Effect of substance P on acetylcholine and dopamine release in the rat striatum: a microdialysis study

Recent advances in the molecular signaling pathways of Substance P in Alzheimer's disease: Link to neuroinflammation associated with toll-like receptors

A significant quantity of substance P (SP) and its receptor, the neurokinin 1 (NK1) receptors are found in the brain. SP is a neuropeptide distributed in the central nervous system and functions as a neurotransmitter, neuromodulator, and neurotrophic factor. The concentrations of SP in the brain and cerebrospinal fluid fluctuate in individuals with Alzheimer's disease (AD). SP is an endogenous ligand for NK1 receptor, enhancing the expression of toll-like receptors (TLR) and vice versa. So, both pathways are interconnected, where activation of one pathway activates the second pathway. Researchers have observed the interaction of TLR with SP in the pathophysiology of AD. Thus, this review discusses various TLRs involved in regulating amyloid processing and its interaction with SP in AD. Further, in AD pathology, SP can regulate the non-amyloidogenic pathway. Recent studies have also demonstrated the capacity of SP in regulating voltage-gated potassium channel currents, emphasizing SP's neuroprotective ability. Therefore, we corroborate the findings linking the SP, NK1R, and TLRs in AD.

Neuronal diversity in the caudate nucleus: A comparative study between camel and human brains

Caudate nucleus (CN) neurons in camels and humans were examined using modified Golgi impregnation methods. Neurons were classified based on soma morphology, dendritic characteristics, and spine distribution. Three primary neuron types were identified in both species: rich-spiny (Type I), sparsely-spiny (Type II), and aspiny (Type III), each comprising subtypes with specific features. Comparative analysis revealed significant differences in soma size, dendritic morphology, and spine distribution between camels and humans. The study contributes to our understanding of structural diversity in CN neurons and provides insights into evolutionary neural adaptations.

Nucleus accumbens local circuit for cue-dependent aversive learning

Response to threatening environmental stimuli requires detection and encoding of important environmental features that dictate threat. Aversive events are highly salient, which promotes associative learning about stimuli that signal this threat. The nucleus accumbens is uniquely positioned to process this salient, aversive information and promote motivated output, through plasticity on the major projection neurons in the brain area. We describe a nucleus accumbens core local circuit whereby excitatory plasticity facilitates learning and recall of discrete aversive cues. We demonstrate that putative nucleus accumbens substance P release and long-term excitatory plasticity on dopamine 2 receptor-expressing projection neurons are required for cue-dependent fear learning. Additionally, we find that fear learning and recall is dependent on distinct projection neuron subtypes. Our work demonstrates a critical role for nucleus accumbens substance P in cue-dependent aversive learning.

Nucleus Accumbens Local Circuit for Cue-Dependent Aversive Learning

Response to threatening environmental stimuli requires detection and encoding of important environmental features that dictate threat. Aversive events are highly salient which promotes associative learning about stimuli that signal this threat. The nucleus accumbens is uniquely positioned to process this salient, aversive information and promote motivated output, through plasticity on the major projection neurons in the brain area. We uncovered a nucleus accumbens core local circuit whereby excitatory plasticity facilitates learning and recall of discrete aversive cues. We demonstrate that putative nucleus accumbens substance P release and long-term excitatory plasticity on dopamine 2 receptor expressing projection neurons is required for cue-dependent fear learning. Additionally, we found fear learning and recall were dependent on distinct projection-neuron subtypes. Our work demonstrates a critical role for Nucleus Accumbens substance P in cue-dependent aversive learning.

Putative neurochemical and cell type contributions to hemodynamic activity in the rodent caudate putamen

Functional magnetic resonance imaging (fMRI) is widely used by researchers to noninvasively monitor brain-wide activity. The traditional assumption of a uniform relationship between neuronal and hemodynamic activity throughout the brain has been increasingly challenged. This relationship is now believed to be impacted by heterogeneously distributed cell types and neurochemical signaling. To date, most cell-type- and neurotransmitter-specific influences on hemodynamics have been examined within the cortex and hippocampus of rodent models, where glutamatergic signaling is prominent. However, neurochemical influences on hemodynamics are relatively unknown in largely GABAergic brain regions such as the rodent caudate putamen (CPu). Given the extensive contribution of CPu function and dysfunction to behavior, and the increasing focus on this region in fMRI studies, improved understanding of CPu hemodynamics could have broad impacts. Here we discuss existing findings on neurochemical contributions to hemodynamics as they may relate to the CPu with special consideration for how these contributions could originate from various cell types and circuits. We hope this review can help inform the direction of future studies as well as interpretation of fMRI findings in the CPu.

What substance P might tell us about the prognosis and mechanism of Parkinson's disease?

The neuropeptide substance P (SP) plays an important role in neurodegenerative disorders, among which Parkinson's disease (PD). In the present work we have reviewed the involvement of SP and its preferred receptor (NK1-R) in motor and non-motor PD symptoms, in both PD animal models and patients. Despite PD is primarily a motor disorder, non-motor abnormalities, including olfactory deficits and gastrointestinal dysfunctions, can represent diagnostic PD predictors, according to the hypothesis that the olfactory and the enteric nervous system represent starting points of neurodegeneration, ascending to the brain via the sympathetic fibers and the vagus nerve. In PD patients, the α-synuclein aggregates in the olfactory bulb and the gastrointestinal tract, as well as in the dorsal motor nucleus of the vagus nerve often co-localize with SP, indicating SP-positive neurons as highly vulnerable sites of degeneration. Considering the involvement of the SP/NK1-R in both the periphery and specific brain areas, this system might represent a neuronal substrate for the symptom and disease progression, as well as a therapeutic target for PD.

How predictive learning influences choice: Evidence for a GPCR-based memory process necessary for Pavlovian-instrumental transfer

Predictive learning endows stimuli with the capacity to signal both the sensory-specific and general motivational properties of their associated rewards or outcomes. These two signals can be distinguished behaviorally by their influence on the selection and performance of instrumental actions, respectively. This review focuses on how sensory-specific predictive learning guides choice between actions that earn otherwise equally desirable outcomes. We describe evidence that outcome-specific predictive learning is encoded in the basolateral amygdala and drives the accumulation of delta-opioid receptors on the surface of cholinergic interneurons located in the nucleus accumbens shell. This accumulation constitutes a novel form of cellular memory, not for outcome-specific predictive learning per se but for the selection of, and choice between, future instrumental actions. We describe recent evidence regarding the cascade of events necessary for the formation and expression of this cellular memory and point to open questions for future research into this process. Beyond these mechanistic considerations, the discovery of this new form of memory is consistent with recent evidence suggesting that intracellular rather than synaptic changes can mediate learning-related plasticity to modify brain circuitry to prepare for future significant events.

High-Frequency Activation of Nucleus Accumbens D1-MSNs Drives Excitatory Potentiation on D2-MSNs

Subtypes of nucleus accumbens medium spiny neurons (MSNs) promote dichotomous outcomes in motivated behaviors. However, recent reports indicate enhancing activity of either nucleus accumbens (NAc) core MSN subtype augments reward, suggesting coincident MSN activity may underlie this outcome. Here, we report a collateral excitation mechanism in which high-frequency, NAc core dopamine 1 (D1)-MSN activation causes long-lasting potentiation of excitatory transmission (LLP) on dopamine receptor 2 (D2)-MSNs. Our mechanistic investigation demonstrates that this form of plasticity requires release of the excitatory peptide substance P from D1-MSNs and robust cholinergic interneuron activation through neurokinin receptor stimulation. We also reveal that D2-MSN LLP requires muscarinic 1 receptor activation, intracellular calcium signaling, and GluR2-lacking AMPAR insertion. This study uncovers a mechanism for shaping NAc core activity through the transfer of excitatory information from D1-MSNs to D2-MSNs and may provide a means for altering goal-directed behavior through coordinated MSN activity.

