Analgesia induced by exposure to a novel environment in rats: effect of concurrent and post-training stressful stimulation

An ethological model for the study of activation and interaction of pain, memory and defensive systems in the attacked mouse. Role of endogenous opioids

The present work reviews neurochemical, physiological and behavioral data recorded from the attacked mouse and integrates them into a model of coping mechanisms during social conflict. More specifically, the possible relationships between systems of pain, memory and defense are presented, with special emphasis on the role of endogenous opioid peptides (EOPs). In recipients of attack, decreased beta-endorphin-like immunoreactivity and changes in opiate and benzodiazepine binding characteristics are found in structures of the brain defensive system. EOPs mediate the social conflict-induced increase of dopamine synthesis in the periaqueductal grey and frontal cortex. Social conflict analgesia in attacked mice is under the control of central opioid and nonopioid (e.g., benzodiazepine, glutamate) mechanisms, and is modified by experience (e.g., long-term analgesic reaction; tolerance). EOPs and pain-inhibitory mechanisms participate in the organization of behavioral defense, recuperative behavior and the memory of attack experience. The data are considered in relation to the perceptual-defensive-recuperative model of fear and pain, forwarded by Bolles and Fanselow.

Neurobiological background of pain and analgesia: the attempt at revaluation according to position of the organism's adaptive activity

The most adequate and successful way to understand the essence of any complex psychophysiological phenomenon, including pain, is obviously the study of its origin, its genesis, i.e., its biological background. Based on critical analysis of recent literature and our own electrophysiological, biochemical and pharmacological data we tried to overcome the difficulties and contradictions derived from the traditional reflex approach and analytical orientation in understanding the experimental investigation of pain-related problems and to determine the neurobiological background of pain and analgesia through the notion of the organism's adaptive activity. Interrelations between the notion of pain and other biological and psychological ideas, the place and functional significance of pain and endogenous analgesic mechanisms in the organization, maintenance and regulation of the organism's adaptive activity, characterization of the involvement of endogenous opioid peptides and monoamines in central processes associated with pain and analgesia, the essence and mechanisms of pain-depressing activity of the opiates are the main stages in our neurobiological consideration of the phenomenon of pain and its natural and pharmacological regulation.

Effects of undernutrition during suckling on novelty-induced analgesia in young and adult rats

The effects of undernutrition on novelty-induced analgesia were investigated in young and adult rats. Rats were undernourished by feeding their dams an 8% casein diet from birth until weaning (21 days of age). Rats were exposed to an open field (novelty) for 2 min and the nociception was measured by the tail-flick method. At adult age, only well-nourished rats presented novelty-induced analgesia, suggesting that early undernutrition abolishes this response. At 21 days of age, the exposure to the open field had no effect on nociception of both nutritional groups, suggesting that some developmental factor is necessary for the emergence of novelty-induced analgesia.