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

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.

Neuroanatomical and psychological considerations in temporal lobe epilepsy

Temporal lobe epilepsy (TLE) is the most common form of focal epilepsy and is associated with a variety of structural and psychological alterations. Recently, there has been renewed interest in using brain tissue resected during epilepsy surgery, in particular 'non-epileptic' brain samples with normal histology that can be found alongside epileptic tissue in the same epileptic patients - with the aim being to study the normal human brain organization using a variety of methods. An important limitation is that different medical characteristics of the patients may modify the brain tissue. Thus, to better determine how 'normal' the resected tissue is, it is fundamental to know certain clinical, anatomical and psychological characteristics of the patients. Unfortunately, this information is frequently not fully available for the patient from which the resected tissue has been obtained - or is not fully appreciated by the neuroscientists analyzing the brain samples, who are not necessarily experts in epilepsy. In order to present the full picture of TLE in a way that would be accessible to multiple communities (e.g., basic researchers in neuroscience, neurologists, neurosurgeons and psychologists), we have reviewed 34 TLE patients, who were selected due to the availability of detailed clinical, anatomical, and psychological information for each of the patients. Our aim was to convey the full complexity of the disorder, its putative anatomical substrates, and the wide range of individual variability, with a view toward: (1) emphasizing the importance of considering critical patient information when using brain samples for basic research and (2) gaining a better understanding of normal and abnormal brain functioning. In agreement with a large number of previous reports, this study (1) reinforces the notion of substantial individual variability among epileptic patients, and (2) highlights the common but overlooked psychopathological alterations that occur even in patients who become "seizure-free" after surgery. The first point is based on pre- and post-surgical comparisons of patients with hippocampal sclerosis and patients with normal-looking hippocampus in neuropsychological evaluations. The second emerges from our extensive battery of personality and projective tests, in a two-way comparison of these two types of patients with regard to pre- and post-surgical performance.

Three-dimensional synaptic organization of the human hippocampal CA1 field

The hippocampal CA1 field integrates a wide variety of subcortical and cortical inputs, but its synaptic organization in humans is still unknown due to the difficulties involved studying the human brain via electron microscope techniques. However, we have shown that the 3D reconstruction method using Focused Ion Beam/Scanning Electron Microscopy (FIB/SEM) can be applied to study in detail the synaptic organization of the human brain obtained from autopsies, yielding excellent results. Using this technology, 24,752 synapses were fully reconstructed in CA1, revealing that most of them were excitatory, targeting dendritic spines and displaying a macular shape, regardless of the layer examined. However, remarkable differences were observed between layers. These data constitute the first extensive description of the synaptic organization of the neuropil of the human CA1 region.

Mu-Opioids Suppress GABAergic Synaptic Transmission onto Orbitofrontal Cortex Pyramidal Neurons with Subregional Selectivity

The orbitofrontal cortex (OFC) plays a critical role in evaluating outcomes in a changing environment. Administering opioids to the OFC can alter the hedonic reaction to food rewards and increase their consumption in a subregion-specific manner. However, it is unknown how mu-opioid signaling influences synaptic transmission in the OFC. Thus, we investigated the cellular actions of mu-opioids within distinct subregions of the OFC. Using in vitro patch-clamp electrophysiology in brain slices containing the OFC, we found that the mu-opioid agonist DAMGO produced a concentration-dependent inhibition of GABAergic synaptic transmission onto medial OFC (mOFC), but not lateral OFC (lOFC) neurons. This effect was mediated by presynaptic mu-opioid receptor activation of local parvalbumin (PV⁺)-expressing interneurons. The DAMGO-induced suppression of inhibition was long lasting and not reversed on washout of DAMGO or by application of the mu-opioid receptor antagonist CTAP, suggesting an inhibitory long-term depression (LTD) induced by an exogenous mu-opioid. We show that LTD at inhibitory synapses is dependent on downstream cAMP/protein kinase A (PKA) signaling, which differs between the mOFC and lOFC. Finally, we demonstrate that endogenous opioid release triggered via moderate physiological stimulation can induce LTD. Together, these results suggest that presynaptic mu-opioid stimulation of local PV⁺ interneurons induces a long-lasting suppression of GABAergic synaptic transmission, which depends on subregional differences in mu-opioid receptor coupling to the downstream cAMP/PKA intracellular cascade. These findings provide mechanistic insight into the opposing functional effects produced by mu-opioids within the OFC.SIGNIFICANCE STATEMENT Considering that both the orbitofrontal cortex (OFC) and the opioid system regulate reward, motivation, and food intake, understanding the role of opioid signaling within the OFC is fundamental for a mechanistic understanding of the sequelae for several psychiatric disorders. This study makes several novel observations. First, mu-opioids induce a long-lasting suppression of inhibitory synaptic transmission onto OFC pyramidal neurons in a regionally selective manner. Second, mu-opioids recruit parvalbumin inputs to suppress inhibitory synaptic transmission in the mOFC. Third, the regional selectivity of mu-opioid action of endogenous opioids is due to the efficacy of mu-opioid receptor coupling to the downstream cAMP/PKA intracellular cascades. These experiments are the first to reveal a cellular mechanism of opioid action within the OFC.

