Sanchez Alyssa N, Alitto Henry J, Rathbun Daniel L, Fisher Tucker G, Usrey W Martin
Center for Neuroscience, University of California Davis, 95618, USA.
Dept. of Ophthalmology, Detroit Inst. of Ophthalmology, Henry Ford Health System, Detroit, MI, 48202, USA.
Curr Res Neurobiol. 2023 Jun 10;4:100096. doi: 10.1016/j.crneur.2023.100096. eCollection 2023.
Burst activity is a ubiquitous feature of thalamic neurons and is well documented for visual neurons in the lateral geniculate nucleus (LGN). Although bursts are often associated with states of drowsiness, they are also known to convey visual information to cortex and are particularly effective in evoking cortical responses. The occurrence of thalamic bursts depends on (1) the inactivation gate of T-type Ca channels (T-channels), which become de-inactivated following periods of increased membrane hyperpolarization, and (2) the opening of the T-channel activation gate, which has voltage-threshold and rate-of-change (δv/δt) requirements. Given the time/voltage relationship for the generation of Ca potentials that underlie burst events, it is reasonable to predict that geniculate bursts are influenced by the luminance contrast of drifting grating stimuli, with the null phase of higher contrast stimuli evoking greater hyperpolarization followed by a larger dv/dt than the null phase of lower contrast stimuli. To determine the relationship between stimulus contrast and burst activity, we recorded the spiking activity of cat LGN neurons while presenting drifting sine-wave gratings that varied in luminance contrast. Results show that burst rate, reliability, and timing precision are significantly greater with higher contrast stimuli compared with lower contrast stimuli. Additional analysis from simultaneous recordings of synaptically connected retinal ganglion cells and LGN neurons further reveals the time/voltage dynamics underlying burst activity. Together, these results support the hypothesis that stimulus contrast and the biophysical properties underlying the state of T-type Ca channels interact to influence burst activity, presumably to facilitate thalamocortical communication and stimulus detection.
爆发性活动是丘脑神经元普遍存在的特征，外侧膝状体核（LGN）中的视觉神经元对此已有充分记录。尽管爆发性活动通常与嗜睡状态相关，但它们也能将视觉信息传递到皮层，并且在诱发皮层反应方面特别有效。丘脑爆发的发生取决于：（1）T型钙通道（T通道）的失活门，在膜超极化增加的时期后它会去失活；（2）T通道激活门的开放，其具有电压阈值和变化率（δv/δt）要求。鉴于爆发事件所基于的钙电位产生的时间/电压关系，可以合理预测膝状体爆发受漂移光栅刺激的亮度对比度影响，高对比度刺激的零相位比低对比度刺激的零相位诱发更大的超极化，随后是更大的dv/dt。为了确定刺激对比度与爆发性活动之间的关系，我们在呈现亮度对比度不同的漂移正弦波光栅时记录了猫LGN神经元的放电活动。结果表明，与低对比度刺激相比，高对比度刺激下的爆发率、可靠性和时间精度显著更高。对视网膜神经节细胞和LGN神经元突触连接的同步记录进行的额外分析进一步揭示了爆发性活动背后的时间/电压动态。这些结果共同支持了这样的假设，即刺激对比度与T型钙通道状态所基于的生物物理特性相互作用，以影响爆发性活动，大概是为了促进丘脑皮质通信和刺激检测。