Substance P Weights Striatal Dopamine Transmission Differently within the Striosome-Matrix Axis

The mammalian striatum has a topographical organization of input-output connectivity, but a complex internal, nonlaminar neuronal architecture comprising projection neurons of two types interspersed among multiple interneuron types and potential local neuromodulators. From this cellular melange arises a biochemical compartmentalization of areas termed striosomes and extrastriosomal matrix. The functions of these compartments are poorly understood but might confer distinct features to striatal signal processing and be discretely governed. Dopamine transmission occurs throughout striosomes and matrix, and is reported to be modulated by the striosomally enriched neuromodulator substance P. However, reported effects are conflicting, ranging from facilitation to inhibition. We addressed whether dopamine transmission is modulated differently in striosome-matrix compartments by substance P.We paired detection of evoked dopamine release at carbon-fiber microelectrodes in mouse striatal slices with subsequent identification of the location of recording sites with respect to μ-opioid receptor-rich striosomes. Substance P had bidirectional effects on dopamine release that varied between recording sites and were prevented by inhibition of neurokinin-1 receptors. The direction of modulation was determined by location within the striosomal-matrix axis: dopamine release was boosted in striosome centers, diminished in striosomal-matrix border regions, and unaffected in the matrix. In turn, this different weighting of dopamine transmission by substance P modified the apparent center-surround contrast of striosomal dopamine signals. These data reveal that dopamine transmission can be differentially modulated within the striosomal-matrix axis, and furthermore, indicate a functionally distinct zone at the striosome-matrix interface, which may have key impacts on striatal integration.

Neurokinin-3 peptide instead of neurokinin-1 synergistically exacerbates kainic acid-inducing degeneration of neurons in the substantia nigra of mice

Neurokinin peptides neurokinin-1 (NK1), neurokinin-3 (NK3), and related receptors are abundantly distributed in the substantia nigra (SN) and evidenced by their possible roles in the Parkinson's disease. Differential intervention roles of NK3 on kainic acid (KA)-induced neuronal injury in the SN of mice were thus in vitro and in vivo studied by Fluoro-Jade C (FJC) staining, immunohistochemistry to tyrosine hydroxylase (TH) or phospho-NMDA receptor, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. It revealed that (i) in contrast to protective effect of NK1 agonist septide that reduced FJC-positive degenerative neurons and lesion volume insulted by KA, NK3 agonist senktide significantly increased FJC-positive ones and lesion volume, and this effect was sufficiently reversed by NK3 antagonist SB218795; (ii) similarly, senktide reduced TH-positive neurons and this effect was antagonized by SB218795, but septide increased TH-positive ones; (iii) mechanistic observation showed differential influences of NK1 and NK3 agonists on phosphorylated-NMDA receptor subunit 1 (phospho-NMDAR1) and glial fibrillary acidic protein-expressing astrocytes, i.e. senktide enhanced of NMDA receptor phosphorylation and astrocyte activity, while septide reduced NMDA receptor phosphorylation and astrocytic response; (iv) cell culture further confirmed the exacerbating effect of NK3 agonist on KA-induced lesion of nigral cells or dopaminergic neurons, in which administration of senktide alone did not show significant cell toxicity. This study presents new evidence that neurokinin NK3 instead of NK1 synergistically exacerbate excitotoxic neuronal degeneration in the SN in a dose-dependent manner and possibly through modulation of NMDA receptor phosphorylation and astrocyte activity, suggesting their potential significance in novel pharmaceutical therapy against Parkinson's disease.

Respiratory reactions to microinjection of bombesin into the solitary tract nucleus and their mechanisms

Acute experiments were performed on urethane-anesthetized adult laboratory rats to investigate the effects of microinjections of 10(-13)-10(-4) M bombesin into the solitary tract nucleus on measures of respiration. Bombesin microinjections were found to stimulate respiration, inducing significant increases in the level of pulmonary ventilation, increases in respiratory volume, and increases in the bioelectrical activity of the inspiratory muscles. The most marked respiratory reactions were seen after intermediate peptide doses (10(-10)-10(-7) M). These respiratory effects of bombesin were found to result from its ability to suppress the inspiration-inhibiting Hering-Breuer reflex at the level of the solitary tract nucleus. The fact that ultralow doses of bombesin were active, along with the distribution of endogenous bombesin and its specific receptors in the solitary tract nucleus, and the ability of this peptide to modulate the Hering-Breuer reflex all provide evidence that bombesin is involved in controlling respiration at the level of the dorsal structures of the respiratory center.

Membrane Associated Functions of Neurokinin B (NKB) on Aβ (25–35) Induced Toxicity in Aging Rat Brain Synaptosomes

The effect of different concentrations (0.1-5 microM) of neurokinin B (NKB) and Abeta (25-35) on acetylcholine esterase (AChE), Na(+)-K(+) ATPase and membrane fluidity (DPH anisotropy) were investigated in rat brain synaptosomes of 3, 9, 18 and 30 months old. An age dependent decrease was observed for all the three parameters studied. An in vitro incubation of isolated brain synaptosomes with Abeta (25-35) showed toxic effects on all the parameters studied and the peptide had concentration and age dependent effects, while NKB showed stimulating effect on the parameters and the combined NKB+Abeta (25-35) incubations showed a partial reversal effect as compared to the Abeta (25-35) alone. Thus, the results suggest a membrane mediated function for NKB and its role in neuromodulation, neuroprotection and antioxidant property against Abeta (25-35) induced toxicity in aging brain functions.

Intracerebral baclofen administration decreases amphetamine-induced behavior and neuropeptide gene expression in the striatum

In a previous study, systemic administration of the GABA(B) receptor agonist, R-(+)-baclofen (2.5 mg/kg, i.p.) blocked acute amphetamine (2.5 mg/kg, i.p.)-induced rearing and neuropeptide (preprodynorphin (PPD), preprotachykinin (PPT), preproenkephalin (PPE), and secretogranin II (SGII)) mRNA expression in the striatum (Zhou et al, 2004). The purpose of the present study was to investigate the site(s) of action of these baclofen effects in the dorsal and ventral striatal circuitries. Infusion of baclofen (75 ng/side) into the ventral tegmental area (VTA), substantia nigra (SN), nucleus accumbens (NA), caudate-putamen (Cpu), or medial prefrontal cortex (mPFC) had no effect on behavioral activity in saline-treated rats habituated to a photocell apparatus. However, intra-VTA infusion of baclofen (75 ng/side) completely blocked, whereas intra-NA and intra-SN infusion of baclofen attenuated, amphetamine-induced vertical activity without affecting amphetamine-induced total distance traveled. In contrast, intramedial PFC and intra-CPu infusion of baclofen had no effect on behavioral activity in amphetamine-treated rats. Infusion of baclofen into the VTA, NA, or SN decreased amphetamine-induced neuropeptide gene expression in the striatum. These results indicate that GABA(B) receptor stimulation within the ventral striatal circuitry is involved in mediating acute amphetamine-induced behaviors and neuropeptide gene expression in the dorsal and ventral striatum. The present study provides information on the potential targets in the brain for baclofen in the initial behavioral and genomic response to amphetamine.

