Low nNOS protein in the locus coeruleus in major depression

Abstract

Disruptions of glutamatergic and noradrenergic signaling have been postulated to occur in depressive disorders. Glutamate provides excitatory input to the noradrenergic locus coeruleus (LC). In this study, the location of immunoreactivity against neuronal nitric oxide synthase (nNOS), an intracellular mediator of glutamate receptor activation, was examined in the normal human LC, and potential changes in nNOS immunoreactivity that might occur in major depression were evaluated. Tissue containing LC, and a non-limbic, LC projection area (cerebellum) was obtained from 11 to 12 matched pairs of subjects with major depression and control subjects lacking major psychiatric diagnoses. In the LC region, nNOS immunoreactivity was found in large neuromelanin-containing neurons, small neurons lacking neuromelanin, and glial cells. Levels of nNOS immunoreactivity were significantly lower in the LC (- 44%, p < 0.05), but not in the cerebellum, when comparing depressed with control subjects. nNOS levels were positively correlated with brain pH values in depressed, but not control, subjects in both brain regions. Low levels of nNOS in the LC may reflect altered excitatory input to this nucleus in major depression. However, pH appears to effect preservation of nNOS immunoreactivity in subjects with depression. This factor may contribute, in part, to low levels of nNOS in depression.

Fig. 1

Photomicrographs showing nNOS – immunoreactive cells from the region of the human LC: (a) large neuron containing neuromelanin, (b) smaller neuron void of neuromelanin, (c) glial cells. Scale bars = 50 μm.

Fig. 2

nNOS immunoreactivity in locus coeruleus (LC) from a single pair used in the analysis, representing three separate anatomical levels: rostral (R), middle (M) and caudal (C). Each well was loaded with 10 μg of total protein. The bottom panel (right and left) shows immunoreactive actin probed with anti-actin antibody on the same blot as a control for protein loading and transfer.

Fig. 3

nNOS immunoreactivity in LC of depressive subjects expressed as percentages of values from paired control subjects. Each bar is an average of duplicate comparisons. The overall relative amount of nNOS was lower in the LC (− 44%, p < 0.05) among depressive subjects compared with individually matched control subjects.

Fig. 4

nNOS immunoreactivity in cerebellum from a single pair used in the analysis. Each well was loaded with 10 μg of total protein. The bottom panel (right and left) shows immunoreactive actin probed with anti-actin antibody on the same blot as a control for protein loading and transfer.

Fig. 5

nNOS immunoreactivity in cerebelli of depressive subjects expressed as percentages of values from paired control subjects. Each bar is the average of duplicate comparisons. The overall relative amount of nNOS was modestly lower (− 12%) in the cerebellum among depressive subjects compared with individually matched control subjects, although this difference did not reach statistical significance.

Fig. 6

Relationships between the amount of nNOS and brain pH in control and major depressives subjects: (a and b) locus coeruleus (c and d) cerebellum.