Evidence for the existence of substance P-containing fibres in striato-nigral and pallido-nigral pathways in rat brain

Gut neuropeptide involvement in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder affecting over 10 million people. A key pathological feature of PD is the accumulation of misfolded α-synuclein (aSyn) protein in the substantia nigra pars compacta. Aggregation of aSyn can form Lewy bodies that contribute to dopaminergic neuron degeneration and motor symptoms, such as tremor, rigidity, and bradykinesia. Beyond the central nervous system, aSyn aggregates have been detected in the gastrointestinal (GI) tract, suggesting a link between peripheral aSyn and nonmotor PD symptoms. GI symptoms, often preceding motor symptoms by up to 20 years, highlight the bidirectional communication between the central nervous system and the enteric nervous system (gut-brain axis) in PD. Although microbiome alterations and intestinal inflammation have been associated with PD, functional impacts on gut-brain signaling or aSyn aggregation remain unclear. Intestinal neuropeptides are key modulators of gut-brain communication, alter immune response to pathogens and environmental toxins, and may contribute to the function of the luminal gut barrier. Dysregulation of gut neuropeptide signaling, including vasoactive intestinal peptide, neuropeptide Y, calcitonin gene-related peptide, ghrelin, cholecystokinin, glucagon-like peptide 1, and substance P, have been associated with pathologic effects of PD in animal models. Despite their potential role in pathogenesis and disease modulation, gut neuropeptide roles in PD are underexplored. This article reviews current knowledge surrounding microbial metabolite and immune influences on gut neuropeptide signaling, aSyn aggregation in the enteric nervous system, and downstream neuroimmune pathway alterations within the context of PD and its mouse models.

Enhancing Post-Stroke Rehabilitation and Preventing Exo-Focal Dopaminergic Degeneration in Rats-A Role for Substance P

Dopaminergic signaling is a prerequisite for motor learning. Delayed degeneration of dopaminergic neurons after stroke is linked to motor learning deficits impairing motor rehabilitation. This study investigates safety and efficacy of substance P (SP) treatment on post-stroke rehabilitation, as this neuropeptide combines neuroprotective and plasticity-promoting properties. Male Sprague Dawley rats received a photothrombotic stroke within the primary motor cortex (M1) after which a previously acquired skilled reaching task was rehabilitated. Rats were treated with intraperitoneal saline (control group, n = 7) or SP-injections (250 µg/kg) 30 min before (SP-pre; n = 7) or 16 h (SP-post; n = 6) after rehabilitation training. Dopaminergic neurodegeneration, microglial activation and substance P-immunoreactivity (IR) were analyzed immunohistochemically. Systemic SP significantly facilitated motor rehabilitation. This effect was more pronounced in SP-pre compared to SP-post animals. SP prevented dopaminergic cell loss after stroke, particularly in the SP-pre condition. Despite its proinflammatory propensity, SP administration did not increase stroke volumes, post-stroke deficits or activation of microglia in the midbrain. Finally, SP administration prevented ipsilesional hypertrophy of striatal SPergic innervation, particularly in the SP-post condition. Mechanistically, SP-pre likely involved plasticity-promoting effects in the early phase of rehabilitation, whereas preservation of dopaminergic signaling may have ameliorated rehabilitative success in both SP groups during later stages of training. Our results demonstrate the facilitating effect of SP treatment on motor rehabilitation after stroke, especially if administered prior to training. SP furthermore prevented delayed dopaminergic degeneration and preserved physiological endogenous SPergic innervation.

Progressive secondary exo-focal dopaminergic neurodegeneration occurs in not directly connected midbrain nuclei after pure motor-cortical stroke

Transsynaptic anterograde and retrograde degeneration of neurons and neural fibers are assumed to trigger local excitotoxicity and inflammatory processes. These processes in turn are thought to drive exo-focal neurodegeneration in remote areas connected to the infarcted tissue after ischemic stroke. In the case of middle cerebral artery occlusion (MCAO), in which striato-nigral connections are affected, the hypothesis of inflammation-induced remote neurodegeneration is based on the temporal dynamics of an early appearance of inflammatory markers in midbrain followed by dopaminergic neuronal loss. To test the hypothesis of a direct transsynaptic mediation of secondary exo-focal post-ischemic neurodegeneration, we used a photochemical induction of a stroke (PTS) in Sprague-Dawley rats restricted to motor cortex (MC), thereby sparing the striatal connections to dopaminergic midbrain nuclei. To dissect the temporal dynamics of post-ischemic neurodegeneration, we analyzed brain sections harvested at day 7 and 14 post stroke. Here, an unexpectedly pronounced and widespread loss of dopaminergic neurons occurred 14 days after stroke also affecting dopaminergic nuclei that are not directly coupled to MC. Since the pattern of neurodegeneration in case of a pure motor stroke is similar to a major stroke including the striatum, it is unlikely that direct synaptic coupling is a prerequisite for delayed secondary exo-focal post ischemic neurodegeneration. Furthermore, dopaminergic neurodegeneration was already detected by Fluoro-Jade C staining at day 7, coinciding with a solely slight inflammatory response. Thus, inflammation cannot be assumed to be the primary driver of exo-focal post-ischemic cell death. Moreover, nigral substance P (SP) expression indicated intact striato-nigral innervation after PTS, whereas opposing effects on SP expression after striatal infarcts argue against a critical role of SP in neurodegenerative or inflammatory processes during exo-focal neurodegeneration.

The pharmacology of neurokinin receptors in addiction: prospects for therapy

Addiction is a chronic disorder in which consumption of a substance or a habitual behavior becomes compulsive and often recurrent, despite adverse consequences. Substance p (SP) is an undecapeptide and was the first neuropeptide of the neurokinin family to be discovered. The subsequent decades of research after its discovery implicated SP and its neurokinin relatives as neurotransmitters involved in the modulation of the reward pathway. Here, we review the neurokinin literature, giving a brief historical perspective of neurokinin pharmacology, localization in various brain regions involved in addictive behaviors, and the functional aspects of neurokinin pharmacology in relation to reward in preclinical models of addiction that have shaped the rational drug design of neurokinin antagonists that could translate into human research. Finally, we will cover the clinical investigations using neurokinin antagonists and discuss their potential as a therapy for drug abuse.

What is the Degree of Segregation between Striatonigral and Striatopallidal Projections?

In contrast to most other brain regions, in the striatum the output neurons (the medium-sized spiny neurons, MSNs) are GABAergic and act by inhibiting their targets. The standard model of the basal ganglia is built on the segregation of information processing in the direct and indirect pathways, which act in opposing directions to control movement. The MSNs participating in these two pathways can be identified according to their projection sites and the proteins they express. The differential expression of two of the five known dopamine receptor subtypes, D1 and D2, in the two populations of MSNs is of particular importance, since it confers to dopamine the ability to exert opposite functional modulation on the direct and indirect pathways. However, beyond this simple view of the striatal output organization, anatomical studies questioned the segregation of direct and indirect projections to the SNr, while other studies disclosed variable degrees of overlapping expression of dopamine receptor subtypes in striatal MSNs. New ways to address these issues have emerged recently, using mouse models in which specific populations of striatal neurons are genetically tagged. Here, we review classical and recent studies supporting the segregation of striatonigral and striatopallidal neurons. We also consider this issue at a functional level by focusing on the regulation of striatal signaling pathways in the two populations of MSNs, which clearly emphasize their profound differences. We discuss the anatomical and functional evidence challenging some aspects of this segregation and outline questions that are still to be addressed.

