Substance P receptor (NK-1) in the central nervous system: possible functions from a morphological aspect

Gene-environment interaction affects substance P and neurokinin A in the entorhinal cortex and periaqueductal grey in a genetic animal model of depression: implications for the pathophysiology of depression

Evidence implies a role for corticotropin-releasing hormone (CRH) and tachykinins, e.g. substance P (SP) and neurokinin A (NKA) in the pathophysiology of depression. We have previously shown that SP- and NKA-like immunoreactivity (-LI) concentrations were altered in the frontal cortex and striatum of the congenitally 'depressed' Flinders Sensitive Line (FSL) compared to the Flinders Resistant Line (FRL) control rats. It is also known that environmental stress may affect brain levels of tachykinins. In view of these results we decided to superimpose maternal deprivation, an early life environmental stressor, onto the genetically predisposed 'depressed' FSL rats and the FRL control rats and use this paradigm as a model of gene-environment interaction. The adult animals were sacrificed, adrenal glands and brains dissected out and SP-, NKA- and CRH-LI levels were determined in ten discrete brain regions. Maternal deprivation led to a marked increase in SP-LI and NKA-LI levels in the periaqueductal grey (PAG) and entorhinal cortex of the 'depressed' FSL strain while it had no significant effect in the FRL controls. Furthermore, specific strain differences in peptide-LI content were confirmed. No difference was found in relative adrenal gland weight, which is consistent with the finding that CRH-LI levels in the hypothalamus were similar across strains, and insensitive to stress in either strain. Taken together, these data are in line with behavioural experiments showing ameliorating effects of NK1 and NK2 receptor antagonists against anxiety and depression-like symptoms in rodents, and therefore further implicate the tachykinin systems in the pathophysiology of depression and adult life psychopathology.

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.

The effects of substance P after central administration on the activity of the mesolimbic system of the rat brain as studied by microdialysis

In vivo microdialysis was used to study the effects of substance P on dopamine, dihydroxyphenylacetic acid, and homovanillic acid levels in the nucleus accumbens in rats. Each animal received sequential injections of physiological saline, 0.1 microg of substance P, and 1 microg of substance P into the lateral ventricle over three days. Dialysates showed increases in dopamine levels in response to neuropeptide, by 41% for the 0.1 microg dose and 71% for the 1 microg dose. The dynamics of these changes also depended on the concentration of the agent. Administration of 1 microg of substance P gave a peak dopamine level at 50 min; the neurotransmitter level remained significantly elevated 75 min after dosage with substance P. The dopamine level was increased only at 75 min when the 0.1 microg dose of neuropeptide was used. Changes in metabolite levels were also dose-dependent. After the 1 microg dose, the dihydroxyphenylacetic acid level increased by 28%, while the 0.1 microg dose produced no significant change in the level of this metabolite. The homovanillic acid level did not respond to administration of substance P at either dose. These data support the suggestion that the influence of substance P on the internal compensation system is to a significant extent mediated by dopaminergic mechanisms and provides a possible explanation for the effects of the neuropeptide seen in a conditioned place preference reflex.

Mechanisms of the influences of the central administration of substance P on ethanol consumption in chronically alcoholic rats

The effects of central administration of substance P (SP) on alcohol consumption and dopamine metabolism in the projections of the mesocorticolimbic and nigrostriatal systems of the brain were studied in chronically alcoholic rats. Rats received 15% ethanol solution for 6 months without choice. Intraventricular administration of SP (1 microg/rat) decreased consumption of 10% ethanol solution by 41% compared with controls in an alcohol free choice test lasting one day. After chronic alcoholism, there was a decrease in the ratio of dihydroxyphenylacetic acid (DOPA) and homovanillic acid (HVA) to dopamine in the nucleus accumbens and striatum in rats subjected to alcoholism, as compared with intact controls. Chronically alcoholic rats treated with SP showed increases in DOPA, HVA, and the DOPA:dopamine and HVA:dopamine ratios in the nucleus accumbens as compared with animals given physiological saline, by 17%, 23%, 9% and 19% respectively. The only increases in the striatum were in the absolute levels of DOPA and HVA, by 28% and 29%, while the ratios of these metabolites to dopamine remained unchanged. Thus, central administration of SP decreased the voluntary consumption of ethanol in the ethanol free choice test and enhanced dopamine metabolism in structures of the mesolimbic and nigrostriatal systems in chronically alcoholic rats.

