Actions of substance P, MIF, TRH and related peptides in the substantia nigra, caudate nucleus and nucleus accumbens

Conformational preferences of alpha-substituted proline analogues

DFT calculations at the B3LYP/6-31+G(d,p) level have been used to investigate how the replacement of the alpha hydrogen by a more sterically demanding group affects the conformational preferences of proline. Specifically, the N-acetyl-N'-methylamide derivatives of L-proline, L-alpha-methylproline, and L-alpha-phenylproline have been calculated, with both the cis/trans isomerism of the peptide bonds and the puckering of the pyrrolidine ring being considered. The effects of solvation have been evaluated by using a Self-Consistent Reaction Field model. As expected, tetrasubstitution at the alpha carbon destabilizes the conformers with one or more peptide bonds arranged in cis. The lowest energy minimum has been found to be identical for the three compounds investigated, but important differences are observed regarding other energetically accessible backbone conformations. The results obtained provide evidence that the distinct steric requirements of the substituent at C (alpha) may play a significant role in modulating the conformational preferences of proline.

Stereoselective Synthesis of Quaternary Proline Analogues

This review describes available methods for the diastereoselective and asymmetric synthesis of quaternary prolines. The focus is on the preparation of alpha-functionalized prolines with the pyrrolidine moiety not embedded in a polycyclic frame. The diverse synthetic approaches are classified according to the bond which is formed to complete the quaternary skeleton.

Effect of thyrotropin-releasing hormone on the locomotor and sensitizing effects of cocaine in rats

The present study was designed to find out whether single and repeated treatment with thyrotropin-releasing hormone (TRH) changed the cocaine-evoked hyperactivation or sensitization, and whether cross-sensitization occurred between TRH and cocaine. Like cocaine (10 mg/kg), TRH (10 mg/kg) increased the basal activation of rats; however, when given in combination with cocaine (10 mg/kg), TRH (5-10 mg/kg) did not change the locomotor effect of cocaine. On day 10, cocaine challenge of rats treated repeatedly with the psychostimulant (days 1-5) significantly enhanced locomotor hyperactivity compared to the effect of acute cocaine injection in saline-treated (days 1-5) animals. When co-administered with cocaine for 5 days during the development of sensitization, TRH (10 mg/kg) enhanced the effect of the challenge dose of cocaine (10 mg/kg) following a 5-day withdrawal. Given acutely with cocaine on day 10 to cocaine-treated animals, TRH (5-10 mg/kg) did not change the expression of cocaine sensitization. Significant enhancement of the locomotor response to TRH (10 mg/kg) challenge was observed in animals treated repeatedly with TRH. The response to TRH (5-10 mg/kg) was stronger in repeated cocaine-treated rats than in saline-injected ones; similarly, the response to cocaine (10 mg/kg) was more potent in TRH-treated animals compared to saline-injected ones (cross-sensitization). In conclusion, our results indicate that exposure to TRH induces sensitization to its locomotor hyperactivity effect. They also show that TRH enhances the development of cocaine sensitization, but affects neither the expression phase of the phenomenon nor the locomotor hyperactivity induced by a single dose of cocaine. Moreover, cross-sensitization between cocaine and TRH has also been demonstrated. These findings also may provide an insight into the relationship between TRH and cocaine in humans exposed to the psychostimulant.

The connections of the dopaminergic system with the striatum in rats and primates: an analysis with respect to the functional and compartmental organization of the striatum

This Commentary compares the connections of the dopaminergic system with the striatum in rats and primates with respect to two levels of striatal organization: a tripartite functional (motor, associative and limbic) subdivision and a compartmental (patch/striosome-matrix) subdivision. The topography of other basal ganglia projections to the dopaminergic system with respect to their tripartite functional subdivision is also reviewed. This examination indicates that, in rats and primates, the following observations can be made. (1) The limbic striatum reciprocates its dopaminergic input and in addition innervates most of the dopaminergic neurons projecting to the associative and motor striatum, whereas the motor and associative striatum reciprocate only part of their dopaminergic input. Therefore, the connections of the three striatal subregions with the dopaminergic system are asymmetrical, but the direction of asymmetry differs between the limbic versus the motor and associative striatum. (2) The limbic striatum provides the main striatal input to dopamine cell bodies and proximal dendrites, with some contribution from a subset of neurons in the associative and motor striatum (patch neurons in rats; an unspecified group of neurons in primates), while striatal input to the ventrally extending dopamine dendrites arises mainly from a subset of neurons in the associative and motor striatum (matrix neurons in rats; an unspecified group of neurons in primates). (3) Projections from functionally corresponding subdivisions of the striatum, pallidum and subthalamic nucleus to the dopaminergic system overlap, but the specific targets (dopamine cells, dopamine dendrites, GABA cells) of these projections differ. Major differences include the following. (1) In rats, neurons projecting to the motor and associative striatum reside in distinct regions, while in primates they are arranged in interdigitating clusters. (2) In rats, the terminal fields of projections arising from the motor and associative striatum are largely segregated, while in primates they are not. (3) In rats, patch- and matrix-projecting dopamine cells are organized in spatially, morphologically, histochemically and hodologically distinct ventral and dorsal tiers, while in primates there is no (bi)division of the dopaminergic system that results in two areas which have all the characteristics of the two tiers in rats. Based on the anatomical data and known dopamine cell physiology, we forward an hypothesis regarding the influence of the basal ganglia on dopamine cell activity which captures at least part of the complex interplay taking place within the substantia nigra between projections arising from the different basal ganglia nuclei. Finally, we incorporate the striatal connections with the dopaminergic system into an open-interconnected scheme of basal ganglia-thalamocortical circuitry.

