No abstract

Limbic structures including the hippocampus are thought to be involved in pain though not much is known of their neuronal responses to noxious stimuli. In this report we show that a prolonged and substantial depression of the dorsal hippocampal CA1 pyramidal cell population spike is produced by a brief but intense noxious stimulus applied to the tail of lightly anaesthetized rats. This depression is temperature-dependent and habituates to subsequent noxious stimuli applied more than 1 h later. Further, the depression is absent when noxious heat is applied in the presence of hippocampal theta rhythm.

No abstract

A controversy exists as to whether morphine attenuates spinal cord nociceptive transmission through a supraspinal site of action. The approach of examining the effects of morphine on spinal cord nociceptive transmission in the presence and absence of spinal cord conduction has led to conflicting conclusions. We have compared the effects of morphine on the rat tail-flick reflex (TFR) in lightly anaesthetized animals in the presence and absence of a spinal cord cold-block. Morphine, administered systemically, was found to be more potent in increasing the latency of the reflex when the spinal cord conduction was present. However, when low doses of morphine were injected intrathecally, morphine was more potent when spinal cord conduction was blocked. These data indicate that systematically administered morphine, at low doses, has a supraspinal site of action in prolonging the onset of the TFR. Conflicting results on this issue do not appear to be due to plasticity changes following spinal cord section or lesions, psychological stress in conscious animals or the presence of tonic bulbospinal inhibition.

In urethane-anesthetized rats, ethanol (1.5 g/kg, i.v.) increased the rate of discharge of cerebellar Purkinje cells, increased their regularity of discharge, and reduced or eliminated the climbing fibre evoked bursts. Most of the neurones responding in this manner exhibited an acute tolerance to the drug. Another group of rats was made alcohol dependent by feeding them for 2 weeks on a diet containing ethanol (12.5-16.5 g/kg per day). Ethanol produced similar but reduced effects on Purkinje cells of these animals.