GABAB receptor stimulation decreases amphetamine-induced behavior and neuropeptide gene expression in the striatum

The purpose of this study was to investigate whether GABA(B) receptor activation blocks acute amphetamine-induced behavioral activity, dopamine release, and neuropeptide mRNA expression in the striatum. Systemic administration of R-(+)-baclofen (1.25 mg/kg, i.p.) did not alter total distance traveled or vertical rearing induced by amphetamine (2.5 mg/kg, i.p.). At 2.5 mg/kg, baclofen did not alter spontaneous motor activity or total distance traveled, but completely blocked vertical rearing induced by amphetamine. At 5.0 mg/kg, baclofen completely blocked both total distance traveled and vertical rearing induced by amphetamine. Quantitative in situ hybridization histochemistry revealed that baclofen (2.5 mg/kg, i.p.) decreased the ability of amphetamine to increase preprodynorphin (PPD), preprotachykinin (PPT), preproenkephalin (PPE), and secretogranin II (SGII) mRNA levels in the striatum without altering the basal levels of these signals. Baclofen also blocked the amphetamine-induced rise in SGII mRNA in the core and shell of the nucleus accumbens and cingulate cortex. In a separate experiment, systemic baclofen (2.5 mg/kg) decreased the amphetamine-induced increase in dialysate dopamine levels in the striatum. These results suggest that reduced striatal dopamine release contributes to the ability of GABA(B) receptor activation to decrease acute amphetamine-induced behavioral activity and striatal neuropeptide gene expression.

The new neurokinin 1-sensitive receptor mediates the facilitation by endogenous tachykinins of the NMDA-evoked release of acetylcholine after suppression of dopaminergic transmission in the matrix of the rat striatum

Using an in vitro microsuperfusion procedure, the NMDA-evoked release of [3H]ACh was studied after suppression of dopamine (DA) transmission (alpha-methyl-p-tyrosine) in striatal compartments of the rat. The effects of tachykinin neurokinin 1 (NK1) receptor antagonists and the ability of appropriate agonists to counteract the antagonist responses were investigated to determine whether tachykinin NK1 classic, septide-sensitive and/or new NK1-sensitive receptors mediate these regulations. The NK1 antagonists, SR140333, SSR240600, GR205171 but not GR82334 and RP67580 (0.1 and 1 microM) markedly reduced the NMDA (1 mm + D-serine 10 microM)-evoked release of [3H]ACh only in the matrix. These responses unchanged by coapplication with NMDA of NK2 or NK3 agonists, [Lys5,MeLeu9,Nle10]NKA(4-10) or senktide, respectively, were completely counteracted by the selective NK1 agonist, [Pro9]substance P but also by neurokinin A and neuropeptide K (1 nM each). According to the rank order of potency of agonists for counteracting the antagonist responses ([Pro9]substance P, 0.013 nM > neurokinin A, 0.15 nM >> substance P(6-11) 7.7 nM = septide 8.7 nM), the new NK1-sensitive receptors mediate the facilitation by endogenous tachykinins of the NMDA-evoked release of ACh in the matrix, after suppression of DA transmission. Solely the NK1 antagonists having a high affinity for these receptors could be used as indirect anti-cholinergic agents.

Innervation of equine airways

Equine obstructive pulmonary disease (COPD), or heaves or recurrent airway obstruction, is a common equine pulmonary disease similar to human asthma and/or CODP. Since bronchospasm and inflammation are the key features in heaves, the purpose of this paper is to review the contribution of neural mechanism that may be relevant to this disease. Equine airway receive cholinergic and adrenergic innervation, as well as observed in many species. It was suggested that the autonomic neural control in asthma might be defective with an imbalance between excitatory and inhibitory pathways, resulting in excessively twitchy airways. Moreover, the recognition that, in addition to classical adrenergic and cholinergic pathway there are non-adrenergic-non-cholinergic inhibitory (iNANC) and excitatory (eNANC) innervation and many mediators, which have potent effects on airway function, has revived interest in neural control of airway.

R+-methanandamide inhibits tracheal response to endogenously released acetylcholine via capsazepine-sensitive receptors

The effects of cannabinoid drugs on the cholinergic response evoked by electrical field stimulation (0.2 ms pulse width, 20 V amplitude, 10 Hz, 7.5 s train duration) in guinea-pig tracheal preparations were investigated. The stable analogue of the endocannabinoid anandamide, R(+)-methanandamide (10(-7)-10(-4) M), produced a dose-dependent inhibition (up to 27+/-5% of control) of electrical field stimulation-mediated atropine-sensitive response. This effect was not blocked by the selective cannabinoid CB(1) receptor antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3 carboxamide hydrochloride (SR 141716A; 10(-6) M), and was not reproduced with the cannabinoid CB(1)/CB(2) receptor agonist R(+)-[2,3-dihydro-5-methyl-[(morpholinyl)methyl]pyrrolo [1,2,3-de]-1,4-benzoxazin-6-yl]-(1-naphthalenyl)methanone mesylate) (WIN 55,212-2; 10(-8)-10(-5) M) or the cannabinoid CB(2) receptor selective agonist 1-propyl-2-methyl-3-(1-naphthoyl)indole (JWH-015; 10(-8)-10(-5) M); it was, on the contrary, antagonized by the vanilloid antagonist 2-[2-(4-chlorophenyl)ethyl-amino-thiocarbonyl]-7,8-dihydroxy-2,3,4,5-tetrahydro-1H-2 benzazepine (capsazepine; 10(-6) M). At the postjunctional level, neither R(+)-methanandamide nor WIN 55,212-2 nor JWH-015 did affect tracheal contractions induced by exogenous acetylcholine (10(-6) M). An inhibitory vanilloid receptor-mediated effect on the cholinergic response evoked by electrical stimulation was confirmed with the vanilloid agonist capsaicin, at doses (3-6 x 10(-8) M) which poorly influenced the basal smooth muscle tone of trachea. In conclusion, our data indicate that in guinea-pig trachea (a) neither CB(1) nor CB(2) cannabinoid receptor-mediated modulation of acetylcholine release occurs; (b) vanilloid VR1-like receptors appear involved in R(+)-methanandamide inhibitory activity on the cholinergic response to electrical field stimulation.

Nandrolone decanoate enhances hypothalamic biogenic amines in rats

PURPOSE

To identify possible mechanisms for an anabolic-androgenic steroid induced increase in aggressive behavior and work capacity, the levels of some biogenic amines considered to be closely related to a systemic hyper-adrenergic state were measured in selected regions of the brain.

METHODS

Wistar male rats were divided randomly into five groups: nontreated (control), oil-vehicle-treated (vehicle) or one of three (therapeutic dose and 10- or 100-fold higher dose) anabolic-androgenic steroid-treated (steroid-1, -2, -3) groups. Rats in the steroid and vehicle groups were given a single dose of nandrolone decanoate or oil vehicle, respectively, one week before tissue sampling. The levels of norepinephrine (NE) and its metabolite, 4-hydroxy-3-methoxyphenylglycol (MHPG), serotonin (5-HT) and its metabolite, 5-hydroxy-indole-3-acetic acid (5-HIAA) were measured in the cerebral cortex, hypothalamus and cerebellum by high-performance liquid chromatography. Immunostaining for c-fos was performed as a confirmation of increased neural activity.

RESULTS

The levels of NE and MHPG were increased by approximately 2- and approximately 7-fold in the hypothalamus of the steroid-2 compared with the control and vehicle groups. The levels of 5-HT and 5-HIAA were approximately 40 and approximately 50% higher in the steroid-2 compared with the control and vehicle groups. A significantly higher number of c-fos expressing neurons were observed in the periventricular region of the steroid-2 than the control and vehicle groups, indicating enhanced neuronal activity after nandrolone decanoate treatment.

CONCLUSIONS

The present results, combined with previously reported findings of physical performance enhancement after anabolic-androgenic steroid treatment, are consistent with the interpretation that elevated levels of adrenergic and serotonergic amines in the hypothalamus could contribute to aggressive behaviors as well as improved physical performance.

