JOURNAL OF

PSYCHIATRIC

RESEARCHJournal of Psychiatric Research 41 (2007) 553–560

www.elsevier.com/locate/jpsychires

Hippocampal volume reduction and HPA-system activity inmajor depression

Michael Colla a,b,*, Golo Kronenberg a, Michael Deuschle b, Kornelia Meichel b,Thomas Hagen c, Markus Bohrer b, Isabella Heuser a

a Department of Psychiatry, Charite, Campus Benjamin Franklin, Eschenallee 3, 14050 Berlin, Germanyb Central Institute of Mental Health, J 5, 68159 Mannheim, Germany

c Department of Neuroradiology, Saarland University, 66421 Homburg/Saar, Germany

Received 9 February 2006; received in revised form 29 May 2006; accepted 23 June 2006

Abstract

Structural imaging studies investigating hippocampal volumes in patients suffering from major depression have yielded mixed results.Here, 24 unipolar depressed in-patients and 14 healthy controls carefully matched for age, gender, and years of education underwentquantitative magnetic resonance imaging (MRI). Saliva cortisol was measured at 0800 and 1600 h in patients during a one-weekwash-out and the following 4 weeks. Hippocampal volumes were significantly reduced in the patient group even after adjusting for intra-cranial brain volume (ICV) and age. Across groups, age was significantly negatively correlated with uncorrected hippocampal volumes.In patients, severity of disease (baseline HAMD scores) and baseline cortisol levels were not related to hippocampal volumes. However,there was a negative association between duration of the index episode before hospitalization and hippocampal volumes. Additionally,hippocampal volumes were significantly negatively correlated with duration of illness. Finally, we observed a trend for higher hippocam-pal volumes in those patients who showed a subsequent decrease in cortisol levels under pharmacotherapy.� 2006 Elsevier Ltd. All rights reserved.

Keywords: Major depression; Hippocampus volume; HPA-System; Magnetic resonance imaging; Hypercortisolemia; Stress

1. Introduction

Major depression is a highly prevalent psychiatric disor-der associated with considerable overall morbidity.Although depression-related abnormalities of the hypotha-lamic-pituitary-adrenal (HPA) system and elevated cortisolconcentrations in patients suffering from major depressionare well established (Heuser et al., 1994; Holsboer, 2000),hippocampal structural changes in depressed patients arestill a topic of debate (de Kloet et al., 2005; McEwen,2005). In the central nervous system (CNS), glucocorti-coids (GCs) modulate neuronal excitability and exert animportant effect on hippocampus-dependent function suchas spatial memory. However, prolonged or repeated distur-

0022-3956/$ - see front matter � 2006 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jpsychires.2006.06.011

* Corresponding author. Tel.: +49 30 8445 8704; fax: +49 30 8445 8726.E-mail address: michael.colla@charite.de (M. Colla).

bances of the neuroendocrine equilibrium with sustainedstress-levels of GCs may have deleterious effects on brainstructure and function: excessive GCs have been shownto induce morphological changes such as atrophy of den-dritic processes particularly in the hippocampus (Watanabeet al., 1992; McEwen, 2005) and to disrupt memory andlearning processes in animals and humans. Furthermore,elevated GCs impair adult hippocampal neurogenesis(Kempermann, 2002; Sapolsky, 2000). Based on these find-ings, one might expect patients with hyperactivity of theHPA system and depression to also show hippocampalstructural alterations and reduced hippocampal volumes(Bremner et al., 1995; Sheline et al., 1996).

So far, neuroimaging studies of hippocampal volumes inmajor depression have yielded conflicting results. Possibleconfounding factors include methodical issues like neuro-anatomical definitions used and, most importantly, variance

554 M. Colla et al. / Journal of Psychiatric Research 41 (2007) 553–560

of clinical variables such as age, age at onset or number ofprevious depressive episodes across different studies. Also,the majority of volumetric studies in depressed patientsdid not analyze cortisol levels. While O’Brien et al. (2004)found no association between hippocampal volume reduc-tion and increased cortisol levels, Axelson and colleaguesdid not observe a difference in amygdalo-hippocampal vol-umes between patients and age-matched controls. However,that study documented an inverse relationship between vol-ume of this brain structure and 11 p.m. cortisol concentra-tions (Axelson et al., 1991). A recent study in outpatientssuffering from major depression did not find either anassociation of baseline or urinary cortisol concentrationswith hippocampal volumes or reduced hippocampal vol-umes in depressed patients as compared to healthy controls(Vythilingam et al., 2004).

