Effect of synthetic substance P on monoaminergic mechanisms in brain

Psychosis Following an Increase in Intrathecal Baclofen

Baclofen is a commonly used medication to treat spasticity in neurologic disorders. In the traumatic brain injury (TBI) population, the intrathecal administration of baclofen is often preferred over oral administration due to cognitive side effects. Here we report on a case of a psychotic episode following an increase in intrathecal baclofen in a young man with a history of a TBI. Although intrathecal baclofen is commonly used and is generally well tolerated, this case highlights an important potential effect of intrathecal baclofen that has rarely been reported in the literature.

LEVEL OF EVIDENCE

V.

Effects of repeated sensory stimulation (electro-acupuncture) and physical exercise (running) on open-field behaviour and concentrations of neuropeptides in the hippocampus in WKY and SHR rats

The effects of repeated sensory stimulation (electro-acupuncture) and physical exercise (running) on open-field behaviour and on hippocampal concentrations of neuropeptide Y, neurokinin A, substance P, galanin and vasoactive intestinal peptide (VIP)-like immunoreactivities were studied in WKY (wistar-Kyoto) and SHR (spontaneously hypertensive) rats. Significantly higher concentrations of substance P-like immunoreactivity, neurokinin A-like immunoreactivity and neuropeptide Y-like immunoreactivity were found in the hippocampus immediately after 3 weeks of treatment (electro-acupuncture and running), but not 1 week after the last (tenth) changes in neuropeptide concentrations were similar in the two rat strains. Open-field behaviour was significantly reduced during the treatment period in both strains. There were significant negative correlations between behaviour and neuropeptide concentrations in SHR rats, suggesting interdependency with sympathetic activity. It is proposed that the effects of electro-acupuncture and physical exercise in rats are related to increases in neuropeptide Y, neurokinin A and substance P in the hippocampus.

Participation of noradrenergic neurotransmission in the suppression by substance P of alpha 2-adrenoceptors at the nucleus reticularis gigantocellularis involved in central cardiovascular regulation in the rat

We applied reverse microdialysis and HPLC analysis to quantify the participation of noradrenergic neurotransmission in the modulation by substance P of alpha 2-adrenoceptors at the nucleus reticularis gigantocellularis involved in cardiovascular regulation, using Sprague-Dawley rats anesthetized with pentobarbital sodium. The efficacy of circulatory suppression of a centrally acting alpha 2-adrenoceptor agonist, guanabenz, was used as the experimental index. Continuous infusion of substance P (600 or 1200 pmol/microliters/min) into the nucleus reticularis gigantocellularis through a stereotaxically positioned microdialysis probe (active exchange length: 500 microns, diameter: 220 microns) for 80 min elicited a reduction in the hypotensive and bradycardiac actions of guanabenz (100 micrograms/kg, i.v.). This implied suppression of alpha 2-adrenoceptor activity correlated positively with the time-course of increase in the estimated extracellular concentration of the undecapeptide and norepinephrine in the nucleus reticularis gigantocellularis. Experimentally elevating the concentration of norepinephrine at this reticular nucleus via microinfusion by reverse microdialysis also decreased the efficacy of the cardiovascular suppression of the aminoguanidine compound. These results suggest that substance P may depress the activity of the alpha 2-adrenoceptors in the nucleus reticularis gigantocellularis that are involved in central cardiovascular regulation via an increase in the extracellular concentration of norepinephrine at this reticular nucleus.

Substance P suppresses the activity of alpha 2-adrenoceptors of the nucleus reticularis gigantocellularis involved in cardiovascular regulation in the rat

