Detailed distribution of nerve growth factor in rat brain determined by a highly sensitive enzyme immunoassay.

We modified a previously reported enzyme immunoassay method to make it more sensitive for quantification of nerve growth factor (NGF), and succeeded in measuring the NGF content in as small as 2 mg (wet weight) of rat brain tissue. Rat brain was cut into about 600 pieces of the same size, and the NGF content in each piece was determined by this method. The findings were as follows: (i) In the cerebral cortex, NGF contents were unevenly distributed, ranging from less than 0.1 to 1.8 ng/g wet wt. The level was highest in the caudal parietal and rostral occipital cortices and lowest in the lateral parietal cortex. (ii) Areas comprising the limbic system such as the cingulate gyrus, pyriform cortex, amygdala, anterior and medial thalamus, hippocampus, septum, and diagonal band of Broca contained high levels of NGF. (iii) In the brain stem and cerebellum, the levels were low; however, a relatively high level was registered in the cerebellar nuclei, lateral vestibular nucleus, ventral cochlear nucleus, superior olive, and pontine reticular nuclei. These findings, taken together with previously published information, suggest that the neurons in the anterior and medial thalamus, pontine reticular nuclei, superior olive, ventral cochlear nucleus, and cerebellar Purkinje cells may be additional populations of NGF-responsive neurons in the rat brain.