In this study, we sought to examine hippocampal vol-umes (hippocampus proper) in relatively severely depressedhospitalized patients in mid- and later life and to evaluatethe interrelationships between hippocampal volumes, keyclinical factors and saliva cortisol measurements.

2. Methods

2.1. Patients and controls

Unipolar depressed inpatients who met DSM-IV diag-nostic criteria for major depressive disorder with a mini-mum score of 18 points on the Hamilton rating scale fordepression (HAMD, 21 items) were recruited for participa-tion in this study (Day �8). Exclusion criteria includedadditional axis I comorbid psychiatric disorders, any cur-rent clinically relevant medical condition, history or evi-dence of stroke or transient ischemic attack and alcohol/substance abuse within 6 months before study entry.

The control group consisted of healthy volunteers care-fully matched for age, education and IQ estimates. A struc-tured interview (SKID) (Wittchen et al., 1997) wasadministered to rule out the presence of current or pastpsychiatric illness. Further exclusion criteria for healthycontrols were first-degree relatives with a psychiatric disor-der, any relevant medical disorders as well as history ofalcohol/substance abuse. Additionally, neither patientsnor controls who had ever suffered a head injury wereincluded.

With the exception of lorazepam and zolpidem patientswere kept off psychotropic medication during the first weekof the study (week �1). Baseline HAMD scores wereassessed at the end of this antidepressant-free week (Day�1). Patients with a score of less than 18 points at theend of this drug-free period were removed from the studyas responders during washout. Patients were then random-ized to treatment with either amitriptyline or paroxetine(Day +1). During the first week of active treatment (week1) amitriptyline and paroxetine were increased to 150 mgor 40 mg, respectively. During the following weeks thistreatment regimen was continued.

Severity of depression was assessed weekly usingHAMD ratings. Patients’ psychiatric family history, ageat onset of illness, length of episode (index episode) andnumber of previous affective episodes were recorded.The protocol had been approved by the local ethics com-mittee and all participants had given written informedconsent.

2.2. Image acquisition

Magnetic resonance imaging (MRI) scans were per-formed toward the end of week �1 when patients were stilloff psychotropic medication. Data were acquired on a 1,5Magnetom VISION� (Siemens, Erlangen, Germany)equipped with a standard circularly polarized head coil. Avacuum-molded head holder (Vac-Pac�, Olympic Medical,Seattle, WA) was employed to reduce motion of the sub-ject’s head. Three-dimensional gradient echo imaging (mag-netization prepared rapid gradient echo, MPRAGE) wasperformed in the sagittal plane, T1-weighted (TR =11.4 ms, TE = 4.4 ms, field of view (FOV) = 269 mm, flipangle = 30�, slice thickness = 1.05 mm, 154 contiguousslices, pixel: 1.05 · 1.05 mm, slab 161 mm, matrixsize = 256 · 256).

2.3. Image analysis

Image analysis was carried out with commercial soft-ware package Analyze� 4.0 (Mayo Clinic, Rochester,MN, USA) on a PC workstation (Pentium II 400 MHz,Windows NT4, SP4). After acquisition, all imaging fileswere transferred to the PC. Images were transformed froma 16-bits information to an 8-bits level and stacked to a 3Ddata set. For ROI analysis the original images with amatrix of 256 · 256 were enlarged to 1024 · 1024 toachieve a precise interactive delineation of the structuresusing the mouse. All hippocampal measurements were car-ried out by two raters, a well-trained rater and a supervis-ing experienced neuroradiologist. Both were blind to thesubject’s identity and group assignment. Intra- and inter-rater reliability were assessed as intraclass correlation coef-ficients (ICCs) (Shrout and Fleiss, 1979). To determineintra-rater reliability, 15 randomly selected hippocampalformations were measured by one rater (KM) at an inter-val of 4 months. The ICC for inter-rater reliability (tworaters measuring the volumes of 38 hippocampal forma-tions each) was 0.94 (two-way ANOVA with single score,fixed raters). Intra-rater reliability (one rater, KM) yieldedICCs of r = 0.91 for the left and r = 0.93 for the right hip-pocampus. For statistical calculations the mean value ofthese two measurements was used. The hippocampal vol-ume (cc.) was obtained by a specific region of interest(ROI) calculation. Hippocampal tissue was assessed sliceby slice using tracing and connectivity tools in coronar ori-entation. The final step was to run a summarizing routinethat calculated the volume of the tissue within the specificROI.

