Substance p reversal of electroconvulsive shock and cycloheximide-induced retrograde amnesia

Neurokinin-1 receptor antagonism by SR140333: enhanced in vivo ACh in the hippocampus and promnestic post-trial effects

Substance P (SP) has memory-promoting, reinforcing and anxiolytic-like effects when applied systemically or centrally. Such effects may be mediated by the neurokinin-1 (NK-1) receptor, since SP preferentially binds to this receptor. We measured the effects of a selective non-peptide NK-1 receptor antagonist, SR140333 (1, 3 and 9 mg/kg i.p.) on ACh levels in frontal cortex, amygdala and hippocampus by microdialysis and HPLC. Levels of ACh in the hippocampus increased dose-dependently immediately after treatment. The same doses of SR140333 given post-trial had minor facilitative effects on inhibitory avoidance learning and open-field habituation, but did not have reinforcing effects in a conditioned place preference (CPP) task. The selective action of NK-1 receptor antagonism on hippocampal ACh may be related to its positive influence on learning.

Preprotachykinin A gene expression after administration of 3,4-methylene dioxymethamphetamine (Ecstasy)

This study tested the effects of 8 days of subchronic administration of 3,4-methylene dioxymethamphetamine (MDMA) (5 mg/kg b.w.) on preprotachykinin A mRNA levels in discrete rat brain regions. In situ hybridization examined preprotachykinin A mRNA levels in the core and shell of the nucleus accumbens, the islands of Calleja, the olfactory tubercle, the dorsal and ventral caudate-putamen, the bed nucleus of the stria terminalis, the medial preoptic area, the medial habenular nucleus and in the postero-dorsal part of the medial amygdala. Higher levels of preprotachykinin A mRNA were found in the core and shell of the nucleus accumbens, in the islands of calleja, in the olfactory tubercle, in the bed nucleus of the stria terminalis, in the medial habenular nucleus and the postero-dorsal part of the medial amygdala, compared to control animals. Conversely, increased preprotachykinin A mRNA levels were observed in the dorsal and ventral caudate-putamen in MDMA treated when compared to control rats. In the social memory test, MDMA significantly impaired rats' short-term working memory. These results show that chronic exposure to MDMA strongly affects preprotachykinin A mRNA levels in discrete rat brain regions. These changes occur in experimental conditions in which working memory is markedly reduced, suggesting that changes in gene expression of tachykinin mechanisms may contribute to the effects of MDMA on memory function.

Reinforcing properties of the neuropeptide substance P in Carassius auratus: evidence of dopaminergic system involvement

The aim of the present study was to investigate whether neuropeptide substance P (SP) has reinforcing effects in Carassius auratus and whether this effect could be related to dopaminergic neurotransmission. For this purpose fishes were put in a three-compartment box in which one compartment gave access to two others that did not directly link. The time spent in each compartment was registered for 10 min to determine a possible preferred compartment. Twenty-four hours later, the fish were given one of the following intraperitoneal treatments: a) Group VEH, injected with the vehicle of substance P; b) Group SP25, injected with SP, 25 micrograms/kg body wt.; c) Group SP50, injected with SP, 50 micrograms/kg; or d) Group HALO, injected with haloperidol (2 mg/kg) 30 min before an injection of SP (50 micrograms/kg). Immediately after the treatment the fish were kept for 30 min in the compartment preferred least the day before. On the next day the fish were retested for 10 min to verify the time spent in each compartment. The results indicate that SP at the dose of 50 micrograms/kg enhanced the time spent on the paired compartment, and that the pretreatment with haloperidol abolished this enhancement. It is suggested that SP has reinforcing effects in C. auratus that may be mediated by the dopaminergic system.

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.

Substance P and neuropsychiatric disorders: an overview

Substance P (SP) is a naturally-occurring tachykinin peptide isolated from brain tissues and gastrointestinal tract. In the brain, substantia nigra and basal ganglia contain relatively high amounts of substance P. There is evidence suggesting that substance P functions as a neurotransmitter. It has been implicated in the pathophysiology of several neuropsychiatric disorders. Substance P may also serve as a useful tool in studying the effects of antidepressant drugs and electroconvulsive therapy. However, the contribution of substance P to the understanding of neuropsychiatric disorders is far from clear. Future studies should focus on the interactions and coexistence of substance P with other neurotransmitters and neuropeptides.

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 increases and prolongs increased output of T4 (CD4) lymphocytes from lymph nodes of sheep in vivo: is it a mediator of immunological memory?

