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Trinh AT, Girardi-Schappo M, Béïque JC, Longtin A, Maler L. Adaptive spike threshold dynamics associated with sparse spiking of hilar mossy cells are captured by a simple model. J Physiol 2023; 601:4397-4422. [PMID: 37676904 DOI: 10.1113/jp283728] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Accepted: 08/17/2023] [Indexed: 09/09/2023] Open
Abstract
Hilar mossy cells (hMCs) in the dentate gyrus (DG) receive inputs from DG granule cells (GCs), CA3 pyramidal cells and inhibitory interneurons, and provide feedback input to GCs. Behavioural and in vivo recording experiments implicate hMCs in pattern separation, navigation and spatial learning. Our experiments link hMC intrinsic excitability to their synaptically evoked in vivo spiking outputs. We performed electrophysiological recordings from DG neurons and found that hMCs displayed an adaptative spike threshold that increased both in proportion to the intensity of injected currents, and in response to spiking itself, returning to baseline over a long time scale, thereby instantaneously limiting their firing rate responses. The hMC activity is additionally limited by a prominent medium after-hyperpolarizing potential (AHP) generated by small conductance K+ channels. We hypothesize that these intrinsic hMC properties are responsible for their low in vivo firing rates. Our findings extend previous studies that compare hMCs, CA3 pyramidal cells and hilar inhibitory cells and provide novel quantitative data that contrast the intrinsic properties of these cell types. We developed a phenomenological exponential integrate-and-fire model that closely reproduces the hMC adaptive threshold nonlinearities with respect to their threshold dependence on input current intensity, evoked spike latency and long-lasting spike-induced increase in spike threshold. Our robust and computationally efficient model is amenable to incorporation into large network models of the DG that will deepen our understanding of the neural bases of pattern separation, spatial navigation and learning. KEY POINTS: Previous studies have shown that hilar mossy cells (hMCs) are implicated in pattern separation and the formation of spatial memory, but how their intrinsic properties relate to their in vivo spiking patterns is still unknown. Here we show that the hMCs display electrophysiological properties that distinguish them from the other hilar cell types including a highly adaptive spike threshold that decays slowly. The spike-dependent increase in threshold combined with an after-hyperpolarizing potential mediated by a slow K+ conductance is hypothesized to be responsible for the low-firing rate of the hMC observed in vivo. The hMC's features are well captured by a modified stochastic exponential integrate-and-fire model that has the unique feature of a threshold intrinsically dependant on both the stimulus intensity and the spiking history. This computational model will allow future work to study how the hMCs can contribute to spatial memory formation and navigation.
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Affiliation(s)
- Anh-Tuan Trinh
- Kavli Institute for Systems Neuroscience, Norwegian University of Science and Technology, Trondheim, Trøndelag, Norway
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
| | - Mauricio Girardi-Schappo
- Departamento de Física, Universidade Federal de Santa Catarina, Santa Catarina, Florianópolis, Brazil
- Department of Physics, University of Ottawa, Ottawa, Ontario, Canada
| | - Jean-Claude Béïque
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
- Brain and Mind Institute, University of Ottawa, Ottawa, Ontario, Canada
- Center for Neural Dynamics, University of Ottawa, Ottawa, Ontario, Canada
| | - André Longtin
- Department of Physics, University of Ottawa, Ottawa, Ontario, Canada
- Brain and Mind Institute, University of Ottawa, Ottawa, Ontario, Canada
- Center for Neural Dynamics, University of Ottawa, Ottawa, Ontario, Canada
| | - Leonard Maler
- Department of Cellular and Molecular Medicine, University of Ottawa, Ottawa, Ontario, Canada
- Brain and Mind Institute, University of Ottawa, Ottawa, Ontario, Canada
- Center for Neural Dynamics, University of Ottawa, Ottawa, Ontario, Canada
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da Silva MP, Ventura RR, Varanda WA. Hypertonicity increases NO production to modulate the firing rate of magnocellular neurons of the supraoptic nucleus of rats. Neuroscience 2013; 250:70-9. [PMID: 23850590 DOI: 10.1016/j.neuroscience.2013.06.067] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2013] [Revised: 06/10/2013] [Accepted: 06/29/2013] [Indexed: 11/27/2022]
Abstract
Increases in plasma osmolality enhance nitric oxide (NO) levels in magnocellular neurosecretory cells (MNCs) of the supraoptic nucleus (SON) and modulate the secretion of both vasopressin (VP) and oxytocin (OT). In this paper, we describe the effects of hypertonicity on the electrical properties of MNCs by focusing on the nitrergic modulation of their activity in this condition. Membrane potentials were measured using the patch clamp technique, in the presence of both glutamatergic and GABAergic neurotransmission blockers, in coronal brain slices of male Wistar rats. The recordings were first made under a control condition (295 mosm/kg H2O), then in the presence of a hypertonic stimulus (330 mosm/kg H2O) and, finally, with a hypertonic stimulus plus 500 μM L-Arginine or 100 μM N-nitro-L-Arginine methyl ester hydrochloride (L-NAME). Hypertonicity per se increased the firing frequency of the neurons. L-Arginine prevented the increase in fire frequency induced by hypertonic stimulus, and L-NAME (inhibitor of nitric oxide synthase) induced an additional increase in frequency when applied together with the hypertonic solution. Moreover, L-Arginine hyperpolarizes the resting potential and decreases the peak value of the after-hyperpolarization; both effects were blocked by L-NAME and hypertonicity and/or L-NAME reduced the time constant of the rising phase of the after-depolarization. These results demonstrate that an intrinsic nitrergic system is part of the mechanisms controlling the excitability of MNCs of the SON when the internal fluid homeostasis is disturbed.
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Affiliation(s)
- M P da Silva
- Department of Physiology, School of Medicine of Ribeirão Preto, University of São Paulo, Avenida Bandeirantes, 3900, 14049-900 Ribeirão Preto, SP, Brazil
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