can enhance adaptive graft effects on learning and memory functions in animals with lesions of the hippocampus. Adult male Wistar rats received a bilateral kainic acid (KA) lesion of the dorsal hippocampus. One week postlesion, bilateral grafts of fetal hippocampal tissue suspension were applied into the damaged region in half of the animals, whereas the other half received sham transplants (physiological saline). Animals of the control group received a bilateral sham lesion of the hippocampus and sham transplants. One week after transplantation surgery, the rats were tested in the place version of the Morris water maze over a period of 9 weeks. Then they were tested for SP-induced conditioned place preference and on a step-through inhibitory avoidance task. All animals received IP injections of either SP (5 or 50 micrograms/kg) or the SP vehicle (0.5 ml/kg). The treatment with SP or the vehicle was begun 1 week after transplantation and was performed 5 days a week over a period of 10 weeks. During behavioral tests in the water maze and avoidance task, application of the substances was performed 5 h after testing. For the conditioned place preference test, the conditioning trials were performed immediately after drug administration; the test trials were given 24 h later. Chronic administration of 50 micrograms/kg SP, but not 5 micrograms/ kg SP, was found to improve water maze performance in lesioned animals with and without grafts. Unexpectedly, the lesion group with the graft without additional SP treatment was not superior to the lesion group devoid of the graft in this task. The rats without lesions of the hippocampus still showed a conditioned place preference to 50 micrograms/kg SP after 9 weeks of repeated SP applications. In the inhibitory avoidance task, the grafts facilitated retention performance independent of whether SP treatment was given. The morphological analysis of the transplants revealed higher graft volumes and a higher diameter of large pyramidal neurons (> 10 microns) in rats chronically treated with 50 micrograms/kg SP.

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.

Neurotrophic effects of substance P on hippocampal neurons in vitro

The potential neurotrophic effect of substance P-like immunoreactivity present in culture media was assessed in rat embryonic day 18 hippocampal cultures. The neurokinin-1 (substance P) receptor antagonist CP-96345 induced neurotoxicity that was dose dependent and attenuated by addition of substance P or the neurokinin-1 agonist [Sar9,Met(O2)11]-SP. These studies suggest that under some conditions neurokinin-1 receptor stimulation promotes neuronal survival.

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.

Distribution of substance P-like immunoreactivity in guinea pig central nervous system

The distribution of substance P-like immunoreactivity (SP-LI) in the guinea pig brain has been studied by immunohistochemistry and the results compared with the distribution in similar regions in the rat brain. In both species, dense SP-LI staining was found in the median eminence, arcuate hypothalamic nucleus, substantia nigra, dorsal raphe and dorsal tegmental nuclei, nucleus of the solitary tract, substantia gelatinosa of the spinal trigeminal nucleus, and spinal cord. Less dense staining was found in the caudate putamen, globus pallidus, nucleus accumbens, habenula, hypothalamic areas, and central grey. SP-LI cell bodies were found in areas previously described for the rat brain including several hypothalamic areas, limbic areas, central grey, and dorsal raphe and solitary tract nuclei. The major difference between the two species was found in the cortex and hippocampus. The guinea pig cortex contained many more SP-LI cells and fibres, distributed in layers II-VI, than the rat cortex. The guinea pig hippocampus contained marked staining, particularly in the pyramidal cell layer of CA1-3 fields of Ammon's horn and in the granular layer of the dentate gyrus, and SP-LI cells in the hilus of the dentate gyrus, whereas rat hippocampus contained few cells and no regions of dense staining. It is concluded that because the guinea pig brain has an extensive distribution of SP-LI in the cortex and hippocampus it resembles the primate brain more closely than does the rat brain.

