The content of the histamine in most mammalian tissues is very low.
   Thus , presentation a simple and sensitive method to assay the histamine
   content in crude extracts tissues is required .

          In this work ,we presented a simple method for the measurement of the
   histamine. 2 mg of rat brains was homogenized in 5 ml of 0.5 M HClO₄ .The
   homogenates were centrifuged (3000*g , 3 min )and supernatants were
   adjusted to pH 5 with 0.4 M HCl. Then the precipitate was removed by
   centrifugation (3000*g, 5 min) , and the supernatants were put into a micro
   centrifuge filter tube ( exclusion molecular weight 10000,Millipor ) and
   centrifuged at 3000 *g, for 5 min and supernatants was put into a tube .The
   histamine was measured spectrophotometrically using 2,4,6-trinitrobenzen
   sulfonate ,at 420 nm. One unit of enzyme activity is defined as the amount 
   of enzyme which will produce 1 micro mole of the histamine per min at 25° C.

          The results presented in this work indicated that the highest content of
   histamine level and histidine decarboxylase  were in hypothalamus.

          The results obtained here clearly showed that this method  is simple,
   sensitive , reliable and could be applied to assay histamine content  and
   histidine decarboxylase activity in the brain.