Fine Structure and Synaptology of the Nitrergic Neurons in Medial Septum of the Rat Brain

Katalin Halasy,Gergely Janzsó,Balázs Szőke

doi:10.1556/018.68.2017.1.1

Abstract

The nitrergic neuron population and certain aspects of their connectivity (peptidergic inputs, co-localization with GABA, synaptic target distribution) were studied in the medial septum of the rat brain. The histochemical localization of NADPH diaphorase and immunohistochemical identification of nNOS at light and electron microscopic level was applied. Double-labeling experiments with galanin and leucine enkephalin, moreover the postembedding GABA immunogold staining was also carried out. NADPH diaphorase- and nNOS-immunopositive neurons could be identified inside the borders of medial septum. Out of their peptidergic inputs galanin- and leucine enkephaline-immunopositive varicose fibers were found in close apposition with nNOS-immunopositive neurons. Based on fine structural characteristics (large indented nucleus, thin cytoplasmic rim, lack of axosomatic synapses) the nitrergic neurons are suggested to be identical with the septal cholinergic nerve cells. Their boutons established asymmetrical synapses mainly on dendritic shafts and spines, some of which were also nNOS-immunopositive. A lower amount of nNOS-immunopositive boutons of presumably extrinsic origin were found to be GABAergic.

Highlights

The septal area, as an interface, connects the limbic telencephalic regions with hypothalamic and brainstem areas
The results show that the medial septal area of the rat is rich in nitrergic neuronal elements of both intrinsic and extrinsic origin
This is in contrast with the human septum, where the medial part has much less immunopositive cells and these are present more densely in the diagonal band of Broca [8]

Summary

Introduction

The septal area, as an interface, connects the limbic telencephalic regions with hypothalamic and brainstem areas. The MS/DB contains primarily cholinergic [32, 35] and GABAergic projection neurons, which are believed to play a pivotal role in the generation of theta frequency oscillation through the wellknown septo-hippocampal interconnection [11, 12, 25]. The MS/DB relays motivational, emotional and autonomic information to the cortical areas via peptidergic afferents from the hypothalamus and monoaminergic afferents from the midbrain [23]. Cholinergic neurons within this complex are considered to be the primary source of acetylcholine to the cortex and hippocampus. The septohippocampal pathway is important for learning and memory-related behaviors, and degeneration of cholinergic MS/DB neurons can be diagnosed in neuropathological disorders such as Alzheimer’s disease [4, 20, 41]

Methods

Results

Conclusion