Morphological evidence for a substance P projection from medial septum to hippocampus

The medial septal nucleus provides one of the major afferents to the hippocampal formation. The two major types of neurons present in the medial septum are cholinergic and GABAergic, but other types of neurons are also present. A small population of substance P-containing neurons is present along the border between the medial and lateral septum, but it is unclear whether these project to the hippocampus. The present study, by employing both anterograde and retrograde tracing techniques, combined with immunocytochemistry for substance P, provides direct morphological evidence for a substance P projection from the lateral region of medial septum to a portion of CA2/3a, which is restricted to the mid-septotemporal portion of the hippocampus.

Distribution of acetylcholinesterase in the hippocampal region of the mouse: II. Subiculum and hippocampus

The distribution of acetylcholinesterase (AChE) was examined in the subiculum and hippocampus of the adult mouse (Mus musculus domesticus). A distinctly stratified AChE pattern was observed in both areas and was compared in detail with cytoarchitectural fields and layers. In the subiculum, the lateral plexiform layer was lightly stained superficially and moderately stained at depth, where it abutted the lateral, moderately stained cell layer. Medially, a moderately stained deep plexiform layer separated the darkly stained superficial plexiform layer from the equally AChE-intense cell layer. At depth, the subicular cell layer was delimited by a band of very high AChE activity. In regio superior of the hippocampus, AChE-intense bands delimited the moderately stained strata moleculare, radiatum, and oriens toward the subjacent layers. In the stratum pyramidale, precipitate insinuated between the cell bodies gave a dark appearance to the deep part of the layer. The homologous strata of regio inferior appeared darker, but the relative staining intensities corresponded largely to those in regio superior. AChE activity in the layer of mossy fibers was almost absent septally but increased gradually to very high levels temporally. The AChE staining pattern, in conjunction with cytochemical and morphological evidence, strongly suggests a division of the pyramidal cell layer of the mouse and rat into superficial and deep substrata and discourages the definition of a prosubiculum in rodents. A comparative analysis of the AChE pattern reveals that: 1) in the subiculum, differences between species are observed within a generalized pattern of medial darkly staining and lateral lightly staining portions; 2) in the hippocampus, a conservation of the AChE pattern is seen in strata associated with intrinsic hippocampal connection; while 3) numerous interspecific differences are found in the stratum moleculare.

Distribution of acetylcholinesterase in the hippocampal region of the mouse: I. Entorhinal area, parasubiculum, retrosplenial area, and presubiculum

The distribution of acetylcholinesterase (AChE) was examined in the multilayered posterior part of the hippocampal region of the adult mouse (Mus musculus domesticus), namely, the entorhinal area, the parasubiculum, the presubiculum, and those parts of the retrosplenial cortex that extend into the posterior hippocampal region (area retrosplenialis 29d and 29e). A modification of the Koelle copper thiocholine method was employed for the histochemical demonstration of AChE. The AChE staining resulted in a distinctly stratified pattern, which has been compared in detail with the fields and layers defined by cyto- and fibro-architecture. Most of the enzyme activity was located in the neuropil, but both moderately and intensely stained nerve cell bodies were observed too. In the entorhinal area two main subfields were identified, which have been designated pars medialis and pars lateralis. In pars medialis, the superficial two thirds of layer I, the interstices between the stellate cell bodies in layer II, and layers IV and VI showed moderate to high content of AChE, whereas layer V and, especially, layer III were poor in enzyme activity. A particular feature was the occurrence of cone-shaped, darkly stained areas within layer II and, occasionally, the deep part of layer I. The staining of pars laterais differed in several respects from that of pars medialis, the most prominent feature being a less conspicuous stratification. In addition, intensely stained somata occurred more frequently than in pars medialis, although they still constituted only a very small minority of the total number of nerve cell bodies. In the parasubiculum, a clear cytoarchitectural subdivision into a posterolateral parasubiculum a and an anteromedial parasubiculum b was observed. These subfields showed, however, only minor differences in AChE staining. Thus, in both subfields, layers I and IV stained intensely, whereas layers II and III showed moderate to intense staining. Layers V and VI did not differ in appearance from the corresponding layers of the entorhinal area. The retrosplenial areas 29d and 29e appeared very light in the AChE pattern, area 29e being the better stained. The presubiculum was very rich in AChE, with layers, I, III and IV being particularly intensely stained. The small nerve cell bodies of layer II were unstained, whereas the intervening neuropil was intensely stained. The distribution of AChE in the mouse was compared with that in the rat, guinea pig, and rabbit, described previously. The staining pattern is largely similar in all four species, but striking species-specific differences do exist.(ABSTRACT TRUNCATED AT 400 WORDS)