Substance P Activates Ca2+-Permeable Nonselective Cation Channels through a Phosphatidylcholine-Specific Phospholipase C Signaling Pathway in nNOS-Expressing GABAergic Neurons in Visual Cortex

To understand the functions of the neocortex, it is essential to characterize the properties of neurons constituting cortical circuits. Here, we focused on a distinct group of GABAergic neurons that are defined by a specific colocalization of intense labeling for both neuronal nitric oxide synthase (nNOS) and substance P (SP) receptor [neurokinin 1 (NK1) receptors]. We investigated the mechanisms of the SP actions on these neurons in visual cortical slices obtained from young glutamate decarboxylase 67-green fluorescent protein knock-in mice. Bath application of SP induced a nonselective cation current leading to depolarization that was inhibited by the NK1 antagonists in nNOS-immunopositive neurons. Ruthenium red and La(3+), transient receptor potential (TRP) channel blockers, suppressed the SP-induced current. The SP-induced current was mediated by G proteins and suppressed by D609, an inhibitor of phosphatidylcholine-specific phospholipase C (PC-PLC), but not by inhibitors of phosphatidylinositol-specific PLC, adenylate cyclase or Src tyrosine kinases. Ca(2+) imaging experiments under voltage clamp showed that SP induced a rise in intracellular Ca(2+) that was abolished by removal of extracellular Ca(2+) but not by depletion of intracellular Ca(2+) stores. These results suggest that SP regulates nNOS neurons by activating TRP-like Ca(2+)-permeable nonselective cation channels through a PC-PLC-dependent signaling pathway.

Substance P immunoreactive cell reductions in cerebral cortex of Niemann-Pick disease type C mouse

Niemann-Pick disease type C (NPC) is characterized by progressive neurodegeneration and arises from mutations in the NPC1 gene. Cholesterol has received most attention in the pathogenesis of NPC, but normalizing lipid levels in humans or mouse does not prevent neurodegeneration. In NPC mouse, neuronal degeneration in the cerebellum is the most commonly detected change, and thus previous studies have tended to focus on the cerebellum, especially Purkinje cells. Although numerous peptides have been found in the mammalian central nervous system, little data on neurotransmitters in NPC are available, and information on neurotransmitter system abnormalities could explain the complex and characteristic deficits of NPC. Thus, we performed an immunohistochemical study on NPC mouse cortices to compare cell numbers exhibiting vasoactive intestinal polypeptide (VIP), neuropeptide Y (NPY), and substance P (SP) immunoreactivity. In terms of VIP and NPY-immunoreactive (ir) cell numbers in the cerebral cortex, SP-ir cells were significantly reduced by about 90% in NPC (-/-) versus NPC (+/+) mouse, and were also mildly decreased in frontal and parietal NPC (+/-) versus NPC (+/+) mouse cortex. This study demonstrates for the first time, reduced number of SP-ir cells in the NPC mouse cortex.