There are receptors on lymphocytes for substance P which are found both on small recirculating and on blast lymphocytes. The principal effect of substance P on lymphocytes appears to be a stimulating one, both in vitro and in vivo. The in vivo administration of substance P to sheep by acute infusion into cannulated afferent lymphatics of peripheral lymph nodes has been found to stimulate efferent lymph flow and the output into efferent lymph of both small recirculating and blast lymphocytes. We here report that substance P both enhances and prolongs the enhancement of the output of T4 (CD4) lymphocytes from lymph nodes of sheep in vivo. This output-stimulating effect appears to be specific to T4 (CD4) lymphocytes and is associated with a depressant effect on the output of T8 (CD8) and B lymphocytes. The output-stimulating effect on small T4 (CD4) lymphocytes is quite prolonged, lasting in excess of 96 h after a single 50 micrograms acute infusion. A brief post-infusion depression in T4 (CD4) lymphocyte output is associated with an equally brief, but marked, elevation in the output into efferent lymph of the arachidonic acid metabolite, thromboxane B2. The output-stimulating effect of substance P on blast T lymphocytes is confined to the T4 (CD4) blast lymphocytes. Substance P or a similar molecule may be of value when a specific T4 (CD4) lymphocyte output stimulant effect is desired. A single prior (6 days) acute infusion of substance P into a popliteal lymph node via its cannulated afferent lymphatic produced profound changes in the response to nodal drainage area immunization with killed S. muenchen bacteria. The latent period prior to increased antibody production was abolished, as was the standard post-immunization 'shutdown' period of decreased output of lymphocytes into efferent lymph. These changes were accompanied by a marked and progressive increase in antibody production. The findings reported here suggest substance P-induced long-term potentiation (LTP) of the immune response and raise the question of an involvement of substance P as a major mediator of immunological memory.

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.

Reinforcing effects of peripherally administered substance P and its C-terminal sequence pGlu6-SP6-11 in the rat

Reinforcing effects of intraperitoneally (IP) administered substance P (SP1-11), its amino-terminal fragment SP1-7 (SPN) and an analog of the carboxy terminus (pGlu6-SP6-11: SPC) were studied in rats. Two conditioned place preference paradigms were used. After three pairings of the drug with a certain environment the effect of the treatment was evaluated in the drug-free state during a test trial. The reinforcing effects of SP (37 nmol) and the equimolar dose of SPC were expressed by a significant increase in the amount of time the animals spent in the treatment environment. Other doses of SP (3.7 and 185 nmol) and SPC (7.4 and 185 nmol) and none of the doses of SPN (37, 185, 370 nmol) influenced the place preference behavior of the rats. The reinforcing effects of SP parallel the known facilitating effects of peripherally administered SP on memory. The amino acids that encode the reinforcing effects of SP may lie within the C-terminal sequence of the SP molecule.

Brain neuron gene expression in the organization of innate and acquired behaviors

In a series of experiments using rats and rabbits, it was determined that regulatory peptides played a role in the mechanisms of learned behavior. Learning a new habit as a conditional avoidance response was accompanied by a considerable increase in brain DNA synthesis, which in turn could result in RNA and protein synthesis activation. The results suggest the following interdependent molecular phenomena: 1) DNA synthesis activation; 2) genome expression of a certain type of oligopeptides; 3) regulation of genome expression of proteins by chromatin nonhistone proteins; 4) regulation of gene expression mechanisms by brain regulatory peptides.

The relationship between reinforcement and memory: parallels in the rewarding and mnemonic effects of the neuropeptide substance P

A theory of reinforcement is presented which accounts for the backward action of a reinforcer on operant behavior in terms of its effect on memory traces left by the operant. Several possible ways in which a reinforcer could strengthen the probability of recurrence of an operant are discussed. Predictions from the model regarding general memory-promoting effects of reinforcers presented posttrial in various learning paradigms are outlined. The theory also predicts a parallelism in reinforcing and memory-promoting effects of stimuli, including drugs. The second part of the chapter outlines experiments investigating memory modulating and reinforcing effects of the neuropeptide substance P. In general, injection of SP is positively reinforcing when injected into parts of the brain where it has been shown to facilitate learning. Peripheral injection of SP is also reinforcing at the dose known to promote passive avoidance learning when presented posttrial.