In situ hybridization analysis of preprotachykinin-A mRNA levels in young and old rats

The present study examined the effects of ageing on preprotachykinin-A (PPT-A) mRNA levels in discrete regions of the rat brain. Semiquantitative analysis of silver grains revealed a 16% statistically significant decrease in PPT-A mRNA in the shell of the nucleus accumbens (AcbSh), a 27.6% statistically significant lower level of PPT-A mRNA in the olfactory tubercle (Tu), a 19.2% and 31. 5% statistically significant decrease in PPT-A mRNA in the dorsal and ventral caudate-putamen (d-CPu) (v-CPu), respectively, a 30% statistically significant lower expression of PPT-A mRNA in the bed nucleus of the stria terminalis (BNST), a 33.7% statistically significant decrease in PPT-A mRNA in the habenula (Hb) and a 30% statistically significant decrease of PPT-A mRNA levels in the postero-dorsal part of the medial amygdala (MePD). No changes in PPT-A mRNA levels were found in the nucleus accumbens, core (AcbC), in the islands of Calleja (Icj), and in the medial preoptic area (mPOA). These results show that ageing of the central nervous system (CNS) is associated with widespread changes in tachykinin gene expression, suggesting that alteration in the tachykinergic system may have implications in the physio-pathology of the elderly.

Intraaccumbens injections of substance P, morphine and amphetamine: effects on conditioned place preference and behavioral activity

The nucleus accumbens of the rat plays a critical role in behavioral activation and appetitive motivation. Within the nucleus accumbens, the shell subarea may be especially relevant, since this site is anatomically related to other brain areas that are considered to play a critical role in the processing of motivation. We investigated the behavioral effects of local drug treatments aimed at the shell of the nucleus accumbens and tested the indirect dopamine agonist d-amphetamine, the opiate agonist morphine, and the neurokinin substance P. These substances are known to exert positive reinforcing effects, and can affect behavioral activity; effects that are physiologically closely related to the nucleus accumbens and its inputs and outputs. Our results show that unilateral microinjections of amphetamine (1.0 microg, 10.0 microg) into the shell of the nucleus accumbens dose-dependently stimulated behavioral activity (locomotion, rears, sniffing), and led to conditioned place preference. Furthermore, the effect of amphetamine on place preference was negatively related to the psychomotor stimulant action on rears. Morphine injections (5.0 microg) also stimulated behavioral activity and elicited contraversive turning, but were ineffective with respect to place preference. Finally, the neuropeptide substance P, injected in a dose range of 0.1-10.0 ng, had no significant behavioral effects. These findings are discussed with respect to the role of dopaminergic, peptidergic and cholinergic mechanisms in the nucleus accumbens. It is suggested that dopamine, opiates, and neurokinins in the shell of the nucleus accumbens are differentially involved in mediating behavioral activity and appetitive motivation.

Reconstruction of the striato-nigro-striatal circuitry by simultaneous double dopaminergic grafts: a tracer study using fluorogold and horseradish peroxidase

The main strategy in neural transplantation for Parkinson's disease (PD) has been the ectopic placement of dopaminergic grafts in the striatum in order to restore dopaminergic innervation to the host striatum. Although intrastriatal transplants usually improve asymmetric rotational behavior in the 6-hydroxydopamine lesioned rodent model of PD, they are less likely to completely restore the more complex sensorimotor behavioral deficits induced by dopamine loss. Re-establishment of the nigrostriatal circuitry and dopaminergic reinnervation of the substantia nigra may be necessary to promote a more complete restoration of function in the dopamine depleted brain and improve the clinical efficacy of dopaminergic transplants. Recently, we demonstrated the reconstruction of the nigrostriatal pathway by simultaneous intrastriatal and intranigral dopaminergic transplants [Mendez et al., J. Neurosci. 16 (1996) 7216-7227.]. Using this strategy, it was found that placing a graft of embryonic ventral mesencephalic tissue in the striatum promoted the growth and guidance of axons from a similar graft placed homotopically in the ventral mesencephalon. Since it is apparent that developing tissue has the ability to promote axonal growth and guidance along the nigrostriatal pathway, the double grafting strategy may contribute to re-establishing host-graft connectivity. The current study provides evidence of reconstruction of the striato-nigro-striatal loop circuitry by simultaneous intrastriatal and intranigral dopaminergic transplants. Injection of the retrograde tracer fluorogold (FG) into the striatum resulted in fluorescent labeled cells within the intranigral grafts. Similarly injection of FG into the nigra resulted in fluorescent labeled cells within the intrastriatal graft and surrounding striatum. Injection of the anterograde tracer horseradish peroxidase (HRP) resulted in the presence of HRP reaction product throughout the target striatum. These results strongly support the re-establishment of nigrostriatal and striatonigral connections between simultaneous intrastriatal and intranigral dopaminergic transplants and suggest reconstruction of the striato-nigro-striatal loop circuitry.

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.