Paucity of enkephalin production in neostriatal striosomal neurons: analysis with preproenkephalin-green fluorescent protein transgenic mice

Whether or not the striosome compartment of the neostriatum contained preproenkephalin (PPE)-expressing neurons remained unresolved. To address this question by developing a sensitive detection method, we generated transgenic mice expressing enhanced green fluorescent protein (GFP) under the specific transcriptional control of the PPE gene. Eight transgenic lines were established, and three of them showed GFP expression which was distributed in agreement with the reported localization of PPE mRNA in the central nervous system. Furthermore, in the matrix compartment of the neostriatum of the three lines, intense GFP immunoreactivity was densely distributed in the neuronal cell bodies and neuropil, and matrix neurons displayed > 94% co-localization for GFP and PPE immunoreactivities. In sharp contrast, GFP immunoreactivity was very weak in the striosome compartment, which was characterized by intense immunoreactivity for mu-opioid receptors (MOR). Although neostriatal neurons were divided into GFP-immunopositive and -negative groups in both the striosome and matrix compartments, GFP immunoreactivity of cell bodies was much weaker (~1/5) in GFP-positive striosomal neurons than in GFP-positive matrix neurons. A similar reciprocal organization of PPE and MOR expression was also suggested in the ventral striatum, because GFP immunoreactivity was weaker in intensely MOR-immunopositive regions than in the surrounding MOR-negative regions. As PPE-derived peptides are endogenous ligands for MOR in the neostriatum and few axon collaterals of matrix neurons enter the striosome compartment, the present results raised the question of the target of those peptides produced abundantly by matrix neurons.

Responses of limbic and extrapyramidal substance P systems to nicotine treatment

RATIONALE

Neuropeptides are linked to the psychopathology of stimulants of abuse, principally through dopamine mechanisms. Substance P (SP) is one of these neuropeptides and is associated with both limbic and extrapyramidal dopaminergic pathways and likely contributes to the pharmacology of these stimulants. The effects of nicotine on these dopamine systems have also been extensively studied; however, its effects on the associated SP pathways have received little attention.

OBJECTIVES

In the present study, we elucidated the effects of nicotine treatment on limbic and extrapyramidal SP systems by measuring changes in associated SP tissue concentrations.

MATERIALS AND METHODS

Male Sprague-Dawley rats received (+/-)nicotine 4.0 mg/kg/day (0.8 mg/kg, intraperitoneally; five injections at 2-h intervals) in the presence or absence of selective dopamine D1 and D2 receptor antagonists or a nonselective nicotinic acetylcholine receptor antagonist.

RESULTS

The nicotine treatment significantly but temporarily decreased substance P-like immunoreactivity (SPLI) content in the ventral tegmental area (VTA) and substantia nigra 12-18 h after drug exposure. The nicotine-mediated changes in SPLI were selectively blocked by pretreatment with mecamylamine as well as a dopamine D1, D2, or both receptor antagonists. Other brain areas that also selectively demonstrated nicotine-related declines in SPLI content included prefrontal cortex, the nucleus accumbens shell, and the very posterior caudate.

CONCLUSIONS

These findings indicate that some limbic and basal ganglia SP systems are significantly affected by exposure to nicotine through processes mediated by nicotinic and dopaminergic receptors, suggesting a role for SP pathways in nicotine's limbic and extrapyramidal effects.

Molecular profiling of striatonigral and striatopallidal medium spiny neurons past, present, and future

Defining distinct molecular properties of the two striatal medium spiny neurons (MSNs) has been a challenging task for basal ganglia (BG) neuroscientists. Identifying differential molecular components in each MSN subtype is crucial for BG researchers to understand functional properties of these two neurons. The two MSN populations are morphologically identical except in their projections through the direct verses indirect BG pathways and they are heterogeneously dispersed throughout the dorsal striatum (dStr) and nucleus accumbens (NAc). These characteristics have made it difficult for researchers to distinguish and isolate these two neuronal populations thereby hindering progress toward a more comprehensive understanding of their differential molecular properties. Researchers began to investigate molecular differences in the striatonigral and striatopallidal neurons using in situ hybridization (ISH) techniques and single cell reverse transcription-polymerase chain reaction (scRT-PCR). Currently the field is utilizing more advanced techniques for large-scale gene expression studies including fluorescence activated cell sorting (FACS) of MSNs, from which RNA is purified, from fluorescent reporter transgenic mice or use of transgenic mice in which ribosomes from each MSN are tagged and can be immunoprecipitated followed by RNA isolation, a technique termed translating ribosomal affinity purification (TRAP). Additionally, the availability of fluorescent reporter mice for each MSN subtype is allowing, scientists to perform more accurate histology studies evaluating differential protein expression and signaling changes in each cell subtype. Finally, researchers are able to evaluate the role of specific genes in vivo by utilizing cell type-specific mouse models including Cre driver lines that can be crossed with conditional overexpression or knockout systems. This is a very exciting time in the BG field because researchers are well equipped with the most progressive tools to comprehensively evaluate molecular components in the two MSNs and their consequence on BG functional output in the normal, diseased, and developing brain.

Localization of substance P in neuronal pathways

The main neuronal systems containing substance P are summarized on the basis of immunohistochemical evidence. The substance P striatonigral projection is one of the most conspicuous of these. Electron microscopic studies using the peroxidase-antiperoxidase technique reveal some heterogeneity in the substance P-immunostained material in the substantia nigra. Immunoreactivity for the peptide is found in terminals establishing both symmetrical and asymmetrical synapses with substantia nigra dendrites. Substance P immunoreactivity in the substantia gelatinosa of the trigeminal nerve and in the skin of the trigeminal territory was found to be depleted after sensory denervation. Electron microscopy showed that in this area of the rat brain substance P-immunoreactive elements are largely associated with dendrites and establish asymmetrical axo-dendritic synapses. Substance P-immunoreactive terminals synapsing with presynaptic dendrites were also observed (i.e. dendrites that themselves are presynaptic to other dendrites). The origin of substance P-containing fibres in the prevertebral ganglia has been investigated in the guinea-pig by combining surgical procedures and immunohistochemistry. Only procedures which disconnected dorsal root ganglia from prevertebral ganglia depleted substance P immunofluorescence in the latter. This substance P-immunoreactive material disappeared after administration of capsaicin. Electron microscopic studies in prevertebral ganglia show that substance P-immunoreactive varicosities establish axodendritic contacts with the sympathetic neurons. These observations provide strong evidence for direct synaptic sensory-autonomic interactions in the prevertebral ganglia involving substance P-containing collaterals of peripheral sensory nerve fibres.

Behavioural effects of substance P through dopaminergic pathways in the brain

Some of the highest concentrations of substance P in forebrain are found in areas where dopaminergic neurons arise or terminate. In the rat, native substance P has been injected directly into brain areas where interactions between substance P and dopamine are suspected. In the ventral tegmental area (A10 dopamine neurons), bilateral infusions of substance P induce locomotor activity and exploration. It is concluded that substance P activates A10 dopamine neurons innervating the limbic system because (i) the behavioural effects resemble those seen after systemic treatment with low doses of d-amphetamine, a drug response known to depend on the integrity of the A10 dopamine neurons; (ii) lesions to the A10 dopamine neurons abolish the behavioural response to intracerebrally infused substance P; and (iii) dopamine antagonist drugs abolish the response to substance P. In parallel experiments substance P was injected into the origins of the nigrostriatal (A9 dopamine neurons) system and found to produce stereotyped behaviour. Substance P analogues protected from enzymic degradation have been studied in these model systems. The prolongation of the behavioural effects is correlated with the presence of undegraded substance P in the ventral tegmental area. Unrelated behavioural responses are also observed, which appear not to be mediated by dopamine neurons, and probably reflect the spread of stable substance P from the ventral tegmental area to other brain sites.