The distribution of serotonin transporter immunoreactivity in hippocampal formation in monkeys and rats

To elucidate the anatomical distribution of the serotonergic neurotransmitter system, we identified serotonin transporter (5-HTT) in the hippocampus of rats and monkeys by immunohistochemistry. A widespread and heterogeneous distribution of 5-HTT-immunoreactive fine fibers was noted in the rat brain. However, in monkeys, punctuate 5-HTT-immunoreactive deposits and fewer fibers were observed. The species difference in 5-HTT immunohistochemical staining pattern may be caused by differences in localization of 5-HTT between species.

Activation of neurokinin-1 receptors promotes GABA release at synapses in the rat entorhinal cortex

We have previously shown that activation of neurokinin-1 receptors reduces acutely provoked epileptiform activity in rat entorhinal cortex in vitro, and suggested that this may result from an increase in GABA release from inhibitory interneurones. In the present study we have made whole cell patch clamp recordings of spontaneous GABA-mediated inhibitory postsynaptic currents as an indicator of GABA release in slices of rat entorhinal cortex, and determined the effects of neurokinin receptor activation on this release. The neurokinin-1 receptor agonists septide and GR73632 provoked a robust increase in the frequency of GABA-mediated currents, and an increase in mean amplitude. The effects were mimicked by substance P, and blocked by a neurokinin-1 receptor antagonist. High concentrations of neurokinin A had similar effects, which were also blocked by the neurokinin-1 receptor antagonist, but agonists at neurokinin-2 or neurokinin-3 receptors were ineffective. The increases in amplitude and frequency of events provoked by septide were prevented by prior blockade of action potential-dependent release with tetrodotoxin. In current clamp recordings from putative interneurones, GR73632 evoked depolarisation and a prolonged discharge of action potentials. Finally, recordings from pyramidal neurones and oriens-alveus interneurones in CA1 of the hippocampus showed that application of GR73632 caused an increase in frequency and amplitude of GABA-mediated inhibitory postsynaptic currents in the former and persistent firing of action potentials in the latter. The results demonstrate that neurokinin-1 receptor activation promotes the release of GABA at synapses on principal neurones in both entorhinal cortex and hippocampus. The abolition of this effect by tetrodotoxin and the excitatory responses seen in interneurones clearly suggest that the neurokinin-1 receptor is localised on the soma-dendritic domain of the inhibitory neurones. Thus, substance P inputs to inhibitory neurones may have a widespread influence on cortical network excitability and could play a role in epileptogenesis and its control.

Neurokinin-receptor-mediated depolarization of cortical neurons elicits an increase in glutamate release at excitatory synapses

Using whole-cell patch-clamp recordings of spontaneous synaptic activity, we have previously shown that activation of neurokinin-1 (NK1) but not NK3 receptors leads to increased GABA release onto principal cells in the rat entorhinal cortex. In the present study, we examine the effect of activation of these receptors on spontaneous excitatory synaptic responses mediated by glutamate. Both neurokinin B (NKB) and the specific NK3 receptor agonist, senktide, increased the spontaneous release of glutamate, and a similar effect was also seen with substance P (SP) and other NK1 receptor agonists. The increased release induced by either SP or senktide was absent in the presence of tetrodotoxin, demonstrating that it was likely to occur via activation of presynaptic excitatory neurons. Current-clamp recordings confirmed that principal neurons were depolarized by both NK3 and NK1 agonists. However, the response to the former but not the latter persisted in tetrodotoxin, allowing us to conclude that NK3 receptor activation provoked glutamate release via recurrent collaterals between principal neurons, whereas the NK1 receptors may be localized to excitatory interneurons. Finally, the increased release induced by senktide, but not SP, was reduced by an antagonist of group III metabotropic glutamate receptors. Thus, glutamate release from recurrent collaterals is facilitated by a presynaptic group III autoreceptor [Evans, D.I.P., Jones, R.S.G. & Woodhall, G.L. (2000) J. Neurophysiol.,83, 2519-2525], whereas the terminals of neurons responsible for the NK1-receptor induced glutamate release may not bear these receptors. These results have implications for control of activity and epileptogenesis in cortical networks.