We evaluated possible interactions between substance P (SP) and the alpha 2-adrenoceptors in the nucleus reticularis gigantocellularis (NRGC) of the medulla oblongata involved in cardiovascular regulation. Adult, male Sprague-Dawley rats anesthetized with pentobarbital sodium (40 mg/kg, i.p., with 10 mg/kg/h i.v. supplements) were used. The circulatory suppressant efficacy of a centrally acting alpha 2-adrenoceptor agonist, guanabenz, was used as the experimental index. Bilateral microinjection of SP (300 or 600 pmol) into the NRGC, a medullary site that is critically involved in the cardiovascular depressive actions of guanabenz, significantly diminished the hypotensive and bradycardiac efficacy of the aminoguanidine compound (100 micrograms/kg, i.v.). This implied reduction in alpha 2-adrenoceptor activity in the NRGC by SP was antagonized by its selective receptor antagonist, [D-Pro2,D-Trp7,9]-SP (1200 pmol). Similarly, attenuation by SP of the cardiovascular suppressant effects of guanabenz was also reversed by immunocytochemically verified depletion of dopamine-beta-hydroxylase-immunoreactive nerve terminals in the NRGC, elicited by the selective noradrenergic neurotoxin, DSP4 (50 micrograms). These data suggest that SP may exert an inhibitory action on the alpha 2-adrenoceptors in the NRGC that are involved in central cardiovascular regulation, possibly via a presynaptic modulation on noradrenergic neurotransmission.

Substance P- and tyrosine hydroxylase-containing neurons in the human dorsal motor nucleus of the vagus nerve

The aim of this study was to provide a comprehensive account of the topography, morphology, and frequencies of the substance P- and tyrosine hydroxylase-containing neurons in the human dorsal motor nucleus of the vagus nerve. The morphology of immunoreactive neurons was studied and the variations of the cell distributions were presented by three-dimensional computer reconstructions. Three types of substance P-like immunoreactive neurons were identified. They were predominantly located in the dorsointermediate, centrointermediate, caudointermediate, and caudal division of the dorsal motor nucleus of the vagus nerve. The morphology of substance P-like immunoreactive neurons varied according to the subnuclei in which they were found. Three types of tyrosine hydroxylase-like immunoreactive neurons were identified, mainly in the periphery of the dorsal motor nucleus of the vagus nerve, including the medial fringe, ventrointermediate, and dorsointermediate subnuclei of the 10. Many cells throughout the ventrointermediate subnucleus of the dorsal motor nucleus of the vagus nerve are seen ventrally to intermingle with the tyrosine hydroxylase neurons of the intermediate reticular zone. Computer reconstructions provided a three-dimensional view of the positions of substance P- and tyrosine hydroxylase-like immunoreactive neurons within the subdivisions of the dorsal motor nucleus of the vagus nerve. The uneven distribution of substance P- and tyrosine hydroxylase-like immunoreactive neurons within the subdivisions suggests an involvement of these substances in some, but not all, autonomic functions of the dorsal motor nucleus of the vagus nerve.

Substance P opens cation channels and closes potassium channels in rat locus coeruleus neurons

Whole-cell recordings were made from neurons of the rat locus coeruleus in a tissue slice removed from rat brain. Substance P caused an inward current in cells voltage-clamped at -60 mV. The effect of substance P was concentration-dependent (30 nM-3 microM) and was mimicked by similar concentrations of substance K and neuromedin K. The inward current resulted predominantly from an increase in membrane cation conductance; in potassium-free solutions it reversed polarity at about 12 mV. Substance P also reduced the conductance of an inwardly rectifying potassium current; this action was studied with low external sodium concentration. It is concluded that substance P excites rat locus coeruleus neurons by activating an intracellular transduction pathway leading to both cation conductance increase and potassium conductance decrease.

Substance P-like immunoreactive fibres in the ventromedial mesencephalic tegmentum of rat

The distribution and morphology of the substance P-like immunoreactive (SP-IR) fibres and terminals in the rat ventromedial mesencephalic tegmentum (VMT) were studied using qualitative and quantitative immunohistochemical methods at light and electron microscopic levels. All five component nuclei of the VMT were examined and the size, number and density of immunoreactive terminals determined. The SP-IR fibres were distributed heterogeneously within the VMT. Under the electron microscope, SP-IR axon terminals contained both clear and dense-cored vesicles and made both symmetrical and asymmetrical synapses. The ultrastructure of the SP-IR terminals appeared to differ between nuclei. Small, clear vesicle terminals made symmetrical synaptic junctions with small calibre dendrites in the paranigral nucleus while large, clear and dense-cored vesicle terminals made asymmetrical junctions with somata and large calibre dendrites in the interfascicular nucleus. Quantitative differences between the VMT nuclei were also seen in the density of SP-IR terminals, the paranigral nucleus contained the highest density and the rostral linear nucleus the lowest. A comparison between the number of SP-IR terminals and the total number of axon terminals in the VMT reveals that the majority of all terminals in the paranigral nucleus were SP-IR, as well as the majority of axosomatic synapses in the interfascicular nucleus. These regional differences in the SP-IR innervation suggest that substance P and related peptides may perform several specific functions within the VMT and therefore have a more variable influence on this region than was previously thought.