The striatonigral substance P pathway and dopaminergic mechanisms

The biosynthesis of 35S-labelled substance P (SP) has been shown in the rat striatum after continuous delivery of [35S]methionine through a push-pull cannula. In vitro and in vivo studies of SP release have demonstrated that release of the peptide depends on nerve activity and is regulated by presynaptic influences. When the 125I-labelled Bolton and Hunter SP derivative was used, specific binding was observed on mesencephalic cells of the mouse embryo in primary cultures and various characteristics of SP receptors could be determined. Finally, the effects of facilitation or prevention of SP transmission in the substantia nigra on the activity of nigrostriatal dopaminergic neurons have been studied in vivo in the cat by measuring dopamine released from nerve terminals and dendrites. The results obtained indicate that the striatonigral SP neurons exert a tonic facilitatory influence on the dopaminergic neurons.

Expression of D1 but not D2 dopamine receptors in striatal neurons producing neurokinin B in rats

Neostriatal projection neurons are known to be largely divided into two groups, striatoentopeduncular/striatonigral and striatopallidal neurons, which mainly express D1 and D2 dopamine receptors, respectively. Recently, a small population of neostriatal neurons have been reported to produce neurokinin B (NKB), and send their axons mainly to the basal forebrain regions. To reveal which type of dopamine receptors were expressed by these NKB-producing neurons, we examined rat striatal neurons by combining immunofluorescence labeling for preprotachykinin B (PPTB), the precursor of NKB, and fluorescence in situ hybridization labeling for dopamine receptors. Fluorescent signals for D1 receptor mRNA were detected in 85-89% of PPTB-immunopositive neurons in the neostriatum, accumbens nucleus and lateral stripe of the striatum, whereas almost no signal for D2 receptor was observed in PPTB-positive striatal neurons. To further reveal intracellular signaling downstream of D1 receptor in PPTB-producing neurons, we used a double immunofluorescence labeling method to study the localization of some substrates for protein kinase A (PKA), which was known to be activated by D1 receptor. Although only 3-7% of PPTB-immunopositive striatal neurons displayed immunoreactivity for dopamine- and cAMP-regulated phosphoprotein of 32 kDa, a well-known PKA substrate expressed in the two major groups of neostriatal projection neurons, 60-64% of PPTB-positive striatal neurons exhibited immunoreactivity for striatal-enriched tyrosine phosphatase. These results suggest that NKB-producing neostriatal neurons are similar to striatoentopeduncular/striatonigral neurons in the usage of dopamine receptor subtypes, but different from the two major groups of neostriatal projection neurons in terms of the downstream signaling of dopamine receptors.

Predominant surface distribution of neurokinin-3 receptors in non-dopaminergic dendrites in the rat substantia nigra and ventral tegmental area

Neurokinin-3 (NK(3)) receptors are prevalent within the substantia nigra (SN) and ventral tegmental area (VTA), where their activation can affect motor and motivational behaviors as well as cardiovascular function and stress responses. These actions are mediated, in part, by dopaminergic neurons in each region. To determine the relevant sites for activation of these receptors, we examined the electron microscopic localization of NK(3) receptors and tyrosine hydroxylase (TH), the catecholamine synthesizing enzyme in dopaminergic neurons in the SN and VTA of rat brain. In each region, immunogold-silver labeling for NK(3) receptors was detected in many somatodendritic profiles, some of which contained TH-immunoreactivity. NK(3)-immunogold particles were largely associated with endomembranes resembling smooth endoplasmic reticulum, and only occasionally located on the plasma membrane in TH-labeled dendrites. In comparison with these dendrites, non-TH immunoreactive dendrites contained significantly more total (VTA) and more plasmalemmal (VTA and SN) NK(3)-immunogold particles. In each region, NK(3) gold particles also were seen in axonal as well as glial profiles, some of which contacted TH-immunoreactive dendrites. The NK(3)-labeled axon terminals formed either symmetric or asymmetric, excitatory-type synapses, the latter of which were significantly more prevalent in the VTA, compared with SN. These results provide the first ultrastructural evidence indicating that NK(3) receptors are available in cytoplasmic reserve in dopaminergic neurons, but more immediately accessible at the plasmalemmal surface of non-dopaminergic dendrites in both the SN and VTA. The activation of these receptors, together with the NK(3) receptors in either the presynaptic axon terminals or glia may contribute to the diverse physiological effects of tachykinins in each region, and most prominently involving excitatory inputs to the VTA.

Subcellular distribution and plasticity of neurokinin-1 receptors in the rat substantia nigra and ventral tegmental area

Neurokinin-1 receptors show activity-dependent changes in their surface distributions that are critical in spinal pain mechanisms, and also may play an important role in the motor and affective behaviors influenced by dopaminergic projections from the substantia nigra and ventral tegmental area. To determine the relevant sites for neurokinin-1 receptor activation in these midbrain regions, we examined the electron microscopic immunolabeling of neurokinin-1 receptors and the dopamine-synthesizing enzyme, tyrosine hydroxylase in normal rats. We also examined whether neurokinin-1 receptor distributions in one or both regions are affected by (1) startle-evoking intense auditory stimulation or (2) acute administration of apomorphine, a dopamine D1/D2 agonist that enhances startle while paradoxically reducing the prepulse inhibition produced by low intensity conditioning stimuli in rat models of schizophrenia. In each region, neurokinin-1 immunogold was located on the plasma membrane and endomembranes of somatodendritic profiles with or without tyrosine hydroxylase. As compared with controls, animals receiving intense auditory stimulation either alone or together with smaller low intensity prepulses showed a significant increase in neurokinin-1-plasmalemmal labeling in non-dopaminergic dendrites of both regions, and a reduction in this labeling in dopaminergic dendrites of the ventral tegmental area. Both effects were diminished following apomorphine administration. In absence of the intense auditory stimulation, however, apomorphine increased neurokinin-1-immunogold particles on the plasma membrane of the non-dopaminergic dendrites exclusively in the substantia nigra. Our results are the first to show that neurokinin-1 receptors have plasmalemmal distributions in dopaminergic and non-dopaminergic neurons that can be differentially modified by startle-evoking auditory stimulation. They suggest that while apomorphine can independently affect neurokinin-1 receptor trafficking in substantia nigra motor circuits, its effects on neurokinin-1 receptor distributions in the ventral tegmental area are exclusively dependent on sensory activation.