The neurobiology and control of anxious states

Fear is an adaptive component of the acute "stress" response to potentially-dangerous (external and internal) stimuli which threaten to perturb homeostasis. However, when disproportional in intensity, chronic and/or irreversible, or not associated with any genuine risk, it may be symptomatic of a debilitating anxious state: for example, social phobia, panic attacks or generalized anxiety disorder. In view of the importance of guaranteeing an appropriate emotional response to aversive events, it is not surprising that a diversity of mechanisms are involved in the induction and inhibition of anxious states. Apart from conventional neurotransmitters, such as monoamines, gamma-amino-butyric acid (GABA) and glutamate, many other modulators have been implicated, including: adenosine, cannabinoids, numerous neuropeptides, hormones, neurotrophins, cytokines and several cellular mediators. Accordingly, though benzodiazepines (which reinforce transmission at GABA(A) receptors), serotonin (5-HT)(1A) receptor agonists and 5-HT reuptake inhibitors are currently the principle drugs employed in the management of anxiety disorders, there is considerable scope for the development of alternative therapies. In addition to cellular, anatomical and neurochemical strategies, behavioral models are indispensable for the characterization of anxious states and their modulation. Amongst diverse paradigms, conflict procedures--in which subjects experience opposing impulses of desire and fear--are of especial conceptual and therapeutic pertinence. For example, in the Vogel Conflict Test (VCT), the ability of drugs to release punishment-suppressed drinking behavior is evaluated. In reviewing the neurobiology of anxious states, the present article focuses in particular upon: the multifarious and complex roles of individual modulators, often as a function of the specific receptor type and neuronal substrate involved in their actions; novel targets for the management of anxiety disorders; the influence of neurotransmitters and other agents upon performance in the VCT; data acquired from complementary pharmacological and genetic strategies and, finally, several open questions likely to orientate future experimental- and clinical-research. In view of the recent proliferation of mechanisms implicated in the pathogenesis, modulation and, potentially, treatment of anxiety disorders, this is an opportune moment to survey their functional and pathophysiological significance, and to assess their influence upon performance in the VCT and other models of potential anxiolytic properties.

Stereospecific blockade of marble-burying behaviour in mice by selective, non-peptidergic neurokinin1 (NK1) receptor antagonists

By analogy with the selective serotonin reuptake inhibitor, fluvoxamine, and the tricyclic agent, clomipramine, the novel, selective, non-peptidergic NK(1) receptor antagonist, GR205,171, dose-dependently and completely blocked marble-burying behaviour in mice: Inhibitory Dose(50)s (ID(50)s), 4.5, 4.8 and 7.6 mg/kg, respectively. In contrast to GR205,171, its isomer, GR226,206, which displays substantially lower affinity for NK(1) receptors, was inactive (> 40.0 mg/kg). By analogy with GR205,171, a further, selective NK(1) antagonist, RP67,580, abolished marble-burying behaviour with an ID(50) of 11.9 mg/kg. At doses significantly reducing marble-burying behaviour, GR205,171 and RP67,580 little influenced motor behaviour. In conclusion, like fluvoxamine and clomipramine, selective, non-peptidergic NK(1) receptor antagonists block marble-burying in mice. Although the biological bases of this behaviour remain unclear, these observations underpin the contention that NK(1) receptors may be implicated in affective disorders.

