Dendritic Trunks Research Articles

Crystal morphologies in thin films of PEO/PMMA blends

Crystallization in thin films of poly(ethylene oxide) in blends with poly(methyl methacrylate) has been studied. The film thickness is fixed at 120 nm, while the blend composition, PMMA molar mass, and crystallization temperature are varied. Blends with a composition of 50/50 (wt% PEO/wt% PMMA) exhibit a variety of morphologies that are highly dependent on PMMA molar mass and crystallization temperature. A needle morphology not previously reported in this system is also observed. For 40/60 blends, dendrites and DBM are observed at high PMMA molar mass. At low PMMA molar mass, a number of morphologies are observed over small changes in the experimental controls. In 35/65 blends, dendritic growth is observed with sidebranches at 45° and 90° to the dendrite trunk at low undercooling and only at 90° for larger undercooling. For 30/70 blends, dendritic growth is observed over a large range of PMMA molar mass and crystallization temperature. Maps demonstrating the role of the control parameters on morphological development are reported. The observed morphologies are believed to result from the combined effects of the lack of crystallizable chains at the growth front, low dimensionality, rejection of non-crystallizable chains, and variation of the effective levels of noise and/or anisotropy.

Effect of foreign particles on the dendritic growth in phase-field theory

The presence of foreign particles in the undercooled melt can influence the evolution of solidification structure and change the dendritic morphology. In this work, according to the KKS model, a hybrid phase field model for binary alloys, which takes into account the random crystallographic orientation, is developed to analyze the effect of misorientation between foreign particles and crystal grains on the dendritic growth. The simulation results show that the influence of foreign particles depends on the particle size, position, numbers and the degree of misorientation. The foreign particles which do not match the initial orientation of the crystal cause the dendrite trunks to deflect and split, leading to the formation of irregular dendritic morphology.

Anodal vs cathodal stimulation of motor cortex: A modeling study

ObjectiveTo explore the effects of electrical stimulation performed by an anode, a cathode or a bipole positioned over the motor cortex for chronic pain management. MethodsA realistic 3D volume conductor model of the human precentral gyrus (motor cortex) was used to calculate the stimulus-induced electrical field. The subsequent response of neural elements in the precentral gyrus and in the anterior wall and lip of the central sulcus was simulated using compartmental neuron models including the axon, soma and dendritic trunk. ResultsWhile neural elements perpendicular to the electrode surface are preferentially excited by anodal stimulation, cathodal stimulation excites those with a direction component parallel to its surface. When stimulating bipolarly, the excitation of neural elements parallel to the bipole axis is additionally facilitated. The polarity of the contact over the precentral gyrus determines the predominant response. Inclusion of the soma-dendritic model generally reduces the excitation threshold as compared to simple axon model. ConclusionsElectrode polarity and electrode position over the precentral gyrus and central sulcus have a large and distinct influence on the response of cortical neural elements to stimuli. SignificanceModeling studies like this can help to identify the effects of electrical stimulation on cortical neural tissue, elucidate mechanisms of action and ultimately to optimize the therapy.

Dendritic excitability and calcium signalling in the mitral cell distal glomerular tuft

The processing of odour information starts at the level of the olfactory glomerulus, where the mitral cell distal dendritic tuft not only receives olfactory nerve sensory input but also generates dendrodendritic output to form complicated glomerular synaptic circuits. Analysing the membrane properties and calcium signalling mechanisms in these tiny dendritic branches is crucial for understanding how the glomerular tuft transmits and processes olfactory signals. With the use of two-photon Ca2+ imaging in rat olfactory bulb slices, we found that these distal dendritic branches displayed a significantly larger Ca2+ signal than the soma and primary dendrite trunk. A back-propagating action potential was able to trigger a Ca2+ increase throughout the entire glomerular tuft, indicative of the presence of voltage-gated Ca2+ conductances in all branches at different levels of ramification. In response to a train of action potentials evoked at 60 Hz from the soma, the tuft Ca2+ signal increased linearly with the number of action potentials, suggesting that these glomerular branches were able to support repetitive penetration of Na+ action potentials. When a strong olfactory nerve excitatory input was paired with an inhibition from mitral cell basal dendrites, a small spike-like fast prepotential was revealed at both the soma and distal primary dendrite trunk. Corresponding to this fast prepotential was a Ca2+ increase confined locally within the glomerular tuft. In summary, the mitral cell distal dendritic tuft possesses both Na+ and Ca2+ voltage-dependent conductances which can mediate glomerular Ca2+ responsiveness critical for dendrodendritic output and synaptic plasticity.