Central noradrenergic pathways are not involved in the pressor response to intracerebroventricular substance P

Intracerebroventricular (i.c.v.) pretreatment of Wistar rats with the catecholaminergic neurotoxin, 6-hydroxydopamine, significantly reduced noradrenaline in the pons/medulla (by 73%) and almost abolished the noradrenaline levels in the spinal cord (by 89%). The pressor response of these animals to i.c.v. angiotensin II (ANGII, 10 ng) was significantly attenuated. In contrast, there was no significant effect on the pressor response to i.c.v. substance P (SP, 100 ng). The results provide evidence that different central pathways mediate the pressor response to ANGII and SP.

Alteration in the histochemical presence of tyrosine hydroxylase and CGRP-immunoreactivities in the eye following chronic sympathetic or sensory denervation

Changes in the content of calcitonin gene-related polypeptide (CGRP) and tyrosine hydroxylase (TH) immunoreactivities in the anterior segment of the rat eye were assessed histochemically in animals subjected to sympathetic ganglionectomy or to chronic sensory denervation induced by neonatal capsaicin treatment. In the sympathectomised eyes there was a marked depletion of TH and increase in CGRP immunoreactivity while in tissue subjected to sensory denervation the reverse was found, raised presence of TH and absence of CGRP-immunostaining. The results suggest important neurotrophic influences by the host tissue or a trophic interaction of one nerve set on another.

Substance-P antagonists: effect on spontaneous and drug-induced locomotor activity in the rat

The substance P (SP) antagonists (D-Pro4, D-Trp7,9, Leu11) SP(4-11), (D-Pro4, D-Trp7,9, Phe11)SP(4-11) and (D-Pro4, D-Trp7,9,10, Leu11) SP (4-11) were infused into the lateral ventricles (i.c.v.) and their effects on spontaneous and drug-induced locomotor activity were investigated. The drug DiMeC7, the stable substance P agonist, was used to stimulate locomotor activity because of its prolonged action. Only (D-Pro4, D-Trp7,9,10) SP (4-11) was found to attenuate the drug-induced increases in motor activity, indicating that it is a substance P antagonist with activity in the CNS.

Substance P in the human brain

The distribution of substance P immunoreactive sites was investigated by immunoenzymatic methods in a large series of paraffin embedded human brain sections from the collection assembled by Oscar and Cécile Vogt several decades ago, as well as from more recent post-mortem material. These studies demonstrated that substance P immunoreactivity was preserved in archival material permitting a detailed account of the localization of immunoreactive cell bodies, fibre networks and tracts in the human brain. Previous observations made on experimental animals and man were confirmed and extended. Additionally, substance P immunoreactive cell bodies were seen in most cortical areas and novel features were noted in the distribution of substance P-containing elements in the tuberal region, corpus striatum, substantia nigra (particularly in relationship to blood vessels) and in association with melanin-containing cells. Reconstruction of some substance P pathways was attempted by the analysis of semi-serial sections in more than one plane. Immunocytochemistry, in combination with image analysis, enabled some measurements of the differential concentrations of substance P immunoreactive material to be made and allowed a close correlation of this with defined anatomical landmarks or enkephalin immunoreactive sites.

Morphological changes of sensory CGRP-immunoreactive and sympathetic nerves in peripheral tissues following chronic denervation

The morphological relationship between sensory and sympathetic nerves was studied in tissues of the eye and the oral cavity following chronic sympathetic or sensory denervation. Immunoreactivities for calcitonin gene-related peptide (CGRP) and tyrosine hydroxylase (TH) were used as indexes to assess the changes of the two nerve populations after denervation. Following surgical sympathectomy, a marked increase of CGRP-containing fibres was seen in all tissues studied, while TH-imunoreactive fibres were totally depleated. Conversely, after capsaicin treatment, an increase of TH-immunoreactive nerves was found in the same tissues, concomitant with a sharp decrease of CGRP-immunoreactive nerves. These changes were particularly evident in iridial stroma and around blood vessels in all tissue, where sensory and sympathetic nerves have a closely overlapping distribution pattern. The altered proportion of sensory peptide- and catecholamine-containing nerves following sympathetic and sensory denervation suggest that there is a reciprocal trophic influence between the two nerve subsets, possibly with the intervention of neurotrophic substances such as nerve growth factor. These results indicate a close interaction between sensory peptidergic and sympathetic nervous systems in peripheral organs.