Bioactive cyclic dipeptides

Cyclic dipeptides are among the simplest peptide derivatives commonly found in nature. Most cyclic dipeptides found to date appear to have emerged as by-products of fermentation and food processing. However, many are endogenous to members of animal and plant kingdoms; these include cyclo(Pro-Leu), cyclo(Pro-Val), cyclo(Pro-Phe), cyclo(Ala-Leu), cyclo(Pro-Tyr), cyclo(Pro-Trp), and cyclo(His-Pro). Although the five cyclic dipeptides--cyclo(His-Pro), cyclo(Leu-Gly), cyclo(Tyr-Arg), cyclo(Asp-Pro), and cyclo(Pro-Phe)--exhibit interesting physiological and/or pharmacological activities in mammals, only one of these, cyclo(His-Pro), has been conclusively shown to be endogenous to mammals. On the other hand, cyclo(Leu-Gly), cyclo(Tyr-Arg), and cyclo(Asp-Pro) are structurally related to endogenous peptides Pro-Leu-Gly-NH2 (melanocyte-stimulating hormone release inhibiting factor), Tyr-Arg (kyotorphin), and Val-Pro-Asp-Pro-Arg (enterostatin), respectively, which may serve as precursor peptides. It needs to be determined, however, whether these peptides can indeed result from the processing of their respective precursors. In conclusion, it appears that cyclic dipeptides are a relatively unexplored class of bioactive peptides that may hold great promise for the future.

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.

Molecular aspects of neuropeptide regulation and function in the corpus striatum and nucleus accumbens

In the corpus striatum and nucleus accumbens, neuropeptides participate along with conventional neurotransmitters such as dopamine, gamma-aminobutyric acid (GABA), acetylcholine and glutamate in the regulation of locomotor activity, stereotyped motor behaviors and neural events related to reward and affective state. The present review concerns itself with four major neuropeptide systems--enkephalin, dynorphin, tachykinins and neurotensin--and it summarizes neuroanatomical and functional studies as well as emphasizing regulatory interactions between neurotransmitters and neuropeptides at the level of neuropeptide gene expression. Dopaminergic transmission emanating from midbrain dopaminergic cell bodies of the substantia nigra and the ventral tegmentum regulates striatal and accumbens neuropeptide levels and their mRNAs. Evidence is presented for D1 or D2 receptor involvement as well as D1-D2 interactions that modulate neuropeptide and mRNA levels in striatum and accumbens neurons. Regulatory influences by GABAergic, serotonergic and cortical (glutamatergic) neurotransmission and via sigma receptors and circulating adrenal steroids are also described. The evidence gathered in many laboratories thus far indicates that these major basal ganglia peptidergic systems are modulated dynamically and sometimes in opposing ways by various neurochemical inputs which alter neuropeptide and neuropeptide mRNA levels over both short- and long-term. Neuropeptide systems are involved in the regulation and execution of motor programs and may also be involved in the control of mood and affect as well as self-administration behavior and behavioral sensitization, especially via the nucleus accumbens and its reciprocal connections with the midbrain, hippocampus and frontal cortex. Glucocorticoids modulate mood as well as self-administration behavior and influence locomotor activity and certain forms of stereotypy. The modulation of striatal proenkephalin and protachykinin mRNA levels by adrenal steroids is described along with distribution of adrenal steroid receptor subtypes. Adrenal steroid regulation of neuropeptide gene expression in striatum, accumbens and midbrain suggests that there may be a wider role for glucocorticoids and for other neuropeptide systems in environmental and drug influences on normal and abnormal behaviors involving the nigrostriatal and mesolimic systems.

Effects of ageing on tachykinin function in the basal ganglia

The effects of ageing on tachykinin-induced behaviours and tachykinin receptors were investigated in the rat. Infusion of the NK-3 tachykinin agonist senktide (0.25, 0.5 and 1 nmol) into the substantia nigra induced locomotion in young (4-6 months) animals but this response was attenuated in middle-aged (12 months) and old (27 months) animals. In contrast, senktide-induced wet dog shakes were not significantly affected by age. In the ventral tegmental area, senktide induced locomotion and wet dog shakes with bell-shaped dose-response curves which were unaffected by age. Senktide suppressed grooming but the effect reached significance in the older animals only. Quantitative receptor autoradiography revealed no effect of age on NK-1 tachykinin receptor density in the striatum while NK-3 receptor density declined in the ventrolateral striatum and to a nonsignificant degree in the substantia nigra but not in other striatal subregions or the ventral tegmental area. We conclude that ageing of the nervous system is not associated with widespread changes in tachykinin binding but differences in behavioural response to tachykinin agonists may reflect changes in other transmitter systems which respond to tachykinin input.

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.

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

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

Effects of two diketopiperazines, cyclo (His-Pro) and cyclo (Asp-Phe), on striatal dopamine: a microdialysis study

The effects of two diketopiperazines, Cyclo (His-Pro) (CHP) and Cyclo (Asp-Phe) (CAP), on striatal extracellular levels of dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), and 5-hydroxyindoleacetic acid (5-HIAA) were examined using in vivo microdialysis in anaesthetized rats. Treatment with neither CHP (0.1-10 mg/kg IP and 0.3 mg/kg i.v.) nor CAP (0.1-10 mg/kg IP and 10 mg/kg PO) significantly changed the efflux of DA, DOPAC, HVA, or 5-HIAA when compared to the effects of treatment with saline. Our results suggest that systemic administration of CHP or CAP alone does not modify striatal dopaminergic neurotransmission. The previous findings of enhanced DA release by systemic administration of thyrotropin releasing hormone (TRH) are probably not explained by formation of CHP from TRH.

