The exposure of normal mice to whole body hyperthermia (1 h WBH at 39 or 40 degrees C), 20 or 48 h prior to total body irradiation (TBI) with lethal doses of gamma-rays affords significant protection as assessed by survival. The radioprotective effect of WBH, as observed in normal mice, diminished in tumour bearing mice depending upon the size of tumour. Treatment of tumour bearing mice with mild WBH, 20 h prior to local irrradiation (LIR), did not protect the transplanted tumour against radiotherapy with a single dose of 20 Gy or fractionated dose (in five fractions) of 7.5 Gy on alternate days. In fact, mild WBH treatment enhanced the tumour regression and increased the mean survival time after fractionated dose therapy. However, the prior mild WBH was found to be ineffective in protecting normal tissue, as assessed by skin contraction after local irradiation (50 Gy). This indicates that mild WBH treatment given 20 h prior to local radiotherapy enhances fibrosarcoma tumour regression but cannot protect skin (normal tissue) against local irradiation. It appears that radioprotection of animals by WBH may be the consequence of its radioprotective effect on haemopoietic tissues mediated through certain cytokines. Perhaps WBH may not have a radioprotective effect on other tissues, as evident from skin contraction studies.

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PubMedDate not supplied

Injury- and use-related plasticity in the primary sensory cortex of adult mammals: possible relationship to perceptual learning.

1. Restricted cochlear lesions in adult animals result in a reorganization of auditory cortex such that the cortical region deprived of its normal input by the lesion is occupied by expanded representations of adjacent cochlear loci (and thus of the frequencies represented at those loci). Analogous injury-induced reorganization is seen in somatosensory, visual and motor cortices of adult animals after restricted peripheral lesions. 2. Rather than constituting a central compensation for the peripheral loss, such reorganization appears to be an extreme form of changes in cortical organization that occur as a consequence of altered patterns of input such as arise from differential use of restricted regions of receptor surfaces ('use-related' reorganization). Thus, the frequency organization of auditory cortex is modified in animals trained to perform a frequency discrimination task and analogous changes in the frequency selectivity of cortical neurons are produced by classical conditioning procedures. 3. Recent evidence from the visual system suggests that changes similar to those involved in injury- and use-related cortical reorganization may underlie some forms of what has been called 'perceptual learning', the improvement in sensory/ perceptual discriminative performance with practice. Some forms of such learning are highly specific to the particular stimuli used in training (i.e. do not generalize to other stimuli), suggesting that the improved performance reflects a change in neural circuitry at a relatively early level of sensory processing. The limited available evidence supports the occurrence of such learning in the auditory system. 4. Recent studies using functional imaging and related techniques indicate that injury- and use-related reorganization occurs in human sensory and motor cortex.

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