Hippocampal Synaptic Expansion Induced by Spatial Experience in Rats Correlates with Improved Information Processing in the Hippocampus

Abstract

Spatial water maze (WM) overtraining induces hippocampal mossy fiber (MF) expansion, and it has been suggested that spatial pattern separation depends on the MF pathway. We hypothesized that WM experience inducing MF expansion in rats would improve spatial pattern separation in the hippocampal network. We first tested this by using the the delayed non-matching to place task (DNMP), in animals that had been previously trained on the water maze (WM) and found that these animals, as well as animals treated as swim controls (SC), performed better than home cage control animals the DNMP task. The “catFISH” imaging method provided neurophysiological evidence that hippocampal pattern separation improved in animals treated as SC, and this improvement was even clearer in animals that experienced the WM training. Moreover, these behavioral treatments also enhance network reliability and improve partial pattern separation in CA1 and pattern completion in CA3. By measuring the area occupied by synaptophysin staining in both the stratum oriens and the stratun lucidum of the distal CA3, we found evidence of structural synaptic plasticity that likely includes MF expansion. Finally, the measures of hippocampal network coding obtained with catFISH correlate significantly with the increased density of synaptophysin staining, strongly suggesting that structural synaptic plasticity in the hippocampus induced by the WM and SC experience is related to the improvement of spatial information processing in the hippocampus.

Locus Coeruleus Phasic, But Not Tonic, Activation Initiates Global Remapping in a Familiar Environment

“…This difference in maps between CA3a/b and CA1 supports evidence that CA3 has a discontinuous response to input changes unlike CA1 (Guzowski et al, 2004). It is also consistent with a new theoretical framing of CA1 and CA3 function, which argues that CA1 is best characterized as providing "gist" representations, whereas CA3 provides detailed representations (Burke et al, 2018). In the present experiment, the changed details of the novel environment (which were many) may have driven the CA3, whereas a similar box in a similar room supported the gist of the earlier representation with LC activation blocked.…”

3,5-T2 and 3,3′,5-T3 Regulate Cerebellar Thyroid Hormone Signalling and Myelin Molecular Dynamics in Tilapia

“…Tissue slices were treated as previously described by Carasatorre et al . 38 . Anti- DIG-POD (1:800) (ROCHE) diluted in TSA was added and the slices were incubated overnight at 4 °C, washed in TBS and TTBS and developed with Tyramide signal amplification-Cy3 (TSA-Cy3; 1:75) detection kit (Perkin-Elmer) in darkness and incubated for 60 min, washed in TBS and TTBS , contrasting with DAPI (1:400 in TBS) (ROCHE), and mounted with medium 1 , 4-Diazabicyclo[2 .…”

Behavior‐associated Neuronal Activation After Kainic Acid‐induced Hippocampal Neurotoxicity is Modulated in Time

“…It is worth considering that under physiological circumstances, synaptic expansion induced by behavioral experience has been associated to the improvement of spatial information processing in the hippocampus, as suggested by an increase in neuronal Arc (Carasatorre et al, ). Thus, the increase in Arc+ somata in lesioned animals that faced a spatial‐exploratory behavior may reflect the activation or recruitment of a number of neurons initially not involved in the task.…”

“…Activity‐regulated cytoskeleton‐associated protein (Arc) is an immediate early gene induced by a variety of conditions including seizures, exploration of novel environments, and spatial learning (Lyford, et al, ; Ramírez‐Amaya et al, ; Messaoudi et al, ; Farris et al, ) all of which activate hippocampal neurons. Basal Arc contents are very low, thus its presence has been widely used as a neuronal activity marker for in vivo analysis of robust neuronal activation (Toyoda et al, ) and for neural activity associated to several types of behavioral experiences (Vazdarjanova et al, , Ramirez‐Amaya et al, ; Carasatorre et al, ; Meconi et al, ).…”

“…Injury‐ as well as exploratory behavior‐induced plasticity in rodents has been extensively documented; plastic events include modifications in mRNA and protein synthesis, which may ultimately impact the activation and function of synapses (Carasatorre et al, ). SYP and Arc are plasticity‐related molecules that reflect structural and functional synaptic modifications.…”