Neurokinin receptors modulate the neurochemical actions of cocaine

The psychostimulant cocaine is an indirect agonist that increases synaptic dopamine (DA) by binding with high affinity to the DA transporter (DAT) and blocking the active transport of synaptic DA back into the terminal. The resulting increase in extracellular DA alters postsynaptic activity in the circuitry of the basal ganglia. This study examines the role of neurokinin receptors on cocaine-evoked DA overflow in the striatum. Male Sprague-Dawley rats (n = 8) were treated with cocaine (10 mg/kg body weight i.p.) acutely or chronically. The pattern of DA release was assessed using in vivo microdialysis. In separate experiments two different neurokinin-1 (NK-1) receptor antagonists (D-Arg(1), D-Pro(2), D-Trp(7,9), Leu(11), or L-733,060) were perfused via the microdialysis probe for one hour in awake and freely moving animals that were subsequently injected i.p. with cocaine. Throughout the procedure, DA release was monitored at 1/2-hour intervals at a flow rate of 1 microl/min. In the groups of rats preperfused with NK-1 antagonists into the striatum, the cocaine-evoked release of DA was significantly reduced. This result suggests a significant role for the NK-1 receptor in the striatal response to acute and chronic cocaine administration.

Facilitation by endogenous tachykinins of the NMDA-evoked release of acetylcholine after acute and chronic suppression of dopaminergic transmission in the matrix of the rat striatum

Using a microsuperfusion method in vitro, the effects of the NK1, NK2, and NK3 tachykinin receptor antagonists SR140333, SR48968, and SR142801, respectively, on the NMDA-evoked release of [3H]-acetylcholine were investigated after both acute and chronic suppression of dopamine transmission in striosomes and matrix of the rat striatum. NMDA (1 mm) alone or with D-serine (10 microm) in the presence of alpha-methyl-p-tyrosine (100 microm) markedly enhanced the release of [3H]-acetylcholine through a dopamine-independent inhibitory process. In both conditions, as well as after chronic 6-OHDA-induced denervation of striatal dopaminergic fibers, SR140333, SR48968, or SR142801 (0.1 microm each) reduced the NMDA-evoked release of [3H]-acetylcholine in the matrix but not in striosome-enriched areas. These responses were selectively abolished by coapplication with NMDA of the respective tachykinin agonists, septide, [Lys5,MeLeu9,Nle10]NKA(4-10), or senktide. Distinct mechanisms are involved in the effects of the tachykinin antagonists because the inhibitory response of SR140333 was additive with that of either SR48968 or SR142801. In addition, the SR140333-evoked response remained unchanged, whereas those of SR48968 and SR142801 were abolished in the presence of N(G)-monomethyl-l-arginine (nitric oxide synthase inhibitor). Therefore, in the matrix but not in striosomes, the acute or chronic suppression of dopamine transmission unmasked the facilitatory effects of endogenously released substance P, neurokinin A, and neurokinin B on the NMDA-evoked release of [3H]-acetylcholine. Whereas substance P and neurokinin A are colocalized in same efferent neurons, their responses involve distinct circuits because the substance P response seems to be mediated by NK1 receptors located on cholinergic interneurons, while those of neurokinin A and neurokinin B are nitric oxide-dependent.

NK-1 receptor blockade decreases amphetamine-induced behavior and neuropeptide mRNA expression in the striatum

The effect of intrastriatal administration of LY306740, a specific NK-1 receptor antagonist, on the behavior and changes in gene expression elicited by the psychomotor stimulant, amphetamine, was studied. Acute administration of amphetamine (2.5 mg/kg, i.p.) caused an increase in behavioral activity and preproenkephalin, preprodynorphin and substance P mRNA expression in the striatum. When amphetamine-treated rats were pretreated with LY306740 (35 and 20 nmoles per side, intrastriatally), there was a significant decrease in amphetamine-induced behavioral activity. Quantitative in situ hybridization histochemistry revealed that both concentrations of LY306740 significantly decreased amphetamine-induced mRNA expression of all three neuropeptides. These data indicate that striatal NK-1 receptors modulate amphetamine-induced behavior and mRNA expression of neuropeptides in the rat striatum.

Substance P in the descending cholinergic projection to REM sleep-induction regions of the rat pontine reticular formation: anatomical and electrophysiological analyses

Release of acetylcholine within the pontine reticular formation (PRF) from the axon terminals of mesopontine cholinergic neurons has long been hypothesized to play an important role in rapid eye movement (REM) sleep generation. As some of these cholinergic neurons are known to contain substance P (SP), we used anatomical, electrophysiological and pharmacological techniques to characterize this projection in the rat. Double immunofluorescence demonstrated that 16% of all cholinergic neurons within the mesopontine tegmentum contained SP; this percentage increased to 27% in its caudal regions. When double immunofluorescence was combined with retrograde tracing techniques, it was observed that up to 11% of all SP-containing cholinergic neurons project to the PRF. Whole-cell patch-clamp recordings from in vitro brainstem slices revealed that SP administration depolarized or evoked an inward current in a dose-dependent manner in all PRF neurons examined, and that these effects were antagonized by a SP antagonist. The amplitude of the SP-induced inward current varied with changes in the Na+ concentration, did not reverse at the calculated K+ or Cl- equilibrium potentials, and was not attenuated in the presence of tetrodotoxin, low Ca2+ concentration or caesium ions. These data suggest that activation of a tetrodotoxin-insensitive cation channel(s) permeable to Na+ is responsible for a SP-induced inward current at resting membrane potentials. The depolarizing actions of SP appeared to be primarily due to activation of the adenylate cyclase pathway, and were additive with cholinergic receptor activation even at maximal concentrations. These data indicate that SP is colocalized in a subpopulation of mesopontine tegmental cholinergic neurons projecting to REM sleep-induction regions of the PRF, and that actions of these two neuroactive substances on PRF neurons are additive. If SP is coreleased with acetylcholine, the additive actions of the two neurotransmitters might heighten the excitability of postsynaptic PRF neurons and ensure the initiation and maintenance of REM sleep.

Cholinergic neurons expressing neuromedin K receptor (NK3) in the basal forebrain of the rat: a double immunofluorescence study

By using a double immunofluorescence method we have examined the distribution of cholinergic neurons expressing neuromedin K receptor (NK3) in the rat brain and spinal cord. The distribution of neuromedin K receptor-like immunoreactive neurons completely overlapped with that of choline acetyltransferase-positive neurons in certain regions of the basal forebrain, e.g. the medial septal nucleus, nucleus of the diagonal band of Broca, magnocellular preoptic nucleus and substantia innominata. Partially overlapping distributions of neuromedin K receptor-like immunoreactive and choline acetyltransferase-positive neurons were found in the basal nucleus of Meynert, globus pallidus, ventral pallidum of the forebrain, tegmental nuclei of the pons and dorsal motor nucleus of the vagus. Neurons showing both neuromedin K receptor-like and choline acetyltransferase immunoreactivities, however, were found predominantly in the medial septal nucleus, nucleus of the diagonal band of Broca and magnocellular preoptic nucleus of the basal forebrain: 66-80% of these choline acetyltransferase-positive neurons displayed neuromedin K receptor-like immunoreactivity. Neurons showing both neuromedin K receptor-like and choline acetyltransferase immunoreactivities were hardly detected in other aforementioned regions of the forebrain, brainstem and spinal cord. The present study has provided morphological evidence for direct physiological modulation or regulation of cholinergic neurons by tachykinins through the neuromedin K receptor in the basal forebrain of rats.

Application of in vivo microdialysis to the study of cholinergic systems

The application of in vivo microdialysis to the study of acetylcholine (ACh) release has contributed greatly to our understanding of cholinergic brain systems. This article reviews standard experimental procedures for dialysis probe selection and implantation, perfusion parameters, neurochemical detection, and data analysis as they relate to microdialysis assessments of cholinergic function. Particular attention is focused on the unique methodological considerations that arise when in vivo microdialysis is dedicated expressly to the recovery and measurement of ACh as opposed to other neurotransmitters. Limitations of the microdialysis technique are discussed, as well as methodological adaptations that may prove useful in overcoming these limitations. This is followed by an overview of recent studies in which the application of in vivo microdialysis has been used to characterize the basic pharmacology and physiology of cholinergic neurons. Finally, the usefulness of the microdialysis approach for testing hypotheses regarding the cholinergic systems' involvement in cognitive processes is examined. It can be concluded that, in addition to being a versatile and practical method for studying the neurochemistry of cholinergic brain systems, in vivo microdialysis represents a valuable tool in our efforts to better comprehend ACh's underlying role in a variety of behavioral processes.