Differential modulation of frontal cortex acetylcholine by injection of substance P into the nucleus basalis magnocellularis region in the freely-moving vs. the anesthetized preparation

In vivo microdialysis was used to assess the effects of unilateral substance P (SP) injection into the nucleus basalis magnocellularis on extracellular levels of acetylcholine (ACh) in the frontal cortex, either in freely moving or urethane-anesthetized rats. The results show that the neurochemical effects of SP are critically dependent on the choice of the experimental preparation: In the freely-moving rat, the injection procedure led to behavioral and concurrent bilateral cholinergic activation in the frontal cortex. This cholinergic activation was ipsilaterally reduced by intrabasalis injection of SP (1 ng), indicating that the peptide exerted an inhibitory influence on the neurochemical effect exerted by handling, intracranial needle insertion, and vehicle injection. In the anesthetized preparation, SP had a biphasic dose-dependent action on cortical ACh: a short-lasting ipsilateral increase immediately after injection (especially with 1 ng), and a delayed bilateral increase after more than 2 h (10, 100 ng). The procedure of inserting the injection needle moderately increased cortical ACh levels. Methodologically, these data are discussed with respect to the importance of using anesthetized vs. freely moving rats and the effects of intraparenchymal injections.

Variations in plasma levels of substance P and effects of a specific substance P antagonist of the NK(1) receptor on preovulatory LH and FSH surges and progesterone secretion in the cycling cynomolgus monkey

These studies investigated the role of substance P (SP) in the regulation of the hypothalamic-pituitary-ovarian axis in cynomolgus monkeys with normal menstrual cycles. Plasma concentrations of SP were determined in blood samples taken every morning in normally menstruating cynomolgus monkeys throughout the menstrual cycle. There was a significant decreasing linear trend of SP during the follicular phase (cycle day -13 to day 0) and a significant inverse relationship between SP plasma values and plasma 17beta-estradiol (E(2)) values from day -13 to day 0 of the adjusted cycle. Correspondingly, SP area under the curve was significantly greater during the follicular phase than the luteal phase. In a second experiment, plasma concentrations of E(2), luteinizing hormone (LH), follicle-stimulating hormone (FSH) and progesterone and length of cycles were measured after five daily intragastric administrations (10 mg/kg) of an NK(1) receptor (SP receptor) antagonist (RPR 100893; 10 mg/kg) initiated after serum E(2) concentrations had exceeded 125 pg/ml. There was a statistically significant reduction in the amplitude (41% of control) and the area under the curve (37% of control) of the preovulatory LH surge. In addition, there was a reduction of the duration of the LH surge (3 +/- 0.1 days in controls vs. 2.1 +/- 0.2 days in treated animals). The present results show for the first time that there are significant variations in plasma levels of SP, with a strong negative correlation with serum levels of E(2) during the follicular phase of the cynomolgus monkey, and that endogenous SP has a potentiating role in the interactive hypothalamo-anterior-pituitary mechanisms which lead to the preovulatory LH and FSH surges during the menstrual cycle in the monkey.

The neurokinin-1 receptor antagonist WIN51,708 attenuates the anxiolytic-like effects of ventralpallidal substance P injection

We reported previously that the neurokinin substance P has anxiolytic-like effects when administered into the nucleus basalis of the rat ventral pallidum. The present study aimed to determine the possible involvement of the neurokinin-1 receptor in the anxiolytic action of intrabasalis substance P injection. Behavioral testing was performed in the rat elevated plus-maze model of anxiety. Microinjection of substance P (1 ng) into the nucleus basalis increased sojourn times on the open arms, excursions into the end of the open arms and scanning over the edge of an open arm, indicative of an anxiolytic-like profile. The non-peptide neurokinin-1 receptor antagonist WIN51,708, administered i.p. 20 min prior to intrabasalis substance P injection, antagonized the anxiolytic effects of the neurokinin in a dose-dependent manner. WIN51,708 at 10 mg/kg diminished, while at the higher dose of 20 mg/kg the antagonist completely blocked, the effect of substance P on anxiety-related behaviors. These findings suggest that the anxiolytic-like effects of substance P in the nucleus basalis are mediated through neurokinin-1 receptive sites.

