S. Vonhof, Anna-Leena Sirén, Giora Feuerstein

• The present study was performed to qua ntify the distribution of a peptide neurotransmitter after microinjection into the medial preoptic area (POM), using a technique suitable for conscious animal preparations. The results indicate that only 50-ni volumes of injected tracer were sufficiently localized with 77 ± 9% recovery in the POM. Injections of higher volumes resulted in an increasing spread of tracer into distant anatomical regions and structures, including the needle tract and cerebral ventricles. The amount of tracer localized in theThe present study was performed to qua ntify the distribution of a peptide neurotransmitter after microinjection into the medial preoptic area (POM), using a technique suitable for conscious animal preparations. The results indicate that only 50-ni volumes of injected tracer were sufficiently localized with 77 ± 9% recovery in the POM. Injections of higher volumes resulted in an increasing spread of tracer into distant anatomical regions and structures, including the needle tract and cerebral ventricles. The amount of tracer localized in the POM decreased to 38±4% (200 nl) (P < 0.05) and 41 ±8% (500 nl) (P <0.05), respectively. The data suggest that the volume of injection is critical for intraparenchymal injections into structures of a diameter of I mm or less, such as the POM and should not exceed 50 nl in conscious animal preparations.…