Postischemic fish oil treatment restores long-term retrograde memory and dendritic density: An analysis of the time window of efficacy.

We reported that fish oil (FO) prevented the loss of spatial memory caused by transient, global cerebral ischemia (TGCI), provided the treatment covered the first days prior to and after ischemia. Continuing these studies, trained rats were subjected to TGCI, and FO was administered for 10days, with a time window of efficacy (TWE) of 4, 8 or 12h post-ischemia. Retrograde memory was assessed up to 43days after TGCI. In another experiment, ischemic rats received FO with a 4- or 12-h TWE, and dendritic density was assessed in the hippocampus and cerebral cortex. The brain lipid profile was evaluated in sham-operated and ischemic rats that were treated with FO or vehicle with a 4-h TWE. Ischemia-induced retrograde amnesia was prevented by FO administration that was initiated with either a 4- or 8-h TWE. Fish oil was ineffective after a 12-h TWE. Independent of the TWE, FO did not prevent ischemic neuronal death. In the hippocampus, but not cerebral cortex, TGCI-induced dendritic loss was prevented by FO with a 4-h TWE but not 12-h TWE. The level of docosahexaenoic acid almost doubled in the hippocampus in ischemic, FO-treated rats (4-h TWE). The data indicate that (i) the anti-amnesic effect of FO can be observed with a TWE of up to 8h, (ii) the stimulation of dendritic neuroplasticity may have contributed to this effect, and (iii) DHA in FO may be the main active constituent in FO that mediates the cognitive and neuroplasticity effects on TGCI.

Robust and enduring atorvastatin-mediated memory recovery following the 4-vessel occlusion/internal carotid artery model of chronic cerebral hypoperfusion in middle-aged rats.

Chronic cerebral hypoperfusion (CCH) is a common condition associated with the development and/or worsening of age-related dementia.We previously reported persistent memory loss and neurodegeneration after CCH in middle-aged rats. Statin-mediated neuroprotection has been reported after acute cerebral ischemia. Unknown, however, is whether statins can alleviate the outcome of CCH. The present study investigated whether atorvastatin attenuates the cognitive and neurohistological outcome of CCH. Rats (12­15 months old) were trained in a non-food-rewarded radial maze, and then subjected to CCH. Atorvastatin (10 mg/kg, p.o.) was administered for 42 days or 15 days, beginning 5 h after the first occlusion stage. Retrograde memory performance was assessed at 7, 14, 21, 28, and 35 days of CCH, and expressed by "latency," "number of reference memory errors" and "number of working memory errors." Neurodegeneration was then examined at the hippocampus and cerebral cortex. Compared to sham, CCH caused profound and persistent memory loss in the vehicle-treated groups, as indicated by increased latency (91.2% to 107.3%) and number of errors (123.5% to 2508.2%), effects from which the animals did not spontaneously recover across time. This CCH-induced retrograde amnesia was completely prevented by atorvastatin (latency: −4.3% to 3.3%; reference/working errors: −2.5% to 45.7%), regardless of the treatment duration. This effect was sustained during the entire behavioral testing period (5 weeks), even after discontinuing treatment. This robust and sustained memory-protective effect of atorvastatin occurred in the absence of neuronal rescue (39.58% to 56.45% cell loss). We suggest that atorvastatin may be promising for the treatment of cognitive sequelae associated with CCH.

What does a comparison of the alcoholic Korsakoff syndrome and thalamic infarction tell us about thalamic amnesia?

In this review, the clinical, neuropsychological, and neuroimaging findings in the alcoholic Korsakoff syndrome and in thalamic amnesia, resulting from focal infarction, are compared. In both disorders, there is controversy over what is the critical site for anterograde amnesia to occur-damage to the anterior thalamus/mammillo-thalamic tract has most commonly been cited, but damage to the medio-dorsal nuclei has also been advocated. Both syndromes show 'core' features of an anterograde amnesic syndrome; but retrograde amnesia is generally much more extensive (going back many years or decades) in the Korsakoff syndrome. Likewise, spontaneous confabulation occurs more commonly in the Korsakoff syndrome, although seen in only a minority of chronic cases. These differences are attributed to the greater prevalence of frontal atrophy and frontal damage in Korsakoff cases.

Glucocorticoids aggravate retrograde memory deficiency associated with traumatic brain injury in rats.