Effects of analogues of substance P fragments on the MAO activity in rat brain

The influence in vitro of analogues of Sp5-11 and SP6-11 substance P fragments on the activity of monoamine oxidase (MAO) in homogenates and crude mitochondrial fractions of rat brain was examined. The rat brain was divided into: I--cerebral cortex, II--hippocampus, III--midbrain, IV--thalamus with hypothalamus, V--cerebellum and VI--medulla oblongata. The obtained results proved that the analogues of SP fragments inhibit selectively the activity of the enzyme in the homogenates of cerebral cortex, hippocampus, midbrain and cerebellum. In the crude mitochondrial fractions the applied analogues of SP fragments caused a slight increase of the enzyme activity. The most significant changes in the activity of MAO were observed in hippocampus homogenate fraction.

A comparison of the anatomical distribution of substance P and substance P receptors in the rat central nervous system

A comparison of anatomical distributions of substance P (SP) and substance P receptors in the rat central nervous system was performed. SP was localized by microdissection and radioimmunoassay and SP fibers and cell bodies by immunohistochemistry. Receptors for 125I-Bolton Hunter labelled SP (125I-BH-SP) were characterized pharmacologically by a slice binding technique in sections that contained primarily striatum. The receptor was saturable and had an equilibrium dissociation constant (KD) of 0.30 nM and maximum number of binding sites (Bmax) of 37.8 fmol/mg protein. Pharmacological characterization using C terminal fragments and naturally occurring analogues of SP reflected characteristics of the receptor which had been shown previously in bioassays and biochemical assays. Comparison of distribution of SP fibers and cell bodies and SP receptors indicated that there is no consistent relationship between the amount of SP receptor and density of SP fibers or cell bodies in a given region of the brain.

A neural plasticity hypothesis of schizophrenia

An extensive research effort has failed, thus far, to conclusively identify a specific disease process (or processes) underlying the behavioral symptoms of schizophrenia. The present paper will entertain the hypothesis that the structural and functional plasticity of the brain can constitute a "nonspecific" biological etiology of schizophrenia. This plasticity need not be accompanied by infectious processes or gross alterations in neurotransmitter levels, enzyme activities, etc. that are specific to schizophrenia. The monkey isolation syndrome provides a precedent for a causal relationship between brain plasticity and pathological behavior. In a speculative manner, it will be demonstrated that neural plasticity concepts can be invoked to potentially explain several aspects of schizophrenia: the various types of behavioral symptoms exhibited by schizophrenics, the regional alterations in brain structure and function seen in chronic schizophrenics, the involvement of genetic and environmental etiological factors, the pharmacological support for the dopamine hypothesis, and the delayed onset of neuroleptic antipsychotic action. Considering the explanatory potential of neural plasticity concepts, a research program which focuses on these concepts seems warranted.

Modulation of locomotor activity by substance P in rats

The effects of intraperitoneally or intracerebrally (DA A-10 area) administered substance P (SP) on locomotor activity of rats were studied in an exact 12-h light/12-h dark cycle changing from dark to light at 6 a.m. SP was administered either at 11 a.m. (light phase, minimal locomotor activity) or at 7 p.m. (dark phase, maximal locomotor activity). The effects of 12.5 micrograms/kg SP intracerebral and 125 micrograms/kg SP intraperitoneal were very similar. In the light phase SP produces excitation but inhibition of locomotion in darkness. Hence, the effect of SP depends on the internal mechanisms controlling motor activity and tends to level off the spontaneous circadian oscillation. We found a long lasting SP effect during both the light and dark period. The present experiments led us to the conclusion that SP has a levelling effect on locomotor activity. Probably this effect might be explained as SP's action on the dopaminergic pathway or dopamine metabolism, because the dopamine content in neurons also has a circadian rhythm.

