Among multiple subspecies of the protein kinase C (PKC) family, type I PKC from the hypothalamus, having the structure related to the γ-sequence, responds to low concentrations of arachidonic acid to exhibit marked enzymatic activity. This mode of activation does not require elevated Ca2+ levels, nor does it depend on diacylglycerol and phospholipid. Type I PKC is expressed only in limited regions of central nervous tissues, such as the hypothalamus. This PKC subspecies is not detected in the pituitary gland. The results suggest that the activation of type I PKC may not always be directly associated with inositol phospholipid hydrolysis, and that this subspecies may play a role in the modulation of specialized functions of the hypothalamus.