Choline acetyltransferase‐immunoreactive neurons and terminals in the rat septal complex: A combined light and electron microscopic study

Abstract

A monoclonal antibody against choline acetyltransferase (ChAT), the acetylcholine synthesizing enzyme, was used to determine the morphological characteristics of cholinergic neurons and axon terminals within the rat septum. Light microscopy revealed numerous large fusiform or multipolar ChAT-immunoreactive neurons in the medial septal nucleus/diagonal band complex (MSDB). In contrast, virtually no immunostained cells were found in the lateral septum (Nc. septalis dorsalis and Nc. septalis lateralis). Fine immunostained fibers were most abundant close to the midline in the MSDB mainly following an ascending course. A few thin ChAT-immunoreactive fibers and terminallike pericellular punctate structures were observed in the inner part of the dorsal septal nucleus. Electron microscopy of ChAT-immunoreactive neurons revealed large cell bodies rich in cytoplasmic organelles. The cell nuclei regularly exhibited multiple invaginations of the nuclear membrane. Only rarely were terminals found that established synaptic contacts on the cell bodies of immunostained neurons. In contrast, numerous terminals formed synaptic contacts on immunoreactive dendrites. ChAT-immunopositive terminals were studied in thin sections from the MSDB and from the dorsal septal nucleus. In both regions they appeared as heavily immunostained vesicle-filled boutons that established symmetric and asymmetric synaptic contacts. In the dorsal septal nucleus immunostained terminals often showed a basketlike arrangement around immunonegative cell bodies. Our fine structural study provides evidence that cholinergic neurons in the MSDB are similar to cholinergic neurons in the basal nucleus and neostriatum, which have been described by other investigators. The presence of cholinergic synapses in the septal complex indicates that this region not only contains cholinergic projection neurons, but receives a cholinergic input itself.

Nerve Growth Factor Rapidly Increases Muscarinic Tone in Mouse Medial Septum/Diagonal Band of Broca

“…In rat, the existence of intraseptal cholinergic collateral projections onto GABAergic neurons, born out of lesioning and ultrastructural studies (Onteniente et al, 1986(Onteniente et al, , 1987Bialowas and Frotscher, 1987;Leranth and Frotscher, 1989;Brauer et al, 1998), is consistent with the notion of a muscarinic tone in the MS/DB . Although equivalent information in mouse is lacking, the pharmacological data presented in this study provide evidence for noncholinergic neurons being subject to a muscarinic tone in the mouse MS/DB.…”

“…In rat, the presence of an ambient level of acetylcholine in the MS/DB is supported by neuroanatomical and electrophysiological evidence, and ultrastructural studies have demonstrated intraseptal cholinergic synapses on GABAergic neurons in the MS/DB (Bialowas and Frotscher, 1987;Leranth and Frotscher, 1989;Brauer et al, 1998;Alreja et al, 2000;Wu et al, 2000). In this study, to demonstrate the presence of ambient acetylcholine in mouse, the acetylcholine esterase inhibitor neostigmine was applied onto MS/DB neurons while the rate of spontaneous firing was monitored.…”

“…Immunocytochemical studies revealed at the ultrastructural level cholinergic innervation of GABAergic neurons in the MS/DB (Bialowas and Frotscher, 1987;Onteniente et al, 1987;Leranth and Frotscher, 1989;Brauer et al, 1998), demonstrating the presence of an intraseptal network of cholinergic collaterals and providing the neuroanatomical substrate for a muscarinic tone in the MS/DB. In this study, we demonstrate that nerve growth factor (NGF) applied directly into the MS/DB rapidly increases muscarinic tone, as reflected by an elevated firing of noncholinergic neurons.…”

Vesicular glutamate transporter 3-immunoreactive pericellular baskets ensheath a distinct population of neurons in the lateral septum

“…Secondly, we wanted to reveal co-localization and the spatial relationship of the VGLUT3-ir PBs with well-defined neuron subpopulations and/or the fiber systems projecting to and passing the LS. Thus, we performed single and double immunofluorescence staining of VGLUT3 and the calcium-binding proteins calbindin (CALB), calretinin (CALR) and parvalbumin (PARV), with choline acetyltransferase (ChAT), tyrosine hydroxylase (TH) and tryptophan hydroxylase (TrpH), and with Wisteria floribunda agglutinin (WFA) revealing perineuronal nets (Bialowas and Frotscher, 1987;Gall and Moore, 1984;Jacobowitz and Winsky, 1991;Kiss et al, 1997;Seeger et al, 1994;Seifert et al, 1998). Triple labeling of VGLUT3 with VGLUT1 and VGLUT2 was performed, as the LS is known to be positive for both glutamatergic markers and it was recently suggested, that projection neurons in the intermediate and ventral LS use glutamate as neurotransmitter (Kaneko et al, 2002;Kocsis et al, 2003;Lin et al, 2003).…”

Fine structure and synaptology of the nitrergic neurons in medial septum of the rat brain

“…The morphological characteristics of nitrergic neurons in the MS (large indented nucleus and narrow cytoplasmic rim) and the rarity of synaptic contacts on their somata suggest that they should be cholinergic neurons. Bialowas and Frotsher [10] have shown that ChAT-immunoreactive neurons possess large nuclei with multiple invaginations of the nuclear membrane and terminals rarely were found in synaptic contact on the cell bodies of positive neurons. This is further supported by the result of Kitchener and Diamond [26]: they had shown that 97% of NADPH-diaphorase reactive neurons in the MS/DB were choline acetyltransferase immunoreactive.…”