Chemical organization of projection neurons in the rat accumbens nucleus and olfactory tubercle

Projection neurons in the ventral striatum, the accumbens nucleus and olfactory tubercle, were examined by combining the retrograde tracing method and immunocytochemistry with antibodies against C-terminals of the preprodynorphin (PPD), preproenkephalin (PPE), preprotachykinin A (PPTA) and preprotachykinin B (PPTB). When the retrograde tracer was injected into the ventral pallidum, about 60% and 40% of retrogradely labeled neurons in the accumbens nucleus were immunoreactive for PPD and PPE, respectively. In contrast, all accumbens nucleus neurons projecting to the ventral mesencephalic regions including the substantia nigra and ventral tegmental area were immunopositive for PPD but not for PPE. Although no olfactory tubercle neurons projected fibers to the mesencephalic regions, 60% and 40% of olfactory tubercle neurons projecting to the ventrolateral portion of the ventral pallidum were immunoreactive for PPD and PPE, respectively, as were the accumbens nucleus neurons. About 70% of accumbens nucleus and olfactory tubercle neurons projecting to the ventral pallidum and all accumbens nucleus neurons projecting to the ventral mesencephalic regions showed PPTA immunoreactivity. A small population (2-12%) of accumbens neurons projecting to the ventral pallidum and mesencephalic regions displayed immunoreactivity for PPTB. Compared with the dorsal striatopallidal projection neurons that were reported to mostly express PPE, it was characteristic of the ventral striatum that only the smaller population (about 40%) of ventral striatopallidal projection neurons expressed PPE. This suggests that the ventral striatopallidal projection system is less specialized than the dorsal striatopallidal system in terms of peptide production, or that the ventral pallidum should be compared with a combined region of the globus pallidus and entopeduncular nucleus in the dorsal system.

A novel technique for quantitative immunohistochemical imaging of various neurochemicals in a multiple-stained brain slice

Here we describe a novel technique for comparative analysis of the distributions of various neurochemicals visualized using multiple immunohistochemistry in the same brain slice. As an example, the distributions of tyrosine hydroxylase, substance P and glutamate decarboxylase in coronal slices of rat brains were compared. Each slice was divided into approximately 220,000-300,000 microareas at 20-microm intervals, and the immunohistochemical intensities of the three substances in each microarea were analyzed independently using a brain mapping analyzer; a microphotometry system previously developed in our laboratory (Sutoo et al., J. Neurosci. Methods, 1998; 85: 161-73). No significant differences between the distribution of each substance were observed in single- and triple-labeled slices. We believe that this method will facilitate the investigation of the functions of the central nervous system and the disorders thereof in various diseases.

Nestin immunoreactivity in local neurons of the adult rat striatum after remote cortical injury

Nestin is a marker for the neuronal and glial precursor cells and is expressed in reactive astrocytes after brain injury. Following restricted neocortical injury, we found that cells with neuronal morphology in the adult rat striatum became immunoreactive for both nestin and the neuronal marker, microtubule-associated protein 2 (MAP-2), but not for the astroglial marker, glial fibrillary acidic protein (GFAP). The number of nestin-positive cells transiently increased in the striatum. Continuous administration of 5-bromo-2'-deoxyuridine (BrdU) after cortical injury did not reveal any newly generated neurons in the striatum. Double-labeling fluorescent immunocytochemistry revealed that the nestin-positive striatal cells were also substance-P-positive. These findings suggest that some factors released from the injured cortex may induce nestin immunoreactivity in striatal neurons.

S 17092: a prolyl endopeptidase inhibitor as a potential therapeutic drug for memory impairment. Preclinical and clinical studies

Any treatment that could positively modulate central neuropeptides levels would provide a promising therapeutic approach to the treatment of cognitive deficits associated with aging and/or neurodegenerative diseases. Therefore, based on the activity in rodents, S 17092 (2S,3aS,7aS)-1][(R,R)-2-phenylcyclopropyl]carbonyl]-2-[(thiazolidin-3-yl)carbonyl]octahydro-1H-indole) has been selected as a potent inhibitor of cerebral prolyl-endopeptidase (PEP). By retarding the degradation of neuroactive peptides, S 17092 was successfully used in a variety of memory tasks. These tasks explored short-term, long-term, reference and working memory in aged mice, as well as in rodents and monkeys with chemically induced amnesia or spontaneous memory deficits. S 17092 has also been safely administered to humans, and showed a clear peripheral expression of its mechanism of action through its inhibitory effect upon PEP activity in plasma. S 17092 exhibited central effects, as evidenced by EEG recording in healthy volunteers, and could improve a delayed verbal memory task. Collectively, the preclinical and clinical effects of S 17092 have suggested a promising role for this compound as an agent for the treatment of cognitive disorders associated with cerebral aging.

The deep mesencephalic nucleus as an output center of basal ganglia: morphological and electrophysiological similarities with the substantia nigra

The deep mesencephalic nucleus (DMN) is a large midbrain reticular region between the superior colliculus, the substantia nigra compacta, the periaqueductal gray, and the medial geniculate body. Although some data suggest that it is involved in nociception and visceral control, its functions remain unclear. In the present study, by using morphological (combination of anterograde and retrograde tracers with immunocytochemistry and in situ hibrydization) and electrophysiological (firing activity and transynaptic response to striatal stimulation) methods, we show that a subpopulation of DMN cells shares many morphological and electrophysiological characteristics with those of the substantia nigra reticulata (SNR). These similarities include the following: 1) firing rate, firing pattern, and conduction velocity; 2) expression of GAD65, GAD67, and PV; 3) excitatory and inhibitory inputs from the striatum; and 4) projections to the ventral thalamus, superior colliculus, and pedunculopontine tegmental nucleus. Some differences were also found. In comparison with SN, DMN cells and striatal afferents are more sparsely distributed and they show conspicuous contralateral projections to the thalamus and superior colliculus. This suggests that, similarly to the SNR, the DMN acts as an output center of basal ganglia and probably facilitates the inter-hemispheric regulation of these centers.

Neuroanatomical localisation of Substance P in the CNS and sensory neurons

The anatomical distribution of Substance P (SP) has been investigated since the development of antibodies against it in the 1970s. Although initial studies were performed with antibodies that also recognised the other endogenous neurokinins, most of the initial descriptions are surprisingly still valid today. In this review, we provide an integrated overview of the pathways containing SP in the central and peripheral nervous systems. The highest densities of SP immunoreactivity occur in the superficial dorsal horn of the spinal cord, in the substantia nigra and in the medial amygdaloid nucleus. In the peripheral nervous system, SP occurs in high concentrations in small diameter primary sensory fibres and in the enteric nervous system. SP is extensively co-localised with classical transmitters and other neuropeptides. In the spinal cord, SP immunoreactive axonal boutons are preferentially presynaptic to neurons expressing the SP receptor, suggesting that the neurokinin acts at a short distance from the release site. In contrast, in the periphery, the situation probably differs in the autonomic ganglia, where the targets are directly innervated by SP, and in other peripheral territories, where SP has to diffuse through the connective tissue to reach the structures expressing the receptor.

