Learning and memory in agmatine-treated rats

McKay BE, Lado WE, Martin LJ, Galic MA, Fournier NM

Pharmacol. Biochem. Behav. 2002 Jun;72(3):551-7

PMID: 12175451

Abstract

Agmatine, a noncompetitive N-methyl-D-aspartate (NMDA) antagonist, was examined for its role in water maze place learning, contextual and auditory-cued (discrete) fear learning and conditioned taste aversion learning, when administered systemically. Male Wistar rats were given saline or 1, 5, 10 or 50 mg/kg agmatine ip 20 min prior to or 30 min following daily training sessions in a hidden-platform (place learning) water maze task. Agmatine did not affect latencies to find the hidden platform or preference for the training quadrant during probe trials. When administered 20 min prior to contextual or auditory-cued fear-conditioning sessions, these doses of agmatine evoked a linear dose-dependent impairment in the magnitude of learned fear to the contextual stimuli when assessed during extinction trials 24 h later, but had no effect on the magnitude of learned fear to the auditory stimulus. Inferences of baseline motor activity and ability to respond to the presentation of footshock stimuli were not affected by the treatment. Injections of 50 mg/kg agmatine concurrently with a malaise-evoking agent following presentations to a novel sucrose solution abolished learned taste aversions; this agent did not evoke conditioned taste aversions alone. These studies indicate that systemically administered agmatine selectively impairs behavioral inferences of specific types of learning and memory.

Spatial heterogeneity not homogeneity of the magnetic field during exposures to complex frequency-modulated patterns facilitates analgesia

Martin LJ, Persinger MA

Percept Mot Skills 2003 Jun;96(3 Pt 1):1005-12

PMID: 12831282

Abstract

24 young (4 mo.) and 24 old (8 mo.) male Wistar rats were exposed for 30 min. on two consecutive days to either a sham-field or to a frequency-modulated magnetic field applied through a pair of solenoids (spatially heterogeneous strength) or a Helmholtz coil (spatially homogeneous strength). The maximum field strength was about 2 microTesla. The rats exposed to the spatially heterogeneous magnetic field but not the homogeneous magnetic field exhibited strong analgesia to thermal stimuli applied to the footpads immediately after the treatment and 30 min. later. The effect accommodated 38% of the variance in the latency to respond to the thermal stimuli. These results suggest that the practice by many researchers in bioelectromagnetism to design coils to generate maximum spatial homogeneity of intensities within the exposure volume when applying complex weak magnetic fields may actually diminish any biological effects.

Chronic administration of the L-type calcium channel blocker nimodipine can facilitate the acquisition of sequence learning in a radial-arm maze

Martin LJ, Fournier NM, Galic MA, Emond MH

Behav Pharmacol 2004 Mar;15(2):133-9

PMID: 15096913

Abstract

Nimodipine, a dihydropyridine L-type voltage-gated calcium-channel blocker, was examined for its potential effect on the acquisition of a complex-arm sequence task in an automated radial maze. Young (60-day-old) male Wistar rats were injected with saline or nimodipine (5 mg/kg) 15 min prior to radial maze training, or immediately following the radial maze testing. The results of the learning task (over 7 days of testing) showed that rats injected with nimodipine each training session acquired the task more quickly and more efficiently compared to saline-treated animals. There were no significant differences for rats that were pre-/post-treated with nimodipine during the maze-learning task. The number of incorrect arm entries and number of additional lever presses in the same arm were found to be significantly lower in rats treated with nimodipine compared to saline-injected controls. The beneficial effect of nimodipine treatment occurred only in rats that were acquiring the task, and not in rats that had already learned the arm sequence paradigm. There were no potential non-specific influences on locomotor activity or appetite caused by chronic nimodipine treatments. These results strongly suggest that nimodipine can facilitate the acquisition of a complex learning task.