Primate anterior cingulate cortex: where motor control, drive and cognition interface

Controversy surrounds the function of the anterior cingulate cortex. Recent discussions about its role in behavioural control have centred on three main issues: its involvement in motor control, its proposed role in cognition and its relationship with the arousal/drive state of the organism. I argue that the overlap of these three domains is key to distinguishing the anterior cingulate cortex from other frontal regions, placing it in a unique position to translate intentions to actions.

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.

The distribution of neuropeptide Y and brain-derived neurotrophic factor immunoreactivity in hippocampal formation of the monkey and rat

The distribution of neuropeptide Y (NPY) and Brain-Derived Neurotrophic Factor (BDNF) in the hippocampal formation of monkey and rat brains was studied immunohistochemically. The NPY-neuronal system is more highly developed in the monkey compared to that in the rat. The distribution of NPY-positive products was coincident with that of abundant BDNF-positive deposits. These observations suggest that the role of BDNF and the interaction of BDNF-NPY may differ between species.

Neurochemical evidence for at least two regional subdivisions within the homing pigeon (Columba livia) caudolateral neostriatum

The distributions of one neurotransmitter, two neurotransmitter-related substances, and five neuropeptides were examined within the homing pigeon caudolateral neostriatum (NCL). All eight neuroactive substances were found within a tyrosine hydroxylase (TH)-dense region that defines the NCL. Overall regional variation in the relative density of these substances suggested at least two neurochemically distinct portions of NCL. Dorsal NCL contained relatively dense staining for TH, choline acetyltransferase, and substance P, whereas vasoactive intestinal polypeptide was more abundant in ventral portions of NCL. Serotonin and cholecystokinin were found to be densest in intermediate portions of NCL. Somatostatin and leucine-enkephalin were homogeneously distributed throughout NCL. The results suggest that NCL may consist of multiple subdivisions. Investigations into the behavioral importance of these regions are necessary to clarify the role of this brain region in avian behavior.

Preprotachykinin-A mRNA expression in the human and monkey brain: An in situ hybridization study

The mRNA expression for preprotachykinin-A (PPT-A) was studied throughout the human and cynomolgus monkey brain to assess the neuroanatomical expression pattern of the PPT-A gene in primates. In situ hybridization showed that the PPT-A mRNA is expressed highly in specific regions of the postmortem human brain, including the striatum, islands of Calleja, hypothalamus (posterior, premammillary, medial mammillary, and ventromedial nuclei), superior and inferior colliculi, periaqueductal gray, and oculomotor nuclear complex. PPT-A mRNA-expressing neurons also were present in the paranigralis (ventral tegmental area) and were scattered in the bed nucleus stria terminalis throughout the sublenticular substantia innominata region, including the diagonal band of Broca and the nucleus basalis of Meynert. In the hippocampus, high PPT-A mRNA expression was localized predominantly to the polymorphic layer of the dentate gyrus; no labeled cells were present in the granular layer. Positively labeled cells also were found scattered in the CA regions as well as in the amygdaloid complex. Neocortical expression of PPT-A mRNA was localized mainly to the deep laminae (layers V/VI), except for the striate cortex (labeling was seen also in superficial layers). The subiculum, thalamus, globus pallidus, ventral pallidum, substantia nigra pars compacta, red nucleus, pontine nuclei, and cerebellum were characterized by very weak to undetectable expression of PPT-A mRNA. An expression pattern was evident in the monkey forebrain similar to that observed in the human, except for the absence of PPT mRNA-expressing cells in the medial mammillary nucleus despite intense expression in supramammillary, lateral mammillary, and premammillary nuclei. Overall, more similarities than differences are apparent between primate species in the expression pattern of the PPT-A gene. J. Comp. Neurol. 411;56-72, 1999.

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.