M. Colla et al. / Journal of Psychiatric Research 41 (2007) 553–560 555

2.4. Neuroanatomical landmarks

The hippocampal formation was delineated according toestablished measurement guidelines derived from mutualcomparisons of MRI and histological data (Niemannet al., 2000). Within the term ‘‘hippocampal formation’’we include the hippocampus proper (CA3, CA2 andCA1), the dentate gyrus and the subiculum. Unlike otherprotocols (Watson et al., 1992), we attempted to excludethe entorhinal area and the parahippocampal gyrus fromthe measurements. For the separation between amygdalaand hippocampal formation, the method described byConvit et al. (1999) was used. In brief, the measuring pro-tocol consists of four subsequent shape segments based ontypical appearance in frontal section planes along the ante-rior–posterior axis. The first three segments comprise thehippocampal head, whereas segment four corresponds tothe body of the retro-commissural hippocampus. The mea-surements start rostrally at a point where the cornu inferiusof the lateral ventricle loses its slit-like appearance, widens,occupies a position lateral to the hippocampus proper andbecomes triangular or boomerang-shaped in the coronalplane. The tracing protocol continues upon identifyingthe most posterior slice rostral to the trigonum, wherethe cella media, the cornu inferius and the occipital hornfuse.

2.5. Intra-cranial brain volume

For measuring the intra-cranial brain volume an auto-matic segmentation routine of the ANALYZE� 4.0. pack-age (Mayo Clinic, Rochester, MN, USA) was used, whichuses a seed-growing threshold approach with consecutivedilations and erosions. Total cerebral gray and white mat-ter (including brainstem, temporal lobes, the optic chiasm,the pituitary and cerebellum), CSF, dura mater and sinuseswere included. The base of the cerebellum delimited theinferior border.

2.6. Hormonal measurements

Saliva cortisol measurements were performed asdescribed previously (Weber-Hamann et al., 2006). Briefly,once at baseline and every other day of the treatment per-iod, saliva for the estimation of free cortisol concentrations(Salivette�, Sarstedt, Germany) was collected from allpatients at 0800 h before breakfast (morning saliva) andthe distribution of medication on the ward. Patients wereuniformly awakened at 0745 h. Afternoon saliva sampleswere obtained at 1600 h. A minimum of 15 saliva samplesper timepoint and at least three samples per timepoint perweek (week �1 to week 4) were required for inclusion infurther statistical analysis.

Clear saliva was used for duplicate analyses of cortisolusing a time-resolved immunoassay with fluorescencedetection. The lower limit of detection was 0.43 nmol/lwith interassay- and intraassay-coefficients of variation of

less than 10% across the expected range of cortisol levels(3–25 nmol/l). Saliva cortisol measurements have beenshown to reflect activity of the hypothalamus-pituitary-adrenal system in depressed patients (Weber-Hamannet al., 2005, 2006).

2.7. Statistical analysis

Statistical analysis was performed with StatView forMacintosh, version 5.0.1 (SAS Institute Inc.). Neuron-atomical comparisons between depressed patients andhealthy control subjects were carried out by means of anal-ysis of variance (ANOVA).

In the literature, both absolute hippocampal volumemeasurements and volumes after different kinds of normal-ization have been reported (e.g. van Petten, 2004). As indi-cated in the text below, absolute hippocampal volumesrepresent raw data with no correction. Measurements werealso normalized through division by total intracranialbrain volume (‘‘intra-cranial brain volume (ICV)-corrected

hippocampal volumes’’). Although ratios have been used asa normalizing procedure in the past (e.g. Chantome et al.,1999), this approach may cause spurious results. Therefore,hippocampal volume measurements were also residualizedagainst intracranial brain volume and age as sequentialcovariates (‘‘residualized hippocampal volumes’’; e.g. Cahnet al., 1998; Convit et al., 2003; Golomb et al., 1994; Magu-ire et al., 2003). The Pearson correlation coefficient withlevel of significance set at 0.05 and two-tailed p valueswas used to determine the significance of correlationsamong and between MRI measures and clinical data.