The behavioural effects of a novel substance P analogue following infusion into the ventral tegmental area or substantia nigra of rat brain

The behavioural response following infusion of a novel, stable substance P (SP) analogue, DiMe-C7, into the ventral tegmental area (VTA) of rats was characterized and contrasted with the response to an equal dose of the parent compound SP. DiMe-C7 produced a longer-lasting behavioural stimulation than SP as evidenced in several behaviours, including locomotor activity, wet dog shakes, rearing and grooming. DiMe-C7-induced locomotor activity and rearing were potentiated by concurrent peripheral administration of D-amphetamine and blocked by pretreatment with haloperidol. Such responses to DiMe-C7 may thus be dependent upon dopaminergic activity. When given immediately following VTA infusion of DiMe-C7, morphine decreased, while naloxone had no effect upon most behavioural measures. The effect of methysergide on DiMe-C7 or SP into the substantia nigra reticulata produced a pattern of responses similar to nature to those produced by VTA infusion but different with respect to time course. These findings suggest that DiMe-C7 is a metabolically stable analogue of substance P which manifests prolonged actions on behaviour when centrally administered. Further, a role for central dopaminergic mechanisms is implicated in DiMe-C7-induced behavioural action.

Extinction of hippocampal theta rhythm evoked by mid-brain stimulation after intracerebroventricular administration of substance P fragment and enkephalin administration in rabbits

Repetitive stimulation of the midbrain reticular formation with electrical stimuli causes extinction of the hippocampal theta rhythm. This phenomenon was used as an indicator of the effect of intracerebroventricular administration of the C-terminal hexapeptide substance P fragment (SP6-11), Leu- and Met-enkephalin on hippocampal electrical activity in the experiments performed on rabbits. Intracerebroventricular administration of SP6-11 caused an increase in the number of trains of pulses required to produce the extinction of the theta rhythm. Both of the enkephalins had opposite effects, the effect of Met-enkephalin being more than twice as strong as Leu-enkephalin. Control administration of C-terminal pentapeptide substance P fragment (SP7-11) and 0.9% NaCl solution had no significant effect on the tested phenomenon.

Substance P-like immunoreactivity in plasma of psychotic patients and effects of neuroleptics and electroconvulsive therapy

Radioimmunoassay of substance P (SP)-like reactivity, using N alpha-tyrosyl-SP, was performed in plasma of psychotic patients. Schizophrenic patients under neuroleptic medication over 1 year, and those patients with organic brain disease showed a significant increase in immunoreactivity. The immunoreactivity in unmedicated schizophrenic patients just before treatment and in depressed patients, both bipolar and major, did not differ significantly from that of controls. The immunoreactivity in unmedicated schizophrenics was followed after medication for a maximum of 5 months. The reactivity decreased in five cases, and increased in three cases. No definite pattern could be discerned between changes in the immunoreactivity, the type of medication administered, and the resultant response to the therapy. Chlorpromazine injection caused no definite acute effect on the plasma level of SP-like immunoreactivity for 120 minutes. Electroconvulsive therapy increased the plasma level of SP-like immunoreactivity for 90 minutes in a male schizophrenic patient.

Opposite effects of naloxone on substance P-induced changes in brain DOPA synthesis and in locomotor activity in rats

Intracerebroventricular injection of substance P (SP) enhanced the synthesis of dopamine and noradrenaline (measured as increase in DOPA formation after inhibition of the aromatic L-amino-acid decarboxylase) in rat brain. These biochemical effects were blocked in most brain regions by pretreatment with naloxone. SP also induced vasodilation, salivation and increased locomotor activity. These effects were not antagonized, but, in the case of locomotor activity, potentiated by naloxone. The data suggest the existence of specific SP-containing neuronal pathways for behavior, which pathways are not related to those regulating the synthesis of brain catecholamines.

