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

Distribution of somatostatin-28 (1-12), calcitonin gene-related peptide, and substance P in the squirrel monkey brainstem: an immunocytochemical study

Using an immunocytochemical technique, we have studied the distribution of fibers and cell bodies containing somatostatin-28 (1-12) [SOM-28 (1-12)], calcitonin gene-related peptide (CGRP), and substance P (SP) in the brainstem of Saimiri sciureus. The distribution of the peptidergic cell bodies was very restricted: perikarya containing SOM-28 (1-12) were only observed in the substantia grisea centralis, while no immunoreactive cell bodies containing CGRP or SP were visualized. Fibers containing SOM-28 (1-12), CGRP, or SP were widely distributed in the brainstem: immunoreactive fibers containing SOM-28 (1-12) showed the most widespread distribution and were the most abundant. The distribution of SOM-28 (1-12)-, CGRP- or SP-immunoreactive fibers was very similar. Colocalization of immunoreactive fibers containing SOM-28 (1-12), CGRP or SP was observed in many brainstem nuclei. A neuroanatomical relationship between CGRP- and SP-immunoreactive fibers was observed, although this relationship was less marked for SOM-28 (1-12) and SP and lower still for SOM-28 (1-12) and CGRP. The widespread distribution of the peptidergic fibers suggests that the studied neuropeptides are involved in many physiological actions.

Honokiol for the Treatment of Neonatal Pain and Prevention of Consequent Neurobehavioral Disorders

This study examined the short- and long-term neuroprotective and analgesic activity of honokiol (a naturally occurring lignan isolated from Magnolia) on developing brains in neonates exposed to inflammatory pain, known to cause neuronal cell death. Postnatal day 4 (P4) neonatal rat pups were subjected to intraplantar formalin injection to four paws as a model of severe neonatal pain. Intraperitoneal honokiol (10 mg/kg) or corn oil vehicle control was administered 1 h prior to formalin insult, and animals were maintained on honokiol through postnatal day 21 (P21). Behavioral tests for stress and pain were performed after the painful insult, followed by morphological examinations of the brain sections at P7 and P21. Honokiol significantly attenuated acute pain responses 30 min following formalin insult and decreased chronic thermal hyperalgesia later in life. Honokiol-treated rats performed better on tests of exploratory behavior and performed significantly better in tests of memory. Honokiol treatment normalized hippocampal and thalamic c-Fos and hippocampal alveus substance P receptor expression relative to controls at P21. Together, these findings support that (1) neonatal pain experiences predispose rats to the development of chronic behavioral changes and (2) honokiol prevents and reduces both acute and chronic pathological pain-induced deteriorations in neonatal rats.

Comparative anatomy of the hippocampal dentate gyrus in adult and developing rodents, non-human primates and humans

There has been substantial progress in our understanding of the hippocampus in the past 70 years. During this time, it has become clear that the hippocampus is not an olfactory-related structure alone, but plays critical roles in other functions that do not necessarily depend on olfaction, such as learning and memory. In addition, it has become clear how important the hippocampus is to a wide variety of neurological disorders and psychiatric illness. Animal models have provided a great resource in such studies, but a frequent question is whether the data from laboratory animals is relevant to man.

Distribution of substance P reveals a novel subdivision in the hippocampus of parasitic South American cowbirds

Parasitic cowbirds monitor potential hosts' nests and return to lay when appropriate, a task that is likely to involve spatial recall. Seasonal and sexual behavioral variations in the cowbirds correlate with anatomical changes in the hippocampal formation. During the breeding season, parasites have larger hippocampal formations than nonparasites. In parasitic species in which females alone perform nest bookkeeping, females have larger hippocampal formations than males. We investigated the distribution of the neuropeptide substance P (SP) in three sympatric cowbirds: two obligate parasites (shiny cowbird and screaming cowbird) and one nonparasite (bay-winged cowbird). Distribution of SP was similar to that in other songbirds, except for a previously undescribed field of dense SP-rich terminals within the hippocampus that we call the hippocampal SP terminal field (SPh). We found robust species differences in the volume of this new area, measured relative to the remainder of the telencephalon. SPh was largest in the generalist parasite (shiny cowbird) and smallest in the nonparasitic species (bay-winged cowbird). In the specialist parasite (screaming cowbird), SPh was smaller than in the generalist parasite but larger than in the nonparasitic species. SPh overlaps with two subdivisions described in the pigeon that have been related to the mammalian dentate gyrus and subiculum. The area containing SPh receives a major input from the lateral mammillary nucleus, which is probably the avian equivalent of the mammalian supramammillary nucleus (SUM), the main source of extrinsic SP input to mammalian hippocampus. SPh may be the termination of a pathway homologous to the SP-rich projection from SUM to the hippocampus in mammals.