Effect of substance P on cytokine production by human astrocytic cells and blood mononuclear cells: characterization of novel tachykinin receptor antagonists

Substance P (SP) has been reported to induce inflammatory cytokine production in human neuroglial cells and peripheral lymphoid cells as well. In order to evaluate the potency of novel non-peptide antagonists of the tachykinin receptors as inhibitors of SP-induced cytokines, we used the astrocytoma cell line U373MG and blood mononuclear cells as models of central and peripheral SP-target cells, respectively. In the first part of this study, we showed that SR 140333, an NK1 tachykinin receptor antagonist, was able to inhibit strongly the SP-induced production of interleukin (IL)-6 and IL-8 in the astrocytoma cell line. The antagonistic activity of SR 140333 toward SP-induced cytokine production was specific and could not be attributed to a general anti-cytokine effect, since cytokine release induced by another inflammatory protein such as IL-1beta was not blocked by this compound. In addition, NK2 and NK3 agonist neuropeptides were at least 1000-fold less effective than SP, while SR 48968 and SR 142801 which are selective NK2 and NK3 receptor antagonists, respectively, displayed a 2.5-3 orders of magnitude lower inhibitory potency than SR 140333. All these data indicated that SR 140333 blocked SP-induced cytokine production in U373MG astrocytic cells via a specific NK1 receptor-mediated process. Since SP has also been described to trigger peripheral blood mononuclear cells (PBMNC) or monocytes to release inflammatory cytokines, we attempted, in the second part of this study, to evaluate the potential antagonistic effect of our compounds on these cells. Experiments on human PBMNC from different donors were carried out to determine first their pattern of cytokine production upon SP stimulation. Surprisingly, we noticed that SP at concentrations ranging from 0.1 to 1000 nM was unable to stimulate the release of any inflammatory cytokine tested. This raises the question of the specificity of the reported in vitro effects of SP on cytokine production by human peripheral immune cells.

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.

Substance P-containing hypothalamic afferents to the monkey hippocampus: an immunocytochemical, tracing, and coexistence study

In order to identify the synaptic connections of substance P-containing afferents within the hypothalamo-hippocampal projection of the monkey, we performed a combined light and electron microscopic, immunocytochemical study, made lesions of the fimbriafornix, and employed retrograde tracing using WGA-HRP. Furthermore, coexistence studies for substance P and GAD were performed to identify the putative transmitters of these hypothalamic projection neurons. A plexus of large substance P-immunoreactive terminals was identified in both the innermost portion of the molecular layer and in CA2. Axon terminals in both plexuses established exclusively asymmetric synapses with spines and dendritic shafts. Substance P-immunoreactive boutons were degenerating 5 days after lesioning, and had disappeared 10 days after ipsilateral fimbria-fornix transection. Thus, these terminals were of extrinsic origin. In contrast, immunoreactive fibers in the outer third of the dentate molecular layer remained unaffected by the lesion. Retrograde tracing combined with immunostaining for substance P revealed the parent cell bodies of the extrinsic substance P-containing afferents in the supramammillary nucleus. Colocalization studies employing a consecutive semi-thin sections technique indicate that these large substance P-containing projection neurons lack GABA as an inhibitory transmitter. These results suggest that hypothalamic afferents of the monkey hippocampus contain substance P. Because these afferents lack GABA as an inhibitory transmitter and establish exclusively asymmetric synapses, this projection may excite hippocampal target neurons.

Sprouting of remaining substance P-immunoreactive fibers in the monkey dentate gyrus following denervation from its substance P-containing hypothalamic afferents