Differential effects on learning by ventromedial vs lateral hypothalamic posttrial injection of substance P

The effects of post-trial injection of substance P (SP) into the lateral hypothalamus (LH) and the ventromedial hypothalamus (VMH) on passive avoidance learning was studied in rats. In the VMH, 50 ng and 500 ng SP influenced neither learning of a step-down avoidance nor of an alcove avoidance response. In contrast to these findings, 500 ng SP injected into the LH significantly enhanced retention of the alcove avoidance task. Similarly, in the step-down avoidance experiment, learning was strongly facilitated by posttrial injection of 50 ng as well as 500 ng SP into the LH. These results, together with our previous data showing amnesia with posttrial injection of SP into amygdala and substantia nigra, suggest that exogenously applied SP influences the activity of those brain regions shown to contain high densities of SP-positive nerve terminals. Interestingly, the effects of posttrial SP injection parallel the effects of post-trial electrical brain stimulation on passive avoidance learning. Hence, posttrial SP retroactively facilitates or impairs learning depending on where in the brain it is injected.

Effects of substance P injected into the substantia nigra

1 Behavioural and biochemical effects of substance P (SP, 1 to 10 mug) administered in a small volume to discrete areas of the rat's brain were studied by means of a refined microinjection technique.2 SP injected unilaterally into the zona reticulata of the substantia nigra elicited dose-dependent contraversive circling and an increase in dopamine turnover in the ipsilateral striatum. SP applied to the zona compacta or zona lateralis, or to the medial lemniscus, evoked ipsiversive turning with a fall in dopamine turnover and a rise in 5-hydroxytryptamine (5-HT) turnover in the corresponding striatum.3 In both cases the onset of turning was immediate, reached a peak at about 5 min and lasted for 10 min. Both types of behaviour were blocked by haloperidol and exaggerated by nialamide.4 Unilateral injections of SP given into the crus cerebri, zona incerta, caudate nucleus, putamen or globus pallidus did not modify the animal's behaviour.5 In rats pretreated with apomorphine or amphetamine, SP induced contraversive circling which was followed by locomotion in the opposite direction.6 Turning responses to a second dose of SP were diminished at 3 h and reproducible at 24 h after the first injection.7 Bacitracin (50 ng) injected into the zona reticulata caused ipsiversive turning. Larger intranigral doses of bacitracin (10 mug), as with intracisternal SP (10 mug), evoked ;barrel rotation'.8 No changes in the free concentrations of aspartate, glutamate, gamma-aminobutyric acid, glycine or alanine were detected in any brain region following an intracisternal injection of 10 mug SP, although glutamine levels were elevated throughout the brain 30 to 60 min later.

Electron microscopic localization of substance P and enkephalin in axon terminals related to dendrites of catecholaminergic neurons

Morphological and pharmacological data suggest that catecholaminergic neurons receive afferent axons positively labeled for the peptides, substance P and [Met5]-enkephalin. In the present study, electron microscopic immunocytochemistry was used to determine whether a positive reaction for these peptides could be localized to axon terminals forming synapses with catecholaminergic neurons in the locus coeruleus and A2 regions of rat brain. Adjacent sections through these areas were incubated with antiserum to either substance P, [Met5]-enkephalin, or tyrosine hydroxylase, a specific marker for catecholaminergic neurons. The sections were subsequently processes by the peroxidase-antiperoxidase immunocytochemical technique. In both the locus coeruleus and A2 region, tyrosine hydroxylase was localized primarily to perikarya and dendrites of intrinsic neurons; whereas substance P and enkephalin-like immunoreactivity was localized to axons and axon terminals. The axon terminals showing positive reactions for substance P and [Met5]-enkephalin were morphologically similar to each other and to one type of axon terminal which formed synapses with dendrites labeled for tyrosine hydroxylase. This type of axon terminal always formed asymmetric synaptic junctions and contained 3-4 large (75-100 nm) dense vesicles (LDVs) and many small (40-60 nm) clear vesicles (SCVs). The reaction product for substance P and [Met5]-enkephalin was distributed throughout the lumen of the LDVs and formed a rim of labeling around the outer boundaries of the SCVs. These findings demonstrate that substance P and [Met5]-enkephalin-positive reactions are selectively localized to subcellular organelles in axon terminals in the locus coeruleus and A2 region of rat brain. They further suggest that the labeled axon terminals form synapses with dendrites of the catecholaminergic neurons.

