Converging evidence points towards a role of insulin signaling in regulating compulsive behavior

Abstract

Obsessive-compulsive disorder (OCD) is a neuropsychiatric disorder with childhood onset, and is characterized by intrusive thoughts and fears (obsessions) that lead to repetitive behaviors (compulsions). Previously, we identified insulin signaling being associated with OCD and here, we aim to further investigate this link in vivo. We studied TALLYHO/JngJ (TH) mice, a model of type 2 diabetes mellitus, to (1) assess compulsive and anxious behaviors, (2) determine neuro-metabolite levels by 1 H magnetic resonance spectroscopy (MRS) and brain structural connectivity by diffusion tensor imaging (DTI), and (3) investigate plasma and brain protein levels for molecules previously associated with OCD (insulin, Igf1, Kcnq1, and Bdnf) in these subjects. TH mice showed increased compulsivity-like behavior (reduced spontaneous alternation in the Y-maze) and more anxiety (less time spent in the open arms of the elevated plus maze). In parallel, their brains differed in the white matter microstructure measures fractional anisotropy (FA) and mean diffusivity (MD) in the midline corpus callosum (increased FA and decreased MD), in myelinated fibers of the dorsomedial striatum (decreased FA and MD), and superior cerebellar peduncles (decreased FA and MD). MRS revealed increased glucose levels in the dorsomedial striatum and increased glutathione levels in the anterior cingulate cortex in the TH mice relative to their controls. Igf1 expression was reduced in the cerebellum of TH mice but increased in the plasma. In conclusion, our data indicates a role of (abnormal) insulin signaling in compulsivity-like behavior.

Conflict of interest statement

I.v.deV., H.A., M.B., C.O., N.R., J.C., J.v.A., A.H., S.W. and G.P. report no financial conflict of interest. S.B. is a director of Psynova Neurotech Ltd and PsyOmics Ltd. In the past 2 years, J.K.B. was a consultant to/member of advisory board of/and/or speaker for Janssen-Cilag BV, Eli Lilly, Shire, Novartis, Roche, and Servier. J.C.G. has in the past three years been a consultant to Boehringer Ingelheim GmbH. Neither J.K.B. nor J.C.G. are employees of any of these companies, and neither are stock shareholders of any of these companies.

Figures

Fig. 1. Increased compulsive- and anxiety-like behaviours are observed in TALLYHO/JngJ mice while compulsive behaviour correlates with blood glucose levels.

a TALLYHO/JngJ (TH) mice show increased compulsive behavior compared to SWR/J mice (the control strain), as seen in a decrease in the spontaneous alternation behavior (37.4 ± 6.8 vs. 62.3 ± 2.1% spontaneous alternation, n = 9 per strain, p = 0.006). b In addition, an increase in the number of repeated arm entries was observed in the TH mice (11.3 ± 4.0 vs. 1.48 ± 0.74% of the total arm entries being repeated arm entries, n = 9 per strain, p = 0.041). c No difference was observed between the two strains in compulsive marble burying (8.2 ± 1.7 vs. 10.1 ± 1.1 marbles buried, n = 9 per strain, p = 0.365). d In addition, TH mice display increased anxiety behavior: a trend was observed toward a TH mice spending less time in the center zone of the open field compared with SWR/J mice (204.6 ± 26.6 vs. 254.2 ± 16.5 s, n = 4 per strain, p = 0.174). e More importantly, TH mice spent less time in the open arms of the elevated plus maze (EPM), suggesting increased anxiety (3.8 ± 0.98 versus 23.7 ± 2.97 s, n = 7 [TH] and n = 9 [SWR/J], p = 0.000096). f Blood glucose levels were negatively correlated with spontaneous alternation behavior (r = −0.495, n = 18, p = 0.037)

Fig. 2. MRS revealed differences in the metabolite content of the dorsomedial striatum (DMS) and anterior cingulate cortex (ACC) in TALLYHO/JngJ mice.

The metabolites of interest are glutamate (Glu), glutamine (Gln), taurine (Tau), N-acetylaspartate (NAA), sum of myo-Inositol and glycine (mI + Gly), total choline (tCho), glucose (Glc), GABA, and glutathione (GSH). MRS data are expressed as ratios of the metabolites relative to the total creatine (tCr) levels. a Glucose (Glc) ratios (relative to tCr) were increased in brains of TALLYHO/JngJ (TH) mice in the DMS compared with the control strain (SWR/J mice) (0.527 ± 0.025 vs. 0.308 ± 0.035, n = 9 [TH] and n = 7 [SWR/J], p = 0.0031). b An increase in glutathione (GSH) ratios (relative to tCr) was observed in the ACC of TH mice (0.325 ± 0.021 and 0.212 ± 0.028, n = 9 [TH] and n = 6 [SWR/J], p = 0.047). Differences in the other metabolites (glutamate [Glu] glutamine [Gln], taurine [Tau], N-acetylaspartate [NAA], the sum of myo-Inositol and glycine [mI + Gly], total choline [tCho], and GABA) failed to reach significance. c Blood glucose concentrations correlated with DMS Glc concentration (r = 0.664, n = 16, p = 0.005). d No significant correlation was observed between the blood glucose concentrations and ACC Glc concentration (r = 0.415, n = 16, p = 0.11). e Interestingly, we observed a significant negative correlation between glucose levels in the DMS specifically, and spontaneous alternation (r = −0.658, n = 16, p = 0.006)

Fig. 3. DTI showed differences in white matter microstructure in brains of TALLYHO/JngJ (TH) mice compared to the control strain (SWR/J).

a The fractional anisotropy (FA) was increased in the corpus callosum (CC) (0.547 ± 0.008 vs. 0.478 ± 0.01, n = 9 per strain, p = 3.7E-05) and decreased in the dorsomedial striatum (DMS) (0.18 ± 0.01 vs. 0.20 ± 0.01, n = 9 per strain, p = 0.01) and superior cerebellar peduncle (SCP) (0.28 ± 0.02 vs. 0.36 ± 0.01, n = 9 per strain, p = 0.003) of TH mice. No differences were observed in the orbitofrontal cortex (OFC), anterior cingulate cortex (ACC), and nucleus accumbens (NAcc). b The same three brain regions showed a decrease in the mean diffusivity (MD) in TH mice: CC (7.44E-04 ± 5.56E-06 vs. 7.78E-04 ± 1.21E-05, n = 9 per strain, p = 0.03), DMS (7.17E-04 ± 1.10E-05 vs. 7.58E-04 ± 1.18E-05, n = 9 per strain, p = 0.02) and SCP (6.50E-04 ± 2.89E-05 vs. 7.44E-04 ± 1.30E-05, n = 9 per strain, p = 0.01). c, d Compulsivity-like behavior as shown by the spontaneous alternation is positively correlated to the FA in DMS and SCP (r = 0.734, n = 18, p = 0.002 and r = 0.548, n = 18, p = 0.02, respectively)

Fig. 4. TALLYHO/JngJ mice show changes in cerebellar and plasma Insulin-like growth factor 1 protein levels.

a The concentration of Insulin-like growth factor 1 (Igf1) is reduced in the cerebellum of TALLYHO/JngJ (TH) mice compared with their controls, SWR/J mice (90.2 ± 12.3 vs. 168.7 ± 15.5 pg/ml, n = 6 [TH] and n = 8 [SWR/J], p = 0.0002). b Interestingly, the concentration of Igf1 is increased in the blood plasma of TH mice (1217.4 ± 453.6 vs. 97.6 ± 22.2 pg/ml, n = 7 [TH] and n = 4 [SWR/J], p = 0.049)