Neurochemical anatomy of fetal hippocampus transplanted into large lesion cavities made in the adult rat brain

The purpose of the present study was to determine whether neurochemicals normally found within neuron somata, fibers, and terminals of the hippocampal formation would also be present in transplanted hippocampal tissue that had developed in lesion cavities made in adult rat brains by aspiration of the hippocampus and overlying dorsolateral neocortex. Embryonic Day 15 or 16 rat brian tissue containing hippocampus with some medial pallial anlage was transplanted into the site of hippocampal aspiration lesions in adult male rats. One hundred ten to one hundred thirty-five days later the brains of these rats were sectioned and processed using the avidin-biotin-horseradish peroxidase immunocytochemical procedure to visualize choline acetyltransferase, met-enkephalin (MENK), neurotensin (NT), somatostatin, substance P, tyrosine hydroxylase (TH), or vasoactive intestinal polypeptide. Sections from two brains were stained using the thiocholine technique for visualization of acetylcholinesterase. All of these substances were found within cell bodies and/or fibers in the transplants. However, several abnormalities were noted. In addition to TH-immunoreactive fibers, TH-immunoreactive cell bodies were found in the transplants. Since TH is not expressed in mature hippocampal or cortical neurons this suggests that mechanisms for suppression of manufacture of this enzyme are lacking or inhibited in the transplants. Further, although all of the peptides were present either in fibers or in both cell bodies and fibers, the density of staining for NT and MENK was less than would be expected for normal hippocampus, and none of the cell bodies or fibers reacting for the peptides exhibited any apparent organization resembling that normally observed in hippocampus or cortex. However, some histological organization was present and the cholinergic markers were associated with this organization. These data suggest that some tropic and/or trophic factor such as nerve growth factor is present in the transplants to guide cholinergic innervation.

Substance P-like immunoreactivity in human prenatal hippocampal formation

Presence and localization of substance P-like immunoreactive neuronal structures in human hippocampal formation during prenatal stages of ontogenesis are reported. In fetuses at 16 and 17 weeks of gestation immunoreactivity is very scarce and represented only by sporadic fibres in Ammon's horn and the entorhinal area. In specimens at 25 and 26 weeks of gestation, more or less intensely labelled perikarya of different morphology are easily detectable in deep layers of Ammon's horn and the hilus of fascia dentata. Immunoreactive beaded fibres are also present at this stage. The possibility of the existence of a substance P-containing extrinsic projection to Ammon's horn is pointed out.

The distribution of substance P in the cerebral cortex and hippocampal formation: an immunohistochemical study in the monkey and rat

The distribution of substance P-containing fibers in the cerebral cortex and the hippocampal formation of the Japanese monkey (Macaca fuscata fuscata) was studied by immunohistochemistry using a monoclonal antibody raised against substance P. The results were compared with the distribution in homologous regions of the rat brain. Substance P-containing fibers and cell bodies were observed in all regions of the cerebral cortex. In deep layers of the neocortex (IV-VI), substance P-immunoreactive fibers formed arrays that ran perpendicular to the surface. These immunoreactive fibers tended to branch as they approached the cortical surface in layers II and III, at which point they were oriented in many directions. The molecular layer (I) of the monkey neocortex contained many granular, substance P-immunoreactive structures, resembling terminal boutons. In contrast to the monkey, rat cortical areas contained substantially fewer substance P-containing fibers. The immunoreactive profiles, mostly fine dot-like structures, were seen uniformly in layers II and IV of the rat neocortex, although in the medial prefrontal cortex many thick, varicose fibers were also observed. Substance P-containing fibers were seen throughout the hippocampal formation of the monkey, including the subiculum and the parahippocampal regions. The regional distribution of immunoreactive fibers was most dense in the molecular layers of dentate gyrus, in the stratum moleculare of the CA1 region, and in the stratum pyramidalis of the CA2 region. In the rat, the hippocampus and dentate gyrus contained fewer immunoreactive fibers. Moderate densities were observed in the rat subiculum and entorhinal cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide Y-containing neurons in the human infant hippocampus

