Denervation supersensitivity to serotonin in rat forebrain: single cell studies

Area of Science:

• Neuroscience
• Neuropharmacology

Background:

• Serotonin (5-hydroxytryptamine, 5-HT) plays a crucial role in regulating neuronal activity in brain regions like the amygdala (AMYG) and ventral lateral geniculate nucleus (vLGN).
• Denervation supersensitivity is a phenomenon where target neurons become more responsive to neurotransmitters after losing their native input.

Purpose of the Study:

• To investigate the development and characteristics of denervation supersensitivity to serotonin (5-HT) in the AMYG and vLGN.
• To elucidate the time course and specificity of this supersensitivity following selective 5-HT neuron destruction.

Main Methods:

• Single cell recordings were employed to measure neuronal responses.
• Microiontophoretic application of neurotransmitters allowed for precise stimulation.
• Histochemical and biochemical techniques assessed changes in 5-HT projections and uptake.

Main Results:

• Destruction of 5-HT projections using 5,7-dihydroxytryptamine (5,7-DHT) led to enhanced neuronal sensitivity to 5-HT within 24 hours, peaking at 7 days.
• The development of supersensitivity paralleled reductions in 5-HT varicosity density and synaptosomal 5-HT uptake.
• Initially selective for 5-HT, supersensitivity later included D-lysergic acid diethylamide (LSD) and, to a lesser extent, norepinephrine (NE) and gamma-aminobutyric acid (GABA) in the AMYG.

Conclusions:

• Selective destruction of 5-HT pathways induces a time-dependent denervation supersensitivity in the AMYG and vLGN.
• This supersensitivity is associated with structural and functional changes in the serotonergic system.
• Chronic inhibition of 5-HT synthesis, unlike denervation, did not induce supersensitivity, suggesting a role for nerve terminal integrity.