Spontaneous firing patterns and axonal projections of single corticostriatal neurons in the rat medial agranular cortex

Abstract

1. Spontaneous fluctuations of membrane potential, patterns of spontaneous firing, dendritic branching patterns, and intracortical and striatal axonal arborizations were compared for two types of corticostriatal neurons in the medial agranular cortex of urethan-anesthetized rats: 1) pyramidal tract (PT) cells identified by antidromic activation from the medullary pyramid and 2) crossed corticostriatal (CST) neurons identified by antidromic activation from the contralateral neostriatum. The ipsilateral corticostriatal projections of intracellularly stained PT neurons as well as contralateral corticostriatal neurons were confirmed after labeling by intracellular injection of biocytin. 2. All well-stained PT neurons had intracortical and intrastriatal collaterals. The more common type (6 of 8) was a large, deep layer V neuron that had an extensive intracortical axon arborization but a limited axon arborization in the neostriatum. The less common type of PT neuron (2 of 8) was a medium-sized, superficial layer V neuron that had a limited intracortical axon arborization but a larger and more dense intrastriatal axonal arborization. Both subclasses of PT neurons had anatomic and physiological properties associated with slow PT cells in cats and monkeys and conduction velocities < 10 m/s. All of the PT cells but one were regular spiking cells. The exception cell fired intrinsic bursts. 3. Intracellularly stained CST neurons were located in the superficial half of layer V and the deep part of layer III. Their layer I apical dendrites were few and sparsely branched. Their axons gave rise to an extensive arbor of local axon collaterals that distributed in the region of the parent neuron, frequently extending throughout the more superficial layers, including layer I. Axon collaterals were also traced to the corpus callosum, as expected from their contralateral projections, and they contributed axon collaterals to the ipsilateral neostriatum. In the neostriatum, these axons formed extended arborizations sparsely occupying a large volume of striatal tissue. All CST neurons were regular spiking cells. 4. Both types of cells displayed spontaneous membrane fluctuations consisting of a polarized state (-60 to -90 mV) that was interrupted by 0.1- to 3.0-s periods of depolarization (-55 to -45 mV) accompanied by action potentials. The membrane potential was relatively constant in each state, and transitions between the depolarized and hyperpolarized states were sometimes periodic with a frequency of 0.3-1.5 Hz. A much faster (30-45 Hz) subthreshold oscillation of the membrane potential was observed only in the depolarized state and triggered action potentials that locked to the depolarizing peaks of this rhythm.(ABSTRACT TRUNCATED AT 400 WORDS)

NMDA-dependent facilitation of corticostriatal plasticity by the amygdala

“…However, this problem might be circumvented if the BLA effect required that multiple pairings with cortical inputs occurred over time before a significant potentiation is achieved. Although 60 such pairings were sufficient to induce LTP in our conditions, the minimum number of coincident cortical-BLA firings might be different in vivo where corticostriatal neurons exhibit sustained spontaneous activity (46,47). In these conditions, BLA inputs might only facilitate cortical synapses that consistently and repeatedly exhibit phasic increases in activity around BLA spikes.…”

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“…In the normal brain in vivo, the neurons of the cerebral cortex and striatum regularly shift to depolarized states from which action potentials are selectively generated (Cowan and Wilson 1994;O'Donnell and Grace 1995;West et al, submitted). These "up" states are dependent on convergent activity of excitatory synaptic inputs to the neuron (Steriade 2001;West et al, submitted).…”

Interaction between neocortical and hippocampal networks via slow oscillations

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