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.

Substance P modulation of striatal dopamine outflow is determined by M(1) and M(2) muscarinic receptors in male wistar rats

Substance P (SP) stimulates striatal dopamine outflow through a cholinergic muscarinic link. SP-induced increase in acetylcholine (Ach) is concentration-dependent, whereas the stimulation of dopamine outflow is seen only over a limited concentration range. M(1) and M(2) receptor stimulation has opposite effects on dopamine outflow. We postulated that the effect of SP on dopamine outflow depends on the M(1)/M(2) balance. We show that Ach (10-2500 microM) stimulates dopamine outflow in striatal slices in a biphasic manner, similar to SP (0.01-100 nM). An inactive SP concentration (10 nM) which was higher than the active concentration range, became active in the presence of the M(2) antagonist methoctramine (100 microM). Conversely, the effect of 1 nM SP was reversed by the M(1) antagonist pirenzepine (1 microM). Our observations show that SP modulation of dopamine outflow is determined by a balance between M(1) and M(2) receptors.

Chemical anatomy of striatal interneurons in normal individuals and in patients with Huntington's disease

This paper reviews the major anatomical and chemical features of the various types of interneurons in the human striatum, as detected by immunostaining procedures applied to postmortem tissue from normal individuals and patients with Huntington's disease (HD). The human striatum harbors a highly pleomorphic population of aspiny interneurons that stain for either a calcium-binding protein (calretinin, parvalbumin or calbindin D-28k), choline acetyltransferase (ChAT) or NADPH-diaphorase, or various combinations thereof. Neurons that express calretinin (CR), including multitudinous medium and a smaller number of large neurons, are by far the most abundant interneurons in the human striatum. The medium CR+ neurons do not colocalize with any of the known chemical markers of striatal neurons, except perhaps GABA, and are selectively spared in HD. Most large CR+ interneurons display ChAT immunoreactivity and also express substance P receptors. The medium and large CR+ neurons are enriched with glutamate receptor subunit GluR2 and GluR4, respectively. This difference in AMPA GluR subunit expression may account for the relative resistance of medium CR+ neurons to glutamate-mediated excitotoxicity that may be involved in HD. The various striatal chemical markers display a highly heterogeneous distribution pattern in human. In addition to the classic striosomes/matrix compartmentalization, the striosomal compartment itself is composed of a core and a peripheral region, each subdivided by distinct subsets of striatal interneurons. A proper knowledge of all these features that appear unique to humans should greatly help our understanding of the organization of the human striatum in both health and disease states.

Early direct and transneuronal effects in mice with targeted expression of a toxin gene to D1 dopamine receptor neurons

The neurochemical profile was examined at postnatal day 3-4 in mutant mice generated by in vivo Cre mediated activation of an attenuated diphtheria toxin gene inserted into the D1 dopamine receptor gene locus. An earlier study of this model had shown that D1 dopamine receptor, substance P and dynorphin were not expressed in the striatum. Quantitative in situ hybridization analysis showed an increase in D2 dopamine receptor and enkephalin messenger RNA expression. The nigrostriatal pathway in the mutant pups was intact with a normal number of dopaminergic neurons in the substantia nigra and the ventral tegmental area in addition to a normal pattern of striatal dopamine transporter and tyrosine hydroxylase immunoreactivity. Quantitative analysis of striatal dopamine transporter density using [3H]mazindol showed a reduction of 26% suggesting a degree of transneuronal down-regulation. There was also a 49% reduction of striatal GABA receptor binding and a 36% reduction of striatal muscarinic receptor binding in mutant pups. The number of healthy striatal neuropeptide Y-containing interneurons was also substantially down-regulated in the mutant striatum. In contrast, there was an increase in the number of striatal cholinergic interneurons. Down-regulated cortical GABA receptor and muscarinic receptor binding was also observed in addition to subtle morphological changes in the neuropeptide Y-expressing population of cortical neurons. The changes reflect the early cascade of events which follows the ablation of D1 dopamine receptor-positive cells. Although extensive changes in a number of striatal and cortical neurons were demonstrated, only subtle transneuronal effects were seen in the nigrostriatal pathway.

Oxytocin, motherhood and bonding

Release of the peptide hormone oxytocin in the brain has been shown to influence both maternal, sexual and social bonding behaviours although there are a number of species differences. This review summarizes findings on the distributions of oxytocin and oxytocin receptors in the brain, together with factors governing their expression, release of the peptide in the brain and its behavioural actions. A model of how oxytocin may act to alter maternal and socio-sexual behaviours is proposed which initially involves activation of oxytocin neurones in a single brain site, the paraventricular nucleus of the hypothalamus (PVN), following vaginal and cervical stimulation. This causes a co-ordinated release of the peptide in the PVN and its terminal projection regions for up to 1 h and this promotes different behavioural components, primarily through modulation of classical transmitter systems.

N- and C-terminal substance P fragments: differential effects on striatal [3H]substance P binding and NK1 receptor internalization

N- and C-terminal substance P (SP) fragments increase striatal dopamine outflow at nanomolar concentrations. This contrasts with their low affinity for NK1 receptors. To explore this discrepancy, we investigated the interaction of SP and SP fragments with NK1 sites in fresh striatal slices, the same model used in the functional studies on dopamine outflow. [3H]SP bound specifically to one site (Kd = 6.6 +/- 0.9 nM; Bmax = 12.6 +/- 0.7 fmol/mg protein). [3H]SP binding was displaced by SP (IC50 = 11.8 nM), but not by SP(1-7) or SP(5-11), up to 10 microM. In contrast, 10 nM SP(1-7) or SP(5-11) induced significant internalization of the NK1 receptor, similar to that induced by SP. We suggest that SP fragments have high affinity for an NK1 receptor conformer which is different from that labelled by [3H]SP.

Action of substance P (neurokinin-1) receptor activation on rat neostriatal projection neurons

Substance P (SP) acts as a neurotransmitter in the neostriatum through the axon collaterals of spiny projection neurons. However, possible direct or indirect actions of SP on the neostriatal output neurons have not been described. Targets of SP terminals within the neostriatum include interneurons, spiny neurons, afferent fibers and boutons. SP induces the release of both dopamine (DA) and acetylcholine (ACh). Since some postsynaptic actions of both DA and ACh on spiny neurons are known, we asked if activation of neostriatal NK1-class receptors is able to reproduce them. The SP NK1-receptor agonist, GR73632 (1 microM), had both excitatory and inhibitory actions on virtually all spiny neurons tested at resting potential. The excitatory action was blocked by atropine and coursed with an increase in firing rate and input resistance (R(N)). The inhibitory action was blocked by haloperidol and coursed with a reduction in firing rate and R(N). Therefore, the release of both DA and ACh induced by NK1-receptor activation modulates indirectly the excitability of the projection neurons. SP facilitates the actions of these transmitters on the spiny neuron. A residual excitatory response to the NK1-receptor agonist was observed in 30% of a sample of neurons tested in the presence of both haloperidol and atropine. The increase in R(N) that accompanied this response could be observed in the presence of 1 microM TTX or 100 microM Cd2+, suggesting a direct effect. Double labeling showed that only SP-immunoreactive neurons were facilitated by NK1-receptor activation in these conditions.

