Therapeutic effects of a restraint procedure on posttraumatic place learning in fimbria-fornix transected rats

Dissociating spatial strategies in animal research: Critical methodological review with focus on egocentric navigation and the hippocampus

One major challenge in animal research on spatial learning and memory pertains to designing methods to dissociate spatial strategies (allocentric vs. egocentric). This is crucial for understanding the underlying cognitive processes and neural circuits that are recruited in navigational tasks. Taking the egocentric reference frames as a starting point, this review argues that in many extensively used spatial paradigms, multiple spatial reference frames are often available to the animals but remain unaccounted for. We discuss the implications this has for the inferences that can be made and propose a decision-algorithm to construct spatial learning paradigms that can reduce the influence of these confounding variables. Furthermore, with these considerations in mind, we review the role of the hippocampus in egocentric navigation forms, i.e. in response learning, egocentric sequential learning and path integration. This choice is based on the controversy surrounding the role of hippocampus in these spatial paradigms. We discuss the possible methodological confounders that may explain the inconclusive results.

Delayed restraint procedure enhances cognitive recovery of spatial function after fimbria-fornix transection

PURPOSE

To i) evaluate the effect of a restraint procedure (7 days, 2 h/day) on place learning after fimbria-fornix transection (FF), ii) investigate effects of early vs. late administration of restraint, and iii) establish effects of the restraint procedure on expression of brain derived neurotrophic factor (BDNF) in prefrontal cortex and hippocampus.

METHODS

Fifty rats subjected to FF or sham surgery and divided into groups exposed to restraint immediately (early restraint) or 21 days (late restraint) after surgery were trained to acquire an allocentric place learning task. In parallel, 29 animals were subjected to FF or sham surgery and an identical restraint procedure in order to measure concentrations of BDNF and corticosterone.

RESULTS

The performance of the sham operated rats was positively affected by the late restraint. In FF-lesioned animals, the late restraint significantly improved task performance compared to the lesioned group with no restraint, while the early restraint was associated with a negative impact on task acquisition. Biochemical analysis after restraint procedure revealed a lesion-induced upregulation of BDNF in FF animals.

CONCLUSIONS

The improved task performance of lesioned animals suggests a therapeutic effect of this manipulation, independent of BDNF. This effect is sensitive to the temporal administration of treatment.

Only repeated administration of the serotonergic agonist 8-OH-DPAT improves place learning of rats subjected to fimbria-fornix transection

Serotonergic agonists may act neuroprotectively against brain injury. This study addressed the therapeutic potential of 8-hydroxy-2-di-n-propylamino-tetralin (8-OH-DPAT), a selective 5-HT1A/7 receptor agonist, after mechanical brain injury, and evaluated its effects in terms of acquisition of an allocentric place learning task in a water maze. Rats were divided into 6 experimental groups, three of which were subjected to bilateral transection of fimbria-fornix (FF), while three groups were given control surgery (Sham). After surgery, within both the lesioned, and sham-operated animals, respectively, one group was administered a single dose of saline, one group was given a single dose (0.5 mg/kg/b.w.) of 8-OH-DPAT, and one group was treated with daily administration of 8-OH-DPAT (0.5 mg/kg/b.w.) for eight days. The acquisition of the water maze based place learning task started on the 8th day post-surgery and continued for 20 days. The results show that the lesioned group subjected to repeated administration of 8-OH-DPAT demonstrated a significantly improved acquisition of the place learning task compared to the vehicle injected lesion group. In contrast, the lesioned group treated with a single administration displayed impaired performance compared to the baseline lesion group. There were no significant effects of the 8-OH-DPAT administration in the sham control groups. We conclude that only the repeated stimulation of the 5-HT1A/7 system was associated with beneficial, recovery enhancing effects.

Cornel iridoid glycoside improves memory ability and promotes neuronal survival in fimbria-fornix transected rats

Cornel iridoid glycoside (CIG) is a main component extracted from a traditional Chinese herb Cornus officinalis. Our previous study found that CIG improved neurological function in cerebral ischemic rats. The aim of this study was to investigate the therapeutic benefit of CIG in rats with fimbria-fornix transection (FFT) and explore the underlying molecular mechanisms. CIG (20, 60 and 180 mg/kg) or vehicle was intragastrically administered once daily to rats, starting immediately after the surgery and lasting for 4 weeks. Morris water maze and step-through tests showed that the memory deficits seen in FFT rats were significantly improved by CIG treatment. Immunohistochemical analysis showed that CIG treatment attenuated the loss of neurons in hippocampus. To elucidate the memory-improving mechanism of CIG, the neurotrophic factors, synaptic proteins and Bcl-2 family proteins in hippocampus were measured by Western blot analysis. FFT reduced hippocampal protein levels of nerve growth factor (NGF), tyrosine receptor kinase A (Trk A), brain-derived neurotrophic factor (BDNF), synaptophysin (SYP) and B-cell lymphoma-2 (Bcl-2), but not levels of tyrosine receptor kinase B (Trk B) and growth-associated protein 43 (GAP-43). FFT also elevated cytochorome C (Cyt c) and bcl-2-associated X protein (Bax). Administration of CIG to FFT rats significantly elevated the expression of NGF, TrkA, BDNF, SYP, GAP-43 and Bcl-2, and decreased the expression of Cyt c and Bax. These results indicated that CIG effectively counteracted cognitive impairments caused by fimbria-fornix lesions, and the mechanisms might be related to promoting neuronal survival and providing a beneficial environment for brain repair.