Persistent and Reversible Morphine Withdrawal‐Induced Morphological Changes in the Nucleus Accumbens

Morphine withdrawal produces a hypofunction of mesencephalic dopamine (DA) neurons which impinge upon medium spiny neurons (MSN) of the forebrain. After chronic treatment rats were either spontaneously or pharmacologically withdrawn from chronic morphine: under these two distinct conditions we studied the effects of withdrawal on spine density of MSN of the core and shell of the nucleus accumbens (NAcc) at various times (1-3-7-14 days). MSN were stained with the Golgi-Cox procedure and analyzed by a confocal laser-scanning microscope. Our analysis shows that both spontaneous and naloxone-induced withdrawal produces a long-lasting but reversible reduction in spines' density in shell MSN, as compared with core MSN. This effect is selectively localized at the level of second-order dendritic trunks and persists up to 14 days when spine density was found within control (pretreatment) values. By contrast, spine density counts of NAcc MSN from rats chronically treated with morphine, did not reveal any change over time. Collectively, the results of the present article suggest that spontaneous and pharmacologically precipitated withdrawal, but not chronic morphine, persistently but reversibly reduce spines' density under a condition of reduced mesolimbic DA transmission, and the reduction of spines' density in second-order dendritic trunks is selectively segregated in the MSN of the shell of the NAcc. Morphine withdrawal dramatically, lastingly, and reversibly reduces spine density, selectively in second-order dendritic trunks of NAcc shell MSN, thereby further impoverishing the already abated DA transmission. These results may be relevant in the most harmful consequences of drug addiction such as craving and loss of control over intake and are in line with recent views suggesting the hypodopaminergic state as a cardinal feature of drug dependence.

Activity-Dependent Dendritic Spine Structural Plasticity Is Regulated by Small GTPase Rap1 and Its Target AF-6

Activity-dependent remodeling of dendritic spines is essential for neural circuit development and synaptic plasticity, but the mechanisms that coordinate synaptic structural and functional plasticity are not well understood. Here we investigate the signaling pathways that enable excitatory synapses to undergo activity-dependent structural modifications. We report that activation of NMDA receptors in cultured cortical neurons induces spine morphogenesis and activation of the small GTPase Rap1. Rap1 bimodally regulates spine morphology: activated Rap1 recruits the PDZ domain-containing protein AF-6 to the plasma membrane and induces spine neck elongation, while inactive Rap1 dissociates AF-6 from the membrane and induces spine enlargement. Rap1 also regulates spine content of AMPA receptors: thin spines induced by Rap1 activation have reduced GluR1-containing AMPA receptor content, while large spines induced by Rap1 inactivation are rich in AMPA receptors. These results identify a signaling pathway that regulates activity-dependent synaptic structural plasticity and coordinates it with functional plasticity.

Morphine withdrawal‐induced morphological changes in the nucleus accumbens

Morphine withdrawal produces a hypofunction of mesencephalic dopamine neurons that impinge upon medium spiny neurons (MSN) of the forebrain. After chronic treatment (from 20 to 140 mg/kg of morphine twice a day over 14 days at escalating doses) rats were withdrawn from chronic morphine spontaneously and pharmacologically. In these two distinct conditions we studied the effects of withdrawal on the morphology of MSN of the core and shell of the nucleus accumbens (Nacc). MSN were stained with the Golgi-Cox procedure and analysed by a confocal laser-scanning microscope (CLSM). Our analysis shows that, shell and core MSN differed significantly for perikarya size and spine density, and the various morphine treatments did not affect the perikarya morphometry. Both spontaneous and naloxone-induced withdrawal produced a similar reduction in spine density in MS shell neurons, as compared with MS core neurons. This effect is selectively localized at the level of second order dendritic trunks where afferents converge. By contrast, spine density counts of accumbens MSN from rats chronically treated with morphine, did not reveal any change. Collectively, the results of the present study are twofold: (i) spontaneous and pharmacologically precipitated withdrawal, but not chronic morphine per se, affects spine density of target structures of a reduced mesolimbic dopamine transmission, and (ii) the reduction of spine density in second order dendritic trunks is selectively segregated in the MSN of the shell of the Nacc. In conclusion, morphine withdrawal dramatically alters spine density, selectively in second order dendritic trunks of Nacc shell MSN, thereby further impoverishing the already abated dopamine (DA) transmission. This is in line with recent views suggesting the hypodopaminergic state as a cardinal feature of opioid dependence.

