Brain : a journal of neurology
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Burning pain was induced in healthy human subjects by intracutaneous injections of capsaicin (20 microl, 0.1%) in the innervation territory of the cutaneous branch of the peroneal nerve and the pain responses were compared with the activation patterns of afferent C-fibres recorded by microneurography. Responsiveness of single units to mechanical or heat stimuli or to sympathetic reflex provocation tests was determined by transient slowing of conduction velocity following activation (marking technique). Capsaicin activated each of 12 mechano-responsive and 17 of 20 mechano-insensitive C-units. ⋯ We did not observe sensitization to brushing or to punctate stimuli in uninjured parts of the innervation territory. Differential capsaicin sensitivity adds to the cumulating evidence for the existence of two categories of functionally different nociceptors in human skin, with a special role for mechano-insensitive fibres in sensitization and hyperalgesia. Possible structural differences between these two categories are discussed, including the role of tetrodotoxin-resistant sodium channels.
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We recently reported on three young patients with severe impairments of episodic memory resulting from brain injury sustained early in life. These findings have led us to hypothesize that such impairments might be a previously unrecognized consequence of perinatal hypoxic-ischaemic injury. Neuropsychological and quantitative magnetic resonance investigations were carried out on five young patients, all of whom had suffered hypoxic-ischaemic episodes at or shortly after birth. ⋯ On the basis of their clinical histories and the pattern of magnetic resonance findings, we attribute the patients' pathology and associated memory impairments primarily to hypoxic-ischaemic episodes sustained very early in life. We suggest that the degree of hypoxia-ischaemia was sufficient to produce selective damage to particularly vulnerable regions of the brain, notably the hippocampi, but was not sufficient to result in the more severe neurological and cognitive deficits that can follow hypoxic-ischaemic injury. The impairments in episodic memory may be difficult to recognize, particularly in early childhood, but this developmental amnesia can have debilitating consequences, both at home and at school, and may preclude independent life in adulthood.