Near-infrared oxymeter prototype for noninvasive analysis of rat brain oxygenation

The feasibility of non-invasive analysis of brain activities was studied in the attempt to overcome the major limitation of actual in vivo methodologies i.e. invasiveness. Optic fibre probes were used as optical head of a novel, highly sensitive near infrared continuous wave spectroscopy (CW-NIR) instrument. This prototype was designed for non-invasive analysis of the two main forms of haemoglobin: oxy-haemoglobin (HbO2) and deoxy-haemoglobin (Hb), chromophores present in biological tissues. It was tested in peripheral tissue (human gastrocnemius muscle) and then reset to perform measurement on rat brain. In animal studies, the optical head was firmly placed using stereotaxic apparatus upon the sagittal line of anaesthetised adult rat's head, without any surgery. Then pharmacological treatments with saline (300µl s.c.) amphetamine (2mg/kg) or nicotine (0.4mg/kg) were performed. Within 10-20 min amphetamine substantially increased HbO2 and reduced Hb control levels. Nicotine produced a rapid initial increase followed by a decrease of HbO2. In contrast to amphetamine, nicotine treatment also reduced Hb and blood volume. These results support the capacity of our CW-NIR prototype to measure non-invasively HbO2 and Hb levels in the rat brain, markers of the degree of tissue oxygenation, index of blood level then of the state of brain metabolism.