In Vivo Biosynthesis of 35S‐Substance P from [35S]Methionine in the Rat Striatum and Its Transport to the Substantia Nigra

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Abstract
Rats with a push-pull cannula implanted in the right striatum were used to study the biosynthesis of 35S-substance P (SP) from [35S]methionine and its transport to the ipsilateral substantia nigra. [35S]Methionine was delivered for 2, 3 or 5 h to the push-pull cannula. 35S-SP in striatal and nigral tissues was estimated after immunoadsorption and HPLC. Higher levels of 35-SP in striatal homogenates were found after a 5-h labelling period. 35S-SP biosynthesis was inhibited when cycloheximide was superfused together with [35S]methionine. The identity of 35S-SP was further checked by its conversion into 35S-SP sulphoxide. After a 5-h labelling period, 35S-SP was also recovered in the substantia nigra. This was not the case after hemisection of striato-nigral fibers. When rats were killed 15 or 24 h after the 5-h labelling period, 35S-SP levels in the substantia nigra were higher than those found just after the 5-h labelling period, while the reverse was observed in the striatum.