Imaging of Spiking and Subthreshold Activity of Mitral Cells with Voltage‐Sensitive Dyes

To obtain a more complete description of individual neurons, it is necessary to complement electrical measurements with technologies such as voltage imaging with intracellular dyes, which permit massive parallel recording from many sites on neuronal processes. Utilizing such an approach, we investigate the functional structure of the mitral cell, the principal output neuron in the rat olfactory bulb. These experiments were designed to determine the number, location, and the stability of spike trigger zones, the excitability of terminal dendritic branches, the pattern and nature of spike initiation and propagation in the primary dendrite, the basic characteristics of the evoked EPSPs at the site of origin (the glomerular tuft), and its attenuation along the primary dendrite. The images of spike trigger zones showed that an action potential can be initiated in three different compartments of the mitral cell: the soma-axon region, the primary dendrite trunk, and the terminal dendritic tuft, which appears to be fully excitable. The amplitude of the EPSPs evoked by olfactory nerve stimulation was determined at the site of origin (glomerular tuft) and its attenuation was monitored optically along the entire length of the primary dendrite.

Voltage imaging from dendrites of mitral cells: EPSP attenuation and spike trigger zones.

To obtain a more complete description of individual neurons, it is necessary to complement the electrical patch pipette measurements with technologies that permit a massive parallel recording from many sites on neuronal processes. This can be achieved by using voltage imaging with intracellular dyes. With this approach, we investigated the functional structure of a mitral cell, the principal output neuron in the rat olfactory bulb. The most significant finding concerns the characteristics of EPSPs at the synaptic sites and surprisingly small attenuation along the trunk of the primary dendrite. Also, the experiments were performed to determine the number, location, and stability of spike trigger zones, the excitability of terminal dendritic branches, and the pattern and nature of spike initiation and propagation in the primary and secondary dendrites. The results show that optical data can be used to deduce the amplitude and shape of the EPSPs evoked by olfactory nerve stimulation at the site of origin (glomerular tuft) and to determine its attenuation along the entire length of the primary dendrite. This attenuation corresponds to an unusually large mean apparent "length constant" of the primary dendrite. Furthermore, the images of spike trigger zones showed that an action potential can be initiated in three different compartments of the mitral cell: the soma-axon region, the primary dendrite trunk, and the terminal dendritic tuft, which appears to be fully excitable. Finally, secondary dendrites clearly support the active propagation of action potentials.

The effect of epidural compression on cerebral cortex: a rat model.

We developed a rat model of epidural plastic bead implantation to study the effect of physical compression on the cerebral cortex. Epidural implantation of a bead of appropriate size compressed the underlying sensorimotor cortex without apparent ischemia, since the capillary density of the cortex was increased. Although the thickness of all layers of the compressed cortex was significantly decreased, no apparent changes in the number of NADPH-diaphorase reactive neurons, reactive astrocytes, or microglial cells were observed, nor were apoptotic neurons observed. In fact, the densities of the neurons in most cortical layers apparently increased. To determine how epidural compression affects neuronal morphology, the dendritic arbors of layer III and V pyramidal neurons were evaluated using a fixed tissue intracellular dye injection technique. Neurons in both layers remained pyramidal in shape and their somatic sizes remained unaltered for at least a month after compression. On the other hand, their total dendritic length was significantly reduced beginning at 3 days post implantation. These analyses showed that apical dendrites were affected sooner than basal ones. The reduction of dendritic length was associated with a drop in the number of dendritic branches rather than dendritic trunks, suggesting the trimming of the peripheral part of the dendritic arbor. Detailed analysis showed that dendritic spines on all dendrites were reduced as early as 3 days following implantation. These results suggest that cortical neurons remodel their structures substantially within 3 days after being subjected to epidural compression.

Dendritic initiation and propagation of spikes and spike bursts in a multimodal sensory interneuron: the crustacean parasol cell.