Bilateral cerebral metabolic effects of pharmacological manipulation of the substantia nigra in the rat: unilateral intranigral application of the putative excitatory neurotransmitter substance P

The metabolic activity of several anatomically distinct brain areas was investigated by means of the quantitative autoradiographic 2-deoxy-D[1-14C]glucose method in awake rats following unilateral intranigral application of the putative excitatory neurotransmitter substance P. The primary goal was to determine the metabolic effects of substance P on the substantia nigra and its targets. Intranigral injection of 1 mM substance P (1.5 microliters) induced metabolic activation locally in the substantia nigra reticulata by 117% and substantia nigra compacta by 35%, as well as distally in the contralateral substantia nigra reticulata by 22% and contralateral substantia nigra compacta by 21%. All the basal ganglia components, the striatum, pallidum, entopeduncular, subthalamic nucleus and nucleus accumbens displayed bilateral metabolic activations after unilateral intranigral substance P injection. Among the principal reticulata efferent projections, the ventromedial, ventrolateral, parafascicular, mediodorsal and centrolateral thalamic nuclei, as well as the pedunculopontine nucleus displayed bilateral metabolic activations after intranigral substance P application. Moreover, unilateral intranigral substance P injection elicited metabolic activations in the thalamic and cortical components of the reticular, intralaminar, limbic and prefrontal systems, mostly bilateral. It is suggested that substance P applied into one substantia nigra reticulata activates the compacta nigrostriatal dopaminergic and the reticulata nigrothalamic GABAergic outputs inducing distal metabolic effects, similar to those elicited by unilateral nigral electrical stimulation [Savaki et al. (1983) J. comp. Neurol. 213, 46-65] and, opposite to several of those induced by intranigral injection of the inhibitory GABAA agonist muscimol [Savaki et al. (1992) Neuroscience 50, 781-794]. Furthermore, it is suggested that the ipsilateral basal ganglia effects induced by intranigral substance P application are mediated via both the compacta dopaminergic nigrostriatal projection and the reticulata GABAergic nigro-thalamocortico-striatal loop, whereas the contralateral basal ganglia and associated thalamocortical effects are due to the activation of the GABAergic reticulata efferents and are mediated via an interthalamic circuitry involving the motor, reticular and intralaminar thalamic nuclei.

Choline acetyltransferase- and substance P-like immunoreactive elements in fetal striatal grafts in the rat: a correlated light and electron microscopic study

Fetal striatal neurons were transplanted into the ibotenic acid-lesioned rat striatum. Three months after transplantation, the graft tissue was processed for choline acetyltransferase- and substance P-like immunoreactivity and was subsequently examined at the light and electron microscopic levels. The study demonstrated that choline acetyltransferase- and substance P-like-immunoreactive neurons were homogenously present throughout fetal striatal grafts, although in decreased numbers compared with those in the normal rat striatum. The majority of the choline acetyltransferase-immunoreactive neurons had fusiform, oval, or polygonal somata with somatic diameters greater than 20 microns and contained deeply invaginated nuclei surrounded by copious cytoplasm. In addition, choline acetyltransferase-immunoreactive neurons with somatic diameters between 10 and 20 microns were also demonstrated. The grafts' substance P-like-immunoreactive neurons, which had somatic diameters between 10 and 25 microns and had oval or polygonal perikarya, could be classified into two types based on their ultrastructural characteristics. Type I neurons contained an unindented nucleus which was surrounded by a thin rim or moderate amount of cytoplasm, whereas Type II immunoreactive neurons contained an indented nucleus which was surrounded by copious cytoplasm. Choline acetyltransferase- and substance P-like-immunoreactive dendrites in the grafts' neuropil were contacted by multiple unlabeled axon terminals. In addition, choline acetyltransferase- and substance P-like-immunoreactive axon terminals forming symmetric contacts with unlabeled dendrites were present within the graft. The study demonstrated that many of the neuroanatomical features of choline acetyltransferase- and substance P-like-immunoreactive elements found in the normal rat striatum are present in mature fetal striatal grafts.

Substance P synaptic interactions with GABAergic and dopaminergic neurons in rat substantia nigra: an ultrastructural double-labeling immunocytochemical study

The distribution of substance P (SP), tyrosine hydroxylase (TH), and glutamic acid decarboxylase (GAD) immunoreactivity in the substantia nigra of the rat was studied by means of an ultrastructural double-labeling immunocytochemical method. Direct synaptic contact between SP-immunoreactive terminals and GAD-positive nigral neurons was more often observed in the pars lateralis than the pars reticularis and was rarely observed in the pars compacta. Substance P-positive terminals also formed synapses with cell bodies and dendrites of TH-positive, dopaminergic neurons in the pars compacta and pars reticulata. Multiple SP-immunoreactive terminals were often observed with symmetrical and, less frequently, asymmetrical synapses on individual TH-containing dendrites. Evidence of SP-containing terminals contacting both GABAergic and dopaminergic neurons in the substantia nigra suggests a direct excitatory action upon nigral projection neurons.

