REGIONAL AND LAMINAR VARIATIONS IN ACETYLCHOLINESTERASE ACTIVITY WITHIN THE FRONTAL-CORTEX OF THE DOG

Two different histochemical methods were applied to analyse acetylchol inesterase (AChE) activity within the frontal lobe cortex (FC) of the dog. Both staining methods revealed AChE reactivity in neuronal cell b odies and fibres. AChE-positive neuronal perikarya varied in size, sha pe, character and intensity of staining. Both pyramidal and non-pyrami dal AChE-rich neurons were found. The pyramidal neurons predominated i n layers III and V of the dog FC. The non-pyramidal cells were present in deep cortical layers and white matter. Labelled cells were distrib uted in a consistent pattern across regions of the dog frontal lobe. A ChE reactivity in fibres showed, in general, a characteristic bilamina r appearance due to the more intense staining in cortical layers I and V. However, in contrast to the cellular labelling, differences in the laminar distribution of AChE-rich fibre bands distinguished three sub regions of the FC: (1) rostral and middle prefrontal and anterior prem otor areas, where AChE was distributed in a bilaminar pattern with two bands of similar, medium-intensive staining overlying layers I and V; (2) dorso-caudal primary and secondary motor areas distinguished by m uch lighter staining of the deep band of AChE activity in layer V; and (3) ventro-caudal subcallosal region in which the bilaminar pattern o f extremely dark labelling in layers I and V was augmented by a third band of strong ACHE activity in layer VI. These findings show that dif ferences in the pattern of ACHE activity parallel some of the cytoarch itectonic zones of the FC previously described in this laboratory (Raj kowska and Kosmal, 1988).