Conditioned avoidance acquisition and extinction following repeated electroconvulsive shock: strain effect and response to vasopressin

Male albino rats (Sabra strain) were exposed to electroconvulsive shock (ECS) once daily for periods ranging from 1 to 13 days, and proactive effects on conditioned avoidance response (CAR) acquisition and extinction were studied. CAR acquisition was intact following both single and repeated ECS, but extinction was accelerated by multiple ECS administration. These findings resembled the effect of repeated ECS on anterograde memory function in humans and confirmed previous observations based on a passive avoidance paradigm. However, extinction was not accelerated in a different rat strain (LC2). Parallel open field activity measures suggested that these findings were not related to ECS-induced alterations in locomotor activity. Administration of arginine vasopressin prior to each ECS, or following acquisition sessions, as well as 1-desamino-8-D-arginine vasopressin administration following acquisition sessions, did not ameliorate ECS-induced deficits in the Sabra rats. Differences between the present paradigm of ECS administration and those in which positive effects of vasopressin and other neuropeptides have been reported are discussed. The potential research applications of a rodent model of ECS-induced memory impairment that parallels deficits encountered in the clinical context are considered.

Facilitation of conditioned inhibitory avoidance by post-trial peripheral injection of substance P

Experiments were undertaken to investigate the effects of the neuropeptide Substance P (SP) on performance of a conditioned inhibitory avoidance response in rats. A single-trial inhibitory avoidance task was employed. In Experiment 1 SP was injected IP immediately after the training trial in doses of 0.5, 5, 50, 100, 250 or 500 micrograms/kg; control animals were injected with diluent vehicle. The group treated with 50 micrograms SP/kg exhibited better avoidance than the other groups. In Experiment 2 the doses of SP used were 1, 50, 250 micrograms/kg, and the control animals were injected with vehicle or not injected at all. Only the 50 micrograms SP/kg treatment group showed significantly better performance. In Experiment 3 50 micrograms/kg SP or vehicle was injected post-trial immediately or 5 hr after the trial. Only the group in which SP was injected immediately after the training trial showed significantly better performance when tested 24 hr later. This result rules out the possibility that SP exerts its effect by a long lasting proactive action on performance during the testing trial 24 hr later.

Substance P facilitation of memory: effects in an appetitively motivated learning task

Food deprived, heterogeneous strain (HS/IBG) mice were trained on two different discrimination tasks for food reinforcement. In one experiment animals were trained to make spatial discriminations in a T maze. Immediately after training they were given subcutaneous injections of either substance P (1 ng/g) or vehicle. Twenty-four hours later the animals were given reversal training in the same maze. The results showed that substance P-treated animals took significantly longer to acquire the reversal habit than did control mice. In a second experiment, animals were trained to make visual discriminations in a T maze. Immediately after reaching acquisition criterion animals were injected with either substance P (1 ng/g) or vehicle. Different groups of mice were retrained on the same task either 1, 2, 3, or 7 days after original learning. Savings scores were calculated and, at every interval, substance P-treated mice retained the task better than control animals. One interpretation of these data is that substance P-treated mice remembered the original task significantly better than vehicle-injected control animals.

Comparison of substance P and enkephalin distribution in rat brain: an overview using radioimmunocytochemistry

The distribution of substance P and leucine enkephalin in mid- and fore-brain areas of the rat was studied using a radioimmunocytochemical method. The secondary antibody was labeled with 125I and the sections apposed to LKB Ultrofilm or emulsion-dipped. In alternate sections an extensive distribution of substance P and enkephalin immunoreactive material was seen in frontal, cingulate, retrosplenial, and entorhinal cortices. Substance P and enkephalin exhibited a remarkable overlap in many of these cortical areas as well as in the nucleus accumbens, caudate, portions of the hypothalamus, amygdala, thalamus and central gray. Differences in distribution were seen in the retrosplenial cortex, septum, ventromedial hypothalamus, hippocampus, the substantia nigra and the superior colliculus. The results provide a detailed immunohistochemical demonstration of the laminar patterns of substance P and enkephalin in the cortex of the rat. The results are discussed in terms of the interaction of substance P and enkephalin. The matches and mismatches of immunoreactive substance P and enkephalin and the locations of their receptors are also examined.

Central action of substance P: possible role in reward

A series of studies had revealed a dualistic role of post-trial injections of substance P in affecting avoidance behavior depending on the site of the brain in which it is applied. Based on these data, the hypothesis was formulated that substance P has brain site-dependent rewarding and punishing properties, a possibility which was assessed in rats trained on a modified T-maze task. Injections of substance P into the medial forebrain bundle (100 ng) or medial septal nucleus (500 ng) served as a positive reinforcer for conditioned place preference learning in the T maze. Injections into the amygdala (50 ng) or substantia nigra (100 ng) did not have such reinforcing properties.