Organization and physiology of the substantia nigra

A comprehensive review of the literature on the anatomy, electrophysiology and pharmacology of the substantia nigra is presented. A diagram is developed taking into account the interneuronal interactions of neurotransmitters and receptors that control firing rates and neurotransmitter releases. The central features of the diagram are a positive dopaminergic feedforward process and a positive feedback mechanism mediated by extrasynaptic substance P diffusing from striatal terminals to dopaminergic dendrites of the zona compacta neurons. This loop can enhance the transmission of information from the striatum through the pars reticulata output neurons. The loop is controlled at the level of zona compacta neurons by a negative feedback supported by the dendritic release of dopamine and boosted by pedunculopontine activation mediated by muscarinic receptors. The output of the loop is controlled by two negative feedforward processes, both involving GABAergic striatonigral afferents. Application of the model to pharmacological studies of diverse behaviors including seizures, turning, and conditioned behaviors reveals unforseen relationships and may offer insights into, and directions for, further analysis of the mechanisms and functions involved.

Behavioural effects of selective tachykinin agonists in midbrain dopamine regions

The effects of selective NK-1, NK-2 and NK-3 tachykinin agonists in midbrain dopamine cell containing regions were investigated in the rat. The NK-3 agonist senktide induced locomotion, rearing and sniffing following infusion into the substantia nigra pars compacta, and to a lesser extent in the ventral tegmental area. These behavioural responses were not seen following infusion of the selective NK-1 agonist [Sar9,Met (O2)11]SP or the NK-2 agonist [N1e10]NKA4-10. In contrast, grooming was induced only by the NK-1 agonist administered into the substantia nigra. Yawning, chewing mouth movements and wet dog shakes were all seen following infusion of senktide into the ventral tegmental area. These findings suggest that (i) dopamine-mediated behavioural responses seen following tachykinin administration into the midbrain are dependent upon stimulation of NK-3 tachykinin receptors, (ii) tachykinin-induced grooming is mediated by stimulation of NK-1 receptors and (iii) some of the previously described 5-HT mediated behaviours seen following administration of NK-3 tachykinin agonists are probably generated by stimulation of 5-HT cell bodies in the ventral tegmental area.

Bursting properties of units in cat globus pallidus and entopeduncular nucleus: the effect of excitotoxic striatal lesions

The bursting properties of units recorded in globus pallidus and entopeduncular nucleus were studied in awake cats sitting quietly before and after ipsilateral excitotoxic striatal lesions. A computerized statistical procedure was used to identify and evaluate bursts in the recorded spike trains. Bursts were assigned a quantitative statistical measure of burst 'strength' (or improbability) - the surprise value. Before the lesion, 34% of units in the globus pallidus and 60% of units in the entopeduncular nucleus exhibited bursts. Burst units had a significantly slower discharge rate and a significantly greater variability of discharge than non-burst units. The mean length of the interspike intervals immediately preceding the bursts was significantly longer than the overall median intervals in burst units. After the lesion, 21% of units in the globus pallidus and 11% of the units in the entopeduncular nucleus exhibited bursts. Burst units had significantly higher discharge rates and lower discharge variability after the lesion. In contrast, the lesion had no significant effect on the rate or variability of non-burst units. The differences between bursting and non-bursting units in discharge rate and variability disappeared after the lesion. In globus pallidus, the lesion resulted in a significant reduction in the mean number of bursts per unit, surprise value per burst, mean length of bursts, and number of spikes per burst, and a significant increase in the mean discharge rate of burst units. In entopeduncular nucleus, the small number of bursts recorded after the lesion precluded a useful statistical comparison of the effect of striatal lesions on the properties of the bursts. This study demonstrates that removing striatal projections to globus pallidus and entopeduncular nucleus decreases bursting in these nuclei, indicating that intact striatal projections are necessary for the normal production of bursts in these regions.

Autoradiographic visualization of NK-3 tachykinin binding sites in the rat brain, utilizing [3H]senktide

The autoradiographic distribution of the selective NK-3 tachykinin agonist [3H]senktide was investigated in rat brain. [3H]Senktide bound with high affinity (KD less than 2.5 nM) and high specificity (greater than 75%) to cerebral cortex and numerous subcortical sites, including the substantia nigra pars compacta. In addition, moderately dense binding was seen in the median but not the dorsal raphe nucleus, and this was disrupted by 5,7-dihydroxytryptamine (5,7-DHT)-induced destruction of 5-HT neurons. 5,7-DHT lesions did not affect the binding of [3H]senktide to forebrain regions, suggesting that 5-HT terminals are devoid of NK-3 receptors.