Distinct modifications by neurokinin1 (SR140333) and neurokinin2 (SR48968) tachykinin receptor antagonists of the N-methyl-D-aspartate-evoked release of acetylcholine in striosomes and matrix of the rat striatum

The effects of SR140333 and SR48968 (neurokinin1 and neurokinin2 tachykinin receptor antagonists, respectively) on the N-methyl-D-aspartate-evoked release of [3H]acetylcholine (previously formed from [3H]choline) were investigated in striosome-enriched areas and in the matrix of the rat striatum using an in vitro microsuperfusion method. In both striatal compartments, SR140333 and SR48968 did not modify the 50 microM N-methyl-D-aspartate-evoked release of [3H]acetylcholine. However, in low concentrations, both SR140333 (0.1 microM to 1 pM) and SR48968 (0.1 microM to 0.1 nM) markedly enhanced the 1 mM N-methyl-D-aspartate (+10 microM D-serine)-evoked release of [3H]acetylcholine in striosome-enriched areas. These responses were dopamine-dependent since they were not observed any more following the local blockade of D2 receptors by sulpiride or of dopamine synthesis by alpha-methyl-p-tyrosine. A dopamine-dependent disinhibitory effect (of lower amplitude) on the 1 mM N-methyl-D-aspartate (+10 microM D-serine)-evoked release of [3H]acetylcholine was also induced by SR48968 (0.1 microM to 0.1 nM) (but not by SR140333) in the matrix. In addition, in the matrix, as shown only in the presence of alpha-methyl-p-tyrosine, both SR140333 and SR48968 reduced the 1 mM N-methyl-D-aspartate (+10 microM D-serine)-evoked response and these non-dopamine-mediated inhibitory effects only occurred at the highest tested concentration (0.1 microM) of the antagonists. Indicating the specificity of these responses, the effects of SR140333 were reproduced by RP67580, another neurokinin1 receptor antagonist and, as expected from previous binding studies, corresponding SR140333 and SR48968 enantiomers were without effect. These results suggest that under potent stimulation of N-methyl-D-aspartate receptors, endogenously released substance P and neurokinin A (or related tachykinins) regulate differently the N-methyl-D-aspartate-evoked release of [3H]acetylcholine in striosomes and in the matrix. The inhibitory effects of these tachykinins on the evoked release of [3H]acetylcholine are mediated by dopamine. On the contrary, their facilitatory responses are only observed in the matrix under blockade of dopamine transmission.

Dopamine D1-like receptor activation excites rat striatal large aspiny neurons in vitro

The aim of this study was to elucidate electrophysiologically the actions of dopamine and SKF38393, a D1-like dopamine receptor agonist, on the membrane excitability of striatal large aspiny neurons (cholinergic interneurons). Whole-cell and perforated patch-clamp recordings were made of striatal cholinergic neurons in rat brain slice preparations. Bath application of dopamine (1-100 microM) evoked a depolarization/inward current with an increase, a decrease, or no change in membrane conductance in a dose-dependent manner. This effect was antagonized by SCH23390, a D1-like dopamine receptor antagonist. The current-voltage relationships of the dopamine-induced current determined in 23 cells suggested two conductances. In 10 cells the current reversed at -94 mV, approximately equal to the K+ equilibrium potential (EK); in three cells the I-V curves remained parallel, whereas in 10 cells the current reversed at -42 mV, which suggested an involvement of a cation permeable channel. Change in external K+ concentration shifted the reversal potential as expected for Ek in low Na+ solution. The current observed in 2 mM Ba2+-containing solution reversed at -28 mV. These actions of dopamine were mimicked by application of SKF38393 (1-50 microM) or forskolin (10 microM), an adenylyl cyclase activator, and were blocked by SCH23390 (10 microM) or SQ22536 (300 microM), an inhibitor of adenylyl cyclase. These data indicate, first, that dopamine depolarizes the striatal large aspiny neurons by a D1-mediated suppression of resting K+ conductance and an opening of a nonselective cation channel and, second, that both mechanisms are mediated by an adenylyl cyclase-dependent pathway.

Electrochemical studies of the effects of substance P on dopamine terminals in the rat striatum

The purpose of this study was to investigate the regulation of dopamine (DA) release and clearance by Substance P (SP) in striatum. In vivo high speed chronoamperometric recording techniques, with Nafion-coated carbon-fiber electrodes, were used to evaluate extracellular DA concentrations in urethane-anesthetized Sprague-Dawley rats. SP was locally applied to striatum. Our data indicate that SP can induce DA release in striatum. However, only about half of the striatal sites respond to SP. Readministration of SP to the same site elicited a smaller DA release. These data suggest that SP-evoked release shows tachyphyllaxis and is heterogeneous in the striatum. Lesioning of DA neurons with 6-OHDA into the medial forebrain bundle abolished DA release induced by SP. It has been shown that SP interacts with three different tachykinin receptors. We found that application of the Neurokinin-1 (NK1) agonist [Sar9, Met (O2)11]SP, but not the NK3 agonist senktide, induced DA release, suggesting that SP-induced DA release may be mediated through NK1 receptors. We further examined SP effects on DA clearance in striatum. We found that pretreatment with SP significantly attenuated extracellular levels of DA after exogeneous application of DA, suggesting that DA clearance is augmented by SP. Taken together, our data demonstrate that substance P facilitates dopamine release and clearance in the striatum.

Distribution of a glucocorticoid-induced orphan receptor (JP05) mRNA in the central nervous system of the mouse

JP05 (originally referred to as glucocorticoid-induced receptor gene or cDNA clone 4.2) designates a gene originally isolated from murine thymoma WEHI-7TG cells after being treated with glucocorticoids and forskolin. This gene is also induced by dexamethasone (a potent glucocorticoid receptor agonist) in isolated normal murine thymocytes. The predicted amino acid sequence was found to share significant similarity to the family of G-protein-coupled receptors, in particular to the tachykinin receptors NK-1, NK-2 and NK-3, with which it has an overall identity of 32%, 31% and 33%, respectively. The results of the present in situ hybridization analysis reveal that JP05 mRNA containing cells are extensively distributed throughout the rostrocaudal extension of the brain and spinal cord. However, the vast majority of the areas with high to moderate levels of JP05 mRNA were localized in the forebrain, primarily within limbic system structures, the dorsal and ventral striatum and in some hypothalamic nuclei. These results are discussed in relation to the central nervous system distribution of glucocorticoid receptor-containing cells and to the tachykinin system.

Facilitation of striatal acetylcholine release by dopamine D1 receptor stimulation: involvement of enhanced nitric oxide production via neurokinin-2 receptor activation

The regulation of striatal cholinergic function by dopamine D1 receptor activation was examined in vivo in urethane-anaesthetized rats with microdialysis probes. Extracellular acetylcholine levels were enhanced by activation of D1 receptors either directly by a striatal application of the D1 receptor agonist (+)-SKF-38393 (3 microM) or indirectly by the release of dopamine evoked by striatal application of neurotensin (0.1 microM) under D2 receptor blockade. SR 144190, a new potent and selective non-peptide neurokinin-2 receptor antagonist (0.03-1 mg/kg, i.p.), dose-dependently reduced the acetylcholine release induced by (+)-SKF-38393 or neurotensin. Furthermore, intrastriatal application of SR 144190 (1 nM) blocked the increase in acetylcholine release induced by the local application of (+)-SKF-38393 (3 microM), neurokinin A (1 microM) or substance P (1 microM). Finally, a role for nitric oxide in mediating the effects of D1 neurokinin-2 receptor activation on acetylcholine release is proposed since local infusion of the competitive inhibitor of nitric oxide synthase, N(G)-monomethyl-L-arginine (0.01-10 microM), blocked the increase in acetylcholine release induced by (+)-SKF-38393 (3 microM), neurotensin (0.1 microM) or neurokinin A (1 microM) without affecting the enhancing effect of the neurokinin-1 agonist septide (0.1 microM).

