Glycine-activated chloride currents of neurons freshly isolated from the prefrontal cortex of young rats

Abstract

Strychnine-sensitive glycine receptors (GlyR) play a major role in the excitability of CNS neurons and are also a major target of many drugs including some general anesthetics and ethanol. The prefrontal cortex (PFC) is an important substrate responsible for cognitive function and for sedation, as well as hypnosis (unconsciousness) which is induced by general anesthetics and ethanol. However, the functions and the physiological and pharmacological properties of GlyRs in mature PFC neurons have not been well studied. In this study, whole-cell currents induced by glycine (IGly) were recorded from freshly isolated PFC neurons of Sprague-Dawley rats aged 5 to 39 postnatal days (neonatal, P5–12; weanling, P17–21 and peri-adolescent, P30–39). We found that most of the neurons examined were responsive to glycine and the response was concentration dependent. With the increase of age, the sensitivity to glycine was significantly decreased and the sensitivity to picrotoxin was significantly increased. Conversely, the changes in sensitivity to strychnine were not significant. Interestingly, IGly of all age groups was suppressed (to different scope) by low concentrations of picrotoxin (≤ 30 µM), which selectively blocked α homomeric GlyRs. Conversely, about 20–65% of IGly remained in the presence of 300 µM picrotoxin, suggesting the picrotoxin-resistant subtype the αβ heteromeric GlyR, was also present. These data provide the first evidence that there are at least two subtypes of functional GlyRs in the PFC neurons of young rats, and their physiological and pharmacological properties change substantially during maturation.

Glycine receptor α3 and α2 subunits mediate tonic and exogenous agonist-induced currents in forebrain

“…In the present study, we first confirmed the presence of specific GlyR-mediated currents in the PFC, striatum, hippocampus, amygdala, and BNST of adolescent mice. Our results are consistent with earlier electrophysiological reports of glycine-activated currents in brain (22,(24)(25)(26)(27)44), as well as studies of GlyR mRNA and protein expression, which demonstrate that four (α1, α2, α3, and β) of the five known GlyR subunits are expressed in the mammalian brain (30,31,36,37,45,46).…”

“…GlyRs also mediate synaptic inhibition in the auditory brainstem (18)(19)(20) and extrasynaptic inhibition in the dorsal raphé (21). There have been a number of reports of glycine responses and expression of strychnine-sensitive GlyRs in higher brain regions (22)(23)(24)(25)(26)(27). However, the nature and function of these receptors have remained obscure.…”

Ethanol Reduces Neuronal Excitability of Lateral Orbitofrontal Cortex Neurons Via a Glycine Receptor Dependent Mechanism

“…A similar finding was reported for neurons in the basolateral amygdala (McCool and Farroni, 2001) suggesting that while a1 GlyRs are the dominant subtype in adult spinal cord (Lynch, 2009), a2 containing GlyRs may generate a significant population of functional neuronal GlyRs in higher brain areas. This conclusion is supported by findings from a recent study showing that dissociated rat PFC neurons generate robust glycine-activated currents that are strychnine-sensitive and exhibit an age-dependent change in picrotoxin sensitivity suggesting a loss of GlyRb subunits (Lu and Ye, 2011). Together with the PCR data, these results suggest that neurons in frontal cortical areas may express substantial numbers of homomeric a2 GlyRs.…”

Strychnine-sensitive glycine receptors on pyramidal neurons in layers II/III of the mouse prefrontal cortex are tonically activated

“…In dissociated PFC neurons, PTX has been shown to block glycine currents (Lu and Ye 2011). We subsequently demonstrated the presence of tonic GlyRs by applying strychnine, which elicited a significant shift (ϳ15 pA) in baseline current in the absence of an effect on the frequency of GABAmediated sIPSCs or isolated mIPSCs.…”

“…In the spinal cord, synaptic GlyRs are formed as a heteropentamer of ␣ 1 -and ␤-subunits; the presence of a ␤-subunit confers synaptic localization through its binding to gephyrin, an anchoring protein that is enriched at synaptic sites (Kirsch 2006). In structures of the postnatal forebrain, there is very low expression of GlyR␣ 1 mRNA compared with the spinal cord, but the expression of GlyR␣ 2 and GlyR␣ 3 has been reported in several brain regions, including the PFC (Jonsson et al 2009;Malosio et al 1991).…”