GABA Neurotransmission of the Suprachiasmatic Nucleus Is Modified During Rat Postnatal Development

Abstract

The suprachiasmatic nucleus (SCN) of the hypothalamus is the brain structure that controls circadian rhythms in mammals. The SCN is formed by two neuroanatomical regions: the ventral and dorsal. Gamma-aminobutyric acid (GABA) neurotransmission is important for the regulation of circadian rhythms. Excitatory GABA effects have been described in both SCN regions displaying a circadian variation. Moreover, the GABAergic system transfers photic information from the ventral to the dorsal SCN. However, there is almost no knowledge about GABA neurotransmission during the prenatal or postnatal development of the SCN. Here, we used whole-cell patch-clamp recordings to study spontaneous inhibitory postsynaptic currents (IPSCs) in the two SCN regions, at two zeitgeber times (day or night), and at four postnatal (P) ages: P3-5, P7-9, P12-15, and P20-25. The results herein show that the three analyzed parameters of the IPSCs, frequency, amplitude, and decay time, were significantly affected by the postnatal age: mostly, the IPSC frequency increased with age, principally in the ventral SCN in both day and night recordings; similarly, the amplitude of IPSCs augmented with age, especially at night, whereas the IPSC decay time was reduced (it was faster) with postnatal age, mainly during the day. Our findings first reveal that parameters of GABA neurotransmission are modified by postnatal development, implying that synaptic adjustments are required for an appropriate maturation of the GABAergic system in the SCN.

Coupling Between Subregional Oscillators Within the Suprachiasmatic Nucleus Determines Free-Running Period in the Rat

“…We first chose parameters for vl and dm that ensure τ V < τ D and free-running τ VD > 24 h. Then, we fixed a T22 intensity and verified the range of coupling strengths that were weak enough to allow entrainment of vl but not of dm under T22, while strong enough to allow their refusion under DD. This range was (0.01 < C < 0.15); thus, if C > 0.15 (too strong), vl and dm do not dissociate under T22, but if C < 0.01 (too weak), they do not refuse in DD due to their different τ (Osuna-Lopez et al, 2021; Suppl. Fig.…”