Neuroendocine aspects of behavioral neurology

(from McNamara and Albert, Clinical Neuropsychology (Valenstein and Heilman, eds.) fourth edition.

Acetylcholine activity is greater in the left human brain as measured by CAT (Amaducci 1981) in temporal lobes and globus pallidus (Glick et al. 1982). Orbitofrontal also received ACH projections. Dopamine is represented most in the corpus striatum (nigrostriatal tract), the cingulate gyrus (mesolimbic system), and the SMA and prefrontal areas (from ventral tegmental area). Only trace DA is found in occipital area, with the most in motor and premotor areas. D1 receptors on pyramidal cells of layer 3 of the cortex and striate modulate glutaminergic receptors through "triads" wherein DA affects neuronal firing patterns. DA (and NE) runs in an a-p plane. NE projects from locus ceruleus (LC) to whole forebrain with collaterals to somatosensory and motor cortex (all 6 layers) and less to temporal and primary visual cortex. The prefrontal area provides the only afferents back to LC and disinhibit firing of LC and impair regulation.

DA and ACH act in concert to affect cognition. Clonidine and physostigmine affect memory in aged monkeys more than either drug alone. DA blockade can be reversed by cholinergic depletion and cholinergic blockade can be reversed by DA depletion.

Memory fields in cortex correspnding to D1 receptor projection fields include the sulcus principalis of the monkey and are crucial in delayed response task. These responses are highly dependent on DA concentrations available and with that aspect of working memory. Clonidine improves performance in DR task after lesioning prefrontal cortex, as well as antergograde memory in patients with Korsakoffs syndrome.