This study analyzed the response of intrinsic substance P-immunoreactive fibers in the monkey dentate gyrus to disruption of the supramammillo-hippocampal projection. This projection normally forms a thin plexus of large, substance P-immunoreactive terminals in the innermost portion of the dentate molecular layer and establishes exclusively asymmetric synapses with dendritic shafts and spines of dentate neurons. Conversely, substance P-containing terminals have never been observed in synaptic contact with granule cell bodies. Ten days after ipsilateral fimbria-fornix transection, the prominent band of large immunostained axons in the inner molecular layer of the ipsilateral fascia dentata disappeared. Four and five weeks following transection, however, some small, substance P-containing terminals were observed in the innermost portion of the dentate molecular layer and the granule cell layer. These terminals established exclusively symmetric synapses with the somata and proximal dendritic shafts of granule cells. These results suggest that, following transection of the hypothalamo-hippocampal fiber tract, presumptive intrinsic substance P-containing axons are capable of sprouting into the granule cell layer and the former termination field of the hypothalamic fibers. The symmetric synapses established with granule cell bodies and their proximal dendrites might indicate a shift from an extrinsic excitation to an intrinsic inhibition of granule cells following disruption of substance P-containing hypothalamic afferents.

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.

Substance P release from rat nucleus accumbens and striatum: an in vivo study using antibody microprobes

Antibody-coated microprobes have provided evidence for the release of neuropeptides in localized regions of the cat spinal cord. We have applied this method to study the release of substance P (SP) from different regions of the rat brain. Anti-SP microprobes were inserted (to a depth of 8 mm) through cortex, striatum, and nucleus accumbens of halothane anaesthetised rats and remained in situ for 10 min. Microprobes (4 control and 10 post-treatment, per rat) were then incubated with 125I-SP and an autoradiographic image produced. In the region of the nucleus accumbens immunoreactive (ir) SP was detected during the first 30 min after intraperitoneal injection of d-amphetamine (4 mg/kg, P < 0.05) but not following saline (P > 0.05). During this time, no release of ir SP was seen over areas of the probes that corresponded to the striatum. At later time intervals (1-4 h) after amphetamine, binding of ir SP was detected along the whole length of the microprobes. Release of SP is thought to be due to the action of dopamine on postsynaptic cells containing this peptide. The later spread of the peptide requires further study.

Morphology and distribution of neuropeptide-containing neurons in human cerebral cortex

Biopsies of human cerebral cortex were fixed by immersion and immunostained for the detection of neuropeptides in neuronal cell bodies and axons. Four neuropeptides (neuropeptide Y, somatostatin, , substance P and cholecystokinin) were visualized in a series of adjacent sections. All populations of immunoreactive neurons had a morphology characteristic of interneurons, with variations in dendritic arborizations and laminar distribution. The cholecystokinin-immunoreactive neurons were most numerous in the supragranular layers, whereas neurons containing the other three peptides occurred mainly in infragranular layers, or even in neurons populating the subcortical white matter. Quantitatively, each population of neuropeptide-containing neurons accounted for 1.4-2.5% of the total neuronal population. The distribution of these neurons varied slightly between cytoarchitectonic divisions, with substance P- and somatostatin-immunoreactive neurons dominating in the temporal lobe and cholecystokinin-immunoreactive neurons in the frontal lobe. Neuropeptide Y-immunoreactive neurons dominated in the gray matter of the frontal half of the hemisphere and in the subcortical white matter of the caudal half of the hemisphere. Furthermore, co-existence of neuropeptide Y or substance P immunoreactivity within somatostatin-immunoreactive neurons could be demonstrated using double labeling immunofluorescence techniques. The axonal plexuses immunoreactive for neuropeptide Y, somatostatin, or substance P were distributed in all layers, with a strong predominance of horizontally oriented fibers in layer I, a moderate plexus of randomly oriented fibers in the supra- and infragranular layers, and a slightly weaker innervation of layer IV. Immunoreactive axons formed, in addition, complex terminal arbors, mostly in older subjects, suggesting that they resulted from an as yet undefined aging process. The present study underlines several aspects of the organization of the neuropeptide-containing neurons of the human cerebral cortex, which are of particular interest in the light of the involvement of these neurons in several neurodegenerative diseases.

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.

