Differential signaling via the same axon of neocortical pyramidal neurons

Abstract

The nature of information stemming from a single neuron and conveyed simultaneously to several hundred target neurons is not known. Triple and quadruple neuron recordings revealed that each synaptic connection established by neocortical pyramidal neurons is potentially unique. Specifically, synaptic connections onto the same morphological class differed in the numbers and dendritic locations of synaptic contacts, their absolute synaptic strengths, as well as their rates of synaptic depression and recovery from depression. The same axon of a pyramidal neuron innervating another pyramidal neuron and an interneuron mediated frequency-dependent depression and facilitation, respectively, during high frequency discharges of presynaptic action potentials, suggesting that the different natures of the target neurons underlie qualitative differences in synaptic properties. Facilitating-type synaptic connections established by three pyramidal neurons of the same class onto a single interneuron, were all qualitatively similar with a combination of facilitation and depression mechanisms. The time courses of facilitation and depression, however, differed for these convergent connections, suggesting that different prepostsynaptic interactions underlie quantitative differences in synaptic properties. Mathematical analysis of the transfer functions of frequency-dependent synapses revealed supralinear, linear, and sub-linear signaling regimes in which mixtures of presynaptic rates, integrals of rates, and derivatives of rates are transferred to targets depending on the precise values of the synaptic parameters and the history of presynaptic action potential activity. Heterogeneity of synaptic transfer functions therefore allows multiple synaptic representations of the same presynaptic action potential train and suggests that these synaptic representations are regulated in a complex manner. It is therefore proposed that differential signaling is a key mechanism in neocortical information processing, which can be regulated by selective synaptic modifications.Neuronal signaling in the neocortex has been the subject of extensive debate (1-3). One approach to this problem is to determine how frequency-dependent changes in synaptic transmission dictate which features of action potentials (APs) trains are transmitted effectively to the postsynaptic neuron (4-6). This characterization of the input (AP) and the output (synaptic response) properties allows assessment of the transfer function of synaptic connections. It has been reported in several nonmammalian systems that synaptic responses via the same axon onto different types of targets can display different frequency-dependent properties (7-12). Dual recordings in the neocortex have revealed that synaptic connections from pyramidal neurons onto some classes of interneurons can display frequency-dependent facilitation whereas transmission onto pyramidal neurons typically displays depression (13-14), suggesting that differential transmission is also likely in mammalian neocortex...

Short-Term Synaptic Plasticity Orchestrates the Response of Pyramidal Cells and Interneurons to Population Bursts

“…Short-term plasticity allows distinct classes of neuron, targeted by the same axon, to respond differentially to the same pre-synaptic drive (Liaw and Berger, 1996;Markram et al, 1998). This diversity of response is a marked feature of the interneuron population .…”

Frequency-dependent synaptic potentiation, depression and spike timing induced by Hebbian pairing in cortical pyramidal neurons

“…However, this decrease was not further analyzed and was treated in Markram and Tsodyks ( 1996) and in later studies (Markram et a!., , 1998b(Markram et a!., , 1998c as consistent with no change at all. The current results suggest that the observed decrease was significant and that it was due to the fact that FOP was not characterized at a phase close to steady-slate at high frequencies.…”

Computação por assembleias neurais em redes neurais pulsadas.

“…Este tipo de fenômeno foi abordado por Markram e colaboradores [37], que apresentou um modelo fenomenológico para simulação desse tipo de adaptação sináptica rápida [98]. Uma representação gráfica do fenômeno pode ser visto na figura seguinte.…”

“…Gráficos mostrando dados experimentais a partir de Markram et al [98], obtidos de neurônios do córtex de ratos. (A) Após um tempo sem receber spikes o neurônio j recompõe sua sinapse, e ao receber o primeiro spike o potencial evocado volta a ser intenso (facilitação).…”

“…Um dos modelos mais conhecido e usado para simular o fenômeno é o de Markram [98], que pode ser definido pelas equações:…”