Veterinary/zoology session

The lateral septum (LS) of the rat is a brain area taking part indirectly in the regulation of food intake. Preliminary studies proved that this brain area is very rich in orexigenic and anorexigenic neuropeptides, moreover that these neuropeptides are in close contact with the GABAergic inhibitory elements of the local neuronal network. Local glutamatergic excitatory neurons are also present here, and excitatory inputs arriving from other parts of the brain also use this amino acid transmitter molecule. Glutamate however is a common amino acid present in every cell as part of the metabolic pool of the various cell types. Thus the detection of the glutamate as neurotransmitter is far from being easy. The recently identified vesicular glutamate transporters provide a very useful tool for this purpose.

The aim of our study was to identify vesicular glutamate transporters (VGLUT-1 and VGLUT-2) and examine their morphology, their postsynaptic target distribution, and neurochemical character. The methods applied were correlated light and electron microscopic immunocytochemistry, pre- and postembedding immunogold methods and immunofluorescence double labellings.

We established that both VGLUT-1 and VGLUT-2 are present in the lateral septum. VGLUT-1 is present in much higher density than VGLUT-2. The punctate stainings suggested that axon terminals were labelled. Electron microscopy showed that the main postsynaptic targets of VGLUT-1-positive terminals were dendritic spines, whereas those of the VGLUT-2-immunreactive profiles were somata and proximal dendrites of immunonegative neurons. Our double-labelling experiments showed that at least a part of their postsynaptic targets are parvalbumin-immunoreactive, thus GABAergic inhibitory neurons. GABAergic targets also were identified with postembedding immunogold reaction. The VGLUT-2-positive terminals were found in contact with NOS-positive and NPY-positive neuronal somata as well.

With the identification of subtypes of excitatory neuronal elements our studies contribute to the better understanding of the neuronal networks of lateral septal area.