| The inferior colliculus (IC) is a principal structure of the auditory midbrain and a significant integrative center within the central auditory pathway. In serves as mammals the IC can be divided into three anatomical subdivisions: the central nucleus (ICc), the dorsal cortex (ICd) and the external cortex (ICx). Unlike the We, the ICx receives its primary inputs from the contralateral and ipsilateral ICc, auditory cerebral cortical areas and from regions of motor and other sensory systems. This wide array of primary projections from both auditory and non-auditory sources makes the ICx a unique structure within the auditory brainstem. The current study supports the notion that the ICx may serve as a center to integrate auditory and non-auditory information, which is modulated by behavioural state. In this study we examined intrinsic membrane properties and synaptic responses of ICx neurons in young rat's brain slice preparations.; Visual whole-cell patch clamp recordings were taken from ICx neurons (N = 99) in coronal slices from rats between the ages of 8 to 11 days. The ICx neurons displayed various types of firing patterns in response to depolarizing and hyperpolarizing current injection, including regular, adaptation, pauser and bursting type. For distribution, the regular type cells constitute the majority (68%), followed by adaptation (17%), pauser (12%) and bursting cells (3%). In response to hyperpolarizing current injection, many ICx neurons illustrated a pronounced sag in the membrane potential, representing a hyperpolarization-activated current (Ih). Some neurons (25%) displayed a Ca2+-dependent rebound depolarization following hyperpolarization of the membrane with negative current injection. In response to depolarizing current injection, 70% of ICx neurons displayed the presence of a Ca2+-mediated potential expressed as Ca2+ spikes/humps, uncovered when Na+ and K+ currents were removed. To study the synaptic responses, a stimulating electrode was placed in the ICc. The graded responses displayed a combination of excitatory and/or inhibitory potentials and pharmacological analyses showed the presence of glutamatergic, GABAergic and glycinergic transmission. Serotonin (5-HT) application showed modulation of the synaptic responses in the ICx. The modulatory effects of 5-HT were most pronounced on the glutamatergic NMDA and AMPA receptor mediated responses. |