Differential effects of haloperidol on phencyclidine-induced reduction in substance P contents in rat brain regions

We investigated the effects of a schizophrenomimetic drug, phencyclidine (PCP), on substance P (SP) contents in the discrete rat brain areas using an enzyme-immunoassay for SP. The acute intraperitoneal (i.p.) administration of PCP (10 mg/kg), which is a noncompetitive antagonist of the N-methyl-D-aspartate (NMDA) type glutamate receptor and a dopamine uptake inhibitor, reduced the concentration of the peptide in the prefrontal cortex, limbic forebrain, striatum, and substantia nigra, but not in the ventral tegmental area, at 60 or 120 min postinjection. A selective noncompetitive NMDA antagonist, dizocilpine hydrogen maleate ((+)-MK-801) (1 mg/kg, i.p.), also caused a decrease in the SP content in the prefrontal cortex and limbic forebrain but failed to alter the content in the other areas studied 30 min thereafter. Dopamine agonists, methamphetamine (4.8 mg/kg, i.p.) and apomorphine (4.4 mg/kg, i.p.), diminished the SP contents in the striatum and substantia nigra 60 min after their injection without effects in the prefrontal cortex, limbic forebrain, and ventral tegmental area. Furthermore, pretreatment with haloperidol (1 mg/kg, i.p.), a D2 preferable dopamine receptor antagonist and a typical antipsychotic, blocked the ability of PCP to decrease the SP concentrations in the substantia nigra but not in the prefrontal cortex. PCP, therefore, might diminish the SP levels by NMDA receptor-mediated and dopamine-independent mechanisms in the prefrontal cortex and limbic forebrain, but by NMDA receptor-independent and dopamine-dependent mechanisms in the striatum and substantia nigra. The haloperidol-insensitive reduction of the frontal SP could be involved in certain neuroleptic-resistant symptoms of PCP-treated animals, PCP psychosis, or schizophrenia.

Distribution of catecholaminergic afferent fibres in the rat globus pallidus and their relations with cholinergic neurons

The topographical distribution of catecholaminergic nerve fibres and their anatomical relationship to cholinergic elements in the rat globus pallidus were studied. Peroxidase-antiperoxidase and two-colour immunoperoxidase staining procedures were used to demonstrate tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT) and choline acetyltransferase (ChAT) immunoreactivities, combined with acetylcholinesterase (AChE) pharmacohistochemistry. TH immunoreactive nerve fibres were seen to enter the globus pallidus from the medial forebrain bundle. The greatest density of such fibres was found in the ventral region of the globus pallidus, which was also characterized by the greatest density of ChAT immunoreactive neurons. TH immunoreactive nerve fibres showed varicose arborizations and sparse boutons, which were occasionally seen in close opposition to cholinergic structures. In all regions of the globus pallidus, there were also larger, smooth TH immunoreactive nerve fibres of passage to the caudate putamen. A smaller number of DBH immunoreactive nerve fibres and terminal arborizations were found in the substantia innominata, internal capsule and in the globus pallidus bordering these structures. A few PNMT immunoreactive nerve fibres in the substantia innominata and internal capsule did not enter the globus pallidus. Electron microscopy revealed TH immunoreactive synaptic profiles in the ventromedial area of the globus pallidus corresponding to the nucleus basalis magnocellularis of Meynert (nBM). These made mainly symmetrical and only a few asymmetrical synaptic contacts with dendrites containing AChE reaction product. The results indicate that cholinergic structures in the nBM are innervated by dopaminergic fibres and terminals, with only a very small input from noradrenergic fibres.

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.

Preprodynorphin-, preproenkephalin-, and preprotachykinin-expressing neurons in the rat neostriatum: an analysis by immunocytochemistry and retrograde tracing

Specific antibodies were produced against C-terminal portions of rat preprodynorphin (PPD), preproenkephalin (PPE), and preprotachykinin A (PPT). PPD, PPE, and PPT C-terminal immunoreactivity was observed in many cell bodies of medium-sized neurons in the rat neostriatum (caudate-putamen). Intense PPE immunoreactivity was found in neuropil of the globus pallidus, whereas intense to moderate PPD and PPT immunoreactivity was distributed in neuropil of the substantia nigra and the entopeduncular nucleus. A double-immunofluorescence analysis revealed that PPE-immunoreactive neostriatal neurons rarely showed immunoreactivity for PPD (<1%) or PPT (<2%). In contrast, more than 95% of PPD-immunoreactive neostriatal neurons showed PPT immunoreactivity, and vice versa. No PPD-, PPE-, or PPT-immunoreactive neostriatal neurons showed immunoreactivity for the markers of neostriatal intrinsic neurons, such as calretinin, choline acetyltransferase, parvalbumin, or somatostatin. When tetramethylrhodamine-dextran amine (TMR-DA) was injected into the substantia nigra, almost all neurons that were labeled retrogradely with TMR-DA showed immunoreactivity for PPD (98%) or PPT (99%), but very few of them exhibited PPE immunoreactivity (1%). After injection of TMR-DA into the globus pallidus, 86%, 17%, and 10% of the retrogradely labeled neurons showed immunoreactivity for PPE, PPD, and PPT, respectively. These results support the notion that the neostriatal projection neurons are divided into at least two groups: The projection neurons of one group contain enkephalins and send projection fibers almost exclusively to the globus pallidus, and the others contain tachykinins and dynorphins/Leu-enkephalin and send projection fibers mainly to the substantia nigra.

Chronic nicotine treatment differentially regulates substance P and tyrosine hydroxylase immunoreactivity in substantia nigra ipsilateral to a unilateral lesion

The present study was carried out with a variety of neuroanatomical techniques to investigate the consequences of chronic continuous nicotine treatment (0.125 mg x kg(-1) x h(-1), s.c., 14 days) on the lesion-induced effects of a partial meso-diencephalic hemitransection. Both the striatonigral substance P (SP) and the nigrostriatal dopamine (DA) pathways were studied. The lesion-induced degenerative changes were most pronounced in the lateral parts of the ipsilateral substantia nigra and striatum. We have previously demonstrated that chronic nicotine infusion counteracts the lesion-induced loss of nigral tyrosine hydroxylase (TH) immunoreactive/Nissl stained DA neurons. The main finding of this study is that this phenomenon also involves changes in the striatonigral pathways. Thus, nicotine induced a disappearance of SP immunoreactive nerve terminals in substantia nigra pars compacta on the lesioned side, while it was again shown to counteract the lesion-induced disappearance of nigral TH immunoreactivity in the same animals. These data are interpreted on the basis of previous electrophysiological findings, where nicotine under similar experimental conditions counteracted the lesion-induced increase in burst firing in vivo in nigral dopamine neurons. Taken together these results indicate that nicotine may act by a reduced SP excitatory input to the nigral DA cells, which rescues them from dying. It is likely that the surviving cells are functional, since increased extracellular striatal DA levels have been observed after nicotine treatment ipsilateral to the lesion in a previous microdialysis experiment in vivo. These findings might contribute to the development of new neuroprotective therapies for patients suffering from neurodegenerative disorders such as Parkinson's disease.

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.

Morphologically distinct subpopulations of neurotensin-immunoreactive striatal neurons observed in rat following dopamine depletions and D2 receptor blockade project to the globus pallidus

It has been reported in previous studies that perikaryal neurotensin immunoreactivity is largely absent in the rat striatum except following striatal dopamine depletion or blockade of dopamine D2 receptors, after which, however, neurotensin immunoreactivity is elicited in at least two distinct subpopulations of striatal neurons [Zahm D.S. (1992) Neuroscience 46, 335-350]. One subpopulation of such cells (type I), prominent following D2 receptor blockade, is located mainly in the matrix compartment in the rostral, dorsomedial and ventrolateral parts of the striatum, and comprises neurons at the large end of the medium-sized spectrum that exhibit intense neurotensin immunoreactivity in perikarya and proximal dendrites, but rarely display Fos immunoreactivity [Senger B. et al. (1993) Neuroscience 57, 649-660]. A second subpopulation (type II) resides predominantly in the patch (striosome) and matrix compartments in the dorsolateral quadrant of the striatum, and is prominent following administration of reserpine. These neurons are at the small end of the medium size range and exhibit very light neurotensin immunoreactivity, with little staining of dendrites. Fos immunoreactivity is frequently co-localized in striatal neurons that exhibit a type II striatal neurotensin response [Brog J.S. and Zahm D.S. (1995) Neuroscience 65, 71-86]. In the current study, neurotensin immunoreactivity was elicited in striatal neurons by ventral mesencephalic 6-hydroxydopamine lesions or administration of reserpine or haloperidol. Irrespective of which drug was given, retrogradely transported Fluoro-Gold was prominently co-localized with neurotensin-like immunofluorescence in the perikarya of striatal neurons following injections of the retrograde tracer into the globus pallidus. Few double-labeled neurons were observed following administration of any of these drugs and injections of Fluoro-Gold into the substantia nigra. It is concluded that two subpopulations of neurotensin-immunoreactive striatal neurons project predominantly to the globus pallidus and minimally to the substantia nigra.

