The European journal of neuroscience
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Comparative Study
The role of the medial supramammillary nucleus in the control of hippocampal theta activity and behaviour in rats.
The medial supramammillary nucleus (mSUM) controls the frequency of hippocampal theta activity, completely in anaethsetized rats and partially in free-moving rats. mSUM could therefore influence hippocampal contributions to cognition and emotion. Using chemical lesions of mSUM in rats, we tested whether mSUM is involved in controlling several hippocampal-dependent functions: (i) defensive behaviour (open field, fear conditioning); (ii) behavioural inhibition (fixed interval schedule, differential reinforcement of low rates schedule); and (iii) spatial learning (water maze). ⋯ There was not always a parallel between changes in theta frequency and behaviour; behaviours changed despite unchanged theta in defensive tasks and learning changed little despite a lower frequency of theta in the water maze task. This suggests that mSUM function impacts on emotional behaviour more than cognition, and can modulate theta and behaviour independently.
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In the adult rat olfactory bulb, neurons are continually generated from progenitors that reside in the lateral ventricle wall. This study investigates long-term survival and cell death of newly generated cells within the adult olfactory bulb. After injecting rats at 2 months of age with 5-bromodeoxyuridine (BrdU), the newly generated cells were quantified over a period of 19 months. ⋯ These newborn cells differentiate more slowly into periglomerular interneurons, with a delay of more than 1 month when compared to the granule cells. The newly generated periglomerular neurons, among them a significant fraction of dopaminergic cells, showed a similar decline in number compared to the granule cell layer and long-term survival for the remaining new neurons of up to 19 months. Rather than replacing old neurons, this data suggests that adult olfactory bulb neurogenesis utilizes the overproduction and turnover of young neurons, which is reminiscent of the cellular dynamics observed during brain development.