Collateral projections from striatonigral neurons to substance P receptor-expressing intrinsic neurons in the striatum of the rat

It is well known that striatonigral neurons produce substance P (SP); however, no SP receptor (SPR) has so far been found in the substantia nigra. On the other hand, a previous study in the rat striatum indicated that SPR was expressed only in cholinergic or somatostatinergic intrinsic neurons (Kaneko et al. [1993] Brain Res. 631:297-303). Thus, it was assumed that SP produced by striatonigral neurons might be released through their intrastriatal axon collaterals to act upon intrinsic neurons in the striatum. To confirm this assumption, the distribution of axon collaterals of striatonigral neurons was examined in the striatum of the rat. The experiments were performed on brain slices by combining retrograde labeling with tetramethylrhodamine-dextran amine, electrophysiological recording, intracellular staining with biocytin, and immunocytochemistry for SPR. The distribution of axons of cholinergic striatal neurons (a group of SP-negative intrinsic striatal neurons) was also examined. It was observed that 16% of varicosities of intrastriatal axon collaterals of striatonigral neurons, as well as 6% of axonal varicosities of cholinergic neurons, were in close apposition to dendrites and cell bodies of SPR-immunoreactive striatal neurons. Since SPR-immunoreactive striatal neurons constituted only 2.7% of the total population of striatal neurons (Kaneko et al. [1993] Brain Res. 631:297-303), it appeared that axonal varicosities of striatonigral neurons were preferentially apposed to SPR-immunoreactive striatal neurons and that the varicosities in close apposition to SPR-immunoreactive neurons were derived more frequently from striatonigral neurons than from cholinergic interneurons. Confocal laser scanning microscopy indicated that axonal varicosities in close apposition to SPR-immunoreactive cells showed synaptophysin immunoreactivity, a marker of synaptic vesicles. In intrastriatal axons of striatonigral neurons, it was further revealed from electron microscopy that axonal varicosities in close apposition to SPR-immunoreactive dendrites, at least a part of them, made synapses of the symmetric type. Striatonigral neurons might release SP preferentially around cholinergic or somatostatinergic intrinsic neurons to regulate them through SP-SPR interactions.

Regulation of dopamine D1 and D2 receptors on striatal acetylcholine release in rats

The effects of dopamine (DA) D1 and D2 receptors on striatal acetylcholine (ACh) releases were investigated by in vivo microdialysis. All drugs were applied via dialysis membrane directly to the striatum. The levels of ACh release were increased by 10(-4) M SKF38393, a D1 receptor agonist. Although 10(-4) M SCH23390, a D1 receptor antagonist, exhibited an increase in the levels of ACh release, the agonist (10(-4) M) induced-increase in the levels of ACh release was suppressed by coperfusion of the antagonist (10(-4) M). In contrast, the levels of ACh release were decreased by the D2 receptor agonist, N-434, in a dose-dependent manner (10(-4) M to 10(-7) M) and increased by the D2 receptor antagonist, sulpiride, in a dose-dependent manner (10(-5) M to 10(-7) M). The agonist (10(-5) M) induced-decrease in the levels of ACh release was suppressed by coperfusion of the antagonist (10(-4) M). Coperfusion of D1 (10(-4) M) and D2 (10(-5) M) agonists blocked both effects of respective drug alone. In order to clarify the effect of endogenous DA, two drugs with different mechanisms for enhancing DA concentration in the synaptic cleft, the DA release-inducer methamphetamine, and the DA uptake inhibitor nomifensine were perfused separately. Both (10(-4) M to 10(-5) M) produced a dose- and a time-dependent decrease in the levels of ACh release. Significant higher levels of ACh release were observed in the striatum of the 6-hydroxydopamine (8 micrograms/10 microliters)-treated rats with significant depletion of striatal DA content. These results suggest that in striatal DA-ACh interaction ACh release, as cholinergic interneuron's activity, is tonically inhibited via the D2 receptor, mainly by dopaminergic input, and the D1 receptor probably modifies the effect of the D2 receptor indirectly.

Actions of substance P on rat neostriatal neurons in vitro

Actions of substance P (SP) on the neostriatal neurons in in vitro rat slice preparations were studied via whole-cell patch-clamp recording. Almost all large aspiny neurons (cholinergic cells) and half of the low-threshold spike (LTS) cells (somatostatin/ NOS-positive cells) showed depolarization or an inward shift of the holding currents in response to bath-applied SP in a dose-dependent manner. In contrast, no responses were observed in fast-spiking (FS) cells (parvalbumin-positive cells) and medium spiny cells. Spike discharges followed by slow EPSPs/EPSCs were evoked by intrastriatal electrical stimulation in the large aspiny neurons. Pretreatment with [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-SP, an antagonist of the SP receptor, reversibly suppressed the induction of the slow EPSPs/EPSCs and unmasked slow IPSCs. The SP-induced inward current, although almost unchanged even after the blockade of Ih channels and voltage-dependent Na+, Ca2+, and K+ channels, changed its amplitude according to the Na+ concentration used in both the large aspiny neurons and LTS cells. Thus, the cation current could account for virtually all of the inward current at resting levels in both neurons. These results suggest that the firing of afferent neurons such as striatonigral medium spiny neurons, one of the possible sources of SP, would increase the firing probability of the two types of interneurons of the neostriatum by SP-receptor-mediated opening of tetrodotoxin-insensitive cation channels.

Tachykinins protect cholinergic neurons from quinolinic acid excitotoxicity in striatal cultures

The neuroprotective effect of tachykinins against excitotoxic death of cholinergic neurons was studied in rat striatal cell cultures. Quinolinic acid (QUIN) and kainic acid (KA) produced a dose dependent decrease in choline acetyltransferase activity, but KA was more potent. Our results show that substance P (SP) totally reversed the toxicity induced by 125 microM QUIN but not by 40 microM KA. This effect was also observed using protease inhibitors or a SP-analog resistant to degradation, [Sar9]-Substance P. The survival of neuron specific enolase- and acetylcholinesterase (AChE)-positive cells after treatment with QUIN alone or in the presence of SP was also examined. We observed that, while a decrease in total cell number produced by QUIN was not prevented by SP treatment, AChE-positive cells were rescued from the toxic damage. To characterize the SP protective effect we used more selective agonists of the three classes of neurokinin (NK) receptors. [Sar9, Met(O2)11]-Substance P (NK1 receptor agonist), [Nle10]-Neurokinin A (NK2 receptor agonist) or [Me-Phe7]-Neurokinin B (NK3 receptor agonist) were all able to block the toxic effect of QUIN on cholinergic activity. These results show that tachykinins provide an important protective support for striatal neurons, suggesting a possible therapeutical benefit in neurodegenerative disorders affecting cholinergic neurons.

N- and C-terminal substance P fragments modulate striatal dopamine outflow through a cholinergic link mediated by muscarinic receptors

The present study investigated whether the modulatory effects of substance P and substance P fragments on striatal dopamine release involve a cholinergic link. Rat striatal slices were incubated with substance P, substance P(1-4), substance P(1-7), substance P(5-11) and substance P(8-11) in the absence or presence of various agents which modify cholinergic transmissions, and endogenous dopamine outflow was measured using high-performance liquid chromatography. The incubation of striatal slices with substance P and its N- and C-terminal fragments (1 nM) induced a significant overflow of endogenous dopamine. Neostigmine (150 nM) potentiated the effects of substance P and its fragments, whereas the incubation with hemicholinium-3 (50 microM) abolished the effects of the peptides on dopamine outflow. The acetylcholinesterase inhibitor and the inhibitor of choline uptake did not have intrinsic effects on dopamine outflow. The muscarinic antagonist atropine (1 microM) reversed completely the effects of substance P and its fragments, whereas the nicotinic antagonists dihydro-beta-erythroidine (0.5 microM) and pempidine (10 microM) were devoid of effects. None of the cholinergic antagonists modified dopamine outflow. The results suggest that substance P and several N- and C-terminal substance P fragments activate cholinergic neurons in striatal slices. The released acetylcholine induces an increased dopamine outflow, mediated by muscarinic receptors. These observations represent additional evidence which supports the functional interactions between substance P, acetylcholine and dopamine in the striatum. Furthermore, they show that substance P fragments may exert neuromodulatory effects through mechanisms similar to those underlying the effects of the parent peptide.