3. Results

3.1. Study population

Twenty-four unipolar depressed inpatients and fourteenhealthy controls carefully matched for age and educationwere enrolled into the study. Patients and controls weresimilar in age, height, body weight, gender, years of educa-tion and IQ estimates (Table 1).

3.2. Volumetric data

3.2.1. Reduced absolute hippocampal volumes in depressed

patientsTable 2 summarizes volumetric data for depressed

patients and matched controls. While intracranial brainvolume was similar in patients and controls, depressedpatients displayed significantly reduced absolute total aswell as absolute right and absolute left hippocampalvolumes.

3.2.2. Reduced hippocampal volumes in depressed patientsafter normalization for intracranial brain volume

Normalization through division by intracranial vault ortotal brain volume is frequently used for comparison of

Table 1Characteristics of the study population

Depressed patients Control subjects

Number of subjects 24 14Gender ratio (female/male) 15/9 8/6

Age (years) 54.5 ± 11.9 53.8 ± 17.7Age range (years) 27–76 28–80Body weight (kg) 74.3 ± 18.4 81.1 ± 20.2Height (cm) 165.5 ± 8.2 170.9 ± 7.1

Education (years) 12.3 ± 2.2 12.6 ± 2.2MWT-B IQ (points) 106.1 ± 14.5 111.3 ± 16.2HAMD (points) 25.3 ± 5.9 n.a.

Continuous variables are displayed as mean values ± STD. MWT-B = multiple choice word fluency test B; HAMD = Hamilton depressionscale.

556 M. Colla et al. / Journal of Psychiatric Research 41 (2007) 553–560

hippocampal volume measurements (‘‘ICV-corrected vol-umes’’; e.g. Chantome et al., 1999; Fujioka et al., 2000;Eberling et al., 2004). ICV-corrected total hippocampalvolumes as well as ICV-corrected right hippocampal vol-umes were significantly reduced in the patient group (Table2). Importantly, we did not observe a correlation betweenICV-corrected total hippocampal volumes and age(r = 0.03, p = 0.87).

3.2.3. Reduced hippocampal volumes in depressed patients

after regressing on intracranial brain volume and age

Across groups, age was significantly negatively corre-lated with absolute total hippocampal volume (r = �0.38,p = 0.02) and intracranial brain volume (r = �0.57,p = 0.0002). Subgroup analyses demonstrated a significantinverse correlation between age and total hippocampal vol-ume in controls (n = 14; r = �0.81, p = 0.0005) and asomewhat weaker relationship in patients (n = 24;r = �0.25, p = 0.23). Furthermore, ICV was also highlycorrelated to absolute total hippocampal volume acrossgroups (r = 0.6, p < 0.0001).

Absolute hippocampal volumes were therefore residual-ized against intracranial brain volume and age (Table 2).Briefly, comparisons between patients and controls con-

Table 2Comparison of hippocampal volumes between depressed patients and control

Volumes (ml) Depressed patients

Absolute left hippocampal volume 1.68 ± 0.27Absolute right hippocampal volume 1.78 ± 0.26Absolute total hippocampal volume 3.46 ± 0.52Intracranial brain volume (ICV) 1057.5 ± 96.1

Left hippocampal (ICV-corr) 1.59 ± 0.22Right hippocampal (ICV-corr) 1.68 ± 0.21Total hippocampal (ICV-corr) 3.28 ± 0.43

Left hippocampal (ICV-age) �45.24 ± 233.55Right hippocampal (ICV-age) �60.66 ± 223.04Total hippocampal (ICV-age) �105.90 ± 443.95

Tissue volumes are displayed as mean values ± STD in cubic centimeters (�mrected for differences in brain size (division by intracranial brain volume); ICV-size and age).

firmed the negative effect of depressive illness on totaland right hippocampal volume measurements.