The reduction of preprotachykinin mRNA in the methamphetamine-induced behavioral sensitization

To study the role of the preprotachykinin A (PPT) mRNA in methamphetamine (MAP)-induced behavioral sensitization, rats were daily injected within MAP (3 or 6 mg/kg, i.p., once a day) or saline for 14 days. Progressive enhancement was observed in MAP-induced stereotyped behavior. After 7 or 14 days of discontinuation of MAP treatment, the rats were decapitated and the brains were prepared for Northern blot analysis using a 32P-labeled oligonucleotide probe. Northern blot analysis revealed that the level of PPT mRNA in the striatum of 3 or 6 mg/kg MAP-treated rats was significantly decreased, compared to that in the saline-treated controls. These findings indicate that PPT mRNA expression plays an important role in MAP-induced long-lasting behavioral sensitization and dopamine hyperactivity.

The effect of the acute and chronic administration of CP 96,345, a selective neurokinin1 receptor antagonist, on midbrain dopamine neurons in the rat: a single unit, extracellular recording study

In this study, we examined the effect of acute and chronic administration of the selective neurokinin1 receptor antagonist CP 96,345 on the basal activity of spontaneously active dopamine (DA) neurons in the substantia nigra pars compacta (SNC) and the ventral tegmental area (VTA). This was accomplished using the technique of in vivo, extracellular single unit recording in anesthetized rats. The intravenous (i.v.) administration of CP 96,345 (0.01-1.28 mg/kg) did not significantly alter the firing rate of spontaneously active DA neurons in the SNC and VTA areas. The acute administration of 5 or 10 mg/kg, i.p., of CP 96,345 produced a significant decrease in the number of spontaneously active SNC and VTA dopamine cells compared to vehicle-treated rats. In contrast to its effect on the number of spontaneously active DA neurons, the administration of 5 mg/kg, i.p., of CP 96,345 did not significantly alter the basal firing pattern of either SNC or VTA DA neurons. The acute administration of CP 96,345 (10 mg/kg, i.p.) significantly potentiated the suppressant action of (+)-apomorphine on the basal firing rate of spontaneously active SNC and VTA DA cells. The chronic administration of CP 96,345 (5 or 10 mg/kg, i.p.) for 21 days also produced a significant decrease in the number of spontaneously active SNC and VTA DA cells compared to vehicle controls. This effect was not reversed by the systemic administration of (+)-apomorphine (50 micrograms/kg, i.v.), suggesting that the reduction in the number of spontaneously active DA cells produced by CP 96,345 is probably not the result of depolarization inactivation. Overall, our results indicate that the tonic activation of NK1 receptors by substance P may be necessary to maintain the spontaneous activity of a proportion of midbrain DA neurons.

Pharmacological characterization of grooming induced by a selective NK-1 tachykinin receptor agonist

Bilateral intranigral administration of the selective NK-1 tachykinin receptor agonist [AcArg6, Sar9, Met(O2)11]SP6-11 (0-1 nmol total bilateral dose) selectively induced grooming in rats. This response was blocked by concurrent intranigral administration of the NK-1 tachykinin receptor antagonist RP 67580 (2 nmol), but not by NK-2 (L-659,877) or NK-3 ([Trp7, beta-Ala8]NKA4-10) antagonists. Pretreatment with systemic opioid (naloxone 1.5 mg/kg) and D1 dopamine (SCH 23390 100 micrograms/kg) receptor antagonists also attenuated tachykinin-induced grooming, which was unaffected by D2 dopamine (sulpiride 30 mg/kg) or 5-HT2A+C (ritanserin 2 mg/kg) antagonists. Grooming induced by intranigral [AcArg6, Sar9, Met(O2)11]SP6-11 was also attenuated by bilateral 6-hydroxydopamine lesions of the substantia nigra. These findings indicate that grooming induced by intranigral tachykinins reflects activation of NK-1 receptors and is dependent upon endogenous dopamine and consequent selective stimulation of D1 dopamine receptors.

Distribution of GABAA receptor alpha 1 subunit-like immunoreactivity in comparison with that of enkephalin and substance P in the rat forebrain

The gamma-aminobutyric acid-A receptor consists of several subunits. In this immunohistochemical study we investigated the regional distribution of the alpha 1 subunit with an antibody directed against a specific amino acid sequence (1-9) of the (1-9) of the alpha 1 subunit. We compared the distribution pattern of the alpha 1 subunit-like immunoreactivity with that of substance P- and enkephalin-like immunoreactivities in adjacent sections of the rat forebrain. alpha 1 subunit-like immunoreactivity appeared in the form of varicosities and fibers. A band-like terminal staining pattern (woolly fibers) that has been shown by others for substance P- and enkephalin-like immunoreactivity is also observed for alpha 1 subunit-like immunoreactivity. In contrast to substance P and enkephalin, numerous alpha 1 subunit-like immunoreactive perikarya were found. The highest density of alpha 1 subunit-like immunoreactive fibers and perikarya was found in the pallidal areas and the substantia nigra pars reticulata whereas the nucleus accumbens and the caudate putamen displayed a low density. alpha 1 subunit-like immunoreactive neurons resembled typical pallidal neurons. Some of these neurons were pericellularly stained with enkephalin-like immunoreactive varicosities in the dorsal pallidum. The distribution pattern of alpha 1 subunit-like immunoreactivity reflects a partial overlap with the substance P and enkephalin system although a differential distribution to each of these peptides was observed for cell bodies, fibers, and axon terminals.

Preproenkephalin and preprotachykinin messenger RNA expression in normal human basal ganglia and in Parkinson's disease

Striatal expression of preproenkephalin and preprotachykinin messenger RNA was studied in normal controls and in patients with Parkinson's disease using in situ hybridization histochemistry. In controls, preproenkephalin messenger RNA was expressed in a population of medium-sized neurons of mean cross-sectional area 165 microns 2, accounting for 66% of striatal medium-sized neurons, whereas preprotachykinin messenger RNA was expressed in a population of medium-sized neurons of mean cross-sectional area 204 microns 2 (23% larger than those expressing enkephalin, P < 0.05), accounting for 58% of medium-sized striatal neurons. Much lower levels of both preproenkephalin messenger RNA and preprotachykinin messenger RNA were expressed by large neurons in the globus pallidus and substantia nigra reticulata. In addition, preproenkephalin messenger RNA was expressed at low levels by neurons in the subthalamic nucleus. In Parkinson's disease cases, there was a statistically significant increase in preproenkephalin messenger RNA expression in the body of the caudate (109% increase, P < 0.05) and in the intermediolateral putamen (55% increase, P < 0.05) due to an increase in the level of gene expression per neuron rather than an increase in the number of neurons expressing preproenkephalin messenger RNA. Similar increases were observed in other putaminal subregions and in the putamen as a whole, but these did not reach statistical significance. No change in preprotachykinin messenger RNA expression was detected. These findings demonstrate selective up-regulation of a striatal neuropeptide system in Parkinson's disease compatible with increased activity of the "indirect" striatopallidal pathway, which is thought to play a crucial role in the pathophysiology of akinesia and rigidity in this condition.

