Stellate and pyramidal neurons in goldfish telencephalon respond differently to anoxia and GABA receptor inhibition

Abstract

With oxygen deprivation, the mammalian brain undergoes hyperactivity and neuronal death while this does not occur in the anoxiatolerant goldfish (Carassius auratus). Anoxic survival of the goldfish may rely on neuromodulatory mechanisms to suppress neuronal hyper-excitability. As γ-aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the brain, we decided to investigate its potential role in suppressing the electrical activity of goldfish telencephalic neurons. Utilizing whole-cell patch-clamp recording, we recorded the electrical activities of both excitatory ( pyramidal) and inhibitory (stellate) neurons. With anoxia, membrane potential (V m ) depolarized in both cell types from −72.2 mV to −57.7 mV and from −64.5 mV to −46.8 mV in pyramidal and stellate neurons, respectively. While pyramidal cells remained mostly quiescent, action potential frequency (AP f ) of the stellate neurons increased 68-fold. Furthermore, the GABA A receptor reversal potential (E GABA ) was determined using the gramicidin perforated-patch-clamp method and found to be depolarizing in pyramidal (−53.8 mV) and stellate neurons (−42.1 mV). Although GABA was depolarizing, pyramidal neurons remained quiescent as E GABA was below the action potential threshold (−36 mV pyramidal and −38 mV stellate neurons). Inhibition of GABA A receptors with gabazine reversed the anoxiamediated response. While GABA B receptor inhibition alone did not affect the anoxic response, co-antagonism of GABA A and GABA B receptors (gabazine and CGP-55848) led to the generation of seizure-like activities in both neuron types. We conclude that with anoxia, V m depolarizes towards E GABA which increases AP f in stellate neurons and decreases AP f in pyramidal neurons, and that GABA plays an important role in the anoxia tolerance of goldfish brain.

GABAA receptors activate fish feeding behaviour via two distinct functional pathways

“…The brain was rapidly removed, placed into agar block and transferred to a Leica VT1000 vibratome slicing chamber. For slice preparation, we used telencephalon as a part of fish brain which is tightly connected to feeding behaviour (Lin et al, 2000), and where GABAR response in C. gibelio was clearly demonstrated (Hossein-Javaheri et al, 2017).…”

GABA receptor inhibition and severe hypoxia induce a paroxysmal depolarization shift in goldfish neurons

“…Owing to close relationship between the two species, it is reasonable to assume that goldfish also express both GABA A receptor subtypes. In a previous study, we reported that when exposed to severe hypoxia without any pharmacological manipulations, membrane potential of both stellate and pyramidal neurons shift toward a depolarizing GABA A reversal potential (E GABA ), inducing an inhibitory shunt in pyramidal cells only; this depolarization sufficiently generates action potentials in the inhibitory stellate cells, suppressing the overall electrical activity of the brain (10). In this experiment, we observed that the application of both 100 μM bicuculline (Fig.…”

“…While recording the electrical activity of goldfish telencephalic neurons following inhibition of GABA A/B receptors, we noticed unusual action potentials that deviated from the expected patterns: depolarization followed by a hyperpolarization ± afterhyperpolarization (10). Particularly of interest, were apparent seizure-like activities (SLA) and a paroxysmal depolarization shift (PDS) in these neurons.…”

“…Action potential threshold (AP th ) was determined by injecting current in steps (1 nA) until an AP was elicited. Recordings were obtained from both pyramidal and stellate telencephalic neurons, and each cell was identified electrophysiologically as described previously (20,10). In short, pyramidal neurons demonstrate rapid adaptation in response to a suprathreshold current, whereas stellate cells showed no accommodation in response to the same stimulus.…”

“…Meanwhile, neuronal membrane potential shifts toward a depolarizing GABAergic reversal potential through a "shunting inhibition" mechanism in goldfish neurons. Although depolarizing, this mechanism simultaneously suppresses excitatory pyramidal neurons and stimulates the inhibitory stellate cells (10). Disruption of GABA signaling is deleterious to cellular survival and leads to irreversible damage (11).…”