Neurotensin and its amide analogue [Gln4]-neurotensin: effects on brain monoamine turnover

Intracerebroventricularly administered neurotensin and [Gln4]-neurotensin (50-200 microgram) increased the formation of Dopa in different brain regions of rats after inhibition of the aromatic L-amino acid decarboxylase. For both neuropeptides these increases were dose dependent (20-150%). In the corpus striatum [Gln4]-neurotensin was twice as active as neurotensin and it tended to be more active also in other brain regions. The brain tyrosine concentrations were also increased. [Gln4]-neurotensin (100-200 microgram) following inhibition of the aromatic L-amino acid decarboxylase, increased the accumulation of 5-hydroxytryptophan in all brain regions by 30-60%. In contrast, neurotensin was completely inactive. In both cases the brain tryptophan concentrations were increased. Both neurotensin and [Gln4]-neurotensin also accelerated the disappearance of dopamine, noradrenaline and 5-hydroxytryptamine after inhibition of monoamine synthesis. These results show an increased brain monoamine turnover induced by both neuropeptides.

Effect of enkephalin and substance P on sympathetic nerve transmission in mouse vas deferens

Effect of methionine-, leucine-enkephalin (met-, leu-enkephalin) and substance P on the transmission in mouse vas deferens was studied. Both met- and leu-enkephalin inhibited electrically induced contraction of vas deferens at 10(-8)-10(7) M, met-enkephalin being 1.4 times more active than leu-enkephalin. Nalorphine (10(-6) M) antagonized these effects. Substance P (10(-9)-10(-7) M) had no effect on the contraction. Met- and leu-enkephalin (10(-7)-10(-5) M) decreased the high potassium induced [3H]-norepinephrine release from vas deferens, while substance P (10(-6) M) significantly increased it. Nalorphine (10(-5) M) reversed the inhibitory effect of met-enkephalin. These results indicate that these peptides modify the transmission of sympathetic nerve in mouse vas deferens.

Baclofen-induced modification of conditioned discriminative avoidance behaviour and contraversive turning in the rat

The effects of baclofen, a gamma-aminobutyric acid derivative, on conditioned avoidance behaviour and on the turning produced by unilateral 6-OHDA lesions of the s. nigra were investigated in rats. The small impairment of conditioned avoidance behaviour induced by baclofen (1-4 mg/kg i.p.) was potentiated by combination with benztropine, an anticholinergic agent. Moreover, baclofen reversed the suppression of avoidance responses and the inhibition of turning induced by physostigmine, suggesting an interaction of baclofen with cholinergic transmission processes at the nigrostriatal level. After alpha-methyltyrosine, baclofen like haloperidol, produced a marked increase in avoidance response failures suggesting an additional inhibitory effect of the compound on dopaminergic transmission. The pattern of results indicates that baclofen affects the feedback-loop regulation processes in the nigrostriatal area of the brain.

Does dopamine play a role in schizophrenia?

Inhibition of central dopamine functions appears to be a common basic property of antipsychotic drugs. The mesolimbic and nigrostriatal portions of the dopaminergic system are probably the main targets of these drugs for the mental and the extrapyramidal actions respectively. Dopaminergic hyperfunction, induced by amphetamines or dopa, may lead to a disturbance mimicking paranoid schizophrenia, lending further support for a key role of dopamine in mental functions. While a primary disturbance in dopamine function in schizophrenia cannot be ruled out, the intimate relationship between dopaminergic and other neuronal systems must be emphasized. The possible involvement of other amine, aminoacid or peptide transmitters in schizophrenia cannot be disregarded.

Effect of substance P on medial forebrain bundle self-stimulation in rats following intracerebral administration

The effect of Substance P infused intracerebrally via chronically implanted electrode-cannulae on self-stimulation induced from the same site was studied in rats. Substance P caused a significant depression of self-stimulation at 60 and 120 microgram/rat. Morphine infused into this site also caused significant depression of self-stimulation, but the doses were considerably lower than those of Substance P (5 and 10 microgram/rat). Pretreatment with naloxone, a narcotic antagonist, significantly antagonized the effects of Substance P on self-stimulation. It is proposed that Substance P modulates self-stimulation by the release of an endogenous morphine-like substance, but the possibility of a direct effect of Substance P was not ruled out.