Role of the striatal cholinergic system in the regulation of learned manipulation in rats

The experiments were performed on adult Wistar male rats trained to push with the forepaw on a fixed piston inside a narrow tube. It was found that after localized intracerebral injection of a cholinergic antagonist into the dorso-lateral (but not medial) neostriatum (i.e., the caudato-putamen) the behavioral performance requiring brief innate movements remained unchanged, but the performance requiring a prolonged pushing movement (> 50 msec) became disrupted. Micoinjection of carbacholine (0.03-3 mu g/l microliters) did not affect the performance of the acquired movements, whereas scopolamine (3 mu g/l microliters) led to the significant decrease in pushing time. We conclude that changes in the state of the dorso-lateral neostriatal cholinergic system result only in disturbances of the sensory-controlled component of a complex instrumental movement.

Neurochemical compartmentalization of the globus pallidus in the rat: an immunocytochemical study of calcium-binding proteins

The globus pallidus external segment forms a major target center of the mammalian striatum which is characterized by neurochemically distinct compartments. The present study was undertaken to determine if a corresponding compartmentalization exists within the globus pallidus external segment in the rat. Immunocytochemical examination of the calcium-binding proteins parvalbumin and calbindin D28kDa, which are present in neurons of the striatal matrix compartment, was employed. The results indicate three neurochemically distinct compartments within the globus pallidus external segment: 1) an area in the medial aspect of the entire length of the globus pallidus that contains dense immunoreactivity for calbindin D28kDa; 2) a narrow rim at the striatopallidal junction in the rostral two-thirds of the globus palidus that contains calbindin D28kDa immunoreactivity designated as the "border zone" of the globus pallidus; and 3) an area between these two zones showing very poor immunoreactivity for calbindin D28kDa but containing parvalbumin immunoreactive neurons. The calbindin D28kDa immunoreactive border zone corresponds to the area of the globus pallidus where striatal inputs converge extensively, whereas the rest of the nucleus is involved in segregated, topographically organized pathways. Parvalbumin-containing neurons are involved in the propagation of striatal output related to striosomal and sensorimotor aspects of basal ganglia function. The present results also indicate that calbindin D28kDa immunoreactivity is completely absent from striosomal neurons and is therefore a useful marker for striatal compartments.

Localization of striatal and nigral tachykinin receptors in the rat

The effects of lesioning mesostriatal dopamine projections or striatal neurons on tachykinin binding in the basal ganglia were assessed in the rat. 6-Hydroxydopamine lesions of the medial forebrain bundle destroyed striatal dopamine terminals as assessed by [3H]mazindol autoradiography, but did not significantly affect the binding of NK-1 ([3H][Sar9,Met(O2)11]substance P) or NK-3 ([3H]senktide) tachykinin ligands in the striatum. 6-Hydroxydopamine lesions significantly reduced NK-3 binding in the substantia nigra pars compacta, but not the ventral tegmental area. In contrast, striatal quinolinic acid lesions reduced both NK-1 and NK-3 binding in the striatum, but failed to affect NK-3 binding in the substantia nigra. These findings suggest that both NK-1 and NK-3 receptors within the striatum are predominantly post-synaptic with respect to dopamine neurons, whereas nigral NK-3 receptors are located on dopaminergic neurons.

Up-regulation of neurotensin mRNA in the rat striatum after acute methamphetamine treatment

The effect of acute subcutaneous administration of methamphetamine on the expression of neurotensin mRNA was investigated in the adult rat striatum. At different time points (2, 6 and 24 h) following drug administration rats were killed, and mRNA levels were quantified both on films and emulsion-dipped tissue sections from two striatal levels. Two hours after methamphetamine injection, a dramatic increase in neurotensin mRNA levels was detected in different areas of the striatum at both rostral and caudal levels. Numerous positive cells were observed in the dorsomedial, dorsolateral and ventrolateral parts of the striatum. This up-regulation reflected an increase both in the number of cells expressing neurotensin mRNA and in the mean mRNA levels. This increase was still present after 6 h and was similar to the 2 h treated group at the rostral level of the striatum, but lower at the caudal one. Twenty-four hours after methamphetamine injection, neurotensin mRNA levels were back to control values, or in some areas even below. A strong increase in neurotensin mRNA-expressing cells was also seen in the olfactory tubercle, and the time-course was similar to the one observed in the striatum. In a second set of experiments, the effect of methamphetamine was evaluated on adjacent striatal sections hybridized with probes directed against neurotensin and substance P mRNAs, respectively. Two hours after drug administration, a significant increase in the levels of both peptide mRNAs was observed (+190% for neurotensin, +80% for substance P). These results demonstrate that methamphetamine is able to induce a dramatic, rapid and transient increase in striatal neurotensin mRNA levels, which may partly account for the elevation in neurotensin peptide levels observed in the striatonigral pathway after methamphetamine. The different anatomical localization of neurotensin mRNA-expressing cells observed after haloperidol and methamphetamine treatments, as well as the fact that the D1 receptor antagonist SCH-23390 is able to counteract the effect of methamphetamine but not that of haloperidol on neurotensin mRNA expression, suggests that there are at least two different subpopulations of neurotensin cells in the striatum. One population is regulated via D1 receptors and projects to the substantia nigra pars reticulata. The second is sensitive to D2 receptor stimulation and may project to the globus pallidus and/or may represent interneurons.

Effects of intranigral injections of colchicine on the expression of some neuropeptides in the rat forebrain: an immunohistochemical and in situ hybridization study

In the present study, we describe the neurochemical effects of intranigral injections of colchicine in the rat forebrain using immunohistochemistry and in situ hybridization. The observations on the injected side are compared to the contralateral one and to the sham-operated rats. We demonstrate that such injections are able to strongly enhance the immunoreactivity for Met-enkephalin (ME), substance P (SP) and neuropeptide Y (NPY) in numerous nerve cell bodies of the limbic system (injected side), whereas the levels of the corresponding mRNAs are differently modified according to the region examined. A clear correlation between the enhancement of the immunostaining for ME and SP and that of the preproenkephalin (PPA) and preprotachychinin gene transcripts was observed in neuronal perikarya of the medial amygdaloid nucleus (SP), of the dorsolateral hypothalamus (ME) and of the ventromedial hypothalamic nucleus (SP). These observations are interpreted as an induction--or increased expression--of neuropeptide genes in neuronal perikarya postsynaptic to nerve fibers originating in the midbrain and brain stem. In this case, colchicine is thought to block the electrophysiological activity of ascending nerve fibers (anterograde and postsynaptic effect). In the case where the enhancement of the immunoreactivity for the studied neuropeptides was associated with no change or a decreased expression of the corresponding genes in the same brain areas, colchicine may have blocked the axoplasmic transport of peptides in nerve fibers projecting to the midbrain and/or brain stem (6). This may result in a retrograde accumulation of peptides in the nerve cell bodies of origin and, eventually, in a negative feedback regulation of the corresponding encoding genes in these perikarya (retrograde and presynaptic effect of colchicine). The drastic behavioral effects of bilateral intranigral injections of colchicine, on ingestive behavior in particular, have been studied in a following paper.

