Embryonic development of GABAergic terminals in the mouse hypothalamic nuclei involved in feeding behavior

Action Sequence Learning Is Impaired in Genetically Modified Mice with the Suppressed GABAergic Transmission from the Thalamic Reticular Nucleus to the Thalamus

The thalamic reticular nucleus (TRN) is a thin sheet of GABAergic neurons surrounding the thalamus, and it regulates the activity of thalamic relay neurons. The TRN has been reported to be involved in sensory gating, attentional regulation, and some other functions. However, little is known about the contribution of the TRN to sequence learning. In the present study, we examined whether the TRN is involved in reward-based learning of action sequence with no eliciting stimuli (operant conditioning), by analyzing the performance of male and female Avp-Vgat-/- mice (Vgatflox/flox mice crossed to an Avp-Cre driver line) on tasks conducted in an operant box having three levers. Our histological and electrophysiological data demonstrated that in adult Avp-Vgat-/- mice, vesicular GABA transporter (VGAT) was absent in most TRN neurons and the GABAergic transmission from the TRN to the thalamus was largely suppressed. The performance on a task in which mice needed to press an active lever for food reward showed that simple operant learning of lever pressing and learning of win-stay and lose-shift strategies are not affected in Avp-Vgat-/- mice. In contrast, the performance on a task in which mice needed to press three levers in a correct order for food reward showed that learning of the order of lever pressing (action sequence learning) was impaired in Avp-Vgat-/- mice. These results suggest that the TRN plays an important role in action sequence learning.

Hypothalamic GABAergic neurocircuitry in the regulation of energy homeostasis and sleep/wake control

Gamma-aminobutyric acid (GABAergic) neuron, as one of important cell types in synaptic transmission, has been widely involved in central nervous system (CNS) regulation of organismal physiologies including cognition, emotion, arousal and reward. However, upon their distribution in various brain regions, effects of GABAergic neurons in the brain are very diverse. In current report, we will present an overview of the role of GABAergic mediated inhibitory neurocircuitry in the hypothalamus, underlying mechanism of feeding and sleep homeostasis as well as the characteristics of latest transcriptome profile in order to call attention to the GABAergic system as potentially a promising pharmaceutical intervention or a deep brain stimulation target in eating and sleep disorders.

Development and persistence of neuropathic pain through microglial activation and KCC2 decreasing after mouse tibial nerve injury

Gamma-amino butyric acid (GABA) is an inhibitory neurotransmitter in the mature brain, but is excitatory during development and after motor nerve injury. This difference in GABAergic action depends on the intracellular chloride ion concentration ([Cl-]i), primarily regulated by potassium chloride co-transporter 2 (KCC2). To reveal precise processes of the neuropathic pain through changes in GABAergic action, we prepared tibial nerve ligation and severance models using male mice, and examined temporal relationships amongst changes in (1) the mechanical withdrawal threshold in the sural nerve area, (2) localization of the molecules involved in GABAergic transmission and its upstream signaling in the dorsal horn, and (3) histology of the tibial nerve. In the ligation model, tibial nerve degeneration disappeared by day 56, but mechanical allodynia, reduced KCC2 localization, and increased microglia density remained until day 90. Microglia density was higher in the tibial zone than the sural zone before day 21, but this result was inverted after day 28. In contrast, in the severance model, all above changes were detected until day 28, but were simultaneously and significantly recovered by day 90. These results suggested that in male mice, allodynia may be caused by reduced GABAergic synaptic inhibition, resulting from elevated [Cl-]i after the reduction of KCC2 by activated microglia. Furthermore, our results suggested that factors from degenerating nerve terminals may diffuse into the sural zone, whereby they induced the development of allodynia in the sural nerve area, while other factors in the sural zone may mediate persistent allodynia through the same pathway.

