Lesioning and recovery of the serotoninergic projections to the hippocampus.
The time course of the changes of the hippocampal 5-hydroxytryptamine (5-HT) system after a lesion of the dorsal afferents to this brain area was studied by measuring the content of 5-HT and of 5-hydroxyindoleacetic acid (5-HIAA) in the dorsal, medial and ventral hippocampus. Furthermore, the binding sites for [3H]5-HT, [3H]ketanserin, [3H]imipramine and [3H]mianserin and a 5-HT-mediated behavior (head-twitch responses) were studied in controls and in animals bearing such a lesion. The contents of 5-HT and of 5-HIAA are higher in the ventral than in the dorsal hippocampus. Seven days after the lesion the 5-HT content decreases by 78% in the dorsal and by 50% in the ventral hippocampus. However, 60 days later, a partial recovery, possibly due to a collateral sprouting, does occur. The ratios between 5-HIAA and 5-HT are also increased 10, 14 and 21 days after the lesion, suggesting an increased utilization of the amine by the remaining neuronal terminals. The Bmax of the recognition sites for [3H]5-HT and [3H]mianserin, but not those for [3H]ketanserin are increased 10 days after the lesion and this increase lasts at least 30 days. Finally, starting 10 days after surgery and lasting for 40 days, a 5-HT-mediated behavior (head-twitch responses) shows supersensitivity. These results suggest that important changes occur in the 5-HT innervation of the hippocampus after a mechanical lesion: among these we showed a slow collateral sprouting, an increased utilization of the amine and a supersensitivity of 5-HT receptors.
D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects; D001921:Brain / Q000378:metabolism; D006624:Hippocampus / Q000378:metabolism / Q000502:physiology*; D006897:Hydroxyindoleacetic Acid / Q000378:metabolism; D007099:Imipramine / Q000378:metabolism; D007650:Ketanserin / Q000378:metabolism; D007700:Kinetics; D008803:Mianserin / Q000378:metabolism; D009416:Nerve Regeneration; D009434:Neural Pathways / Q000502:physiology; D051381:Rats; D011985:Receptors, Serotonin / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism* / Q000494:pharmacology; D013574:Synaptosomes / Q000378:metabolism
D011985:Receptors, Serotonin; D008803:Mianserin; D012701:Serotonin; D006897:Hydroxyindoleacetic Acid; D007650:Ketanserin; D007099:Imipramine