Kichigina V F, Kutyreva E S, Sudnitsyn V V
Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino.
Zh Vyssh Nerv Deiat Im I P Pavlova. 2003 Nov-Dec;53(6):754-65.
It was shown by us earlier that bilateral intracerebroventricular injection of alpha2-adrenoreceptor agonist clonidine produced a dose-dependent effect on theta oscillations in the septohippocampal system of awake rabbits. A relatively low dose of clonidine (0.5 microgram) attenuated and a high dose (5 micrograms) significantly enhanced the rhythmic activity. It was suggested that the effect of the low dose of clonidine is mediated by presynaptic alpha2-adrenoreceptors were as postsynaptic alpha2-adrenoreceptors. In this article sensory neuronal responses in the medial septal area (MS) were analyzed against the background of the theta activity modulation by different clonidine doses. Different effects of the low and high doses of the agonist were revealed. The low dose of clonidine (0.5 microgram in 5 microliters into each lateral ventricle) which produced a decrease in the theta activity resulted in attenuation of excitation and enhancement of inhibition, i.e., the number of activating effects significantly decreased and inhibitory responses were more frequent and distinct. The high dose of clonidine (5 micrograms in 5 microliters) which produced a sharp increase in the theta activity led to a significant decrease in the reactions of the MS cells to sensory stimuli (from 76.8% in the control to 45% under clonidine) independently on the initial reaction character. Persisted excitatory and inhibitory responses became less distinct than the initial ones except single excitatory reactions. The results suggest that alpha2-adrenoreceptors are involved in the control of the sensory reactivity of MS neurons. A sharp decrease in neuronal reactivity during stable rhythmical oscillations developing under the influence of high dose of clonidine confirm the role of the theta rhythm in the septohippocampal system as an active filter in information selection and registration.
我们之前的研究表明，双侧脑室内注射α2 - 肾上腺素能受体激动剂可乐定对清醒家兔海马隔区系统的θ振荡产生剂量依赖性效应。相对低剂量的可乐定（0.5微克）会减弱，而高剂量（5微克）则会显著增强节律性活动。有人认为，低剂量可乐定的作用是由突触前α2 - 肾上腺素能受体介导的，而高剂量的作用则是由突触后α2 - 肾上腺素能受体介导的。在本文中，我们分析了在不同剂量可乐定调节θ活动的背景下，内侧隔区（MS）的感觉神经元反应。揭示了激动剂低剂量和高剂量的不同作用。低剂量的可乐定（每侧脑室5微升中含0.5微克）导致θ活动减少，同时兴奋减弱、抑制增强，即激活效应的数量显著减少，抑制反应更加频繁和明显。高剂量的可乐定（5微升中含5微克）使θ活动急剧增加，导致MS细胞对感觉刺激的反应显著减少（从对照组的76.8%降至可乐定处理后的45%），且与初始反应特征无关。除了单个兴奋反应外，持续的兴奋和抑制反应变得不如初始反应明显。结果表明，α2 - 肾上腺素能受体参与了MS神经元感觉反应性的控制。在高剂量可乐定影响下产生的稳定节律性振荡期间，神经元反应性急剧下降，这证实了海马隔区系统中θ节律作为信息选择和记录的主动过滤器的作用。
