MAGNETIC-RESONANCE-IMAGING OF NMDA-INDUCED LESION OF THE MEDIAL PREOPTIC AREA AND CHANGES IN SLEEP, TEMPERATURE AND SEX BEHAVIOR

Destruction of the medial preoptic area (mPOA) neurons of rat brain, i nduced by intracerebral injection of N-methyl D-aspartic acid (NMDA), has been studied by employing the non-invasive Magnetic Resonance Imag ing (MRI) technique. Changes in the MRI images are compared and correl ated with the functional changes after the mPOA lesion. The progress o f the lesion at the injected site has been monitored (using MRI) from 15 min to 1 month after the stereotaxic microinfusion of NMDA (5 mu g in 0.2 mu l). This study shows that the localised hyperintense (bright ) area starts appearing at the mPOA from 3 h after NMDA injection, and the brightness increases progressively for about 2 days. The size and brightness of the hyperintense area decrease thereafter. It has not b een possible to locate the lesion site after 3 days, using MRI, except in one rat where a vacuole-like area was seen at the NMDA injected si te on postmortem histological examination. The reduction in sleep afte r the mPOA lesion does not show any correlation with the changes in MR I, as it persists throughout the 3 weeks of recording. On the other ha nd, the initial drastic reduction in male sex behaviour and the increa se in body temperature correlated to some extent with the increased br ightness in MRI at the site of lesion. The size and location of the hy perintense area, observed during the first 2 days, match with the lesi oned area which was histologically identified after 1 month of NMDA ad ministration. Control administration of normal saline into the mPOA di d not produce any alteration in the brightness of the MRI image and pr actically no loss of neurons at the injected site. Though some functio nal changes have correlation with the alteration in MRI, this cannot b e used to interpret the changes in all the physiological parameters. T his study also demonstrates that the disappearance of the brightness i n MRI should not be taken to indicate a positive prognosis. Though the lesion could not be seen in MRI within 2 hours, its detection after 3 -4 h (but within 3 days) after NMDA lesion would give very valuable in formation for long term studies.