Invasion of dendrites by spikes and spike bursts can play a critical role in regulating the output of central neurons by modifying their dynamic input-output relationships. Back-propagating bursts can modulate voltage-gated channels in the short term and can also modify long-term responses to synaptic input. Determining the morphological site of spike initiation and the mode of propagation through the dendritic arbor is therefore crucial to an understanding of a neuron's functional properties. I used electrophysiological methods to study parasol cells in isolated, perfused head preparations of the freshwater crayfish Procambarus clarkii to determine the compartment of origin of orthodromically activated action potentials and bursts that propagate within the dendritic arbor and to examine the identity of low-amplitude, electrotonically recorded spike events that are present in more than one-half of the intracellular recordings obtained from dendrites in these neurons. Experiments using antidromic activation of parasol cell axons indicated that electrotonically recorded spikes probably are generated in neighboring parasol cells, to which the impaled neurons are electrically coupled. Both paired intracellular recordings and extracellular field potential measurements were used to compare arrival times of antidromic and orthodromic spikes at loci in the vicinity of the trunk and the basal branch compartments of parasol cell dendrites. These methods provided consistent results, indicating that synaptically evoked action potentials are initiated at a site on the trunk, from which point they back-propagate into the basal branches within the hemiellipsoid body, and presumably, also orthodromically to the axon. Data are presented suggesting that bursts also arise at a trunk locus, but one that is different from the initiation point of single spikes evoked by excitatory postsynaptic potentials (EPSPs). Morphological specializations between the dendritic trunk and basal branches may facilitate back-propagation of spikes and spike bursts into the basal branches.

On the Crystallization Process of Hypoeutectic Al‐6 % Cu,Unmodified and Sr‐Modified Al‐2 % Si Solidification Alloys

The solidification process of some hypoeutectic aluminum alloys was studied over a wide range of cooling rates. Microsegregation effects were characterized by the minimum concentration of solute found in primary dendrite trunks (see Figure for a typical example), using microprobe analysis, and the fraction of eutectic phases evaluated as a function of the cooling rate. Finally, a non‐equilibrium thermodynamic model of the process, which is able to explain some of the experimental observations, was developed.

Firing activity and postsynaptic properties of morphologically identified neurons of ventral oral pontine reticular nucleus

The ventral part of the oral pontine reticular nucleus (vRPO) is an important region for the generation and maintenance of REM sleep. Firing activity and synaptic response properties of morphologically identified vRPO neurons have been investigated in urethane-anaesthetized cats. Extracellular recordings were performed through recording micropipettes and neurons were extracellularly stained with biocytin. Two types of neurons were identified under spontaneous conditions: type I neurons (77%) are characterized by non-rhythmic firing; type II neurons (23%) display single spikes firing rhythmically at between 7 and 22 Hz. Type I neurons displayed ellipsoid somata with thick dendritic trunks and axons that arose from either the soma or the initial dendritic segment; these axons could not be clearly followed. Type II neurons showed polygonal somata with radial dendrites; their axons branched at a small distance from the soma. Electrical stimulation of the contralateral vRPO elicited responses in both neuron types (57% and 31%, respectively); this effect was blocked by the non-NMDA glutamatergic receptor antagonist CNQX. Electrical stimulation of the PpT evoked orthodromic responses in type I neurons (41%) and inhibited the firing rate of all type II neurons for 50–100 ms. Both effects were blocked by the muscarinic receptor antagonist atropine. The cholinergic agonist, carbachol, increased the firing rate in most type I neurons and inhibited most type II neurons in these animals. The results demonstrated that the activity of vRPO neurons is modulated through the postsynaptic activation exerted by extrinsic afferents on cholinergic and glutamatergic receptors.

Multiple modes of action potential initiation and propagation in mitral cell primary dendrite.

The mitral cell primary dendrite plays an important role in transmitting distal olfactory nerve input from olfactory glomerulus to the soma-axon initial segment. To understand how dendritic active properties are involved in this transmission, we have combined dual soma and dendritic patch recordings with computational modeling to analyze action-potential initiation and propagation in the primary dendrite. In response to depolarizing current injection or distal olfactory nerve input, fast Na(+) action potentials were recorded along the entire length of the primary dendritic trunk. With weak-to-moderate olfactory nerve input, an action potential was initiated near the soma and then back-propagated into the primary dendrite. As olfactory nerve input increased, the initiation site suddenly shifted to the distal primary dendrite. Multi-compartmental modeling indicated that this abrupt shift of the spike-initiation site reflected an independent thresholding mechanism in the distal dendrite. When strong olfactory nerve excitation was paired with strong inhibition to the mitral cell basal secondary dendrites, a small fast prepotential was recorded at the soma, which indicated that an action potential was initiated in the distal primary dendrite but failed to propagate to the soma. As the inhibition became weaker, a "double-spike" was often observed at the dendritic recording site, corresponding to a single action potential at the soma. Simulation demonstrated that, in the course of forward propagation of the first dendritic spike, the action potential suddenly jumps from the middle of the dendrite to the axonal spike-initiation site, leaving the proximal part of primary dendrite unexcited by this initial dendritic spike. As Na(+) conductances in the proximal dendrite are not activated, they become available to support the back-propagation of the evoked somatic action potential to produce the second dendritic spike. In summary, the balance of spatially distributed excitatory and inhibitory inputs can dynamically switch the mitral cell firing among four different modes: axo-somatic initiation with back-propagation, dendritic initiation either with no forward propagation, forward propagation alone, or forward propagation followed by back-propagation.