Substance P receptor-immunoreactive neurons in the rat neostriatum are segregated into somatostatinergic and cholinergic aspiny neurons

Immunochemical characteristics of neostriatal neurons producing substance P receptor (SPR) were examined in adult rats by double- and triple-immunofluorescence methods. In the neostriatum, SPR immunoreactivity was detected in large and medium-sized aspiny neurons. Virtually all SPR-immunoreactive neurons in the neostriatum contained somatostatin (SS) or choline acetyltransferase (ChAT), but not parvalbumin. All SS- and ChAT-immunoreactive neurons in the neostriatum showed SPR immunoreactivity. The co-existence of SS and ChAT was, however, not found in single neurons expressing SPR immunoreactivity. The present results indicate that neostriatal neurons immunoreactive for SPR are segregated into 2 groups: (1) medium-sized, spiny somatostatinergic, and (2) large, aspiny cholinergic neurons.

A selective lesion of striatonigral neurons decreases presynaptic binding of [3H]hemicholinium-3 to striatal interneurons

We have used the suicide transport agent, volkensin, to produce selective lesions of striatal efferent neurons projecting to the substantia nigra in the rat. In order to evaluate potential trans-synaptic effects, we examined cholinergic interneurons intrinsic to the striatum following destruction of striatonigral projection neurons by nigral injection of volkensin. There was no change in the number of large interneurons identified either by Nissl stain or by immunocytochemistry for choline acetyltransferase, indicating that volkensin was not directly toxic to this group of neurons. However, [3H]hemicholinium-3 binding to the choline re-uptake site on the presynaptic cholinergic terminals decreased. No change in [3H]hemicholinium-3 binding was seen after destruction of dopaminergic afferents with 6-hydroxydopamine. Striatonigral afferents to the cholinergic interneurons contain substance P which has been shown to stimulate acetylcholine release. The decrease in [3H]hemicholinium-3 binding may reflect loss of this afferent input. However, striatonigral neurons are an efferent target of the cholinergic interneuron as well, and a presynaptic effect due to loss of target neurons also may contribute.

Distribution of the inositol 1,4,5-trisphosphate receptor, P400, in adult rat brain

The distribution of the inositol 1,4,5-trisphosphate receptor protein, P400, was investigated in adult rat brain by immunocytochemistry with the monoclonal antibody 4C11 raised against mouse cerebellar inositol 1,4,5-trisphosphate receptor protein. Immunoreactive neuronal cell bodies were detected in the cerebral cortex, the claustrum, the endopiriform nucleus, the corpus callosum, the anterior olfactory nuclei, the olfactory tubercle, the nucleus accumbens, the lateral septum, the bed nucleus of the stria terminalis, the hippocampal formation, the dentate gyrus, the caudate-putamen, the fundus striatum, the amygdaloid complex, the thalamus, the caudolateral part of the hypothalamus, the supramammillary nuclei, the substantia nigra, the pedunculopontine tegmental nucleus, the ventrotegmental area, the Purkinje cells in the cerebellum, the dorsal cochlear nucleus, the subnucleus oralis and caudalis of trigeminal nerve, and the dorsal horn of the spinal cord. Immunoreactive fibres were found in the medial forebrain bundle, the globus pallidus, the stria terminalis, the pyramidal tract, the spinal tract of trigeminal nerve, and the ventral horn of spinal cord. Nerve fibres forming a dense plexus ending in terminal-like boutons were detected in relation to nonimmunoreactive neurons of the dentate, interpositus, and fastigial nuclei of the cerebellum and around neurons of the vestibular nuclei. This receptor protein binds a specific second messenger, inositol 1,4,5-trisphosphate, which produces a mobilization of intracellular Ca2+ and a modulation of transmitter release.

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

In vivo microdialysis in urethane anaesthetised rats was used to investigate the effects of substance P (SP) on acetylcholine (ACh) and dopamine (DA) release in the rat striatum. Results showed that SP elicited a dose-dependent increase in ACh release between 1 and 50 pmol/l. The rise in ACh release occurred both during SP administration and for up to 60 min after it. Dose-response curves either based on the initial rise in ACh release, or the total duration of increased release, showed a bell shape with 100 fmol/l and 5 nmol/l doses failing to significantly alter release and a 500 pM dose being less effective than 50 pmol/l. In contrast to this, SP did not significantly alter DA release at doses ranging between 100 fmol/l and 5 nmol/l. There was evidence for a strong desensitisation effect of SP administration since after initial treatment with SP subsequent doses of the peptide, even at very high doses, failed to provoke further changes in ACh still showed the expected increase in release in response to a potassium challenge. Physalaemin and neurokinin A increased ACh release with a similar potency to SP at a 50 pmol/l dose whereas neurokinin B and neuropeptide gamma, while increasing ACh release at a 50 pmol/l dose, were less potent than SP. The effect of SP on ACh release is probably mediated via NK-1 receptors since ACh release in response to SP was reduced in a dose dependent manner by the NK-1 receptor antagonists CP-96,345 and RP-67580.

Immunohistochemical evidence for a neurotensin striatonigral pathway in the rat brain

The distribution and origin of neurotensin-like immunoreactivity in the substantia nigra pars reticulata of the rat have been analysed using immunohistochemistry combined with different drug treatments and lesioning techniques. In normal rats, a distinct but weakly fluorescent network of neurotensin-immunoreactive fibers was found in the central part of the substantia nigra pars reticulata. When the animals were treated with reserpine, which suppresses dopamine transmission, a similar pattern of immunoreactivity was found, though the intensity of staining was slightly enhanced. However, when rats were treated with methamphetamine, a potent dopamine releaser, the intensity of immunoreactivity was dramatically increased. In particular, densely packed neurotensin-immunoreactive fibers were found at the dorsal border and at the ventral periphery of the substantia nigra pars reticulata. This pattern of immunoreactivity was found to be similar to that displayed by dynorphin. In the nucleus caudatus, several neurotensin-immunoreactive cell bodies were seen after reserpine treatment. Morphologically similar perikarya were observed in methamphetamine-treated rats, but they were less numerous, whereas no cell bodies were detectable in untreated animals. When a unilateral mechanical transection or an ibotenic acid injection was performed in the striatum, the patterns of neurotensin as well as dynorphin and substance P immunoreactivities in the substantia nigra pars reticulata were strongly affected. Both types of lesion caused a marked, parallel depletion of all three immunoreactive substances on the side ipsilateral to the lesion, where a restricted area was virtually devoid of immunoreactive elements. Thus the present study provides evidence for the existence of a unilateral neurotensin striatonigral pathway, terminating in the pars reticulata. The origin of the neurotensin fibers in the pars compacta has not been established but does not appear to be the caudate nucleus. These results together with evidence from the literature suggest that methamphetamine induced a massive release of dopamine from nigral dendrites acting on presynaptic D1 dopamine receptors located on neurotensinergic terminals leading to a marked increase in neurotensin-like immunoreactivity in the pars reticulata.