Inhibitory interneurons target precise membrane regions on pyramidal cells, but differences in their functional effects on somata, dendrites and spines remain unclear. We analyzed inhibitory synaptic events induced by cortical, fast-spiking (FS) basket cells which innervate dendritic shafts and spines as well as pyramidal cell somata. Serial electron micrograph (EMg) reconstructions showed that somatic synapses were larger than dendritic contacts. Simulations with precise anatomical and physiological data reveal functional differences between different innervation styles. FS cell soma-targeting synapses initiate a strong, global inhibition, those on shafts inhibit more restricted dendritic zones, while synapses on spines may mediate a strictly local veto. Thus, FS cell synapses of different sizes and sites provide functionally diverse forms of pyramidal cell inhibition.DOI: http://dx.doi.org/10.7554/eLife.07919.001

Long-lasting memories are formed when the stimulus is temporally distributed (spacing effect). However, the synaptic mechanisms underlying this robust phenomenon and the precise time course of the synaptic modifications that occur during learning remain unclear. Here we examined the adaptation of horizontal optokinetic response in mice that underwent 1 h of massed and spaced training at varying intervals. Despite similar acquisition by all training protocols, 1 h of spacing produced the highest memory retention at 24 h, which lasted for 1 mo. The distinct kinetics of memory are strongly correlated with the reduction of floccular parallel fiber-Purkinje cell synapses but not with AMPA receptor (AMPAR) number and synapse size. After the spaced training, we observed 25%, 23%, and 12% reduction in AMPAR density, synapse size, and synapse number, respectively. Four hours after the spaced training, half of the synapses and Purkinje cell spines had been eliminated, whereas AMPAR density and synapse size were recovered in remaining synapses. Surprisingly, massed training also produced long-term memory and halving of synapses; however, this occurred slowly over days, and the memory lasted for only 1 wk. This distinct kinetics of structural plasticity may serve as a basis for unique temporal profiles in the formation and decay of memory with or without intervals. cerebellar motor learning | AMPA receptor reduction | synapse shrinkage and elimination D uring learning, memories are formed in a specific population of neuronal circuits and are consolidated for persistence (1, 2). These memory processes are supported by discrete subcellular events such as reversible modifications in the efficacy of synaptic transmission (3-5) or persistent structural modifications in the size and number of synaptic connections (6-8). However, how these synaptic modifications relate to the dynamics of formation and decay of memories in behaving animals remains elusive. Memory formation and its persistence are also sensitive to the temporal features of stimulus presentation, as observed in the well-known "spacing effect." Training trials that include resting intervals between them (spaced training) produce stronger and longer-lasting memories than do the same number of trials with no intervals (massed training) (9). The spacing effect has been observed in a variety of explicit and implicit memory tasks (10-13), and the molecular mechanisms supporting this phenomenon have been reported (14-18). Various intracellular signaling molecules such as CREB (19), mitogen-activated protein (MAP) kinase (20, 21), and PKA (22, 23) underlie the spacing effect and are implicated in the remodeling of neuronal structures (23). In vitro studies showed that spaced stimuli induced the protrusion of new filopodia (20) and the recruitment of new synapses (24) in hippocampal neurons. However, despite the existence of numerous behavioral and molecular studies, no conjoint study has elucidated the synaptic correlates that underpin the expression of the spacing effect du...

The rock pigeon (RP) and the laughing dove (LD) are common and widely distributed species in African countries, including Egypt. The present work was carried out to characterize the comparative features of the glandular stomach (proventriculus) in these two birds, which share diets and habitats. In both species, the proventriculus is an elongated spindle obliquely situated in the cranial two‐thirds of the body cavity. The length and weight of the proventriculus in the RP were about one and half times greater than that of the LD. Histologically, the proventricular wall generally consisted of the mucosa (thickest), submucosa, muscular and serosa layers. The proventricular glands occupied most of the wall of the proventriculus within the lamina propria of the mucosa. The glands are tubuloalveolar in type, consist of variable shaped lobules and are more condensed in LD than in RP. At the proventricular‐gizzard junction (PGJ), the proventricular glands were observed external to the tubular glands of the gizzard in the RP, whereas in LD, these glands end abruptly and are separated from the tubular glands of the gizzard by a short distance. A scanning electron microscopy (SEM) of the proventricular lumen in RP revealed that the openings of the proventricular glands have an irregular outline surrounded by concentrically arranged mucosal folds that resemble a rosette shape. In the LD, these openings have a regular outline surrounded by thinner, widely spaced mucosal folds. To our knowledge, these results identified the structure of the proventriculus in RP and LD for the first time.

Most glutamatergic inputs in the neocortex originate from the thalamus or neocortical pyramidal cells. To test whether thalamocortical afferents selectively innervate specific cortical cell subtypes and surface domains, we investigated the distribution patterns of thalamocortical and corticocortical excitatory synaptic inputs in identified postsynaptic cortical cell subtypes using intracellular and immunohistochemical staining combined with confocal laser scanning and electron microscopic observations in 2 thalamorecipient sublayers, lower layer 2/3 (L2/3b) and lower layer 5 (L5b) of rat frontal cortex. The dendrites of GABAergic parvalbumin (PV) cells preferentially received corticocortical inputs in both sublayers. The somata of L2/3b PV cells received thalamic inputs in similar proportions to the basal dendritic spines of L2/3b pyramidal cells, whereas L5b PV somata were mostly innervated by cortical inputs. The basal dendrites of L2/3b pyramidal and L5b corticopontine pyramidal cells received cortical and thalamic glutamatergic inputs in proportion to their local abundance, whereas crossed-corticostriatal pyramidal cells in L5b exhibited a preference for thalamic inputs, particularly in their distal dendrites. Our data demonstrate an exquisite selectivity among thalamocortical afferents in which synaptic connectivity is dependent on the postsynaptic neuron subtype, cortical sublayer, and cell surface domain.