Substance P-containing pyramidal neurons in the cat somatic sensory cortex

Light and electron microscopic immunocytochemical methods were used to verify the possibility that neocortical pyramidal neurons in the first somatic sensory cortex of cats contain substance P. At the light microscopic level, substance P-positive neurons accounted for about 3% of all cortical neurons, and the vast majority were nonpyramidal cells. However, 10% of substance P-positive neurons had a large conical cell body, a prominent apical dendrite directed toward the pia, and basal dendrites, thus suggesting they are pyramidal neurons. These neurons were in layers III and V. At the electron microscopic level, the majority of immunoreactive axon terminals formed symmetric synapses, but some substance P-positive axon terminals made asymmetric synapses. Labelled dendritic spines were also present. Combined retrograde transport-immunocytochemical experiments were also carried out to study whether substance P-positive neurons are projection neurons. Colloidal gold-labelled wheat germ agglutinin conjugated to enzymatically inactive horseradish peroxidase was injected either in the first somatic sensory cortex or in the dorsal column nuclei. In the somatic sensory cortex contralateral to the injection sites, a few substance P-positive neurons in layers III and V also contained black granules, indicative of retrograde transport. This indicates that some substance P-positive neurons project to cortical and subcortical targets. We have therefore identified a subpopulation of substance P-positive neurons that have most of the features of pyramidal neurons, are the probable source of immunoreactive axon terminals forming asymmetric synapses on dendritic spines, and project to the contralateral somatic sensory cortex and dorsal column nuclei. These characteristics fulfill the criteria required for classifying a cortical neuron as pyramidal.

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 somatostatin-immunoreactive cell bodies and fibers in the neocortex of Macaca fuscata

The distribution of somatostatin-immunoreactive cell bodies and processes was studied in the cerebral cortex of the macaque monkey (Macaca fuscata), by applying an immunohistochemical technique with a monoclonal antibody raised against somatostatin tetradecapeptide. Many somatostatin-immunoreactive cell bodies and processes were observed in all regions of the cerebral cortex, i.e., frontal, parietal, temporal, insular, occipital, and cingulate cortices, and also in the underlying white matter. Three types of somatostatin-containing cell bodies were distinguished in the cerebral cortex. These cell bodies were distributed in layers II to VI of the cortex, and also in the underlying white matter. There were dense deposits of somatostatin-containing granular structure in layers I and II, and many somatostatin-containing processes in layers IV and V. The present observations demonstrate that in the primate neocortex somatostatin 14-containing neuronal systems are as highly developed as other prosomatostatin-derived peptides but differ from the latter systems in terms of cell morphology and fiber distribution.

Ontogeny of substance P-immunoreactive structures in the primate cerebral neocortex

The distribution and the ontogeny of substance P (SP)-immunoreactive structures were investigated in the various cortical areas of macaque monkey cerebrum at embryonic day 120 (E120), embryonic day 140 (E140), newborn (Nb), postnatal day 30, postnatal day 60 (P60) and adult stages, using an immunohistochemical method. SP-immunoreactive cell bodies and fibers were detectable at E120 and the cell number increased until Nb stage. At E140, many immunoreactive cells were present in the upper part of layer V. Some of them seemed to be developing pyramidal cells which ascended their fibers toward layer I. After Nb stage, the number of immunoreactive structures decreased. By P60, the distribution patterns of SP-immunoreactive structures reached the adult level. Between Nb and P60, we occasionally observed structures which were presumably degenerated neurons and fibers. The distribution and developmental ontogeny of immunoreactivities were different among the various cortical areas. In areas OC and FA (von Bonin and Bailey), we observed the high densities of immunoreactive fibers and terminals, in spite of low numbers of cell somatas. While, in the association areas (areas FD, PE, TA and TE), there existed larger numbers of immunoreactive cells at E140 and newborn stages, following the decrease of cell number until P60. Our present study shows the transient increase and the following decrease of the numbers of SP-immunoreactive cells. Since we observed SP-immunoreactive pyramidal cells and degenerating cells during development, the decrease of immunoreactivities may be due to both cell death and change in phenotype.

