Abstract
The nucleus reuniens (RE) of the midline thalamus has been shown to strongly innervate structures of the limbic forebrain, prominently including the hippocampus (HF) and the medial prefrontal cortex (mPFC) and to exert pronounced excitatory effects on HF and mPFC. It was unknown, however, whether RE projections to, and hence actions on, the HF and mPFC originate from a common or largely separate groups of RE neurons. Using fluorescent retrograde tracing techniques, we examined the patterns of distribution of RE cells projecting to HF, to the mPFC or to both sites via axon collaterals. Specifically, injections of the retrograde tracers Fluorogold (FG) or Fluororuby (FR) were made in the mPFC and in various subfields of HF and patterns of single (FG or FR) or double labeled (FG + FR) cells in RE were determined. Pronounced numbers of (single) labeled neurons were present throughout RE with FG or FR injections, and although intermingled in RE, cells projecting to the mPFC were preferentially distributed along the midline or in the perireuniens nucleus (pRE), whereas those projecting to HF occupied a wide mediolateral cross sectional area of RE lying between cells projecting to the mPFC. Approximately, tenfold more labeled cells were present in RE with ventral compared to dorsal CA1 injections. Like single labeled neurons, double labeled cells were found throughout RE, but were most densely concentrated in areas of greatest overlap of FG+ and FR+ neurons or mainly in the lateral one-third of RE, medial to pRE. Depending on specific combinations of injections, double labeled cells ranged from approximately 3–9% of the labeled neurons. The nucleus reuniens has been shown to be a vital link in limbic subcortical–cortical communication and recent evidence indicates a direct RE involvement in hippocampal and medial prefrontal cortical-dependent behaviors. The present findings indicate that RE is critically positioned to influence the HF and mPFC, and their associated behaviors, via separate or collateral projections to these sites.
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Abbreviations
- CA1,d,v:
-
Field CA1 of Ammon’s horn, dorsal, ventral division
- CA3:
-
Field CA3 of Ammon’s horn
- DB:
-
Double labeled cell
- DBS:
-
Deep brain stimulation
- EC, l, m:
-
Entorhinal cortex, lateral, medial division
- FG:
-
Fluorogold
- FR:
-
Fluororuby
- HF:
-
Hippocampal formation
- IL:
-
Infralimbic cortex
- MCS:
-
Minimally conscious state
- mPFC:
-
Medial prefrontal cortex
- mt:
-
Mammillothalamic tract
- PFC:
-
Prefrontal cortex
- PL:
-
Prelimbic cortex
- pRE:
-
Perireuniens nucleus of thalamus
- PT:
-
Paratenial nucleus of thalamus
- PV:
-
Paraventricular nucleus of thalamus
- PVHy:
-
Paraventricular nucleus of hypothalamus
- RAM:
-
Radial arm maze
- RE:
-
Nucleus reuniens of thalamus
- RH:
-
Rhomboid nucleus of thalamus
- slm:
-
Stratum lacunosum moleculare
- SMT:
-
Submedial nucleus of thalamus
- SUB,v:
-
Subiculum, ventral division
- VS:
-
Vegetative state
- 3V:
-
Third ventricle
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This research was supported by National Science Foundation grant IOS 0820639 to RPV.
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Hoover, W.B., Vertes, R.P. Collateral projections from nucleus reuniens of thalamus to hippocampus and medial prefrontal cortex in the rat: a single and double retrograde fluorescent labeling study. Brain Struct Funct 217, 191–209 (2012). https://doi.org/10.1007/s00429-011-0345-6
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DOI: https://doi.org/10.1007/s00429-011-0345-6