Does microwave irradiation have other than thermal effects on histological staining of the mammalian CNS? A light microscopical study of microwave stimulated staining under isothermal conditions in man and rat.

The question whether or not microwave irradiation exerts other than thermal effects on histological staining is still a matter of controversy. The present study was undertaken to reveal or reject such a so far hypothetical non-thermal irradiation effect. A device was developed, which enables exposure of histological sections or tissue pieces to microwave irradiation under isothermal conditions, i.e. with synchronous removal of the internal heat produced. Three classical neuroanatomical staining methods were tested on human and rat CNS. As control, identical procedures were performed without simultaneous microwave irradiation. The experiments were performed at three different temperature levels ranging from 5 to 50 degrees C. In none of the cases studied was a light microscopically appreciable difference observed between the microwave and non-microwave versions of a stain at the same temperature. The hypothesis of a separate non-thermal effect of microwave irradiation on histological staining is therefore rejected.