Disruption of Neocortical Lamina V Neuronal Bursts by Serotonin in Urethane Anaesthetized Rats

Abstract

Time-shared high speed cyclic voltametry using carbon fibre multibarrelled microelectrodes was used to monitor the concentration of 5-Hydroxytryptamine administered by iontophoresis to locations in lamina V of Sm 1 neocortex and to record spontaneous neuronal spike activity. In the absence of 5-Hydroxytryptamine at any one recording location the firing of two or more individual units was seen to be synchronized so that the pattern of multi-unit activity consisted of synchronized clusters of spike activity interspersed with period of neuronal silence. The repetition rate of such clusters of neuronal activity was seen to be between 0.5 and 4 Hz. Maximum concentrations of 2.7 × 10⁻⁷M 5-Hydroxytryptamine produced by iontophoresis disrupted synchronized neuronal cluster activity. 5-Hydroxytryptamine at a concentration of 6.2 × 10⁻⁸M resulted in a greater than 50% inhibition of activity for 47 single units but a change in firing pattern from cluster restricted high frequency activity to a continuous mode of firing for a separate population of 11 units. Intraperitoneal administration of P-Chloroamphetamine produced similar changes of neuronal firing and hence loss of synchrony.

Key Words:

• Serotonin
• Sml Neocort
• burst activity
• single units
• 5-Hydroxytryptamine
• rat