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

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.

Cocaine- and amphetamine-regulated transcript (CART) peptide-immunopositive neuronal elements in the lateral septum: rostrocaudal distribution in the male rat.

The morphological features and distribution of cocaine- and amphetamine-regulated transcript peptide immunoreactivity (CART-IR) were studied in the lateral septum (LS) of male rats using light and electron microscopic immunocytochemistry and computer-aided densitometry. CART-IR was detected along the rostrocaudal axis of the LS in varicose axonal fibers only, although immunoreactive cell bodies and dendrites were not detected. Pericellular basket-like arrangements around immunonegative cell bodies were present. From among the targets of such pericellular baskets, glutamic acid decarboxylase (GAD)-immunopositive and NPY-immunoreactive somata were identified. Thin varicose axons were present in each section, whereas thick varicose axons were restricted to the sections of rostral position only. CART-IR was observed in varicose fibers forming a dense subependymal plexus, from which solitary varicose fibers entered the ependymal layer. The fine structure of varicosities was similar to that of other neuropeptide-containing fibers. Small varicosities established asymmetrical synaptic contacts mainly with dendrites and dendritic spines, and larger varicosities established symmetrical synapses with somata and dendritic shafts. CART-to-CART connections were not revealed. The density curve of the CART-IR along the rostrocaudal axis of LS was found to be paraboloid. CART is known as one of the most anorexigenic peptides. These results serve as basis for further physiological studies concerning the biological significance of lateral septal CART peptide in the regulation of food intake.

Somato-dendritic nicotinic receptor responses recorded in vitro from the medial septal diagonal band complex of the rodent.

The medial septal diagonal band area (MS/DB), made up of GABAergic and cholinergic neurones, plays an essential role in the generation and modulation of the hippocampal theta rhythm. To understand the part that the cholinergic neurones might play in this activity, we sought to determine whether postsynaptic nicotinic receptor responses can be detected in slices of the rodent MS/DB by puffing on acetylcholine (ACh). Neurones were characterized electrophysiologically into GABAergic and cholinergic neurones according to previous criteria. Responses of the MS/SB neurones to ACh were various combinations of fast depolarizations (1.5-2.5 s), fast hyperpolarizations (3-4 s) and slow depolarizations (20-30 s), the latter two being blocked by atropine. The fast depolarizations were partially or not blocked with cadmium and low calcium, tetrodotoxin, and antagonists of other ionotropic receptors, and were antagonized with 25 microm mecamylamine. Pharmacological investigation of the responses showed that the alpha 7* nicotinic receptor type is associated with cholinergic neurones and 10% of the GABAergic neurones, and that non alpha 7* nicotinic receptor subtypes are associated with 50% of the GABAergic neurones. Pharmacological dissection of evoked and spontaneous postsynaptic responses, however, did not provide evidence for synaptic nicotinic receptor transmission in the MS/DB. It was concluded that nicotinic receptors, although prevalent on the somatic and/or dendritic membrane compartments of neurones in the MS/DB, are on extrasynaptic sites where they presumably play a neuromodulatory role. The presence of alpha 7* nicotinic receptors on cholinergic neurones may also render these cells specifically vulnerable to degeneration in Alzheimer's disease.