3.3. Effects of gender on hippocampal volume measurements

in the study sample

All hippocampal volume measurements were compara-ble between male (n = 15) and female participants(n = 23) across groups (absolute total hippocampal vol-ume: 3.78 ± 0.40 vs. 3.5 ± 0.52, ANOVA, age as covariate:F = 0.008, DF = 34, p = 0.93; ICV-corrected total hippo-campal volume: 3.38 ± 0.30 vs. 3.37 ± 0.43, ANOVA, ageas covariate: F = 1.47, DF = 34, p = 0.23; total hippocam-pal volume residualized against brain size and age(ICV-age): 5.7 ± 175.5 vs. �3.7 ± 223.7, ANOVA, age ascovariate F = 1.2, DF = 34, p = 0.28).

ANOVA with factors gender and study group (patientsvs. controls) and age as a covariate was also used to com-pare absolute hippocampal volume measurements. Forabsolute right hippocampal volume, this analysis yieldeda significant effect of study group (F = 4.7, DF = 30,p = 0.04, 1 � b = 0.55) whereas neither gender (F = 0.1,DF = 30, p = 0.74, 1 � b = 0.62) nor age (F = 1.92,DF = 30, p = 0.18, 1 � b = 0.26) reached statistical signif-icance. For absolute total hippocampal volume and abso-lute left hippocampal volume, the statistical power of thisanalysis was extremely low (absolute total hippocampalvolume: study group F = 3.2, DF = 30, p = 0.08,1 � b = 0.39; gender F = 0.4, DF = 30, p = 0.84,1 � b = 0.05; age F = 2.41, DF = 30, p = 0.13,1 � b = 0.31; absolute left hippocampal volume: studygroup F = 1.74, DF = 30, p = 0.2, 1 � b = 0.24, genderF = 0.004, p = 0.95, 1 � b = 0.05, age F = 2.66, DF = 30,p = 0.11, 1 � b = 0.34).

3.4. Clinical data

3.4.1. No significant correlation between baseline HAMDscores and hippocampal volume measurements

Patients’ baseline HAMD scores are given in Table 1. Wedid not observe a significant correlation between baseline

subjects

Control subjects F value DF p Value

1.86 ± 0.15 4.9 36 0.032.00 ± 0.18 8.0 36 0.013.86 ± 0.32 6.6 36 0.01

1096.7 ± 113.5 1.3 36 0.26

1.70 ± 0.10 2.9 36 0.101.83 ± 0.12 5.4 36 0.033.53 ± 0.20 4.3 36 0.05

77.56 ± 80.49 3.6 36 0.06103.98 ± 107.17 6.7 36 0.01181.54 ± 172.22 5.4 36 0.03

l). Absolute measurements are the uncorrected volumes. ICV-corr = cor-age = adjusted for differences in brain size and age (residualized after brain

Fig. 1. Correlation between hippocampal volumes and duration of indexepisode.

M. Colla et al. / Journal of Psychiatric Research 41 (2007) 553–560 557

HAMD scores (week �1) and total hippocampal volume(absolute total hippocampal volume: r = �0.1, p = 0.65;ICV-corrected total hippocampal volume: r = �0.05,p = 0.82; total hippocampal volume residualized againstbrain size and age: r = �0.07, p = 0.75).

3.4.2. Hippocampal volume measurements, duration of

illness, number of depressive episodes and duration of index

episode

In first episode patients, duration of illness equals theduration of the index episode whereas in all others, this var-iable represents the time [weeks] since the first occurrence ofa major depressive episode irrespective of disease-freeintervals. Duration of illness was significantly negativelycorrelated with total hippocampal volume (absolute totalhippocampal volume: r = �0.57, p = 0.0035; ICV-corrected total hippocampal volume: r = �0.41, p = 0.051;total hippocampal volume residualized against brain sizeand age: r = �0.42, p = 0.04) (Fig. 1). We also observed anegative correlation between the number of depressive epi-sodes and total hippocampal volume (absolute total hippo-campal volume: r = �0.27, p = 0.21; ICV-corrected totalhippocampal volume: r = �0.24, p = 0.26, total hippocam-pal volume residualized against brain size and age:r = �0.24, p = 0.26). The correlation between duration ofindex episode and hippocampal volume was r = �0.06,p = 0.78 (absolute total hippocampal volume), r = �0.42,p = 0.04 (ICV-corrected total hippocampal volume) andr = �0.37, p = 0.08 (total hippocampal volume residualizedagainst brain size and age).

