Ketamine and phencyclidine (PCP) are noncompetitive antagonists of the N-methyl-D-aspartate (NMDA) type of ligand-gated glutamate receptors. Both agents have high abuse liability, and may produce dependence. Tolerance to the reinforcing effects of drugs of abuse is widely regarded as a key component of the dependence process. Therefore, the present study was conducted to examine whether tolerance develops to the reinforcing effects of ketamine, and whether PCP and dizocilpine, a noncompetitive NMDA antagonist with negligible abuse liability, produce cross-tolerance to the reinforcing effects of ketamine. Further, identification of the neural mechanisms that underlie tolerance to the reinforcing effects of drugs may yield information regarding drug dependence.
Abstract: Prior hypotheses as to the etiology of near-death experiences (NDEs) have been limited to psychiatric explanations or brief discussions of endorphins as causative agents. We present a neurophysiological explanation for NDEs based on their similarities with lysergic acid-, ketamine-, and hypercampnia-induced hallucinations. We believe the core NDE is genetically imprinted and triggered by serotonergic mechanisms.
Date: Autumn 1989
Creator: Morse, Melvin L.; Venecia, David, Jr. & Milstein, Jerrold
Abstract: This paper is a critique of Karl Jansen's hypothesis that near-death and ketamine experiences are caused by blockade of N-methyl-D-aspartate receptors. An assumption that consciousness and its alterations are merely the product of neuronal activity is only one of many possible beliefs about reality. An alternative, which can be verified through one's own direct experiences, is that consciousness is always a subject and body is only its object. The objects come and go; consciousness remains.
Abstract: Although ketamine can induce a state similar to a near-death experience (NDE), there is a striking difference between experiences induced by ketamine used in a recreational context and in an operating room. Ketamine is a noncompetitive antagonist of the N-methyl-D-aspartate receptro, as is ibogaine, the main alkaloid of a shrub used in Central Africa to induce NDEs in a religious context. Ibogaine can also elicit different experiences when used in a hallucinatory context or in initiatic rituals, where a superficial state of coma is induced. These data raise the question of whether the chemically-induced NDE-like experience is related to the use of a particular kind of substance or to a genuine comatose state.
Article discussing a biological basis for near-death experiences (NDEs). For example, conditions that precipitate NDEs, such as hypoxia, ischemia, hypoglycemia, and temporal lobe epilepsy, have been shown to release a flood of glutamate, overactivating N-methyl-D-aspartate (NMDA) receptors and resulting in neurotoxicity.
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