Reinforcing effects of neurokinin substance P in the ventral pallidum: mediation by the tachykinin NK1 receptor

The neurokinin substance P has reinforcing effects when administered into the nucleus basalis of the rat's ventral pallidum and these effects are encoded by its carboxy-terminal amino acid sequence. The present study examined the effect of prior treatment with the tachykinin NK1 receptor antagonist WIN51,708 on the conditioned place preference produced by intrabasalis injection of substance P and its carboxy-terminal heptapeptide analog dimethyl-C7. Pretreatment with WIN51,708 (10 and 20 mg/kg, i.p.) dose-dependently reversed the place preference produced by intrabasalis substance P (0.74 pmol). The carboxy-terminal analog dimethyl-C7 (0.74 pmol) was also found to act as a reinforcer following injection into the nucleus basalis region, but unlike for substance P, the behavioral effects of dimethyl-C7 could not be completely antagonized by joint administration of the NK1 antagonist. When injected alone, WIN51,708 did not influence the preference behavior. These findings suggest that the reinforcing effects of substance P in the nucleus basalis region might be mediated via NK receptive sites. The failure of WIN51,708 to completely antagonize the behavioral effects of dimethyl-C7 is interesting in the light of evidence, indicating that the carboxy-terminal substance P analog shows higher affinity for the tachykinin NK3 than for the NK1 receptor subtype.

Substance P attenuates and DAMGO potentiates amygdala glutamatergic neurotransmission within the ventral pallidum

The amygdala (AMG), nucleus accumbens (NA) and ventral pallidum (VP) influence goal-oriented behaviors. However, the nature of the interactions among these regions has not been well characterized. Anatomical studies indicate that excitatory amino acids are contained in VP inputs from the AMG, and the NA is a primary source of VP substance P (SP) and opioids. The present study was designed to functionally characterize the NA and AMG projections to the VP, and to assess if opioids and SP can modulate AMG-mediated excitatory neurotransmission within the VP. To do so, extracellularly recorded electrophysiological responses of single VP neurons to electrical activation of VP afferents were monitored during microiontophoretic application of treatment ligands in chloral hydrate-anesthetized rats. The anatomically described glutamatergic inputs from the AMG, and SP inputs from the NA, were pharmacologically verified. It also was determined that even though iontophoretically applied SP increased the spontaneous activity of VP neurons, at ejection current levels that were below those necessary to produce this effect (termed sub-threshold), the tachykinin attenuated AMG stimulation-evoked glutamatergic neurotransmission. SP failed to modulate the excitations induced by iontophoretically applied glutamate suggesting that SP modulation of AMG-evoked excitations were mediated via a decrease in the pre-synaptic release of glutamate. Like SP, the effects of sub-threshold ejection currents of micro opioid agonist DAMGO on AMG-evoked responses were not predicted by the opioid's effects on spontaneous VP neuronal activity; DAMGO inhibited spontaneous firing but potentiated AMG-evoked glutamatergic neurotransmission. The opioid also potentiated effects of exogenous glutamate implying an interaction at a post-synaptic site. These results indicate that tachykinin and opioid neuropeptides contained in NA projection neurons can differentially modulate AMG glutamatergic inputs to the VP.

Evaluation of PD 154075, a tachykinin NK1 receptor antagonist, in a rat model of postoperative pain

