Modulation of locomotor activity by substance P in rats

Perspective role of Substance P in Amyotrophic Lateral Sclerosis: from neuronal vulnerability to neuroprotection

The neuropeptide Substance P (SP) and its preferred Neurokinin1 Receptor (NK1R) are known to participate in the physiopathology of neurodegenerative diseases and mainly exert a neuroprotective role. In the present work, we have described the involvement of SP and NK1R in Amyotrophic Lateral Sclerosis (ALS). This was demonstrated by the detection of altered levels of SP in the brain, spinal cord and cerebrospinal fluid (CSF) of patients and preclinical models of ALS, and by its ability to inhibit excitotoxicity-induced neurodegeneration in ALS animal models. These data are supported by results indicating an excitatory effect of SP at the motor neuron (MN) level, which promotes locomotor activity. ALS patients are characterized by a differential susceptibility to MNs degeneration, since sphincters and extraocular muscles are classically spared. It is hypothesized that SP may play a role in the maintenance of the ocular system and the innervation of the pelvic floor by contributing directly or indirectly to the selective resistance of this subset of MNs.

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

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

A newly identified extrinsic input triggers a distinct gastric mill rhythm via activation of modulatory projection neurons

Neuronal network flexibility enables animals to respond appropriately to changes in their internal and external states. We are using the isolated crab stomatogastric nervous system to determine how extrinsic inputs contribute to network flexibility. The stomatogastric system includes the well-characterized gastric mill (chewing) and pyloric (filtering of chewed food) motor circuits in the stomatogastric ganglion. Projection neurons with somata in the commissural ganglia (CoGs) regulate these rhythms. Previous work characterized a unique gastric mill rhythm that occurred spontaneously in some preparations, but whose origin remained undetermined. This rhythm includes a distinct protractor phase activity pattern, during which a key gastric mill circuit neuron (LG neuron) and the projection neurons MCN1 and CPN2 fire in a pyloric rhythm-timed activity pattern instead of the tonic firing pattern exhibited by these neurons during previously studied gastric mill rhythms. Here we identify a new extrinsic input, the post-oesophageal commissure (POC) neurons, relatively brief stimulation (30 s) of which triggers a long-lasting (tens of minutes) activation of this novel gastric mill rhythm at least in part via its lasting activation of MCN1 and CPN2. Immunocytochemical and electrophysiological data suggest that the POC neurons excite MCN1 and CPN2 by release of the neuropeptide Cancer borealis tachykinin-related peptide Ia (CabTRP Ia). These data further suggest that the CoG arborization of the POC neurons comprises the previously identified anterior commissural organ (ACO), a CabTRP Ia-containing neurohemal organ. This endocrine organ thus appears to also have paracrine actions, including activation of a novel and lasting gastric mill rhythm.

Substance P as a novel anti-obesity target

BACKGROUND & AIMS

Substance P (SP) is an 11-amino acid peptide that belongs to the tachykinin family of peptides. SP acts in the brain and in the periphery as a neuropeptide, neurotransmitter, and hormone affecting diverse physiologic pathways, mainly via its high-affinity neurokinin-1 receptor (NK-1R). Its presence in the hypothalamus and other areas of the brain that regulate feeding as well as in the stomach and small intestine prompted us to investigate its role on appetite control and energy balance.

METHODS

CJ 012,255 (CJ), a SP antagonist that binds to NK-1R, was injected into lean, diet-induced obese (DIO), and genetically obese (ob/ob) mice, and its effects on body weight, adiposity, and insulin sensitivity were investigated.

RESULTS

CJ administration prevented weight gain and accumulation of fat after 2 weeks of high-fat feeding, whereas similar CJ treatment in obese mice (following 3 months of high-fat diet) resulted in weight loss, reduction in adiposity, and improvement of insulin sensitivity, in part because of inhibition of food intake. The effects of SP in the control of energy balance are, at least in part, leptin independent because CJ treatment was also effective in leptin-deficient mice. Peripheral SP administration resulted in a mild, dose-dependent increase in food intake, evident 3 hours post-SP injection.

CONCLUSIONS

CJ reduces appetite and promotes weight loss in mice. We speculate that NK-1R antagonists, already tested in clinical trials for various diseases, may represent a potential target against obesity.

Influence of passive avoidance learning by substance P in the basolateral amygdala

Neuropeptide substance P (SP) has reinforcing and memory facilitating effects after its peripheral or central application. Rats self-inject SP into the ventromedial caudate-putamen and SP microinjections into the basal forebrain induce place preference with a simultaneous increase of dopamine level. In the amygdaloid body SP positive neurones and terminals have been identified. The aim of the present study was to examine the possible reinforcing effects of SP in the basolateral amygdala (ABL). CFY male rats were conditioned in two-compartment passive avoidance paradigm and place preference was examined in two-compartment-box and in circular open field. Animals were microinjected bilaterally with 10 ng SP, 100 ng SP or vehicle solution (0.4 microl/side) into the ABL. Results showed that post-shock infusion of 10 ng SP significantly enhanced passive avoidance learning while 100 ng SP was ineffective. In two-compartment-box and in circular open field place preference did not develop after SP treatments, however. Our data are the first to demonstrate that SP in the ABL is involved in learning and memory processes related to aversive situations. Results that SP microinjections were not followed by rewarding-reinforcing consequences in place preference paradigms indicate that the local SP network in the ABL is not involved in neuronal circuitry responsible for addictive behaviour.