Intranigral substance P modulation of striatal dopamine: interaction with N-terminal and C-terminal substance P fragments

The effects of unilateral injections of two substance P fragments, the N-terminal substance P (1-7) (SP1-7) and the C-terminal substance P (6-11) (SP6-11) into the substantia nigra, pars reticulata on dopamine (DA) release in the ipsilateral striatum of halothane-anaesthetized rats were studied using microdialysis. SP1-7 and SP6-11 were also tested for their ability to modify the DA stimulation produced by intranigral injections of SP or neurokinin A (NKA). In addition, the SP antagonist Spantide I was tested for its ability to modify the DA stimulation produced by an intranigral injection of SP1-7. Intranigral injections of SP1-7 (0.001-5.0 nmol) inhibited DA release after low doses (0.001-0.01 nmol), but stimulated DA release after high doses (0.1-5.0 nmol). Striatal dihydroxyphenylacetic acid (DOPAC) levels increased moderately after high doses of SP1-7 (1.0-5.0 nmol). Intranigral injections of SP6-11 (0.01-5.0 nmol) inhibited DA release, but enhanced striatal DOPAC levels, dose-dependently. SP1-7 (0.01-0.1 nmol), but not SP6-11 (0.1 nmol), blocked the stimulation of striatal DA release produced by intranigral SP (0.07 nmol). Neither SP1-7 (0.1 nmol) nor SP6-11 (0.1 nmol) could modify the stimulation of striatal DA release produced by intranigral NKA (0.09 nmol). The increase in DA release after a high dose of SP1-7 (1.0 nmol) was not modified by co-administration with Spantide I (0.07 nmol).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of excitotoxic striatal lesions on single unit activity in globus pallidus and entopeduncular nucleus of the cat

Striatal projections to the globus pallidus and entopeduncular nucleus are thought to be GABAergic and inhibitory. Thus, striatal lesions might be expected to increase the spontaneous discharge rate of neurons in these nuclei. To test this prediction, we recorded spontaneous single unit activity from awake cats sitting quietly before and 7-160 days after striatal lesions. Striatal lesions were produced by injecting ibotenic acid into the caudate nucleus and putamen. Median, standard deviation, mean, and coefficient of variation of the interspike intervals were calculated for each unit. In globus pallidus the striatal lesion resulted in a significant decrease in median interval length, i.e. an increase in the discharge rate. The prelesion median of 36 ms (S.E.M. = 2.3) decreased 11% to a postlesion value of 32 ms (S.E.M. = 2.1). The lesion also resulted in a significant decrease in the variability of interspike intervals. The coefficient of variation, 1.31 (S.E.M. = 0.08) before the lesion, decreased 25% to 0.97 (S.E.M. = 0.06) after the lesion. In entopeduncular nucleus, the lesion had no statistically significant effect on the rate of activity, but a significant decrease in the variability of activity occurred. The median interval was 33 ms (S.E.M. = 3.3) before the lesion and decreased 2% to 32 ms (S.E.M. = 2.4). The coefficient of variation decreased 48% from 1.44 (S.E.M. = 0.1) to 0.73 (S.E.M. = 0.03). These observations support the hypothesis that loss of GABAergic inputs to the globus pallidus results in disinhibition. The discharge rate in entopeduncular nucleus was not affected by the striatal lesion, suggesting that striatal substance P or subthalamic excitatory inputs may have a role in regulating discharge rate in the entopeduncular nucleus.

N- and C-terminal fragments of substance P: spinal effects in the rat tail flick test

Evidence exists to suggest that within the CNS, substance P may be enzymatically cleaved into fragments which may mediate some of the effects of substance P. As we have previously reported on the spinal effects of substance P, the present study examines the effects of selected substance P fragments on reaction time in the tail flick test. Peptides were administered via a chronically implanted intrathecal catheter to the L5 vertebral level in the rat. Administration of 6.5 nmoles of SP(1-7) produced a transient decrease in reaction time at 1 min after injection with a return to above control values by 5 min. Similar administration of SP(7-11) produced a smaller decrease in reaction time at 6 min which lasted until 16 min. Administration of 6.5 nmoles of SP(1-9), SP(8-11) and of CSF were without effect. As the effects of SP(1-7) on reaction time resembled those of similar administration of substance P in the earlier experiments, these results suggest that this fragment may be the active component involved in facilitating the tail flick reflex. Substance P may be degraded to the active fragment prior to receptor activation or alternatively, substance P and SP(1-7) may act on the same receptor.

Acute reduction of brain substance P induced by nicotine

Ten minutes after a single injection of 0.8 mg/kg nicotine SC (free base) the level of substance P-like immunoreactivity (SPLI) was reduced by 61-73% in rat caudate-putamen, nucleus accumbens, and olfactory tubercle, with smaller and not significant reductions in the frontal cortex, substantia nigra, and ventral tegmental area. The nicotinic receptor antagonist mecamylamine (1.0 mg/kg IP) prevented the reductions in SPLI. The rapidity and the degree of the changes in SPLI after nicotine exceed those previously reported for other agents and implicate substance P neurotransmission as a major component of nicotinic action.

Dopamine-containing neurons in the mammalian central nervous system: electrophysiology and pharmacology

A decade of research culminated in the late 1950's with the demonstration that dopamine was a chemical neurotransmitter within the mammalian brain. Since this time, dopaminergic neuronal systems have been extensively studied using numerous techniques. This paper will review the last 14 years of electrophysiological investigation on neurochemically identified dopamine-containing neurons in the central nervous system. This will include an examination of both the electrophysiological and pharmacological characteristics in these cells, as well as the resulting insights into the regulation of dopamine cell electrical activity which is derived from this work.

