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On the co-occurrence of startles and hippocampal sharp waves in newborn rats
Karl A E Karlsson1, Ethan J Mohns, Gonzalo Viana di Prisco
1Department of Biomedical Engineering, School of Science and Engineering, Reykjavik University, Reykjavik, Iceland. karlsson@ru.is
Insights
Early in development, infant rat startles mechanistically trigger hippocampal sharp wave (SPW) events. This link is crucial for neural circuit assembly, as demonstrated by experiments in young, freely moving rats.
Area of Science:
- Neuroscience
- Developmental Neuroscience
- Mammalian Neurophysiology
Background:
- Hippocampal sharp waves (SPWs) are early neural patterns in infant mammals.
- Startles are among the earliest observed behavioral events in mammals.
- The mechanistic link between these early events remains largely unexplored.
Purpose of the Study:
- To investigate the mechanistic relationship between startles and hippocampal sharp waves (SPWs) in early development.
- To determine if startles precede and potentially trigger SPWs in neonatal rats.
- To explore the developmental role of this potential neural-behavioral linkage.
Main Methods:
- Utilized electromyography (EMG) to detect startles and intrahippocampal silicon depth electrodes for SPWs in 1-4 day old rats.
- Compared SPW and startle occurrences in intact pups versus pups with surgically separated hippocampal formations.
- Recorded concurrent neural activity, including gamma oscillations and neocortical spindles.
Main Results:
- In intact neonatal rats, a majority of SPWs were preceded by startles with an average latency of 161 ms.
- Surgical separation of the hippocampus from the brainstem resulted in independent occurrences of startles and SPWs.
- Gamma oscillations and passively propagating neocortical spindles were also observed, independent of startle-SPW linkage.
Conclusions:
- Startles mechanistically precede and likely trigger hippocampal sharp waves (SPWs) in neonatal rats.
- This early co-occurrence facilitates Hebbian synaptic plasticity, contributing to neural circuit development.
- The findings reveal a fundamental mechanism shaping early brain circuitry through coordinated neural and behavioral events.
Abstract:
Hippocampal sharp waves (SPWs) are among the earliest neural population patterns observed in infant mammals. Similarly, startles are among the earliest behavioral events observed. Here we provide evidence indicating that these two events are linked mechanistically soon after birth in freely moving and head-fixed 1 to 4-day-old rats. EMG electrodes and intrahippocampal silicon depth electrodes were used to detect the presence of startles and SPWs, respectively. In intact pups, the majority of sharp waves were preceded by startles (average latency: 161 ms). When the hippocampal formation was surgically separated from the brainstem, however, sharp waves and startles still occurred, but now independently. In addition, unrelated to startles or SPWs, gamma oscillations were detected in several subjects, as were neocortical "spindles" that propagated passively into the hippocampus. The co-occurrence of sharp waves and startles provides the opportunity for Hebbian changes in synaptic efficacy and, thus, is poised to contribute to the assembly of neural circuits early in development.
