Different Contribution Of CA1/CA3 To Spontaneous Synchronized Activities Of Intact Hippocampus In Vitro

Hippocampus,an important component of the mammal limbic system,plays a crucial role in learning and memory,spatial compass and other functions.And the hippocampal synchronized neural activity has been suggested to be closely involved in the realization of these functions.Substantial studies have been conducted to reveal the neural mechanisms of hippocampal synchronized neural activity,but further illumination is still necessary.Here,on isolated complete hippocampus of young rats,we investigated the internal network mechanisms of CA1 synchronized neural activity.First,highly synchronized neural activity in CA1 area was both observed with extracellular LFP recording.Next we transected the isolated complete hippocampus from CA3 side,dividing 3/4 widtfh of the hippocampus.Recording of LFP in both sides of CA1 area revealed a significant synchronization of neural activity in first hour,which was not observed 3 or 5 hours after transection.On the contrary,when the transection was conducted from CA1 side,the synchronized neural activity was not observed in the first hour,but there was significant recover of synchronization 3 hours after transection,and full recover to the synchronization level of complete hippocampus 5 hours after transection.To further investigate the recovering process of synchronized neural activity after transection from CA1 side,we measured the activity synchronization over time of CA1 pyramidal neurons with dual perforated patch clamp.A similar result was shown that no synchronization was observed in the first 2 hours,but recording revealed high synchronization reaching the level of complete hippocampus 4 hours after transection.In conclusion,synchronization of neural activity in CA1 area relies on the completeness of CA1 and CA3 internal networks.The existence of CA1 internal connections can keep synchronized neural activity for short time,but the long-term maintenance of synchronization requires the input from CA3.Meanwhile,input from complete CA3 can support gradual recovering of synchronized neural activity in internally disconnected CA1 area.Our findings provide new insights into hippocampal CA1 synchronized neural activity.