Direct demonstration of interactions between substance P immunoreactive terminals and tyrosine hydroxylase immunoreactive neurons in the substantia nigra of the rat: an ultrastructural study

The results of many anatomical, physiological, and pharmacological studies suggest that substance P-containing neurons of the striatum project to the substantia nigra, and that substance P influences the activity of dopaminergic nigrostriatal neurons. The purpose of the present ultrastructural study was to employ dual immunocytochemical labeling to determine the morphological basis for the observed actions of substance P on nigral dopaminergic neurons. Substance P-like and tyrosine hydroxylase-like immunoreactivities were localized simultaneously at the ultrastructural level in the substantia nigra of the rat. A double label method was utilized which relied on a combination of the peroxidase-antiperoxidase method (Sternberger, 1979) for substance P, and immunogold or silver enhanced immunogold labeling for tyrosine hydroxylase. The present results indicate that tyrosine hydroxylase immunoreactive (THLI) dendrites in the substantia nigra receive synaptic input from terminals exhibiting substance P-like immunoreactivity. These findings support the idea that substance P is a major neurotransmitter in the striatonigral loop, and suggest that striatal substance P neurons act directly upon nigral dopaminergic cells.

Interaction between thyrotropin-releasing hormone and the mesolimbic dopamine system

The involvement of the mesolimbic dopamine (DA) system in the excitatory behavioral effects of thyrotropin-releasing hormone (TRH) has been a controversial topic. In this study TRH was injected into the nucleus accumbens, lateral ventricles or ventral tegmental area and changes in spontaneous motor activity and metabolism of DA in the nucleus accumbens and striatum measured. Injection of TRH into all three areas of the brain produced an increase in photocell counts of locomotor activity and, in the nucleus accumbens, a significant decrease in photocell counts of rearing was measured. Injection of TRH into the nucleus accumbens caused a marked increase in metabolism of DA in both the nucleus accumbens and striatum. A smaller increase in metabolism of DA was also observed after injection of TRH into the lateral ventricles, but no significant change was found after intra-ventral tegmental administration of TRH. These data indicate that while TRH probably acts in the nucleus accumbens to enhance the metabolism of DA, and presumably release of DA, the excitatory behavioral effect of TRH is only partially mediated by this dopaminergic mechanism.

Substance P-containing terminals in synaptic contact with cholinergic neurons in the neostriatum and basal forebrain: a double immunocytochemical study in the rat

Antibodies against substance P and choline acetyltransferase (ChAT) have been used in a sequential double-immunocytochemical ultrastructural study of the rat forebrain. The peroxidase-anti-peroxidase procedure was used for both antigens, however, two different substrates for the peroxidase reactions were used. The substance P-immunoreactive sites were first localized using 3,3'-diaminobenzidine as the substrate, then the ChAT-immunoreactive sites were localized using benzidine dihydrochloride. The reaction product formed by the two substrates was distinguishable in both the light and electron microscopes. Using this procedure, the cell bodies and proximal dendrites of identified cholinergic neurons in the neostriatum were found to receive symmetrical synaptic input from substance P-immunoreactive boutons. A similar pattern of substance P-immunoreactive synaptic input was observed onto magnocellular basal forebrain cholinergic neurons in the ventral pallidum and ventromedial globus pallidus. In both the striatum and basal forebrain substance P-immunoreactive boutons were also seen in contact with structures that did not display ChAT immunoreactivity.

Comparison of the effects of substance P, neurokinin A, physalaemin and eledoisin in facilitating a nociceptive reflex in the rat

The postulated existence of different types of tachykinin receptor in the spinal cord provided the basis for the present study; substance P, neurokinin A, eledoisin and physalaemin were administered intrathecally in the awake, restrained rat to compare their effects on reaction time in the tail-flick test. Each peptide was delivered via a chronically implanted subdural catheter to the lower lumbar vertebral level of the spinal cord. Intrathecal administration of 10 micrograms of substance P (6.5 nmol), eledoisin (8.0 nmol) or physalaemin (7.9 nmol) decreased the reaction time, respectively, to 22.5, 24.3 and 20.8% of the mean preadministration control values at 1 min after injection; similar administration of 6.5 nmol of neurokinin A produced a smaller decrease in reaction time, to only 49.5% of preadministration values. These effects were transient, the reaction times returning to preadministration values within 5 min. Each peptide also produced an initial vocalization followed by increased restlessness. Analysis of the dose-response curves indicated that the rank order of potency of the fitted curves for these peptides was physalaemin greater than or equal to substance P greater than or equal to eledoisin greater than neurokinin A. The results suggest that the receptor involved in facilitation of the tail-flick reflex resembles a substance P receptor rather than a receptor for one of the other endogenous neurokinins and that this receptor may bear some resemblance to the SP-P type postulated to exist in peripheral tissues.

Ventral tegmental area infusion of substance P, neurotensin and enkephalin: differential effects on feeding behavior

The neuropeptides substance P, neurotensin and [Met]enkephalin are found in the ventral tegmental area, site of the A10 dopamine cell bodies. Evidence suggests a functional interaction between these peptides and the dopaminergic neurons. All three peptides have been shown to exert an activating effect on these neurons. The present study analyzed the effects of ventral tegmental area infusion of neurotensin, substance P and D-ala-[Met]enkephalin on feeding behavior. These effects were studied in both food-deprived and satiated rats. During a 30 min test, the following parameters were registered: latency to eat, total food intake, food spillage, number of eating bouts and duration of eating. Similar measures were taken for drinking. In deprived rats substance P (0.5, 3.0 micrograms) increased latency to eat but did not affect other parameters, and substance P did not affect eating in satiated rats. Neurotensin (0.5, 2.5 micrograms) increased latency to eat and markedly reduced food consumption in deprived rats and had no effect in satiated rats. D-Ala-[Met]enkephalin (0.1, 1.0 micrograms) stimulated feeding behavior in both deprived and satiated rats. These results show that although the different peptides are presumed to activate the dopaminergic A10 neurons, their effects on feeding behavior can be differentiated. The findings are discussed in terms of motor and motivational mechanisms, and the relative contributions of specific and non-specific influences on feeding are considered.

