Physiology & behavior
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The susceptibility to pentylenetetrazol (PTZ)-induced seizures during postnatal ontogeny [postnatal day (PN) 10-220] was investigated in two rat strains. The WAG/Rij strain, genetically prone for developing generalized absence epilepsy, and Wistar rats were tested and compared at PN 10, 26, 30, 70, 90, 125, and 220 on the PTZ-convulsive threshold. A subconvulsive dose of 25-mg/kg PTZ was administered every 15 min, and the occurrence of clonic and tonic-clonic seizures was scored. ⋯ From that age onwards, the seizure threshold significantly decreased and reached a minimum at PN 220. Between strain comparisons showed that WAG/Rij rats have a lower tonic-clonic seizure threshold than Wistar rats. The data indicate that changes in susceptibility first quickly decreases until PN 26-30 and then tend to monotonically increase with age, and that genetically prone nonconvulsive WAG/Rij rats are more vulnerable to convulsive seizures induced by PTZ than Wistar rats.
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Physiology & behavior · Aug 2000
Entrainment of the rat motor activity rhythm: effects of the light-dark cycle and physical exercise.
The circadian system is believed to be composed of a population of oscillators that couple together and generate a single rhythm. If this coupling is not strong enough, the circadian system can be dissociated into two or more groups of oscillators, and this is manifested in a dissociation of the overt rhythm into at least two circadian components. This study aims to examine the influence of factors, such as the difference in impact between T and tau, light intensity, and access to a running wheel, on the distribution of motor activity throughout the light-dark (LD) cycle and the dissociation of the rhythm. ⋯ Results show that the distribution of motor activity throughout the cycle and the after effects observed in the rhythm under DD depended on light intensity and access to the wheel. Moreover, under T23, some rats showed two simultaneous circadian components whose manifestation also depended on the experimental conditions. The results indicate that the strength of circadian entrainment to LD cycles in the rat depends on three factors: the period length of the LD cycle, light intensity used during the light phase, and access to a running wheel.
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Physiology & behavior · May 2000
Randomized Controlled Trial Clinical TrialEffects of hypnosis on diffuse noxious inhibitory controls.
The neurophysiological mechanisms of hypnotic analgesia are still under debate. It is known that pain occurring in one part of the body (counterstimulation) decreases pain in the rest of the body by activating the diffuse noxious inhibitory controls (DNICs). The aim of this study was to explore the effects of hypnosis on both pain perception and heterotopic nociceptive stimulation. ⋯ Both hypnosis and DNICs were able to modify the perception of pain. It seems likely that DNICs and hypnosis use the same descending inhibitory pathways for the control of pain. The susceptibility of the subject is a critical factor in hypnotically induced analgesia.
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Physiology & behavior · May 2000
Capsaicin, acid and heat-evoked currents in rat trigeminal ganglion neurons: relationship to functional VR1 receptors.
Activation of primary trigeminal (TG) neurons by protons, capsaicin, or heat can evoke a variety of sensations, including tingling, stinging, warmth, and burning. Capsaicin and acid are trigeminal stimulants that are important in gustatory physiology. These stimuli can activate H(+)-gated ion channels and heterologously expressed VR1 receptors (vanilloid receptor 1). ⋯ Heating TG neurons evoked a thermally active, capsazepine-inhibitable current with threshold temperature of 43 degrees C and Vr = 5 mV that is also present in neurons activated by and protons (Sp) and capsaicin (Sc). These data suggest that TG neurons have functional receptors that behave similarly to VR1. Activation of such receptors should result in a burning sensation, whereas activation of the transient and biphasic currents should result in other taste descriptors.
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Physiology & behavior · Mar 2000
Food anticipatory activity and photic entrainment in food-restricted BALB/c mice.
The BALB/c mouse was evaluated as a model for the study of entrainment of circadian rhythms by feeding schedules. Mice were housed in a 12:12-h light-dark (LD) environment with food available for 3-5 h/day (5 h before dark onset). Food anticipatory activity (FAA) rhythms were evident in all mice, ranging from robust in some to weak and variable in others. ⋯ In some cases, free-running rhythms entrained to feeding time, and in other cases, the period of the free run lengthened toward 24 h. These data show that restricted feeding in BALB/c mice can engage a circadian mechanism driving FAA rhythms and can also modulate the phase of photic entrainment, possibly by a direct entraining effect on the light-entrained rhythm. The BALB/c mouse strain, in several respects, appears to be a useful model for the study of scheduled feeding and circadian rhythms.