Administration of glucocorticoid to patients with head injury has previously been demonstrated to impair memory. We hypothesize that glucocorticoids promote post-traumatic hippocampal apoptosis, resulting in retrograde memory deficiency associated with traumatic brain injury (TBI). In the present study, we tested this hypothesis by measuring spatial memory deficiency in rats subjected to fluid percussion injury (FPI) and receiving dexamethasone (DXM at 0.5-10 mg/kg) or methylprednisolone (MP at 5-30 mg/kg); we also examined neuronal apoptosis in hippocampus. Adult male Wistar rats were trained for the acquisition of spatial memory, then subjected to FPI and tested for spatial reference memory on post-injury days 7 and 14 using the Morris Water Maze. Brain tissue from injured rats was examined 24 h to 2 weeks after injury. The percent time in the goal quadrant, which measures spatial reference memory, was significantly lower in injured rats receiving either high-dose DXM or MP than in control groups. TUNEL-positive cells in hippocampus were first detected 24 h post-injury, plateauing at 48h. The number of TUNEL-positive cells was significantly higher in injured rats treated with either DXM or MP. The data suggest that glucocorticoid therapy for TBI may increase neuronal apoptosis in hippocampus and, as a result, aggravate retrograde memory deficits induced by TBI.

Absence of systems consolidation of fear memories after dorsal, ventral, or complete hippocampal damage.

We examined the effects of dorsal, ventral, or complete damage to the hippocampus on long-term retention of a Pavlovian conditioned fear response to a tone and a context paired with foot shock. Rats received a fear conditioning episode, in which a tone and context or context-alone were paired with foot shock. Two days or 12 weeks later, they received sham, dorsal, ventral, or complete NMDA-induced damage of the hippocampus. During a retention test conducted 2 weeks after surgery, the sham control rats exhibited high levels of freezing in the context and in the presence of the tone. Rats with dorsal, ventral, or complete hippocampal damage displayed very little freezing in the context at either learning-surgery intervals. Partial hippocampal damage tended to cause a smaller but consistent deficit in conditioned responding to context at the shorter (2 day) learning-surgery interval. Rats with hippocampal damage did not display less severe retrograde amnesia for more remote (12 weeks) memories. A similar pattern of results was observed for freezing to the tone. We find that the severity of retrograde amnesia for fear conditioning is related to the extent of the damage and that there is consistent and severe retrograde amnesia for remote contextual and cued fear memories. These findings support the idea that the hippocampal formation plays an essential and possibly permanent role in fear memories.

Two routes to losing one's past life: a brain trauma, an emotional trauma.

Organic and psychogenic retrograde amnesia have long been considered as distinct entities and as such, studied separately. However, patterns of neuropsychological impairments in organic and psychogenic amnesia can bear interesting resemblances despite different aetiologies. In this paper, two cases with profound, selective and permanent retrograde amnesia are presented, one of an apparent organic origin and the other with an apparent psychogenic cause. The first case, DD, lost his memory after focal brain injury from a nail gun to the right temporal lobe. The second case, AC, lost her memory in the context of intense psychological suffering. In both cases, pre-morbid autobiographical memory for people, places and events was lost, and no feeling of familiarity was experienced during relearning. In addition, they both lost some semantic knowledge acquired prior to the onset of the amnesia. This contrasts with the preservation of complex motor skills without any awareness of having learned them. Both DD and AC showed mild deficits on memory tests but neither presented any anterograde amnesia. The paradox of these cases--opposite causes yet similar clinical profile--exemplifies the hypothesis that organic and psychogenic amnesia may be two expressions of the same faulty mechanism in the neural circuitry.

Retrograde amnesia and the volume of critical brain structures.

There are many controversies concerning the structural basis of retrograde amnesia (RA). One view is that memories are held briefly within a medial temporal store ("hippocampal complex") before being "consolidated" or reorganised within temporal neocortex and/or networks more widely distributed within the cerebral cortex. An alternative view is that the medial temporal lobes are always involved in the storage and retrieval (reactivation) of autobiographical memories (multiple trace theory). The present study used quantitative magnetic resonance imaging (MRI) in 40 patients with focal pathology/volume loss in different sites, to examine the correlates of impairment on three different measures of RA. The findings supported the view that widespread neural networks are involved in the storage and retrieval of autobiographical and other remote memories. Brain volume measures in critical structures could account for 60% of variance on autobiographical memory measures (for incidents and facts) in diencephalic patients and for 60-68% of variance in patients with frontal lesions. Significant correlations with medial temporal lobe volume were found only in the diencephalic group, in whom they were thought to reflect thalamic changes, but not in patients with herpes encephalitis or hypoxia in whom the temporal lobes were particularly implicated. The latter finding fails to support one of the main predictions of multiple trace theory, as presently expounded.