PD 154075 ([(2-benzofuran)-CH2OCO]-(R)-alpha-MeTrp-(S)-NHCH(CH3) Ph) is a selective tachykinin NK1 receptor antagonist. Its effect on development and maintenance of thermal and mechanical hypersensitivity was examined in a rat model of surgical pain. When administered 30 min before surgery, PD 154075 dose-dependently (3-100 mg/kg, s.c.) prevented the development of thermal and mechanical hypersensitivity with respective minimum effective doses of 10 and 30 mg/kg. These antihypersensitivity effects lasted for 72 h. In contrast, the administration of PD 154075 (30 mg/kg, s.c.) after surgery had little or no effect on these nociceptive responses. PD 154075 antagonised thermal hypersensitivity induced by intrathecal administration of substance P, over the same dose range that blocked surgical hypersensitivity. However, it only partially blocked the thermal hypersensitivity induced by the selective NK2 receptor agonist [betaAla8]neurokinin A-(4-10). Morphine dose-dependently (1-6 mg/kg, s.c.) lengthened isoflurane and pentobarbitone-induced sleeping time in the rat. In contrast, PD 154075 (3-100 mg/kg, s.c.) did not interact with these anaesthetics. It is suggested that tachykinin NK1 receptor antagonists, such as PD 154075, may possess therapeutic potential as pre-emptive antihypersensitive agents.

Variations in levels of substance P-encoding beta-, gamma-preprotachykinin and substance P receptor NK-1 transcripts in the rat hypothalamus throughout the estrous cycle: a correlation between amounts of beta-preprotachykinin and NK-1 mRNA

Using a sensitive RNase protection assay, the simultaneous quantification of hypothalamic beta-, gamma-preprotachykinin (PPT) and SP receptor NK-1 transcripts was performed throughout the estrous cycle. The amounts of these 3 transcripts were up-regulated during diestrus II-proestrus night (2-, 1.5- and 1.3-fold, respectively). These levels returned to low values during the proestrous day in the case of gamma-PPT mRNA and during the estrus-diestrus I night in the cases of beta-PPT and NK-1 mRNAs. These results implicate a differential regulation in amounts of the two alternatively spliced PPT transcripts. The 160 hypothalami of this study had been previously assayed for amounts of substance P (SP) and neurokinin A (NKA) peptides [P. Duval, V. Lenoir, S. Moussaoui, C. Garret and B. Kerdelhué, Substance P and neurokinin A variations throughout the rat estrous cycle; comparison with ovariectomized and male rats: I. Plasma, hypothalamus, anterior and posterior pituitary, J. Neurosci. Res., 45 (1996) 598-609]. Variations in mRNA and peptide levels were compared by statistical analysis. Surprisingly, variations in SP level paralleled those in beta-PPT mRNA level and variations in NKA level paralleled those of gamma-PPT mRNA level, although beta- and gamma-PPT transcripts encode both SP and NKA. Furthermore, the level of NK-1 mRNA was positively correlated with the level of beta-PPT mRNA (r = 0.90, P < 10(-58)) and with the level of SP peptide (r = 0.30, P < 10(-3)) but not with the level of NKA peptide. This analysis suggests that SP receptor NK-1 mRNA could be physiologically regulated by SP peptide in the rat hypothalamus.

Stimulatory effect of a specific substance P antagonist (RPR 100893) of the human NK1 receptor on the estradiol-induced LH and FSH surges in the ovariectomized cynomolgus monkey

Utilizing a human NK1 receptor antagonist (RPR 100893), the present in vivo study was designed to test the hypothesis that endogenous substance P (SP) modulates the action of 17beta-estradiol in inducing luteinizing hormone (LH) and follicle stimulating hormone (FSH) surges in ovariectomized cynomolgus monkey. Plasma concentrations of LH and FSH as well as NK1 receptor antagonist and SP were measured during the development of the negative and positive feedback phases which follow a single administration of estradiol benzoate (50 microg/kg) to long-term ovariectomized monkeys. Daily administration by gastric intubation of 1 mg/kg or 10 mg/kg of the NK1 receptor antagonist (RPR 100893) leads to detectable levels of the antagonist in the blood of treated animals for at least 6 hr after its administration. These levels are in agreement with the experimentally determined IC50 value of the antagonist. The most striking finding of this study is that LH and FSH releases are enhanced during the descending arm of the estradiol benzoate-induced LH and FSH surges, which suggests that endogenous SP normally has an inhibitory role during this time. The enhancement of LH release is approximately 50%, regardless of the amount of the NK1 antagonist used. However, the enhanced FSH release is more important. Furthermore, blockade of the NK1 receptor with the smaller dose of the antagonist leads to a small, but significant, increase in plasma levels of SP, indicating that blockade of SP receptors leads to an increased release of SP. Collectively, these results further substantiate the link which exists between the ovarian steroid 17beta-estradiol and SP systems. Also, for the first time, these results demonstrate an inhibitory involvement of the human NK1 receptor in the 17beta-estradiol-induced pseudo-ovulatory gonadotropin surges in the ovariectomized monkey.

