Hippocampus
-
Comparative Study
Status epilepticus during old age is not associated with enhanced hippocampal neurogenesis.
Increased production of new neurons in the adult dentate gyrus (DG) by neural stem/progenitor cells (NSCs) following acute seizures or status epilepticus (SE) is a well known phenomenon. However, it is unknown whether NSCs in the aged DG have similar ability to upregulate neurogenesis in response to SE. We examined DG neurogenesis after the induction of continuous stages III-V seizures (SE) for over 4 h in both young adult (5-months old) and aged (24-months old) F344 rats. ⋯ Moreover, the number of newly born cells that migrate abnormally into the dentate hilus (i.e., ectopic granule cells) after SE in the aged hippocampus is 92% less than that observed in the young adult hippocampus after similar SE. Thus, SE fails to increase the addition of new granule cells to the GCL in the aged DG, despite a considerable upregulation in the production of new cells, and SE during old age leads to much fewer ectopic granule cells. These results have clinical relevance because earlier studies have implied that both increased and abnormal neurogenesis occurring after SE in young animals contributes to chronic epilepsy development.
-
The medial septum and diagonal band complex (MS-DB) is believed to play a key role in generating theta oscillations in the hippocampus, a phenomenon critical for learning and memory. Although the importance of the MS-DB in hippocampal theta rhythm generation is generally accepted, it remains to be determined whether the MS-DB alone can generate hippocampal oscillations or is only a transducer of rhythmic activity from other brain areas. Secondly, it is known that hippocampal theta rhythm can be separated into an atropine-sensitive and insensitive component. ⋯ Interestingly, the application of the muscarinic receptor antagonist atropine produced only a partial decrease in the amplitude, without modification of the frequency, of theta. These results show for the first time, that upon optimal excitation, the MS-DB alone is able to generate hippocampal oscillations in the theta frequency band. Moreover, these MS-DB generated theta oscillations are mediated by muscarinic and nonmuscarinic receptors and have a pharmacological profile similar to theta rhythm observed in awake animals.
-
Prenatal infection is a major stressful experience leading to enhanced susceptibility for mental illnesses in humans. We recently reported in rats, that oxidative stress and glutathione (GSH) shortage occurred in fetal male brain after lipopolysaccharide (LPS) to the dams and that these responses might be involved in the neurodevelopmental deficits observed in adolescent offspring. Furthermore, pretreatment with N-acetylcysteine (NAC) before LPS avoided both delayed synaptic plasticity and mnesic performance deficits. ⋯ This treatment did not prevent the LPS-induced synaptic plasticity impairment. These results point to fetal hippocampal GSH as a major target of the detrimental effects of in utero LPS challenge. The therapeutic window of NAC extends up to birth, suggesting that this drug might be clinically useful even after an immuno-inflammatory episode.
-
Schizophrenia is mostly a progressive psychiatric illness. Although cognitive changes in chronic schizophrenia have been investigated, little is known about the consequences of a single psychotic episode on memory mechanisms and formation. We investigated changes in hippocampal long-term potentiation (LTP) and spatial memory in a rat model of an acute psychotic episode. ⋯ LTP was profoundly impaired in freely moving rats 7 days after MK801 application. Four weeks after treatment, a slight recovery of LTP was seen, however marked deficits in long-term spatial memory were evident. These data suggest that treatment with MK801 to generate an acute psychotic episode in rats, gives rise to grave disturbances in synaptic plasticity and is associated with lasting impairments with the ability to form spatial memory.
-
It has been well established that the hippocampal formation plays a critical role in the formation of memories. However, functional specialization within the hippocampus remains controversial. Using functional magnetic resonance imaging (fMRI) during a face-name associative encoding task, followed by a postscan recognition test for face memory and face-name pair memory, we investigated the roles of anterior and posterior hippocampal regions in successful encoding of associations and items. ⋯ In contrast, the posterior hippocampal formation showed activation above baseline during attempted encoding of face-name pairs, but no evidence of differential activation based on subsequent memory. Furthermore, exploratory whole-brain analyses revealed that a parahippocampal region, most likely corresponding to perirhinal cortex, showed subsequent memory effects for faces. These data provide evidence for functional specialization within the hippocampal formation based on the associative nature of the stimuli and subsequent memory.