Nonlinear Relationship Between Spike-Dependent Calcium Influx and TRPC Channel Activation Enables Robust Persistent Spiking in Neurons of the Anterior Cingulate Cortex

Abstract

Continuation of spiking after a stimulus ends (i.e. persistent spiking) is thought to support working memory. Muscarinic receptor activation enables persistent spiking among synaptically isolated pyramidal neurons in anterior cingulate cortex (ACC), but a detailed characterization of that spiking is lacking and the underlying mechanisms remain unclear. Here, we show that the rate of persistent spiking in ACC neurons is insensitive to the intensity and number of triggers, but can be modulated by injected current, and that persistent spiking can resume after several seconds of hyperpolarization-imposed quiescence. Using electrophysiology and calcium imaging in brain slices from male rats, we determined that canonical transient receptor potential (TRPC) channels are necessary for persistent spiking and that TRPC-activating calcium enters in a spike-dependent manner via voltage-gated calcium channels. Constrained by these biophysical details, we built a computational model that reproduced the observed pattern of persistent spiking. Nonlinear dynamical analysis of that model revealed that TRPC channels become fully activated by the small rise in intracellular calcium caused by evoked spikes. Calcium continues to rise during persistent spiking, but because TRPC channel activation saturates, firing rate stabilizes. By calcium rising higher than required for maximal TRPC channel activation, TRPC channels are able to remain active during periods of hyperpolarization-imposed quiescence (until calcium drops below saturating levels) such that persistent spiking can resume when hyperpolarization is discontinued. Our results thus reveal that the robust intrinsic bistability exhibited by ACC neurons emerges from the nonlinear positive feedback relationship between spike-dependent calcium influx and TRPC channel activation. Neurons use action potentials, or spikes, to encode information. Some neurons can store information for short periods (seconds to minutes) by continuing to spike after a stimulus ends, thus enabling working memory. This so-called "persistent" spiking occurs in many brain areas and has been linked to activation of canonical transient receptor potential (TRPC) channels. However, TRPC activation alone is insufficient to explain many aspects of persistent spiking such as resumption of spiking after periods of imposed quiescence. Using experiments and simulations, we show that calcium influx caused by spiking is necessary and sufficient to activate TRPC channels and that the ensuing positive feedback interaction between intracellular calcium and TRPC channel activation can account for many hitherto unexplained aspects of persistent spiking.

Role of Transient Receptor Potential Canonical Channels in Heart Physiology and Pathophysiology

“…Interestingly, TRPC3, 6, and 7 are directly activated by diacylglycerol (DAG), while TRPC1, 4, and 5 are insensitive to DAG (35,36). Furthermore, some TRPC channels (e.g., TRPC4 and 5) have been shown to be activated by intracellular Ca 2+ (37-40), therefore presumably conferring a positive feedback loop (41) or functional interactions between TRPC and other Ca 2+ -permeable channels (e.g., LTCC) (38). It will need further studies to determine whether the effect of Ca 2+ is direct or mediated by calmodulin.…”

Switching between persistent firing and depolarization block in individual rat CA1 pyramidal neurons

“…Both lines of research used cholinergic stimulation of cells. PF in CA1 pyramidal neurons was shown to involve the CAN current (Knauer et al, 2013), which is thought to be mediated by TRPC channels (Ratté et al, 2018;Reboreda et al, 2011;Yan et al, 2009). DB was shown to involve TRPC5 (Tai et al, 2011) and other channels (Fraser & MacVicar, 1996;Kuzmiski, Barr, Zamponi, & MacVicar, 2005;Kuzmiski & MacVicar, 2001 In slices of the lateral septum from mice a comparison of an elevated spiking rate and DB was conducted in interneurons (Tian et al, 2014).…”

“…In contrast, moderate elevations in cholinergic activation are associated with wakefulness and mnemonic processes in vivo (Hasselmo, ; Kametani & Kawamura, ). In vitro, moderate concentrations of cholinergic agonists support persistent firing (PF) in the entorhinal cortex (Egorov, Hamam, Fransén, Hasselmo, & Alonso, ) and hippocampus (Jochems & Yoshida, ; Knauer, Jochems, Valero‐Aracama, & Yoshida, ; McQuiston & Madison, ), among other regions (Dembrow, Chitwood, & Johnston, ; Egorov, Unsicker, & von Bohlen und Halbach, ; Kawasaki, Palmieri, & Avoli, ; Rahman & Berger, ; Ratté, Karnup, & Prescott, ; Yan, Villalobos, & Andrade, ). Similarly to the epileptiform activity, PF in vitro is also initiated by a brief current injection (Egorov et al, ).…”

“…In contrast, moderate elevations in cholinergic activation are associated with wakefulness and mnemonic processes in vivo (Hasselmo, 1999;Kametani & Kawamura, 1990). In vitro, moderate concentrations of cholinergic agonists support persistent firing (PF) in the entorhinal cortex (Egorov, Hamam, Fransén, Hasselmo, & Palmieri, & Avoli, 1999;Rahman & Berger, 2011;Ratté, Karnup, & Prescott, 2018;Yan, Villalobos, & Andrade, 2009). Similarly to the epileptiform activity, PF in vitro is also initiated by a brief current injection (Egorov et al, 2002).…”

“…Although the downstream effects of muscarinic receptor stimulation have been intensely studied (Caulfield, Robbins, Higashida, & Brown, 1993;Halliwell & Adams, 1982;Strübing, Krapivinsky, Krapivinsky, & Clapham, 2001;Yan et al, 2009), they are not yet fully understood (Dasari, Abramowitz, Birnbaumer, & Gulledge, 2013;Reboreda, Jiménezdíaz, & Navarro-lópez, 2011). Transient receptor potential channels of the canonical type (TRPC channels), which are highly expressed in CA1 pyramidal neurons (Chung et al, 2006;Fowler, Sidiropoulou, Ozkan, Phillips, & Cooper, 2007;Strübing et al, 2001) and thought to mediate a nonselective cationic current (CAN current, I CAN ) (Partridge & Swandulla, 1988;Reboreda et al, 2011), seem to mediate both response types in vitro (Yan et al, 2009;Reboreda et al, 2011;Tai, Hines, Choi, & MacVicar, 2011;Zhang, Reboreda, Alonso, Barker, & Séguéla, 2011;Ratté et al, 2018; but see Zylberberg & Strowbridge, 2017). This is consistent with recent in vivo studies showing that TRPC channels play an important role in epileptic seizures (Phelan et al, 2012(Phelan et al, , 2013Phelan, Shwe, Abramowitz, Birnbaumer, & Zheng, 2014;Zheng, 2017; as well as in working memory (Bröker-Lai et al, 2017).…”