Receptor localization in the mammalian dorsal horn and primary afferent neurons

The dorsal horn of the spinal cord is a primary receiving area for somatosensory input and contains high concentrations of a large variety of receptors. These receptors tend to congregate in lamina II, which is a major receiving center for fine, presumably nociceptive, somatosensory input. There are rapid reorganizations of many of these receptors in response to various stimuli or pathological situations. These receptor localizations in the normal and their changes after various pertubations modify present concepts about the wiring diagram of the nervous system. Accordingly, the present work reviews the receptor localizations and relates them to classic organizational patterns in the mammalian dorsal horn.

Association of substance P and its receptor with efferent neurons projecting to the greater curvature of the rat stomach

Retrograde tracing and immunocytochemistry were used to identify and map the distribution of substance P (SP) and its receptor (NK-1r) associated with gastric motor neurons in the dorsal motor nucleus of the vagus (DMV) in the rat brain stem. The presence of peptide and receptor in surrounding regions within the dorsal vagal complex were also observed. Injection of the retrograde tracer Fluorogold (FG) into the greater curvature of the stomach produced bilateral labelling of neurons within the DMV. The majority of the NK-1r immunoreactivity appeared as an intricate lattice of fibres with a small number of immunoreactive cell bodies. The NK-1r-labelled fibres were detected within the DMV in close association with FG-labelled neurons and in the region between the DMV and nucleus of the solitary tract (NTS). A proportion of FG-labelled neuronal cell bodies were also labelled with NK-1r (7% of total). The greatest density of NK-1r-labelled fibres was observed at the rostral end of the FG-labelled neuron columns in the DMV (close to the IV ventricle) in the region where gastric vagal afferents terminate. Little NK-1r labelling was observed at the caudal end of the FG-labelled neuron tracts adjacent to the central canal. In the coronal plane, the NK-1r-labelled fibres were seen at the edges of the DMV extending into overlying NTS. Substance P was visualized as a dense network of fibres spanning the entire length of the DMV and in close association with FG-labelled neurons. Substance P staining was also detected in the NTS and in the ventral AP. Most of the association between SP/NK-1r immunoreactive fibres was observed within the DMV and at the border between the DMV and NTS. These findings suggest that SP directly regulates a subpopulation of efferent neurons in the DMV which project to the greater curvature of stomach.

The effects of neurokinin-1 receptor agonists on spinal motoneurones of the neonatal rat

The effects of substance P (SP) and the selective NK1 receptor agonist [Sar9Met(O2)11] substance P on neonate rat spinal motoneurones were examined using intracellular recordings. Bath-administration of SP (0.1-3 microM) or [Sar9Met(O2)11] substance P (0.01-3 microM) induced a tetrodotoxin (TTX)-insensitive (10 microM) depolarization and a tetraethylammoniumchloride (TEA)-sensitive (3 mM) decrease in membrane conductance. The duration of the slow afterhyperpolarizations (AHPs) following the action potentials were significantly reduced (p = 0.003) by both NK1 receptor agonists. The mean duration of the sAHPs (+/- SEM) in control was 67.8 +/- 6.3 ms whereas in the presence of SP and [Sar9Met(O2)11] substance P their duration was reduced to 41.7 +/- 4.6 ms. Low Ca2+ (0.2 mM)-containing artificial cerebrospinal fluid (ACSF) or addition of BaCl2 or CdCl2 (2 mM) reduced the durations of the slow AHPs by 55%. In the presence of these agents SP and [Sar9Met(O2)11] substance P practically abolished the remaining slow AHPs, suggesting that the agonists also reduce a calcium-independent current. None of the effects induced by the NK1 receptor agonists were antagonized by the NK1 receptor antagonists (+/-)-CP-96,345 (10 microM), RP 67580 (1 microM) or GR 82334 (3-5 microM). In conclusion this study demonstrates that SP and [Sar9Met(O2)11] substance P elicit their effects on NK1 receptors by modulating at least two potassium currents, namely IK and ICa(K).

