Retrieval effects of beta-endorphin and naloxone, and the novelty-induced antinociception in the developing rat

Modulation of learning and memory by natural polyamines

Spermine and spermidine are natural polyamines that are produced mainly via decarboxylation of l-ornithine and the sequential transfer of aminopropyl groups from S-adenosylmethionine to putrescine by spermidine synthase and spermine synthase. Spermine and spermidine interact with intracellular and extracellular acidic residues of different nature, including nucleic acids, phospholipids, acidic proteins, carboxyl- and sulfate-containing polysaccharides. Therefore, multiple actions have been suggested for these polycations, including modulation of the activity of ionic channels, protein synthesis, protein kinases, and cell proliferation/death, within others. In this review we summarize these neurochemical/neurophysiological/morphological findings, particularly those that have been implicated in the improving and deleterious effects of spermine and spermidine on learning and memory of naïve animals in shock-motivated and nonshock-motivated tasks, from a historical perspective. The interaction with the opioid system, the facilitation and disruption of morphine-induced reward and the effect of polyamines and putative polyamine antagonists on animal models of cognitive diseases, such as Alzheimer's, Huntington, acute neuroinflammation and brain trauma are also reviewed and discussed. The increased production of polyamines in Alzheimer's disease and the biphasic nature of the effects of polyamines on memory and on the NMDA receptor are also considered. In light of the current literature on polyamines, which include the description of an inborn error of the metabolism characterized by mild-to moderate mental retardation and polyamine metabolism alterations in suicide completers, we can anticipate that polyamine targets may be important for the development of novel strategies and approaches for understanding the etiopathogenesis of important central disorders and their pharmacological treatment.

Effect of naloxone and morphine on arcaine-induced state-dependent memory in rats

RATIONALE

Arcaine is a competitive antagonist of the polyamine binding site at the N-methyl-D-aspartic acid receptor which induces state-dependent recall. However, no study has addressed the involvement of other neurotransmitter/neuromodulators in arcaine-induced state dependency.

OBJECTIVES

The current study investigates whether the opioid system is involved in arcaine-induced state-dependent memory retrieval of the inhibitory avoidance task (IA) in rats.

RESULTS

The systemic administration of arcaine (30 mg/kg, intraperitoneally (i.p.)) or morphine (5 mg/kg, i.p.) 0, 3, 6, or 9 h post-training, reduced step-down latencies at testing. Arcaine (30 mg/kg, i.p.) or morphine (5 mg/kg, i.p.) injection 30 min before testing reversed the performance deficit induced by administration of arcaine or morphine 0, 3 or 6, but not 9 h post-training. The reversal of arcaine-induced impairment of IA performance was completely transferred to morphine and vice versa. The association of low and ineffective doses of morphine and arcaine (10 and 1.5 mg/kg, respectively) were additive and caused state dependency. Naloxone (2 mg/kg, 3 min post-training, or 1 mg/kg, 1 h pre-test, i.p.) reversed the amnesia and the state dependency induced by morphine and arcaine.

CONCLUSION

These results suggest that state dependency induced by arcaine involves the opioid system.

Arcaine and MK-801 make recall state-dependent in rats

RATIONALE

The polyamines putrescine, spermidine, and spermine are a group of aliphatic amines that may act as physiological modulators of the N-methyl-D-aspartate (NMDA) receptor, a glutamate receptor implicated in memory formation and consolidation. Arcaine is a competitive antagonist of the polyamine binding site at the NMDA receptor, the post-training administration of which impairs memory of various tasks.

OBJECTIVES

In this study, we investigated whether the administration of arcaine and MK-801 alters the memory of the step-down inhibitory avoidance task, and whether the effects of these NMDA antagonists involve state-dependency mechanisms, in adult male Wistar rats.

RESULTS

The administration of arcaine (30 mg/kg, i.p.) or MK-801 (0.03 mg/kg, i.p.) immediately after training impaired inhibitory avoidance performance at testing. Arcaine- and MK-801-induced performance impairment was reversed by the administration of arcaine (30 mg/kg, i.p.) and MK-801 (0.03 mg/kg, i.p.), respectively, 30 min before testing. Response transfer also occurred if arcaine substituted MK-801 at testing, and vice-versa.

CONCLUSION

These results suggest that arcaine and MK-801 induce state-dependent recall and that, probably due to their ability to decrease NMDA receptor function, one drug can substitute for the other at testing, demonstrating a cross-state dependency between arcaine and MK-801.

Antinociceptive effects of brain rewarding system in the developing rabbit: behavioral and electrophysiological analysis

The modulating effects of electrical stimulation (ES) in the reward sites (RSs) of the hypothalamus and adjacent brain areas on the defensive reaction (DR) in response to peripheral noxious stimulation (PNS) and on evoked potentials (EPs) recorded in the thalamic centromedian-parafascicular complex (CM-Pf) to the same PNS have been investigated in 20-40-, 41-60-day old and 3-5-month old rabbits. Previously, RSs were identified by the method of intracranial self-stimulation (ICSS). Behavioral and electrophysiological testings successively performed on each rabbit first awake and then anaesthetized have revealed the ES in all investigated RSs to inhibit DR and EPs. These effects were not observed if the stimulating electrode tip was localized in emotionally neutral brain sites. In behavioral testings, the antinociceptive effect of rewarding stimulation was positively correlated with the ICSS intensity in given brain sites regardless of the age of the rabbits. In electrophysiological testings, a similar dependence of nociceptive EPs inhibition on emotional values of stimulated brain sites (determined as a rate of lever pressings during ICSS) was discovered only in 20-40-day and 3-5-month old rabbits. Stimulation of low emotional value RSs (low rate (LR)-rabbits) exerted a weaker inhibitory influence in 3-5-month old rabbits in comparison with 20-40- and 41-60-day old rabbits both in behavioral and electrophysiological testings. The weakest antinociceptive effect of rewarding stimulation among the rabbits with a high rate of lever pressings (HR-rabbits) was found in 41-60-day olds in electrophysiological testings. In 41-60-day old rabbits, we have observed a discrepancy between the behavioral analgesia and its electrophysiological correlates. It may be suggested that the observed peculiarities of antinociceptive influences produced by RSs ES are determined by the age factors of neurotransmitter brain systems.

Endogenous opiates: 1991

This paper is the fourteenth installment of our annual review of research concerning the opiate system. It includes papers published during 1991 involving the behavioral, nonanalgesic, effects of the endogenous opiate peptides. The specific topics this year include stress; tolerance and dependence; eating; drinking; gastrointestinal and renal function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.