Using immunohistochemistry, high concentrations and widespread distribution of neuropeptide Y-immunoreactive (NPY-IR) neurons were found and examined in each region of the hippocampal formation from birth to 42 years. NPY interneurons are particularly numerous in the stratum oriens of the CA1 subfield, in the deep layers of the subicular complex and entorhinal cortex. They are multipolar round, ovoid or triangular or bipolar and fusiform. There is a dense network of NPY-IR nerve fibers in the subicular complex and the entorhinal cortex. In addition, numerous NPY-IR nerve cell bodies and fibers are observed in the angular bundle and the adjacent white matter and this contrasts with the absence of NPY immunoreactivity in the fiber tracts of the alveus. These NPY-IR neurons which correspond to the interstitial neurons of the white matter, have the morphology and the size of the interneurons detected in the cortex. During the postnatal brain growth spurt which corresponds to the phase of rapid myelination, there is no decline in total number of NPY-IR neurons but there is a decrease in density. They have been spread apart by the growth of the rest of the tissue. So in humans, the total number of NPY nerve cell bodies in the hippocampal system, firmly established at birth, is not modified during consequent brain growth which continues until ages 3-4 years and stays stable at least until age 42 years.

The supramammillary region of the cat sends substance P-like immunoreactive axons to the hippocampal formation and the entorhinal cortex

A combined method of the tracing of WGA-HRP (wheat germ agglutinin-conjugated horseradish peroxidase) and the immunohistochemistry of substance P (SP) showed that many SP-like immunoreactive neurons in the supramammillary nucleus of cat hypothalamus sent their axons to the hippocampal formation. SP-like immunoreactive axons in the hippocampal formation and entorhinal cortex were markedly reduced in number ipsilaterally after placing an electrothermic lesion in the supramammillary region of the hypothalamus.

Intrinsic connections of the retrohippocampal region in the rat brain: III. The lateral entorhinal area

This paper describes the retrohippocampal projections of individual layers of the lateral entorhinal area as studied by the method of anterograde transport of the lectin Phaseolus vulgaris leucoagglutinin (PHA-L) in the rat. As in the medial entorhinal area (EA), (Köhler, '86a) PHA-L injections restricted to individual layers of the lateral EA resulted in labeling of sparse projections to the subicular complex (e.g., subiculum, pre- and parasubiculum), whereas projections to the perirhinal area and piriform cortex were prominent. All PHA-L injections resulted in the labeling of axons projecting longitudinally within the entorhinal area, in both dorsal and ventral directions, albeit the ventral projections were the most prominent ones. PHA-L injections into layers 2a and 2b resulted in labeling of axons that could be followed into layers 2a, 2b, and layer 1 on both sides of the injection site. Whereas numerous axons appeared to terminate in layer 2, most fibers ascended into layer 1, where they ran in a medial direction, passing the medial EA, around the parasubiculum to the presubiculum. Numerous axons were found to take a lateral route running past the lateral aspect of the lateral EA to the piriform cortex. The axons running medial in layer 2 did not enter the medial EA. After PHA-L injections into layer 3, a large number of axons left the labeled cells on both sides of the injection site, in addition to massive projections that ascended into layers 2b, 2a and 1, just above the injection. Few axons entered layers 2-6 of the medial EA, but numerous axons innervated layer 1, where they were found to run in the outer half of this layer. The axons running in a medial direction reached layer 1 of the presubiculum, whereas the laterally oriented ones innervated the molecular layer of the piriform cortex. PHA-L injections into layer 4 resulted in massive labeling of projections to all superficially located layers. Layers 1, and 2b through 5 were innervated lateral to, and layer 4 medial to, the injection site. After a PHA-L injection into layer 5, ascending projections were found innervating layers 1 through 4. The terminal fields were found to be particularly dense in the deep parts of layer 3 and in layer 1. This projection expanded laterally, but few projections reached into the medial sector of the lateral EA or into the medial EA.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of substance K-like and substance P-like fibers and cells in the rat hippocampus

