Structural plasticity in hippocampal cells related to the facilitative effect of intracranial self-stimulation on a spatial memory task.

Abstract

Posttraining intracranial self-stimulation (SS) in the lateral hypothalamus facilitates the acquisition and retention of several implicit and explicit memory tasks. Here, intracellular injections of Lucifer yellow were used to assess morphological changes in hippocampal neurons that might be specifically related to the facilitative posttraining SS effect upon the acquisition and retention of a distributed spatial task in the Morris water maze. We examined the structure, size and branching complexity of cornus ammonis 1 (CA1) cells, and the spine density of CA1 pyramidal neurons and granular cells of the dentate gyrus (DG). Animals that received SS after each acquisition session performed faster and better than Sham ones--an improvement that was also evident in a probe trial 3 days after the last training session. The neuromorphological analysis revealed an increment in the size and branching complexity in apical CA1 dendritic arborization in SS-treated subjects as compared with Sham animals. Furthermore, increased spine density was observed in the CA1 field in SS animals, whereas no effects were observed in DG cells. Our results support the hypothesis that the facilitating effect of SS on the acquisition and retention of a spatial memory task could be related to structural plasticity in CA1 hippocampal cells.

Intracranial self-stimulation also facilitates learning in a visual discrimination task in the Morris water maze in rats

“…The electrical activation of the medial forebrain bundle (MFB) via Intracranial self-stimulation (ICSS) has been confirmed in our and other laboratories as a treatment capable of consistently facilitating the acquisition and retention in a wide array of experimental paradigms, for both implicit [1], [2], [3], [4] and explicit memory [5], [6], in rats. Several mechanisms of action have been proposed to explain these facilitating effects of ICSS on learning and memory.…”

“…Learning and memory facilitation has also been linked to structural plasticity induced by ICSS [11]. Recent work undertaken in our laboratory has shown an increase in the density of dendrite spines in the CA1 neurons of the hippocampus in rats that received ICSS after training in a spatial task [6]. These morphological modifications could be related to changes in the expression of several plasticity-related genes caused by the posttraining ICSS treatment, with increased levels of Nurr1, c-Fos and Arc protein consistently being found in hippocampus, amygdala, dorsal striatum, lateral hypothalamus or retrosplenial cortex [12], [13], [14], [15].…”

Arc protein expression after unilateral intracranial self-stimulation of the medial forebrain bundle is upregulated in specific nuclei of memory-related areas

“…This was done in a single session of 2500 self-administered trains of stimulant current at each particular OI using the same Skinner box where ICSS behavior had been established. The parameters of the stimulation in terms of frequency, intensity and number of trains administered were the same as previous studies since it has been shown to effectively enhance memory, both implicit [ 33 – 35 ] and explicit [ 6 , 8 ].…”

“…The use of ICSS in animals allows us to unequivocally ensure that stimulation activates the reward system in a functional manner. In a similar way to F-DBS, ICSS of the LH has a reliable enhancing effect on hippocampus-dependent explicit memory [ 6 – 8 ]. However, while F-DBS affects fornix fibers, ICSS of the LH activates the MFB.…”

“…Additionally, MFB-ICSS induces differential time course mRNA expression of some synaptic plasticity-related genes including Arc in the amygdala and the hippocampus [ 18 , 19 ]. ICSS-treated rats showing a facilitated spatial memory have also long-lasting structural changes including extended dendritic arborization of pyramidal CA1 neurons [ 6 ]. Thus, based on the fact that Arc protein is a well-known marker of synaptic plasticity events associated with the memory consolidation process [ 20 ] and is also involved in long-term spine enlargement [ 21 ], we initially set out to determine the effect of MFB-ICSS has on Arc protein levels in the different sub-regions of the hippocampus and in the retrosplenial cortex.…”