User:Yoosername/sandbox

Median Raphe Nucleus

User:Casey waggett

According to a study by McKenna and Vertes, around 8 –12% of cells of the median raphe nucleus were retrogradely double-labeled after paired injections in the Medial septum CA1 region, Medial Septum CA3 region, Medial Septum Dentate Gyrus of the dorsal hippocampus, the lateral Medial Septum Dentate Gyrus, and the Medial Septum ventral hippocampus. These cells of the median raphe nucleus that send collateral projections to the Medial Septum and hippocampus may serve a unique role in modulation of desynchronization of hippocampus EEG. Most of the fibers that distribute to the medial septum terminate selectively within the medial septum-vertical limb of the diagonal band nucleus (MS/DBv) and lateral aspects of lateral septum

Also, the MnR has significantly more single- and double-labeled cells after paired injections to various Medial Septum and hippocampus regions than in DnR which demonstrate that MnR has more and stronger projections to the Medial Septum and hippocampus than the DnR.

Most of the pronounced projections to hippocampal formation (HF) distribute to the stratum lacunosum-molecular of Ammon’s horn and granule cell layer and adjacent inner molecular layer of the dentate gyrus (DG).

Also, Median raphe nucleus suppresses theta bursts of the medial septal area neurons. Numerous studies reveal that lesions in the Median raphe nucleus continuously caused ongoing theta activity andwhen the median raphe nucleus was injected with pharmacological agents, the neurons displayed inhibited activity or reduced excitatory to drive them to produce theta at short latencies and for long durations. Therefore, Median Raphe nuecleus is functional antagonist of the reticular formation which plays a critical role in hippocampal theta generation.

It has been shown that the median raphe nucleus is a contributor of serotonergic agents, especially 5-HT to the hippocampus. These findings, together with the demonstration that serotonergic agents block Long Term Potentiation (LTP) and 5-HT antagonists enhance LTP and/or memory makes it clear that the median Raphe nucleus plays a part in formation of long term memory in the hippocampus.

It has  been  shown that  serotonin-containing  neurons of  MR selectively  contact GABAergic  cells of both the septum and hippocampus. With the demonstration that GABAergic cells of the septum  and  hippocampus inhibit  projection  cells of  respective structures

Notes:

Injections in :

the CA1 and CA3 regions of Ammon’s horn of the dorsal hippocampus & the DG of the dorsal hippocampus & DG/CA1 of the ventral hippocampus (vHF) -> medial  or  lateral regions  of  the MS/DBv

CA1 and MR region: single and double-labeled cells  were:  (1) intermingled in MR (2) extended dorsoventrally throughout MR (3) were predominantly localized  to  medial regions  of  MR.

Medial MS and DG

As shown, pronounced numbers of single- and double-labeled cells were  present  throughout the  rostrocaudal  extent of MR. There were approximately equal numbers of (single) labeled cells in MR  with  MS and DG injections. Double-labeled  cells(triangles) were interspersed with single-labeled cells. In general, double-labeled cells were concentrated along the midline in MR, and there was a progressive decline in numbers of double-labeled cells from the rostral to caudal MR.

The main  findings of  the  present report  were  as follows:

(1)   pronounced numbers of retrogradely labeled cells (approximately50 cells/section) were present in MR with injections in the MS or in various regions of the hippocampus;

(2)   single- and double-labeled cells were intermingled throughout MR and present in greater numbers in rostral vs. caudal MR

(3)   significantly more single- and double-labeled cells were present in MR than in DR with all combinations of  injections. These findings  demonstrate that MR projects strongly to the MS and hippocampus, and that a significant population of MR neurons (8 –12%) sends col-lateral projections to both sites.

MR projects extensively to the lateral and medial aspects of MS

MR distributes strongly to the septum  and primarily originate from rostral pole of MR and terminate in MS and lateral part of lateral septum (LS) but avoid intermediate LS.

MR projects densely throughout hippocampus recent  studies  have demonstrated  that  MR fibersdistribute  throughout  the hippocampus,  and  terminate densely  inthe stratum lacunosum-moleculare of Ammon’s horn and the gran-ule cell layer and overlying molecular layer of DG [36,59]. MRprojections to the hippocampus were shown to primarily originatefrom the rostral pole of MR

It has  been  shown that  serotonin-containing  neurons of  MRselectively  contact (and  putatively  excite) GABAergic  cells  ofboth the septum and hippocampus These find-ings, together with the demonstration that GABAergic cells of theseptum  and  hippocampus inhibit  projection  cells of  respectivestructures

Fewer labeled cells in DR than in MR with injections in septum or in hippocampus for both single labeled and double labeled