Behavioral alterations occur without changes in amyloid tracer distribution in a streptozotocin-induced mouse model of type 1 diabetes

Background: Diabetes mellitus is associated with cognitive dysfunction and an increased risk of dementia [1]. Experimental and clinical studies further suggest that diabetes-related brain dysfunction may involve neurovascular [2] and glymphatic disturbances [3]; however, early-stage functional changes preceding overt pathology remain poorly characterized.

Aim: This study aimed to investigate early metabolic, behavioral, and brain alterations in a streptozotocin (STZ)-induced mouse model of diabetes, with a focus on locomotor activity, cognitive performance, and regional amyloid distribution.

Methods: Male CD1 mice (28–31 weeks old) received multiple low-dose STZ injections (50 mg/kg for 5 consecutive days) for the development of Type 1 Diabetes Mellitus, while control animals received citrate buffer. Metabolic and behavioral analyses were performed in control (n = 5) and diabetic (n = 7) groups. Fasting blood glucose (FBG) and body weight were monitored at weeks 1, 2, and 4. Behavioral assessments were conducted one month post-induction using the open field test (OFT) and Y-maze. Spontaneous alternation was used as an index of task performance. For glymphatic assessment, fluorescently labeled amyloid beta (Aβ-488) was injected via the cisterna magna, and brains were collected 15 minutes post-injection. Tissues were fixed in paraformaldehyde, cryoprotected in sucrose gradients, embedded in OCT, and sectioned at 20 µm thickness. Amyloid distribution was quantified across cortex, hippocampus, dentate gyrus, brain parenchyma, and ventricles. Imaging data were obtained from 8 animals, yielding multiple observations per region (e.g., cortex n = 42). Statistical analyses included Welch’s t-test, two-way ANOVA, and mixed-effects modeling.

Results: STZ-treated mice exhibited significantly elevated fasting blood glucose levels compared to controls across all time points (group effect p < 0.0001; time p = 0.014; interaction p = 0.02). Post-hoc analysis confirmed higher glucose levels in diabetic mice at weeks 1 (p = 0.004), 2 (p = 0.0004), and 4 (p = 0.0007). Body weight was significantly reduced in diabetic mice (p = 0.006). In the OFT, no significant differences were observed in locomotor activity parameters; however, diabetic mice displayed increased freezing behaviour without changes in time spent in the center (p = 0.67). In the Y-maze, diabetic mice showed reduced spontaneous alternation (p = 0.03), accompanied by decreased total arm entries (p = 0.03). Amyloid distribution did not differ significantly between groups in any region analyzed: cortex (n = 42 observations, 8 mice, p = 0.50), hippocampus (n = 36, p = 0.72), dentate gyrus (n = 36, p = 1.00), brain parenchyma (n = 36, p = 0.53), and ventricles (n = 28, p = 0.72).

Conclusion: Early-stage diabetes induces measurable alterations in behavioral performance prior to detectable changes in regional amyloid distribution. Diabetic mice showed altered freezing behaviour and Y-maze task performance, whereas early amyloid tracer distribution at 15 minutes remained unchanged across the analysed brain regions. These results suggest that functional behavioural changes may emerge before detectable alterations in early glymphatic tracer influx.

References

1. Biessels, G. J., & Despa, F. (2018). Cognitive decline and dementia in diabetes mellitus: mechanisms and clinical implications. Nature Reviews Endocrinology, 14(10), 591-604.
2. Özkan, E., Çetin-Taş, Y., Şekerdağ, E., Yiğit, B., Shomalizadeh, N., Sapancı, S., … & Gürsoy-Özdemir, Y. (2023). Hyperglycemia with or without insulin resistance triggers different structural changes in brain microcirculation and perivascular matrix. Metabolic Brain Disease, 38(1), 307-321.
3. Jiang, Q., Zhang, L., Ding, G., Davoodi-Bojd, E., Li, Q., Li, L., … & Zhang, Z. (2017). Impairment of the glymphatic system after diabetes. Journal of Cerebral Blood Flow & Metabolism, 37(4), 1326-1337.