Hyper-Formation of GABA and Glycine Co-Releasing Terminals in the Mouse Cerebellar Nuclei after Deprivation of GABAergic Inputs from Purkinje Cells

GABA and glycine are inhibitory neurotransmitters. However, the mechanisms underlying the formation of GABAergic and glycinergic synapses remain unclear. The influence of GABAergic input deprivation on inhibitory terminal formation was investigated using Purkinje cell (PC)-specific vesicular GABA transporter (VGAT) knockout (L7-VGAT) mice, in which GABA release from PCs diminishes in an age-dependent manner. We compared the late development of GABAergic and glycinergic terminals in the cerebellar nucleus (CN) between control and L7-VGAT mice. In the control CN, the density of glutamate decarboxylase (GAD)-positive dots remained unchanged between postnatal 2 months (P2M) and 13 months (P13M), whereas glycine transporter 2 (GlyT2)-positive dots increased in density during this time frame. No difference in the density of GlyT2-positive dots was observed between control and L7-VGAT mice at P2M, but the density was significantly higher in the L7-VGAT fastigial nuclei (FN) than the control FN at P13M. When VGAT was absent from PC terminals, GlyT2-positive dots included GAD and VGAT and formed synapses. These results indicated that GABAergic terminals were formed by P2M, glycinergic terminals were actively formed after P2M, and more glycinergic terminals were formed in the L7-VGAT FN than in the control FN, suggesting that the increased glycinergic terminals may derive from interneurons within the FN and may also release GABA. These results suggest that the deprivation of GABAergic inputs from PCs may accelerate the formation of co-releasing terminals derived from interneurons and that the inhibitory terminal numbers and types may be regulated by the quantity of functional GABAergic inputs.

Circuit development in the master clock network of mammals

Daily rhythms are generated by the circadian timekeeping system, which is orchestrated by the master circadian clock in the suprachiasmatic nucleus (SCN) of mammals. Circadian timekeeping is endogenous and does not require exposure to external cues during development. Nevertheless, the circadian system is not fully formed at birth in many mammalian species and it is important to understand how SCN development can affect the function of the circadian system in adulthood. The purpose of the current review is to discuss the ontogeny of cellular and circuit function in the SCN, with a focus on work performed in model rodent species (i.e., mouse, rat, and hamster). Particular emphasis is placed on the spatial and temporal patterns of SCN development that may contribute to the function of the master clock during adulthood. Additional work aimed at decoding the mechanisms that guide circadian development is expected to provide a solid foundation upon which to better understand the sources and factors contributing to aberrant maturation of clock function.

A proteomics-metabolomics approach indicates changes in hypothalamic glutamate-GABA metabolism of adult female rats submitted to intrauterine growth restriction

PURPOSE

Intrauterine growth restriction (IUGR) has been shown to induce the programming of metabolic disturbances and obesity, associated with hypothalamic derangements. The present study aimed at investigating the effects of IUGR on the protein and metabolite profiles of the hypothalamus of adult female rats.

METHODS

Wistar rats were mated and either had ad libitum access to food (control group) or received only 50% of the control intake (restricted group) during the whole pregnancy. Both groups ate ad libitum throughout lactation. At 4 months of age, the control and restricted female offspring was euthanized for blood and tissues collection. The hypothalami were processed for data independent acquisition mass spectrometry-based proteomics or targeted mass spectrometry-based metabolomics.

RESULTS

The adult females submitted to IUGR showed increased glycemia and body adiposity, with normal body weight and food intake. IUGR modulated significantly 28 hypothalamic proteins and 7 hypothalamic metabolites. The effects of IUGR on hypothalamic proteins and metabolites included downregulation of glutamine synthetase, glutamate decarboxylase, glutamate dehydrogenase, isocitrate dehydrogenase, α-ketoglutarate, and up-regulation of NADH dehydrogenase and phosphoenolpyruvate. Integrated pathway analysis indicated that IUGR affected GABAergic synapse, glutamate metabolism, and TCA cycle, highly interconnected pathways whose derangement has potentially multiple consequences.

CONCLUSION

The present findings suggested that the effects of IUGR on GABA/glutamate-glutamine cycle may be involved in the programming of obesity and hyperglycemia in female rats.