Depression and Temporal Lobe Epilepsy: Expression Pattern of Calbindin Immunoreactivity in Hippocampal Dentate Gyrus of Patients Who Underwent Epilepsy Surgery with and without Comorbid Depression

Abstract

Purpose: Changes in calbindin (CB) expression have been reported in patients with temporal lobe epilepsy (TLE) with controversial implications on hippocampal functions. The aim of this study was to determine the CB immunoreactivity in hippocampal dentate gyrus of patients who underwent epilepsy surgery for drug-resistant TLE with and without comorbid depression and/or memory deficits.

Methods: Selected hippocampal samples from patients with TLE who underwent epilepsy surgery were included. Clinical and complementary assessment: EEG, video-EEG, MRI, psychiatric assessment (structured clinical interview, DSM-IV), and memory assessment (Rey auditory verbal learning test, RAVLT; Rey-Osterrieth complex figure test, RCFT), were determined before surgery. Hippocampal sections were processed using immunoperoxidase with the anti-calbindin antibody. The semiquantitative analysis of CB immunoreactivity was determined in dentate gyrus by computerized image analysis (ImageJ).

Results: Hippocampal sections of patients with TLE and HS (n = 24) and postmortem controls (n = 5) were included. A significant reduction of CB+ cells was found in patients with TLE (p < 0.05, Student's t-test). Among TLE cases (n = 24), depression (n = 12) and memory deficit (n = 17) were determined. Depression was associated with a higher % of cells with the CB dendritic expression (CB-sprouted cells) (F(1, 20) = 11.81, p = 0.003, hp² = 0.37), a higher CB+ area (μm²) (F(1, 20) = 5.33, p = 0.032, hp² = 0.21), and a higher optical density (F(1, 20) = 15.09, p = 0.001, hp² = 0.43) (two-way ANOVA). The GAF scale (general assessment of functioning) of DSM-IV inversely correlated with the % of CB-sprouted cells (r = -0.52, p = 0.008) and with the CB+ area (r = -0.46, p = 0.022).

Conclusions: In this exploratory study, comorbid depression was associated with a differential pattern of CB cell loss in dentate gyrus combined with a higher CB sprouting. These changes may indicate granular cell dysmaturation associated to the epileptic hyperexcitability phenomena. Further investigations should be carried out to confirm these preliminary findings.

Figure 1

Hippocampal dentate gyrus from controls and patients with TLE and hippocampal sclerosis.

Figure 2

Hippocampal sections from postmortem control (a) and TLE with HS (b–i). PL: polymorphic layer; ML: molecular layer; GL: granular cell layer. (a) Qualitative analysis of postmortem control shows homogeneous CB+ granular cell morphology and staining and the absence of GL dispersion and/or ectopic localization. (b–e) Qualitative examination of dentate gyrus sections from TLE patients showed lower CB+ cell density among all dentate gyri (cases 5, 6, 14, and 15 of Table 1). (f–i) Qualitative examination of dentate gyrus sections from TLE+D patients showed a pattern with a reduced number of CB+ granular cells predominantly among basal layers (basal granule cells are predominantly CB negative), with a great proportion of strong CB+ cells located in outer layers, with CB-positive arborization (CB+ sprouted cells), ectopic localization (inner molecular layers), higher CB+ content (higher staining intensity and CB+ area), and longer apical CB+ sprouted fibers projecting into ML (arrows). Basal CB+ sprouted processes are also observed (cases 20, 21, 23, and 24 of Table 1). Magnification (20x), scale bar 30 μm.

Figure 3

Semiquantitative analysis of dentate gyrus CB immunoreactivity observed in TLE patients and postmortem controls. Postmortem controls showed a significant higher number of CB+ cells, with a significant reduction of CB+ sprouted cells comparing with TLE patients (^∗Student's t-test, p < 0.05).

Figure 4

Patients with normal memory showed a lower counting of CB+ cells comparing with TLE patients with memory deficits (^∗p < 0.05). Depression factor was significantly associated with higher % of CB+ cells with positive dendritic processes (sprouted cells), a higher CB+ optical density (MGV), and a higher CB+ area (^∗p < 0.05) (two-way ANOVA). No interactions were observed between factors.

Figure 5

The GAF (global assessment of functioning, DSM-IV) inversely correlated with the % of CB sprouted cells (r = −0.52, p = 0.008), with the CB+ area (r = −0.46, p = 0.022), and with the optical density (mean gray value) (r = −0.33, p = 0.14).