Substance P (SP) and substance K (SK) are structurally related peptides which are both encoded in the preprotachykinin A gene. The distribution of SP- and SK-like fibers and cell bodies in the rat hippocampus were studied by immunohistochemistry. The distribution of SK-like fibers was similar to that of SP-like fibers but there were few SK-like fibers. Fibers for both peptides were prominent in the dorsal and ventral subiculum and at the junction of CA2 and CA3. SP- and SK-like cell bodies were noted in the subiculum and in the stratum oriens of CA1 and CA2. SP- and SK-like cells were also noted in the ventral dentate gyrus but only SP-like cells were found in the dorsal dentate gyrus.

Somatostatin immunoreactive neurons in the human hippocampus and cortex shown by immunogold/silver intensification on vibratome sections: coexistence with neuropeptide Y neurons, and effects in Alzheimer-type dementia

The distribution of somatostatinlike immunoreactivity was studied in the hippocampal formation, retrohippocampal region, and temporal cortex in the human brain. Tissues from surgical biopsy and postmortem cases were used, and the immunogold/silver method on vibratome sections was introduced for routine applications in conjunction with primary antisera that recognise somatostatin-14 or somatostatin-28. Somatostatin-28 antisera readily stained numerous neurons, dendrites, and extensive axonal networks throughout the hippocampus and neighbouring cortex. Liquid phase absorption provided controls for specificity. The most prominent accumulations of somatostatin immunoreactive neurons and axons occurred in the hilus of the area dentata, in CA1, and in the entorhinal and perirhinal cortices. Axonal plexuses occurred throughout the hippocampal subfields but were particularly dense in those regions rich in somatostatin neurons. The distribution of somatostatin immunoreactive neurons and fibers parallels the distribution of neuropeptide Y (NPY) neurons and fibers in the hippocampus and cerebral cortex to a remarkable extent. Double labelling experiments with antisera against neuropeptide Y and somatostatin indicate a considerable frequency of coexistence of the two peptides in single neurons, particularly in large multipolar cortical neurons and also in the small bipolar white matter neurons. Regional variations exist in the amounts of coexistence found in the hippocampal subfields; somatostatin-NPY coexistence is particularly high in the hilus of the area dentata, the subicular complex, and the deep layers of the entorhinal and perirhinal cortices. In the hippocampi and temporal cortices in cases of Alzheimer-type dementia compared to those of age-matched control brains, there is a significant to severe loss of somatostatin immunoreactive neurons and axons. This loss is most severe in those regions with the highest indices of neurofibrillary tangles and neuritic plaques-the hilus of the area dentata, CA1, and the entorhinal and perirhinal cortices. Surviving somatostatin neurons are distorted with short dendrites and truncated axons. Neuritic plaques identified on double label experiments with thioflavin include somatostatin axons but not neurons.