Differential expression of oxytocin receptor mRNA in the developing rat brain

The embryonic and postnatal localizations of oxytocin receptor mRNA in the developing rat brain were studied by in situ hybridization histochemistry. The hybridization signal was first detected at embryonic-day 13 in the primordium of the dorsal motor nucleus of vagus. Other positive regions progressively appeared after this time. The developmental profile of oxytocin receptor gene expression could be classified into two types; transient expression and constant abundant expression. The caudate putamen, cingulate cortex, the anterior thalamic nuclei, and the ventral tegmental area belonged to the first type. In these regions, oxytocin receptor mRNA was expressed intensely only during the early postnatal period. The regions such as the anterior olfactory nucleus, tenia tecta, some amygdaloid nuclei, piriform cortex, the ventromedial hypothalamic nucleus, subiculum, the prepositus hypoglossal nucleus and the dorsal motor nucleus of vagus showed constant expression of oxytocin receptor mRNA at high levels throughout development and in the adult. These findings concurred well with those of the ontogenic studies using receptor binding autoradiography with a ligand specific to oxytocin. Thus, the transient expression of oxytocin receptor during development was regulated at the transcriptional level in several brain regions, and oxytocin may play a role in brain development as well as in neural transmission in the mature brain.

Morphological characterization of substance P receptor-immunoreactive neurons in the rat spinal cord and trigeminal nucleus caudalis

Although there is considerable evidence that primary afferent-derived substance P contributes to the transmission of nociceptive messages at the spinal cord level, the population of neurons that expresses the substance P receptor, and thus are likely to respond to substance P, has not been completely characterized. To address this question, we used an antibody directed against the C-terminal portion of the rat substance P receptor to examine the cellular distribution of the receptor in spinal cord neurons. In a previous study, we reported that the substance P receptor decorates almost the entire dendritic and somatic surface of a subpopulation of spinal cord neurons. In the present study we have taken advantage of this labeling pattern to identify morphologically distinct subpopulations of substance P receptor-immunoreactive neurons throughout the rostral-caudal extent of the spinal cord. We observed a dense population of fusiform substance P receptor-immunoreactive neurons in lamina I at all segmental levels. Despite having the highest concentration of substance P terminals, the substantia gelatinosa (lamina II) contained almost no substance P receptor-immunoreactive neurons. Several distinct populations of substance P receptor-immunoreactive neurons were located in laminae III-V; many of these had a large, dorsally directed dendritic arbor that traversed the substantia gelatinosa to reach the marginal layer. Extensive labeling was also found in neurons of the intermediolateral cell column. In the ventral horn, we found that labeling was associated with clusters of motoneurons, notably those in Onuf's nucleus in the sacral spinal cord. Finally, we found no evidence that primary afferent fibers express the substance P receptor. These results indicate that relatively few, but morphologically distinct, subclasses of spinal cord neurons express the substance P receptor. The majority, but not all, of these neurons are located in regions that contain neurons that respond to noxious stimulation.

Identification of the metabotropic glutamate receptor-1 protein in the rat trigeminal ganglion

Anti-metabotropic glutamate receptor-1 monoclonal antibody was raised and applied for immunohistochemistry in the rat trigeminal ganglion. The antibody detected 145-kDa single band of protein in the immunoblot analysis. In immunohistochemistry, neurons in the trigeminal ganglion showed immunostaining with various intensity, almost irrespective of their cell size. The results indicate that metabotrophic glutamate receptors play an important role in somatic sensation together with ionotropic ones.