Immunohistochemical analysis of the visual wulst of the pigeon (Columba livia)

The avian wulst, a laminated "bulge" in the dorsal telencephalon, contains several distinct regions. The posterolateral portion (visual wulst) has been proposed to be an avian equivalent of the mammalian striate cortex. The present study examines specific neurotransmitters and neuropeptides within the visual wulst by immunohistochemical techniques. Antisera and monoclonal antibodies against choline acetyltransferase (ChAT), nicotinic acetylcholine receptor (nAChR), tyrosine hydroxylase (TH), serotonin (5-HT), glutamic acid decarboxylase (GAD), gamma-aminobutyric acid A receptor (GABAAR), cholecystokinin (CCK), substance P (SP), leucine-enkephalin (L-ENK), neurotensin (NT), neuropeptide Y (NPY), somatostatin (SRIF), corticotropin-releasing factor (CRF), and vasoactive intestinal polypeptide (VIP) were used. Somata and neuropil displaying specific immunoreactivity were generally distributed in accordance with the laminar cytoarchitectonic organization of the wulst. The superficial layer of the wulst, the hyperstriatum accessorium, contained the highest densities of TH-, 5-HT-, SP-, NPY-, SRIF-, CRF-, and VIP-positive neuropil in the wulst, whereas the highest density of CCK- and NT-staining was found in the deepest layer of the wulst, the hyperstriatum dorsale. In addition to the traditionally defined four laminae of the wulst, the immunoreactive staining revealed several subregions within each lamina. The most dorsolateral portion of the wulst contained the highest densities of ChAT- and L-ENK-stained fibers in the wulst, as well as moderately dense staining of neuropil for 5-HT-, TH-, SP-, and CCK-like immunoreactivity. The nAChR-immunoreactivity was faint and distributed rather uniformly throughout the wulst. The results suggest that the wulst consists of multiple regional variations within layers comparable to laminar variations found within different cytoarchitectonic areas of the mammalian neocortex.

Distribution of neurotensin-containing fibers in the frontal cortex of the macaque monkey

The distribution of neurotensin-containing fibers was examined in the frontal cortex of the monkey Macaca fuscata using the immunoperoxidase histochemical technique. An extremely dense network of neurotensin-containing fibers was observed in the medial prefrontal regions. The majority of cortical neurotensin fibers was observed in the anterior cingulate cortex (Walker's area 24) and adjacent medial prefrontal regions (areas 6 and 32). In area 24, the fiber density was similar to that in the nucleus accumbens. Immunoreactive fibers were particularly dense in two pyramidal layers (III, V). The medial prefrontal regions, areas 6 and 32, contained a moderate density of immunoreactive fibers. This regional distribution of neurotensin-containing fibers was not observed in other cortical fiber systems that contained substance P, somatostatin, or tyrosine hydroxylase. No neurotensin-containing cell bodies were observed in the frontal cortex. The present study demonstrates that the laminar and regional distributions of neurotensin-containing fibers are unique when compared to those of substance P- or somatostatin-containing fibers, and also distinct from that of catecholaminergic fibers. The distribution of telencephalic neurotensin fibers points to a relationship with limbic structures.

Isolation and identification of a peptide from rat brain which inhibits [3H]TCP binding

1. A stereospecific radioreceptor binding assay for the phencyclidine analogue [3H]TCP was utilized to screen for inhibitors of binding in extracts of rat brain. 2. Extracts were prepared from rat cortex and hippocampus by methods employing aqueous acid or acidified methanol. Samples were fractionated by reversed phase-HPLC (RP-HPLC) and tested for activity in the radioreceptor assay. Three zones of activity were detected. The most active fraction was further purified by high performance-size exclusion chromatography. 3. Size exclusion chromatography revealed two zones of activity, corresponding to mol. wts of 4000-8000 Da and 1000-2000 Da. Final purification of the lower molecular weight material was achieved by RP-HPLC. 4. Two well-separated peaks were shown to be homogeneous. Their amino acid sequences were determined by automated Edman degradation and data base searching identified these two peaks as the undecapeptide Substance P and its oxidized counterpart (Substance P sulfoxide). 5. Comparative HPLC of synthetic Substance P, or its sulfoxide, as well as spectral analysis confirmed the identity of the isolated peptides. 6. Synthetic Substance P inhibits specific [3H]TCP binding in the radioreceptor assay.