Distribution of [3H]cholecystokinin octapeptide binding sites in the hippocampal region of the rat brain as shown by in vitro receptor autoradiography

The distribution of binding sites for the neuropeptide cholecystokinin octapeptide in the rat hippocampal region was studied by using quantitative in vitro receptor autoradiography. Biochemical analysis of [3H]cholecystokinin octapeptide binding to tissue sections of the hippocampal region showed it to be of high affinity, to be saturable and approximately 50% specific at saturating concentrations. The binding of [3H]cholecystokinin octapeptide to hippocampal sections was dose-dependently blocked by cholecystokinin octapeptide, cholecystokinin and by pentagastrin. The autoradiographic analysis showed high densities of [3H]cholecystokinin octapeptide binding sites in the hilus of the area dentata, the outer three layers of the retrosplenial area and the presubiculum, layer 3 of the medial, but not the lateral, entorhinal area and the deep and superficial parts of layer 1 and 2, respectively of both the medial and the lateral entorhinal area. Medium binding densities were found in the parasubiculum and remaining layers of the entorhinal area and low densities occurred in the subiculum and in all subfields of Ammon's horn. The angular bundle and fornix-fimbria lacked specific [3H] cholecystokinin octapeptide binding sites. A very similar pattern of binding densities was found for [3H]pentagastrin. Comparisons of the cholecystokinin octapeptide receptor distribution with the cholecystokinin octapeptide innervation of the hippocampal region suggest that there exists a relatively good concordance in some hippocampal subfields such as the presubiculum and the entorhinal area between binding sites for [3H]cholecystokinin octapeptide and cholecystokinin-immunoreactive afferent input.

Distribution of neurons and axons immunoreactive with antisera against neuropeptide Y in the normal human hippocampus

The detailed distribution of neuropeptide tyrosine (neuropeptide Y; NPY) immunoreactive neurons and fibers is given for the normal human hippocampus. These neuronal elements are detected by a polyclonal antibody raised against the unconjugated peptide and controls were obtained by using liquid phase absorption immunocytochemistry. The description covers the distribution in the area dentata, the hippocampal subfields CA3 and CA1, the subicular complex, and the entorhinal area. Each region is distinct in its NPY content. In general, the hippocampal NPY immunoreactive neurons fall into distinct classes--large hilar neurons; cortical small bipolar or bitufted neurons; medium-sized multipolar neurons in the deep cortical layers; and finally the distinct, small bipolar NPY neurons of the white matter bundles. None of the NPY neurons are pyramidal; many are likely to be local circuit neurons, but some appear to have extrinsic connections. The NPY immunoreactive axonal innervation is dense throughout the hippocampus but shows distinct regional differences in the hippocampal subdivisions. The area dentata has hilar NPY immunoreactive neurons and radial varicose fibers scattered throughout without a clear laminar preference. Subfield CA3 is comparatively the weakest NPY-containing region and contrasts with CA1, which is well endowed with reactive neurons and a rich and unusual axonal innervation, with distinct laminar axonal specializations. The subicular complex is well endowed with cells and fibers and the parasubiculum consistently displays unusually heavy NPY innervation. The entorhinal area exhibits a rich cortical distribution pattern, like that previously described for the human cerebral cortex (Chan-Palay et al; J. Comp. Neurol. 238:382-390, '85a,b). The fimbria, alveus, and angular bundle have NPY neurons embedded within the white matter. Like the NPY immunoreactive innervation of the hippocampal regions of laboratory animals, the human NPY innervation seems to follow a common fundamental pattern with respect to cell locations, cell morphology, and axonal innervation. The difference, however, is the greater complexity and profusion of the NPY-immunoreactive axonal plexuses in the human hippocampus. This rich peptide network within the hippocampus with likely extrahippocampal interconnections raises questions concerning coexistence with other neuroactive substances, the functions of such substantial networks, and how they are altered in human neurological disease.