Facilitation of tunnel maze performance by systemic injection of the neurokinin substance P

The effect of peripheral injections of substance P (SP) on performance in two different configurations of an automated tunnel maze was examined in three experiments. In two experiments, the effect of pretrial SP injections (10-1000 micrograms/kg) on performance in the hexagonal and radial maze configuration of an automated tunnel maze was investigated. In the hexagonal maze, which measures activity, exploratory efficiency, habituation, and perimeter walking, injection of SP affected perimeter walking only. In the radial maze, SP produced a facilitation of measures of efficiency and long-term and short-term memory without affecting activity. In the third experiment, the effect of pre- and posttrial injections of SP (50 or 500 micrograms/kg) on performance in the radial maze configuration was tested. Again, pretrial injections of 500 micrograms of SP facilitated performance with respect to measures of efficiency and short- and long-term memory; 50 micrograms produced a weaker effect. Virtually no effect was seen with posttrial injections.

Tachykinin antagonists inhibit the morphine withdrawal response in guinea-pigs

This study was an investigation of the effects of the tachykinin antagonists, spantide and (D-Pro4, D-Trp7,9,10)substance P 4-11, injected intracerebroventricularly (ICV), on the locomotor and behavioural responses of guinea-pigs to substance P (SP) injected ICV and to naloxone-induced morphine withdrawal. SP, 50 nmol, produced increased locomotor activity and behaviour that mimicked the response induced by injection of naloxone hydrochloride, 15 mg/kg, in guinea-pigs treated 2 h previously with morphine sulphate, 15 mg/kg. Spantide or (D-Pro4, D-Trp7,9,10)SP4-11, 10 nmol, reduced the locomotor and behavioural responses to SP and to morphine withdrawal. The results support the suggestion that SP or a related tachykinin might be a mediator of the opioid withdrawal response in the central nervous system as has been proposed for the enteric nervous system.

Facilitation of memory by peripheral administration of substance P and naloxone using avoidance and habituation learning tasks

This paper summarizes results of a series of experiments dealing with the effects of the neuropeptide substance P (SP) on avoidance learning and habituation. Several doses of SP (0.5, 5, 50, 100, 250, 500 micrograms/kg) were administered posttrial intraperitoneally (IP). Three inhibitory one-trial avoidance tasks were used; uphill, step-down and step-through (alcove). Habituation was measured in an open field by recording the number of rearings. The posttrial injection of SP facilitated avoidance responses as well as reduced rearing in a dose- and time-dependent way. Pretraining and pretest injections (IP) of naloxone facilitated avoidance behavior and potentiated the action of SP, also in a dose-dependent manner. These results demonstrate that: a) peripheral posttraining administration of SP enhances memory; b) SP facilitates not only aversive or positively motivated learning tasks, but also habituation, which is a form of learning that involves neither positive nor negative reinforces; c) SP does not exert its effect by a long-lasting proactive action on performance during the testing trial; d) naloxone potentiates the SP posttraining effect. These data, therefore, suggest that memory-enhancing effects of SP are, at least in part, mediated via interactions between this peptide and endogenous opioid systems.

Substance P enhancement of inhibitory avoidance learning: mediation by the N-terminal sequence

Experiments were performed to investigate the effects of intraperitoneally administered undecapeptide substance P (SP), its N-terminal fragment SP(1-7) (SPN) and the C-terminal analog [pGlu6]-SP(6-11) (SPC) on inhibitory avoidance learning, using a one-trial up-hill avoidance task. In Experiment 1 rats were injected with either SP (50 micrograms/kg), SPN (3.3, 33, 167, 333 micrograms/kg) or SPC (2.7, 27, 134, 268 micrograms/kg) immediately after the training trial. Controls received the diluent vehicles. When tested 24 hr later, rats injected with 50 micrograms/kg SP (37 nmol/kg) and 167 micrograms/kg SPN (185 nmol/kg) exhibited longer step-up latencies than vehicle-treated controls. None of the other doses of SPN nor of the C-terminal fragment influenced performance. In Experiment 2, 167 micrograms/kg SPN or vehicle was injected posttrial either immediately or 5 hr after the training trial. Retention latencies 24 hr later were longer for rats treated with 167 micrograms/kg SPN immediately after the training trial. Performance of the SPN 5-hr delay group did not differ from that of the vehicle-injected controls, ruling out proactive effects of SPN on recall.