3.5. Hormonal data

3.5.1. No significant correlation between baseline saliva

cortisol and hippocampal volume measurements

A complete set of cortisol measurements was availablefor 23 patients. We did not detect a significant correlationbetween morning cortisol obtained during the washout per-iod and any hippocampal volume measurements (absolutetotal hippocampal volume: r = �0.19, p = 0.38; ICV-cor-rected total hippocampal volume: r = �0.08, p = 0.72;total hippocampal volume residualized against intracere-bral brain volume and age: r = 0.07, p = 0.76). Similarly,we did not detect an association between saliva cortisol lev-els obtained at 1600 h during week �1 and any hippocam-pal volume measurements (absolute total hippocampalvolume: r = �0.26, p = 0.24, ICV-corrected total hippo-campal volume: r = 0.07, p = 0.75; total hippocampal vol-ume residualized against intracerebral volume and age:r = 0.04, p = 0.85).

3.5.2. Trend for higher hippocampal volumes in patients who

show a decrease in HPA-system activity under

pharmacotherapyWe calculated the difference between cortisol levels dur-

ing week +4 and week �1 (Dcort. = cortisol levels: week+4 � week �1). Negative values for Dcort. reflect a reduc-

tion in cortisol levels over time, indicating a decrease inoverall HPA-system activity between weeks 4 and �1.The correlation between morning Dcort. and hippocampalvolume measurements was r = �0.49, p = 0.02 (absolutetotal hippocampal volume), r = �0.39, p = 0.07 (ICV-cor-rected total hippocampal volume) and r = �0.39, p = 0.066(total hippocampal volume residualized against intracere-bral volume and age). Importantly, we also observed a sig-nificant correlation between duration of illness andmorning Dcort. (r = 0.45, p = 0.03). Multiple regressionof morning Dcort. against both duration of illness andage revealed a significant overall effect (r = �0.56,p = 0.023) and correlation coefficients of either variablealone showed a trend (duration of illness: t = 1.83,p = 0.081; age: t = 1.76, p = 0.09).

4. Discussion

This study investigated differences in hippocampal vol-umes of 24 unipolar depressed in-patients and 14 carefullymatched healthy controls. The principal finding of thisinvestigation is the significant reduction in hippocampalvolume measures relative to matched controls in hospital-ized patients suffering from major depression. Acrossgroups, we also observed a significant negative correlationbetween age and absolute hippocampal volume. Total hip-pocampal volume normalized by division through intracra-nial brain volume showed a significant negative correlationwith the duration of the index episode. Additionally, hip-pocampal volumes were significantly negatively correlatedwith duration of illness. Severity of disease (baselineHAMD scores) and baseline cortisol levels were not related

558 M. Colla et al. / Journal of Psychiatric Research 41 (2007) 553–560

to hippocampal volume. Finally, we observed a trend forhigher hippocampal volumes in patients who showed asubsequent decrease in HPA-system activity underpharmacotherapy.

The relationship between depression and hippocampalstructural alterations remains a topic of intense discussion.Both normal (e.g. Axelson et al., 1991; Inagaki et al., 2004;Rusch et al., 2001; Vakili et al., 2000) and reduced (e.g. She-line et al., 1996, 1999; MacQueen et al., 2003) hippocampalvolumes have been reported. Conflicting findings in volu-metric studies of the hippocampus in major depressionmay be related in large part to sample characteristics (e.g.study of outpatients: Vythilingam et al., 2004; recruitmentof depressed subjects via advertisements in local media:Rusch et al., 2001; depression in breast cancer survivorswho remitted without pharmacotherapy; Inagaki et al.,2004). On the whole, studies of more severely depressedpatients are more likely to demonstrate hippocampal struc-tural abnormalities (e.g. multiple depressive episodes: Mac-Queen et al., 2003; treatment-resistant depression: Hsiehet al., 2002; Shah et al., 1998). Two recent independentmeta-analyses of MRI studies (Campbell et al., 2004;Videbech and Ravnkilde, 2004) described reduced left andright hippocampal volumes in unipolar depressed patients.Here, in a group of relatively severely depressed patientswho required hospitalization we also found significant hip-pocampal atrophy. As compared to healthy controls,depressed patients displayed significantly reduced hippo-campal volumes bilaterally. Importantly, after normalizingfor differences in brain size, ICV-corrected total and righthippocampal volumes were still significantly reduced inpatients. This finding remained significant also after regress-ing for intracranial brain volume and age.

