Biology Reference
In-Depth Information
rat mPFC in vivo according to their firing properties in response to current injection; regular
firing, inactivating bursting and non-inactivating bursting (Degenetais et al. 2002). Similar
firing properties were recorded in vitro (Yang et al. 1996). In addition, several types of
interneuron have been identified (Kawaguchi and Kubota 1997).
Horizontal cortico-cortical connections are made between layer 2/3 pyramidal neurons in
the prelimbic and infralimbic cortices (Lewis and Gonzalez-Burgos 2000; Gabbott et al.
2003). In primates, layer 3 neurons in the PFC form “stripes” when axons are labelled with
biotinylated dextran amine (BDA), revealing reciprocal connections (Melchitzky et al. 2001).
Fifty percent of the local connections made within these stripes are to interneurons, while
90% are to excitatory neurons in other stripes, suggesting that layer 3 neurons in the PFC
function in modules. Indeed in primates, synaptic reverberation contributing to working
memory is thought occur at cortico-cortical synapses in layer 3 (Levitt et al. 1993; Kritzer and
Goldman-Rakic 1995; Gonzalez-Burgos et al. 2000; Lewis and Gonzalez-Burgos 2000). As
with other cortical regions, layer 5 pyramidal neurons are the output cells of the PFC and
project to many other cortical and subcortical regions. In addition to local inputs, afferents
terminating in layer 2/3 also arise from other cortical regions, such as the contralateral mPFC,
the entorhinal cortex and association cortices, the mediodorsal nucleus of the thalamus
(Kuroda et al. 1998), the hippocampus and the amygdala. Afferents terminating in layer 5
arise intrinsically, together with afferents from other cortical regions, the hippocampus, the
amygdala and the thalamus (Jay and Witter 1991; Gonzalez Burgos et al. 2007).
Dual recordings from pairs of pyramidal neurons in other regions of the neocortex have
shown that connections between layer 2/3 pyramidal neurons and layer 5 pyramidal neurons
are mostly made on the apical dendrites of layer 5 neurons, whereas connections between
layer 5 pyramidal neurons are made on the basal dendrites of layer 5 neurons (Letzkus et al.
2006; Sjostrom and Hausser 2006). To date, connectivity between layer 5 pyramidal neurons
has only been examined in the ferret mPFC. These connections were also made on the basal
dendrites, and occurred in approximately 12% of pairs of neurons, similar to the connection
rate observed in the visual cortex (Wang et al. 2006). However the incidence of reciprocal
connections in these pairs was double that seen in the visual cortex, and was most frequently
observed between pyramidal neurons with similar firing properties and synaptic properties
(Wang et al. 2006). This may be attributable to the substantially higher number of dendritic
spines on mPFC pyramidal neurons compared to visual cortical pyramidal neurons, providing
the mPFC with advanced computational abilities (Elston 2003). Paired recordings have yet to
be made between layer 2/3 and layer 5 pyramidal neurons in the mPFC, thus the properties of
these connections are currently unknown. However, synapses on pyramidal neurons in the
mPFC at both inputs express both α-amino-3-hydroxy-5-methyl-4-issoxazoleproprionic acid
(AMPA) and N-methyl-D-aspartate (NMDA) receptors (Hirsch and Crepel 1991; Kang
1995).
3.
S
HORT
-T
ERM
P
LASTICITY IN THE
PFC
Short-term plasticity is the change in strength of synaptic responses over a short time
period that occurs with repetitive stimulation. There are several types of short-term plasticity.
Over a period of milliseconds, during a train of excitatory postsynaptic potentials (EPSPs),