Distribution and neurochemical character of substance P receptor (SPR)-immunoreactive striatal neurons of the macaque monkey: accumulation of SP fibers and SPR neurons and dendrites in "striocapsules" encircling striosomes

The striatal distribution of the substance P receptor (SPR) protein was examined in relation to its ligand, the neuro-peptide SP, as well as to the neurochemical and compartmental composition of the neostriatum in rhesus monkeys (Macaca mulatta) in immunohistochemical experiments. About 2% of striatal neurons, displaying varicose, virtually spine-free dendrites characteristic of large and medium-sized aspiny interneurons, expressed SPR immunoreactivity. SPR/choline acetyltransferase, SPR/somatostatin, SPR/GABA, SPR/calbindin D28k, and SPR/parvalbumin double immunolabeling experiments demonstrated that SPR-positive cells are either cholinergic or somatostatinergic. Comparison of SP and SPR immunoreactivities in double-labeled and adjacent single-labeled sections revealed compartment-specific match and mismatch between the densities of the peptide and receptor. A matching high density of SP fibers and SPR cells and dendrites was only observed in the rim of the striosome compartments. To our knowledge, this is the first evidence for an anatomical border comprised of dendritic processes that separate striatal compartments. We have termed these zones "striocapsules," because they encircle and encapsulate striosomal cell islands. In the striatal matrix, an abundance of SPR-labeled profiles was complemented with light SP staining. By contrast, in the core of the striosomes, SPR labeling was sparse and SP staining intense. SP-positive axon-like puncta frequently contacted SPR-positive dendrites in all striatal compartments. The SP receptor/ligand match indicates a sharp increase in the efficacy of SP action in the striocapsules, and suggests that the influence of SP might be heightened in this striatal subcompartment.

Presynaptic and postsynaptic subcellular localization of substance P receptor immunoreactivity in the neostriatum of the rat and rhesus monkey (Macaca mulatta)

The substance P receptor (SPR) gene is expressed at high levels in basal ganglia, but the paucity of information about localization of the encoded receptor protein has limited our understanding of this peptide's involvement in cellular and subcellular mechanisms in this region. Morphological evidence in the rodent striatum indicates that SPRs are expressed in postsynaptic neuronal elements, while pharmacological studies suggest the existence of presynaptic SPRs in this structure. We have examined the issue of subcellular distribution of this receptor protein in rat and primate neostriatal tissue, employing an antiserum raised against SPR. Electron microscopic analysis revealed that SPR immunoreactivity is present in presynaptic and postsynaptic neuronal elements in both species. In agreement with earlier studies, SPR immunoreactivity was found predominantly in perikarya and dendrites of a small subset of striatal neurons, the large and medium-sized aspiny interneurons. In addition, a small but significant proportion of the immunoreaction product was localized in presynaptic profiles, both in axons and axon terminals. The majority of SPR immunoreactive boutons formed asymmetric synapses with dendrites and dendritic spines. The association of SPRs with asymmetric synapses provides a morphological substrate for peptidergic modulation of excitatory neurotransmission of extrastriatal origin. A minor proportion of immunolabeled axons established symmetric synaptic junctions with unlabeled dendrites. The presence of SPRs in these synapses suggests a presynaptic peptidergic modulation of intrinsic striatal transmitter systems. The observations in this study also indicate that SPR mediates a complex combination of postsynaptic and presynaptic effects on acetylcholine release in the mammalian striatum.

Evidence for modulatory effects of substance P fragments (1-4) and (8-11) on endogenous dopamine outflow in rat striatal slices

The effects of substance P-(1-4) and substance P-(8-11) on endogenous dopamine outflow in rat striatal slices were investigated. The dose-response curves (0.01 nM to 1 microM) were bell-shaped for both peptides, with significant increases in dopamine outflow at 0.1 and 1 nM. Dopamine overflow elicited by 1 nM substance P-(1-4) or substance P-(8-11) and 25 mM KCl was additive. Although substance P-(8-11) contains a truncated tachykinin sequence, the tachykinin NK1 receptor antagonist WIN 51,708 (17 beta-hydroxy-17 alpha-ethynyl-5 alpha-androstano[3,2-b]pyrimido[1,2- a]benzimidazole (2.5 nM) fully reversed its effect. The interaction between the antagonist and 1 nM substance P-(1-4) was statistically not significant. The data constitute the first evidence that the fragments substance P-(1-4) and substance P-(8-11) could exert central effects and suggest that they may play a role in neuromodulation in the basal ganglia.

Striatal interneurones: chemical, physiological and morphological characterization

The neostriatum is the largest component of the basal ganglia, and the main recipient of afferents to the basal ganglia from the cerebral cortex and thalamus. Studies of the cellular organization of the neostriatum have focused upon the spiny projection neurones, which represent the vast majority of neurones, but the identity and functions of interneurones in this structure have remained enigmatic despite decades of study. Recently, the discovery of cytochemical markers that are specific for each of the major classes of striatal interneurones, and the combination of this with intracellular recording and staining, has revealed the identities of interneurones and some of their functional characteristics in a way that could not have been imagined by the classical morphologists. These methods also suggest some possible modes of action of interneurones in the neostriatal circuitry.

Effects of L-DOPA on preproenkephalin and preprotachykinin gene expression in the MPTP-treated monkey striatum

The cellular expression of the genes encoding the neuropeptides enkephalin and substance P were examined in the caudate nucleus and putamen of parkinsonian 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated cynomolgus monkeys by in situ hybridization using radioactive antisense oligonucleotides coupled with computer-assisted image analysis. Behavioural evaluation of the animals revealed two levels of motor impairment; one group moderately impaired and the other severely disabled. A marked increase in the cellular content of preproenkephalin A messenger RNA was observed in medium-sized (106 +/- 9 microns2) cells in the caudate-putamen of all MPTP animals when compared with controls, the increase being greatest in the most severely impaired animals. By contrast, a marked reduction in the cellular abundance of preprotachykinin gene expression was detected in striatal cells (101 +/- 16 microns2) of these same MPTP animals. These changes in neuropeptide gene expression were not associated with a change in the density (approximately 10 cells per mm2) of messenger RNA-expressing cells. L-DOPA treatment of two of the severely-impaired MPTP monkeys resulted in a dissociation of expression of these two genes: the cellular abundance of preproenkephalin A remained elevated whilst preprotachykinin levels were normalized and comparable with controls. No change in the cellular abundance of preprotachykinin messenger RNA was observed in cells of the insular cortex or a small discrete population of large cells (208 +/- 27 microns2) in the ventral putamen. These results demonstrate that MPTP treatment of primates results in a marked potentiation in preproenkephalin messenger RNA coupled with a attenuation in preprotachykinin messenger RNA in the dopamine-denervated caudate-putamen. L-DOPA therapy given on an intermittent schedule reverses the decrease in preprotachykinin messenger RNA, but fails to reverse the increase in preproenkephalin messenger RNA in the same animal. These observations suggest that a dissociation of the activity of these two neuropeptide systems may underlie the improvement in motor skill that accompanies dopamine replacement therapy and that this dissociation may be instrumental in the long-term complications associated with L-DOPA therapy.