Numerous studies have described effects of aging on hip-pocampal volume (e.g. Walhovd et al., 2005; Raz et al.,1997). Across groups, we also observed a significant nega-tive correlation between age and absolute hippocampalvolumes as well as between age and ICV. Our results there-fore emphasize the necessity to control for age-associatedvolume loss in volumetric investigations of the hippocam-pal formation in depression. Normalization through divi-sion by ICV entirely eliminated the relationship betweenage and hippocampal volume in our dataset (correlationbetween ICV-corrected total hippocampal volume andage: r = 0.03, p = 0.87, see above). However, the intensityof the effect of aging has been reported to differ across dif-ferent brain areas (e.g. Allen et al., 2005; Raz et al., 2004).Therefore, partial correlations after adjusting for ICV andage were also performed.

The second aim of this investigation was to study hippo-campal volumes in depressed patients in relation to clinicalcharacteristics and cortisol status. Since the original obser-vation that plasma cortisol concentrations are elevated indepression (Sachar, 1967), dysregulation of the HPA systemand insensitivity to glucocorticoid-feedback suppressionhave been extensively investigated. The hippocampus is amain regulator of HPA-system feedback loops as demon-

strated in animal experiments. Furthermore, preclinicalresearch was able to show that prolonged exposure to glu-cocorticoids elicits morphologic changes in the hippocam-pus with atrophy of dendritic processes, impairedneurogenesis and possibly neuronal death (de Kloet et al.,1998; McEwen and Sapolsky, 1995). Clinical studies inpatients with Cushing disease have also confirmed smallerhippocampi (Bourdeau et al., 2002; Starkman et al., 1992).

Remarkably, we did not detect a connection betweeneither baseline depressive symptomatology (HAMDscores) or, more interestingly, between baseline saliva cor-tisol and hippocampal volume measurements. The latterfinding is consistent with results of a recent study showingthat reduced hippocampal volumes in depressed individu-als were not correlated with saliva cortisol levels (O’Brienet al., 2004). However, baseline psychopathology and base-line saliva cortisol reported here only represent a snapshotof the present intensity of disease severity and thus not nec-essarily past cortisol levels that might have had untowardseffects on the brain. In line with this interpretation, weobtained evidence for a negative association between theduration of the index episode before hospitalization andhippocampal volume. This observation also fits well witha recent study demonstrating that longer periods duringdepressive episodes without adequate antidepressant treat-ment are associated with reductions in hippocampal vol-ume (Sheline et al., 2003). Interestingly, our results alsoseem to suggest that larger hippocampal volume is associ-ated with faster normalization of HPA-hyperactivity undertreatment.

Like most other studies in the field, this investigation islimited by its retrospective nature. Especially in olderpatients with multiple depressive episodes, we found it dif-ficult to obtain reliable information regarding the durationof each individual episode. The ‘‘duration of illness’’ vari-able reported here is potentially more precise, but the valid-ity of the negative correlations between this variable andseveral hippocampal volume measurements is called intoquestion by the fact that age, medical history, drug effectsand long disease-free intervals have to be taken into consid-eration as important confounds. Still, it is interesting tonote that we also observed a trend for a higher numberof depressive episodes in patients with smaller hippocampalvolumes suggesting that hippocampal volume reduction isa result of cumulative insults.

In conclusion, our vigorous methodological approachwith distinct volume corrections adds to accumulating evi-dence of a negative association between depression andhippocampal volume, irrespective of age and gender. Mostlikely, hyperactivity of the HPA-system contributestowards hippocampal volume loss.

Acknowledgements

The authors thank Katharina Schmalfeld and WaltraudVanSyckel for editing the manuscript. This work wasfunded by DFG De 660/1-1 (to M.D. and I.H.).

M. Colla et al. / Journal of Psychiatric Research 41 (2007) 553–560 559

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