AMPA receptors are modulated by tachykinins in rat cerebellum neurons

The peptides of the tachykinin family are widely distributed within the mammalian peripheral and central nervous systems and play a well-recognized role as neuromodulators, although their direct action on cerebellum granule cells have not yet been demonstrated. We have examined the effect of the best known members of the family, substance P (SP), neurokinin A (NKA), and neurokinin B (NKB) on alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors from rat cerebellar granule cells in culture to assess the ability of these peptides to regulate the glutamatergic input. Both NKA and NKB, but not SP, produce a significant enhancement of ionic current through AMPA receptors activated by the agonist kainate in 53.5 and 46% of patched neurons, respectively. This effect was not observable in the presence of MEN 10,627 and Trp(7)betaAla(8), NKA and NKB competitive antagonist receptors, respectively, indicating that the current modulations were mediated by the respective receptors. NKB also produces a significant enhancement of ionic current through the AMPA receptors activated directly by its agonist AMPA and cyclothiazide, an allosteric modulator that selectively suppresses desensitization of AMPA receptors. The presence of NK3 receptors was demonstrated in these neurons by RT-PCR amplification of total RNA extracted from cerebellar granule cells, using NK3-specific primer pairs. Immunocytochemistry experiments, using a specific polyclonal antibody directed against NK3, also confirmed the presence of NK3 receptors and their co-localization with the GLUR2 AMPA subunit in about 54% of cerebellar granule neurons. This study adds the tachykinins to the list of neuromodulators capable of exerting a excitatory action on cerebellar granule cells.

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.

The supramammillo-hippocampal and supramammillo-septal glutamatergic/aspartatergic projections in the rat: a combined [3H]D-aspartate autoradiographic and immunohistochemical study

It is well established that the supramammillary nucleus plays a critical role in hippocampal theta rhythm generation/regulation by its direct and indirect (via the septal complex) connections to the hippocampus. Previous morphological and electrophysiological studies indicate that both the supramammillo-hippocampal and supramammillo-septal efferents contain excitatory transmitter. To test the validity of this assumption, transmitter specific retrograde tracer experiments were performed. [3H]D-aspartate was injected into different locations of the hippocampus (granular and supragranular layers of the dentate gyrus and CA2 and CA3a areas of the Ammon's horn) and septal complex (medial septum and the area between the medial and lateral septum) that are known targets of the supramammillary projection. Consecutive vibratome sections prepared from the entire length of the posterior hypothalamus, including the supramammillary area, were immunostained for calretinin, tyrosine hydroxylase, or calbindin, and further processed for autoradiography. Radiolabeled, radiolabeled plus calretinin-containing, and calretinin-immunoreactive neurons were plotted at six different oro-caudal levels of the supramammillary area. The results demonstrated that following both hippocampal and septal injection of the tracer, the majority of the retrogradely radiolabeled (glutamatergic/aspartatergic) cells are immunoreactive for calretinin. However, non-radiolabeled calretinin-containing neurons and radiolabeled calretinin-immunonegative cells were also seen, albeit at a much lower density. These observations clearly indicate the presence of glutamatergic/aspartatergic projections to both the hippocampus and septal complex. It may be assumed that this transmitter could play a role in hippocampal theta rhythm generation/regulation.

Intraventricular administration of substance p increases the dendritic arborisation and the synaptic surfaces of Purkinje cells in rat's cerebellum

Substance P was infused in the lateral ventricles of twenty Lewis rats for twenty days. On the twentieth day the animals were sacrificed and the cerebellar cortex was processed for electron microscopy. The ultrastructural morphometric analysis revealed that the Purkinje cell dendritic arborisation and the number of the synapses between the parallel fibres and the Purkinje cell dendritic spines were much higher than in control animals. Numerous unattached spines of the secondary and tertiary dendritic branches of the Purkinje cells were also seen in the molecular layer either free or surrounded by astrocytic sheath. The increased number of synapses between the Purkinje cell dendrites and the parallel fibres in the animals, which received substance P intraventricularly, in correlation to control animals, supports a neurotrophine-like activity of the substance P in the mammalian cerebellum, enforcing the pre-programmed capability of the Purkinje cells to develop new synaptic surfaces.

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.

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.

