Age-dependent concomitant changes in synaptic dysfunction and GABAergic pathway in the APP/PS1 mouse model

Synaptic dysfunction is a well-documented manifestation in animal models of Alzheimer's disease pathology. In this context, numerous studies have documented reduction in the functionality of synapses in various models. In addition, recent research has shed more light on increased excitability and its link to seizures and seizure-like activities in AD patients as well as in mouse models. These reports of hyperexcitability contradict the observed reduction in synaptic function and have been suggested to be as a result of the interplay between inhibitory and excitatory neuronal mechanism. The present study therefore investigates functional deficiency in the inhibitory system as complementary to the identified alterations in the glutamate excitatory pathway in AD. Since synaptic function deficit in AD is typically linked to progression/pathology of the disease, it is important to determine whether the deficits in the GABAergic system are functional and can be directly linked to the pattern of the disruption documented in the glutamate system. To build on previous research in this field, experiments were designed to determine if previously documented synaptic dysfunction in AD models is concomitantly observed with excitation/inhibition imbalance as suggested by observation of seizure and seizure-like pathology in such models. We report changes in synaptic function in aged APPPS1 mice not observable in the younger cohort. These changes in synaptic function are furthermore accompanied by alteration in the GABAergic neurotransmission. Thus, age-dependent alteration in the inhibitory/excitatory balance might underpin the symptomatic changes observed with the progression of Alzheimer's disease pathology including sleep disturbance and epileptic events.

Altered gastrointestinal and metabolic function in the GPR39-obestatin receptor-knockout mouse

BACKGROUND & AIMS

The G-protein-coupled receptor GPR39 is a member of a family that includes the receptors for ghrelin and motilin. Recently the peptide obestatin was identified as a natural ligand for GPR39. The objective of this study was to gain insight into the biological function of the GPR39 receptor.

METHODS

GPR39(-/-) mice were generated and analyzed.

RESULTS

Endogenous GPR39 expression was detected in the brain (septum-amygdala) and the gastrointestinal system (parietal cells, enterocytes, neurons, and pancreas). Gastric emptying of a solid meal (measured by the (14)C octanoic breath test) in GPR39(-/-) mice was accelerated significantly with a gastric half-emptying time of 49.5 +/- 2.2 minutes compared with 86.9 +/- 8.4 minutes in GPR39(+/+) mice. A more effective expulsion of distally located pellets (30%-75% of length) was observed in the colon of GPR39(-/-) mice. Four hours after pylorus ligation, the volume of gastric secretion was increased significantly (GPR39(-/-): 638 +/- 336 microL; GPR39(+/+): 225 +/- 170 microL), but gastric acid secretion was unchanged. The mature body weight and body fat composition of GPR39(-/-) mice was significantly higher compared with GPR39(+/+) mice, but this was not related to hyperphagia because 24-hour food intake did not differ between both genotypes. In contrast, deficiency of the GPR39 receptor led to reduced hyperphagia after fasting. The cholesterol levels were increased significantly in the GPR39(-/-) mice.

CONCLUSIONS

Our data partially confirm and extend the described in vivo effects of obestatin and suggest that this peptide plays a functional role in the regulation of gastrointestinal and metabolic function through interaction with the GPR39 receptor.