Selective activation of mesolimbic and mesocortical dopamine metabolism in rat brain by infusion of a stable substance P analogue into the ventral tegmental area

Microinfusion of the metabolically stable substance P (SP) agonist, [pGlu5,MePhe8,Sar9]-SP5-11 (DiMe-C7), into the ventral tegmental area (VTA) of rat brain increased levels of the dopamine (DA) metabolite dihydroxyphenylacetic acid in the prefrontal cortex (+ 120%) and nucleus accumbens (+30%) but not in other regions of forebrain. In contrast, infusions of DiMe-C7 or SP into the lateral ventricles or microinfusions of SP into VTA failed to elicit increases in DOPAC levels in forebrain. DA levels were unaffected by SP or DiMe-C7 regardless of the route of administration. These data and previous studies suggest a role for endogenous SP in the modulation of mesocortical and mesolimbic DA neurones.

Interactions between neuropeptides and dopamine neurons in the ventromedial mesencephalon

Cholecystokinin (CCK), enkephalin, neurotensin (NT), substance P (SP) and substance K (SK) are five neuropeptides that exist in neuronal perikarya or fibers in the vicinity of the A10 dopamine neurons in the ventromedial mesencephalon. Based upon this anatomical proximity, many investigations have been evaluating the possibility that these peptides may influence the function of the A10 dopamine neurons. A variety of experimental techniques have been employed in this regard, including anatomical, electrophysiological, neurochemical and behavioral methodologies. Measurement of immunoreactive peptide levels with radioimmunoassay, and visualization of peptidergic neurons and fibers with immunocytochemistry has demonstrated not only that peptides exist in the vicinity of A10 dopamine neurons, but using double labeling techniques NT and CCK have been found to coexist with dopamine in the same neuron. Further, by combining retrograde tracing technique with immunocytochemistry, the origin of some peptidergic afferents to the ventromedial mesencephalon has been determined. With the exception of CCK-8, microinjection into the ventromedial mesencephalon of rats with all the peptides or potent analogues produces a dose-related increase in spontaneous motor activity. For SP, NT and enkephalin the motor response has been blocked by dopamine antagonists. Further, an increase in dopamine metabolism in mesolimbic dopamine terminal fields is produced concurrent with the behavioral hyperactivity. These data indicate that SP, SK, enkephalin and NT can activate dopamine neurons in the ventromedial mesencephalon. This postulate is supported by electrophysiological studies showing an excitatory action by iontophoretic administration of peptide onto dopamine neurons. However, in some studies, excitatory electrophysiological effects were not observed. While some observations are contradictory, sufficient data has accumulated that tentative postulates and conclusions can be made about how these peptides may influence the A10 dopamine neurons. Further, speculations are offered as to the role this modulatory action may play in the many behaviors and pathologies thought to involve these dopamine neurons.

Time-course and regional distribution of the metabolic effects of bromocriptine in the rat brain

Local cerebral glucose utilization (LCGU) and motor behavior were examined in awake Fischer-344 rats after administration of the dopaminergic agonist bromocriptine (BROMO). LCGU was measured using the [14C]2-deoxyglucose technique in 63 brain regions at 1,2,3 or 4 h after BROMO 20 mg/kg, and at 4 h after BROMO 100 mg/kg i.p. At 2 h, LCGU was reduced significantly in 13% of the 63 regions examined. The affected regions are related to the topographical distribution of dopaminergic innervation in the brain. At 3-4 h, LCGU remained depressed in some of the above dopaminergic regions, but was elevated significantly in regions which are involved in sensorimotor function. BROMO also produced two behavioral effects depending on time after administration. Locomotor activity was depressed at 1-2 h, and stereotyped behavior appeared at 3-4 h. The time-dependent effects of BROMO may reflect progressively increasing brain concentrations of the drug or of its active metabolites. The coincidence of locomotor depression and reduction of LCGU in dopaminergic regions suggests a role of dopamine autoreceptors in regulation of motor function. Metabolic stimulation of many non-dopaminergic regions when stereotypy is evident suggests that circuit(s) involving these areas may contribute to stereotypy.

Are the proposed substance P receptor sub-types, substance P receptors?

Recently, a number of laboratories have postulated the existence of receptor sub-types for substance P. This review is intended to represent a critical appraisal of these reports. In the majority of cases, the evidence for the existence of receptor sub-types has been obtained from observed potency differences of agonists. The problems with this approach are discussed. In addition, information obtained through substance P antagonists, binding studies and investigations of second messenger systems is presented and discussed in relation to the above receptor subdivisions. It is concluded that the present results are consistent with the existence of three receptor sub-types; however, it is suggested that substance P is the natural agonist for only one of these receptors, and that substance K and tuftsin may be the transmitters for the other two receptor sub-types.