Substance P enhances NMDA channel function in hippocampal dentate gyrus granule cells

Substance P (SP)-containing afferents and the NK-1 tachykinin receptor to which SP binds are present in the dentate gyrus of the rat; however, direct actions of SP on principal cells have not been demonstrated in this brain region. We have examined the effect of SP on N-methyl--aspartate (NMDA) channels from acutely isolated dentate gyrus granule cells of adult rat hippocampus to assess the ability of SP to regulate glutamatergic input. SP produces a robust enhancement of single NMDA channel function that is mimicked by the NK-1-selective agonist Sar9, Met(O2)11-SP. The SP-induced prolongation of NMDA channel openings is prevented by the selective NK-1 receptor antagonist (+)-(2S, 3S)-3-(2-methoxybenzylamino)-2-phenylpiperidine (CP-99,994). Calcium influx or activation of protein kinase C were not required for the SP-induced increase in NMDA channel open durations. The dramatic enhancement of excitatory amino acid-mediated excitability by SP places this neuropeptide in a key position to gate activation of hippocampal network activity.

GABAergic cells are the major postsynaptic targets of mossy fibers in the rat hippocampus

Dentate granule cells communicate with their postsynaptic targets by three distinct terminal types. These include the large mossy terminals, filopodial extensions of the mossy terminals, and smaller en passant synaptic varicosities. We examined the postsynaptic targets of mossy fibers by combining in vivo intracellular labeling of granule cells, immunocytochemistry, and electron microscopy. Single granule cells formed large, complex "mossy" synapses on 11-15 CA3 pyramidal cells and 7-12 hilar mossy cells. In contrast, GABAergic interneurons, identified with immunostaining for substance P-receptor, parvalbumin, and mGluR1a-receptor, were selectively innervated by very thin (filopodial) extensions of the mossy terminals and by small en passant boutons in both the hilar and CA3 regions. These terminals formed single, often perforated, asymmetric synapses on the cell bodies, dendrites, and spines of GABAergic interneurons. The number of filopodial extensions and small terminals was 10 times larger than the number of mossy terminals. These findings show that in contrast to cortical pyramidal neurons, (1) granule cells developed distinct types of terminals to affect interneurons and pyramidal cells and (2) they innervated more inhibitory than excitatory cells. These findings may explain the physiological observations that increased activity of granule cells suppresses the overall excitability of the CA3 recurrent system and may form the structural basis of the target-dependent regulation of glutamate release in the mossy fiber system.

Tachykinins may modify spontaneous epileptiform activity in the rat entorhinal cortex in vitro by activating GABAergic inhibition

The effects of substance P and related tachykinins on intrinsic membrane properties and synaptic responses of neurons in cortical slices were determined. Substance P had no detectable effect on membrane properties of principal neurons in layer II or V of the rat medial entorhinal cortex or on neurons in either layer of the anterior cingulate cortex. Specific agonists at the neurokinin1-receptor were also without effect as were agonists at both neurokinin1- and neurokinin3-receptors. Substance P hyperpolarized a small number of principal neurons. These responses were weak and desensitized with repeated applications. Similar effects were seen with other neurokinin1-receptor agonists. Excitatory synaptic potentials mediated by either alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate- or N-methyl-D-aspartate-receptors in principal neurons of the entorhinal cortex were unaffected by substance P. Responses of entorhinal neurons to iontophoretically applied glutamate and N-methyl-D-aspartate were also unaffected. Inhibitory synaptic potentials mediated by either GABA(A)- or GABA(B)-receptors in entorhinal neurons were slightly but consistently enhanced by substance P. Neurons identified as interneurons on the basis of their firing characteristics were consistently depolarized by substance P. These responses also desensitized with repeated applications. Spontaneous epileptiform discharges evoked in entorhinal cortex by perfusion with a GABA(A)-receptor antagonist (bicuculline), were reduced in frequency and, sometimes, in duration by substance P. This effect was mimicked by other neurokinin1-receptor agonists and blocked by neurokinin1-receptor antagonists. It was also mimicked by neurokinin A but not by a specific neurokinin1-receptor agonist. The reduction in frequency of discharges was also mimicked by a GABA(B)-receptor agonist, L-baclofen, and blocked by the GABA(B)-receptor antagonist, CGP55845A. Neurokinin B, and a specific neurokinin1-receptor agonist (senktide), increased the frequency and (sometimes) duration of epileptiform discharges. Substance P could also increase frequency but this usually succeeded or preceded a decrease in frequency. The effect of neurokinin B was reduced by a metabotropic glutamate receptor antagonist. Substance P appears to have little direct effect on principal neurons of the entorhinal cortex but may hyperpolarize them indirectly by activating interneurons and releasing GABA. This indirect inhibition may be responsible for the ability of substance P to reduce the frequency of epileptiform discharges in the entorhinal cortex and may suggest that neurokinin1-receptor agonists have potential as anticonvulsant drugs.