Combined effects of complex magnetic fields and agmatine for contextual fear learning deficits in rats

Temporally-patterned magnetic fields induce complete fragmentation in planaria

A tandem sequence composed of weak temporally-patterned magnetic fields was discovered that produced 100% dissolution of planarian in their home environment. After five consecutive days of 6.5 hr exposure to a frequency-modulated magnetic field (0.1 to 2 µT), immediately followed by an additional 6.5 hr exposure on the fifth day, to another complex field (0.5 to 5 µT) with exponentially increasing spectral power 100% of planarian dissolved within 24 hr. Reversal of the sequence of the fields or presentation of only one pattern for the same duration did not produce this effect. Direct video evidence showed expansion (by visual estimation ∼twice normal volume) of the planarian following the first field pattern followed by size reduction (estimated ∼1/2 of normal volume) and death upon activation of the second pattern. The contortions displayed by the planarian during the last field exposure suggest effects on contractile proteins and alterations in the cell membrane’s permeability to water.

COMPLEX MAGNETIC FIELDS ENABLE STATIC MAGNETIC FIELD CUE USE FOR RATS IN RADIAL MAZE TASKS

Male Wistar rats were trained in an eight-arm radial maze task (two sessions per day, delayed-non-matching-to-sample) that included an intramaze static magnetic field "cue" (185 microT) specific to the entrance point of one of the arms. Rats were exposed daily for 60 min to a complex magnetic field waveform (theta-burst pattern, 200-500 nT), presented with several different interstimulus intervals (ISIs), either immediately following training sessions or immediately preceding testing sessions. Application of the theta-burst stimulus with a 4000 ms ISI significantly improved the rats' memory for the arm of the radial maze whose position was indicated by the presence of a static magnetic field cue. Reference memory errors were homogeneously distributed among all eight arms of the maze for sham-exposed rats, and among the other seven arms of the maze for complex magnetic field-treated rats. These results suggest that static magnetic field cues may be salient orienting cues even in a microenvironment such as a radial maze, but their use as a cue during maze learning in rats is dependent on whole-body application of a specific time-varying complex magnetic field.

Behavioral changes with brief exposures to weak magnetic fields patterned to stimulate long-term potentiation

Brief whole body exposures of rats to weak (1 microT) complex magnetic fields whose patterns induce long term potential (LTP) when applied as electric current to hippocampal slices produced powerful behavioral changes. Rats exposed for 30 min before but not 30 min after hourly training sessions for spatial memory displayed impairments comparable to those elicited by complete electrode-induced saturation of hippocampal activity. Exposure to the same LTP-patterned magnetic fields after weaning during the induction of limbic seizures produced diminished learning of conditioned contextual fear during adulthood. However exposure to magnetic fields designed to simulate a "virtual" hippocampal state during acquisition of a timed inhibitory task (DRL) facilitated performance. These results show that physiologically-patterned magnetic fields can produce dramatic changes in behavior when they are applied during states associated with marked synaptic plasticity.

Agmatine : metabolic pathway and spectrum of activity in brain

Agmatine is an endogenous neuromodulator that, based on animal studies, has the potential for new drug development. As an endogenous aminoguanidine compound (1-amino-4-guanidinobutane), it is structurally unique compared with other monoamines. Agmatine was long thought to be synthesised only in lower life forms, until its biosynthetic pathway (decarboxylation of arginine) was described in the mammalian brain in 1994. Human arginine decarboxylase has been cloned and shown to have 48% identity to ornithine decarboxylase. In neurons of the brain and spinal cord, agmatine is packaged into synaptic vesicles and released upon neuronal depolarisation. Other evidence of a neuromodulation role for agmatine is the presence of a specific cellular uptake mechanism and a specific metabolic enzyme (agmatinase; which forms putrescine).Initially, agmatine was conceptualised as an endogenous clonidine-displacing substance of imidazoline receptors; however, it has now been established to have affinity for several transmembrane receptors, such as alpha(2)-adrenergic, imidazoline I(1) and glutamatergic NMDA receptors. In addition to activity at these receptors, agmatine irreversibly inhibits neuronal nitric oxide synthase and downregulates inducible nitric oxide synthase. Endogenous agmatine is induced in response to stress and/or inflammation. Stressful conditions that induce agmatine include hypoxic-ischaemia and cold-restraint stress of ulcerogenic proportion. Induction of agmatine in the brain seems to occur in astrocytes, although neurons also synthesise agmatine. The effects of injected agmatine in animals include anticonvulsant-, antineurotoxic- and antidepressant-like actions. Intraperitoneal or intracerebroventricular injections of agmatine rapidly elicit antidepressant-like behavioural changes in the rodent forced swim test and tail suspension test. Intraperitoneal injections of agmatine into rats and mice also elicit acute anxiolytic-like behavioural changes in the elevated plus-maze stress test. In an animal model of acute stress disorder, intraperitoneal agmatine injections diminish contextual fear learning. Furthermore, intraperitoneal injections of agmatine reduce alcohol and opioid dependence by diminishing behaviour in a rat conditioned place preference paradigm. Based on these findings, agmatine appears to be an endogenous neuromodulator of mental stress. The possible roles and/or beneficial effects of agmatine in stress-related disorders, such as depression, anxiety and post-traumatic stress disorder, merit further investigation.

Neuromagnetic dialogue between neuronal minicolumns and astroglial network: A new approach for memory and cerebral computation

Rapidly accumulating experimental data over the past two decades discloses extremely complex neuro-glial interactions and provides new insights regarding novel roles of glial cells, particularly astrocytes, in complex functions. Widespread astrocytic processes, interconnected by gap junctions, form an extremely large physiological syncytium. This structure in conjunction with neuronal activity, very likely contributes to cognitive functions. Based on electrophysiological and neuroanatomical data, the present hypothesis proposes a self-organised, iterative and reciprocal magnetic interaction between neurones and astrocytes to explain neurocomputation, including memory processing, in the human neocortex.

Weekly Treatments with a Burst-Firing Magnetic Field Alters Behavior in the Elevated plus Maze after Two Sessions

In a split-litter design, rats were either injected with 15 mg/kg of clomipramine or saline from postnatal Days 8 through 21. Other rats from the same litters were not injected. When the rats were 90 days of age, the rats were tested once per week for five weeks in an elevated plus maze that contained two open arms (no walls) and two walled arms. Following each test, they were exposed (total of 4 exposures) for 30 min. to a burst-firing magnetic field (1 microTesla) that has been shown to reduce depression in human beings. After two treatments, the rats exposed to the burst-firing fields spent about half the amount of time in the open arms compared to the sham-field exposed rats. The interaction between adult treatment and whether the rats had received the antidepressant before weaning was not significant statistically. These results suggest that at least two weekly sessions may be required before significant changes in behavior occur after weekly 30-min. exposures to these potentially “therapeutic” magnetic fields.