Intrinsic connections of the retrohippocampal region in the rat brain. II. The medial entorhinal area

The present study describes the efferent projections and terminal distributions within the retrohippocampal region of individual layers of the rat medial entorhinal area (MEA) as studied by the methods of anterograde transport of the lectin Phaseolus vulgaris leucoagglutinin (PHA-L) and retrograde transport of the fluorescent dye Fast Blue (FB). Analysis of the PHA-L injections that were relatively well restricted to single layers of the MEA reveals very sparse projections to the parasubiculum, presubiculum, and subiculum, while numerous projections within the MEA are found. The course and the termination of the intra-entorhinal projections differ depending upon the particular layer under study, and marked differences are found between the deep and the superficial layers in terms of the divergence of their respective projections. However, the general intra-entorhinal orientation of these projections is essentially the same for all layers: longitudinal with a slightly oblique course, such that at ventral levels the center of a particular terminal field is always located lateral to the center of the respective PHA-L injection. PHA-L injections into layer II label axons running horizontally within this layer as well as within the deep part of layer I, and PHA-L injections into the medial sector of layer II reveal horizontal projections that innervate most of the second layer. The horizontal projections of layer III are more restricted than those of layer II but both layer II and III have prominent longitudinal projections directed ventrally. From layers II and III, numerous axons project to the deep layers (IV-VI) probably en route to extra-entorhinal structures, since no major terminal fields were detected in the deep layers. The PHA-L and the FB experiments show that the deep layers (in particular IV and VI) have far more divergent intra-entorhinal projections than have layers II and III. PHA-L injections into layers IV, V, and VI reveal widespread efferent projections to all of the more superficially located layers of the MEA in addition to projections to the lateral EA. The retrograde transport studies show that layers IV and VI are the major sources of these divergent projections and that cells situated throughout the entire medial to lateral width of these layers project to every sector of the retrohippocampal region. Taken together, the findings of the present experiments suggest that (1) all layers of the MEA have longitudinal projections directed primarily toward the ventral (or temporal) part of this cortex, (2) the projections of layers II and III are relatively restricted compared of the deeper layers.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuropeptide Y innervation of the hippocampal region in the rat and monkey brain

Using antibodies to neuropeptide Y (NPY) in combination with immunohistochemical techniques we have studied the distribution of cell bodies and nerve terminals containing NPY immunoreactivity (-i) in the hippocampal region of rats and monkeys (cynomolgus). In colchicine-pretreated rats a large number of NPY-positive cells are present in all areas of the hippocampal region. The NPY-i cells range in size from small (diameter across soma: 10-15 micron) to large (approximately 20 micron). Most of the NPY-i cells are situated in the hilus, in the subgranular zone of the area dentata, and in the stratum oriens of Ammon's horn. A majority of these are polymorphic cells but cells of different morphology are present in these layers as well. These include small spheroid cells and dentate pyramidal basket cells that are distinct from the polymorphic cells in the subgranular zone. The subicular complex (e.g., the subiculum, pre-, and parasubiculum) and the entorhinal area contain fewer NPY-i cells than the rest of the hippocampal region. In the dorsal parts of the pre- and parasubiculum numerous small cells are scattered throughout all layers, while in the entorhinal area the NPY-stained cells are situated primarily in the deep layers (V and VI). In the ventral part of the lateral entorhinal area large multipolar and bitufted cells are found in layers II-VI. In the untreated monkey brain NPY-positive cells are found in the hilus of the area dentata and in the deep (IV through VI) layers of both the medial and lateral entorhinal area. Fewer NPY-stained cells are present in the subicular complex and in the entorhinal area. In the monkey as well as in the rat, NPY-stained cells are present in the angular bundle and in the alveus. A dense network of NPY-i fibers innervates the entire hippocampal region in both the rat and the monkey. The hippocampal NPY-i preterminal processes are present primarily in stratum moleculare of Ammon's horn and in the outer one-third of this layer in the area dentata. The NPY-positive innervation of the dentate molecular layer is far more prominent in the monkey than in the rat brain. Numerous NPY-stained fibers are scattered in other areas as well. In all retrohippocampal structures, and in particular the entorhinal area, the NPY-i fibers form a massive network that innervates all layers to about the same extent, with the exception of the molecular layer, which is more densely innervated than the other layers.