Conditioned place preference in the corral: a procedure for measuring reinforcing properties of drugs

A novel conditioned place preference (CPP) method is described. The behavioral testing apparatus is a circular open field consisting of 4 uniform quadrants that are equally preferred by the rats prior to drug treatment. In an illustrative experiment, rats received an i.p. injection of either morphine (10 mg/kg), substance P (50 micrograms/kg) or vehicle (phosphate-buffered 0.01 M acetic acid in saline) on 3 consecutive days and were placed into their assigned treatment quadrant. Four animals were simultaneously treated with the aid of barriers, which restricted each rat to its treatment quadrant. On the test for CPPs, when provided a choice between the 4 quadrants, rats treated with morphine and substance P exhibited preferences for the quadrant which had been paired with the drugs, illustrating the usefulness of this procedure for assessing the reinforcing properties of the two drugs. Gross locomotor activity was not influenced by either treatment. The advantages of this version of the CPP method over the conventional shuttle-box procedures are discussed.

Nigral 5-HT and substance P-induced enhancement of passive avoidance retention

Peripheral, posttraining injection of substance P (SP) has been shown to facilitate the retention of aversive and appetitive learning tasks, suggesting that SP may play a role in information processing. In addition, SP may modulate the release of nigrostriatal monoamines, which have also been linked with avoidance learning. This paper examines the interaction between SP and nigrostriatal monoamines by observing the behavioral effects of neurochemical lesions on SP-induced avoidance retention, and by measuring changes in nigrostriatal monoamine activity and receptor regulation following avoidance training and SP injection. In Expt. 1, 5,7-dihydroxytryptamine lesions of the substantia nigra, but not the caudate, attenuated the retention-enhancing effects of posttraining SP injection. Further, 6-hydroxydopamine lesions of the substantia nigra produced a deficit in avoidance conditioning that was reversed by posttraining SP injection. Expts. 2 and 3 demonstrated that although passive avoidance training and posttraining SP injections did not significantly alter nigral 5-hydroxytryptamine (5-HT) activity, SP increased 5-HT1 receptor density. It was concluded that SP may affect avoidance retention by modulating nigral 5-HT activity.

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.

Behavioural effects of tachykinins and related peptides

Substance P (SP) and related tachykinins administered either intracerebroventricularly or directly into the ventral tegmental area of the mesencephalon of rat brain caused increased locomotor activity, grooming behaviour and wet dog shakes. Kassinin, eledoisin, neurokinin A and DiMe-C7, agonists with some selectivity for the SP-E-receptor elicited the greatest locomotor activity and wet dog shake responses, whereas SP and physalaemin which are more selective for the SP-P-receptor were most effective in eliciting the grooming response.

The effect of substance P and its fragments on passive avoidance retention and brain monoamine activity

It has been shown that substance P(SP), as well as its carboxy and amino terminal fragments, affects a wide range of behaviors. In order to test the CNS activity of these fragments, we measured their effects on passive avoidance learning and monoamine activity. Following one-trial passive avoidance training, mice were injected intraventricularly with either a carboxy or amino terminal SP fragment (SP-C or SP-N), SP itself or phosphate-buffered saline (PBS). SP-N enhanced avoidance retention, which was tested 24 h after training. In a second experiment, monoamine activity was measured one hour after intraventricular injection of SP, PBS or SP fragments. SP-C decreased both nigral 5-hydroxyindoleacetic acid/5-hydroxytryptamine (5-HIAA/5-HT) and, to a lesser extent, 3,4-dihydroxyphenylacetic acid/dopamine, while SP-N increased nigral 5-HIAA/5-HT. It was concluded that SP-N and SP-C can exert behavioral and neurochemical effects that may be independent of the parent SP molecule.

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.

The effects of thyrotropin-releasing hormone, metabolites and analogues on locomotor activity in rats

Thyrotropin-releasing hormone (TRH) has generally been reported to increase locomotor activity in rats; however there are also some negative reports. In order to identify the possible causes for this discrepancy, the effects of intra-cerebroventricular injection of TRH, its metabolites 'acid TRH' (TRH-OH) and His-Pro-diketopiperazine (DKP), and two analogues 3-methyl-His-TRH and RX 77368 (3,3-dimethyl-Pro-TRH), were assessed using photocell activity cages. All compounds were tested in groups of eight rats in the afternoon (1300-1700 h), but in addition TRH and DKP were tested in two further groups of rats during the morning (0900-1230 h). TRH and DKP failed to induce a significant rise in activity during the morning test period, but TRH did have a significant effect when tested in the afternoon. Both TRH and TRH-OH caused dose dependent increases in locomotor activity, whereas DKP and the two analogues had no effect. This stimulation of activity was shown to be at least partly mediated by dopamine since locomotor enhancement was blocked in a second experiment using the dopamine antagonist alpha-Flupenthixol. The results are discussed in terms of actions on the mesolimbic dopamine system, and the importance of circadian variations within this system to the expression of peptide effects in general.