Emotional and Spontaneous Locomotor Behaviors Related to cerebellar Daidzein-dependent TrkB Expression Changes in Obese Hamsters

Abstract

Current evidence supports the beneficial role of phytoestrogens in metabolic diseases, but their influences on spontaneous motor and anxiety behaviors plus neuroprotective effects have still not been completely elucidated. With the present study, neuro-behavioral activities were correlated to daidzein (DZ)-dependent expression changes of a high affinity catalytic receptor for several neurotrophins, and namely tropomyosin-related kinase B receptor (TrkB) in the cerebellar cortex of high-fat diet (HFD) hamsters (Mesocricetus auratus). Indeed, these changes appear to be tightly linked to altered plasma lipid profiles as shown by reduced low-density lipoproteins plus total cholesterol levels in DZ-treated obesity hamsters accounting for increased spontaneous locomotor together with diminished anxiety activities in novel cage (NCT) and light/dark box (LDT) tests. For this latter case, the anxiolytic-like hamsters spent more time in the light compartment, which was retained the aversive area of the LDT box. As for the evaluation of the neurotrophin receptor site, significantly elevated TrkB levels were also detected, for the first time, in the cerebellum of obese hamsters treated with DZ. In this condition, such a treatment widely led to an overall improvement of HFD-induced neurodegeneration damages, above all in the Purkinje and granular layers of the cerebellum. In this context, the notably active TrkB signaling events occurring in a DZ-dependent manner may turn out to be a key neuroprotective element capable of restoring normal emotional and spontaneously linked locomotor behaviors regulated by cerebellar cortical areas especially in obesity-related conditions.

Keywords: Anxiety; Crebellum; Neuroprotection; Obesity; Polyphenols; TrkB.

Fig. 1

Evaluation of the anxiolytic activity of DZ using the LDT on A) time (sec ± S.E.M., compared to the total duration of the test of 300 sec) spent in the light compartment and in the dark compartment, latency to enter the dark compartment, rearing (time spent standing on the hind legs), and risk assessment (time in which incomplete head and/or body extends that dips from the dark to the light compartment); B) number (average of the number of times ± S.E.M.) of transitions between compartments and risk assessment in CTRL, HFD, and HFD + DZ 2w hamster groups. Statistical differences were evaluated by using a two-way ANOVA followed by post hoc Newman-Keul’s multiple range test when p-value < 0.05. *p < 0.05, **p < 0.01, ***p < 0.001. *Significant difference compared with CTRL group; a, b, c Significant difference of HFD + DZ 2w compared with HFD group

Fig. 2

Evaluation of the anxiolytic activity of DZ using the LDT on A) time (sec ± S.E.M., compared to the total duration of the test of 300 sec) spent in the light compartment and in the dark compartment, latency to enter the dark compartment, rearing, and risk assessment; B) number (average of the number of times ± S.E.M.) of transitions between compartments and risk assessment-number in CTRL, HFD, and HFD + DZ 4w hamster groups. Statistical calculations were handled as reported in Fig. 1

Fig. 3

Evaluation of the spontaneous locomotor activity in A) CTRL, HFD, and HFD + DZ 2w and B) CTRL, HFD, and HFD + DZ 4w hamster groups using the NCT on time (sec ± S.E.M. compared to the total duration of the test of 300 sec) spent in: mobility (movement in the cage), rearing (standing on hind limbs), wall-rearing (standing on hind limbs and touching the walls of the cage with forelimbs), sniffing (sniffing sawdust), digging (digging sawdust with forelimbs, often kicking it away with hind limbs), grooming (licking own fur, sometimes using forepaws, passing them over the nose with a series of brief, horizontal movements), and climbing (escape behavior). Statistical calculations were handled as reported in Fig. 1

Fig. 4

Western blot analysis of TrkB expression (O.D. ± S.E.M.) in cerebellar cortex of A) CTRL, HFD, and HFD + DZ 2w and B) CTRL, HFD, and HFD + DZ 4w hamsters. C) Representative image of coronal cerebellar cortex sections stained with (I) Nissl and (II; III; IV) ACS. Photograms of ACS showing dark damaged neuronal perikarya that indicate the different levels of neurodegeneration (arrows; Scale bar = 100 µm). D) Estimation of neurodegeneration (% ± S.E.M.) of degenerated neurons in ML, PL, and GL of HFD, and HFD + DZ 4w groups with respect to CTRL. Statistical calculations were handled as reported in Fig. 1. Abbreviations: ML, molecular layer; PL, Purkinje layer; GL, granular layer