Growth of dendrites in a rapidly solidified Al-23 Sr alloy

The microstructure of the melt-spun Al-23 wt% Sr alloy has been investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The phases present in the melt-spun Al-23 Sr alloy are identified to be α-Al and Al 4Sr, identical to those in the ingot-cast alloy. Rapid solidification has a marked effect on the morphology of the primary Al 4Sr phase and the preferred orientations of its dendrites in the Al-23 Sr alloy. The primary Al 4Sr phase in the melt-spun Al-23 Sr alloy is dendritic, quite different from the coarse slab-like Al 4Sr in the ingot-cast alloy. Some primary Al 4Sr dendrites develop into secondary branches in directions 45° to the dendrite trunks but others continue to branch in the directions perpendicular to the trunks. Moreover, tertiary and higher-order branches are also observed in the melt-spun Al-23 Sr alloy. The preferred crystallographic orientations of the Al 4Sr dendrites with 45° and 90° branches are determined to be the 〈1 0 0〉 and 〈1 1 0〉 directions, respectively. Rapid solidification enhances the formation of the Al 4Sr dendrites with 45° branches in the 〈1 0 0〉 direction.

Signaling of Layer 1 and Whisker-Evoked Ca2+and Na+Action Potentials in Distal and Terminal Dendrites of Rat Neocortical Pyramidal NeuronsIn VitroandIn Vivo

Dendritic regenerative potentials play an important role in integrating and amplifying synaptic inputs. To understand how distal synaptic inputs are integrated and amplified, we made multiple simultaneous (double, triple, or quadruple) and sequential (4–12 paired) recordings from different locations of single tufted layer 5 pyramidal neurons in the cortex <i>in vitro</i> and studied the spatial and temporal properties of their dendritic regenerative potential initial zone. Recordings from the soma and from trunk, primary, secondary, tertiary, and quaternary tuft branches of the apical dendrite of these neurons reveal a spatially restricted low-threshold zone ∼550–900 μm from the soma for Ca²⁺-dependent regenerative potentials. Dendritic regenerative potentials initiated in this zone have a clearly defined threshold and a refractory period, and they can propagate actively along the dendrite before evoking somatic action potentials. The detailed biophysical characterization of this dendritic action potential initiation zone allowed for the further investigation of dendritic potentials in the intact brain and their roles in information processing. By making whole-cell recordings from the soma and varied locations along the apical dendrite of 53 morphologically identified layer 5 pyramidal neurons in anesthetized rats, we found that three of the dendritic potentials characterized <i>in vitro</i> could be induced by spontaneous or whisker inputs <i>in vivo</i>. Thus layer 5 pyramidal neurons of the rat neocortex have a spatially restricted low-threshold zone in the apical dendrite, the activation or interaction of which with the axonal action potential initiation zone is responsible for multiple forms of regenerative potentials critical for integrating and amplifying sensory and modulatory inputs.

Signaling of layer 1 and whisker-evoked Ca2+ and Na+ action potentials in distal and terminal dendrites of rat neocortical pyramidal neurons in vitro and in vivo.

Dendritic regenerative potentials play an important role in integrating and amplifying synaptic inputs. To understand how distal synaptic inputs are integrated and amplified, we made multiple simultaneous (double, triple, or quadruple) and sequential (4-12 paired) recordings from different locations of single tufted layer 5 pyramidal neurons in the cortex in vitro and studied the spatial and temporal properties of their dendritic regenerative potential initial zone. Recordings from the soma and from trunk, primary, secondary, tertiary, and quaternary tuft branches of the apical dendrite of these neurons reveal a spatially restricted low-threshold zone approximately 550-900 microm from the soma for Ca2+-dependent regenerative potentials. Dendritic regenerative potentials initiated in this zone have a clearly defined threshold and a refractory period, and they can propagate actively along the dendrite before evoking somatic action potentials. The detailed biophysical characterization of this dendritic action potential initiation zone allowed for the further investigation of dendritic potentials in the intact brain and their roles in information processing. By making whole-cell recordings from the soma and varied locations along the apical dendrite of 53 morphologically identified layer 5 pyramidal neurons in anesthetized rats, we found that three of the dendritic potentials characterized in vitro could be induced by spontaneous or whisker inputs in vivo. Thus layer 5 pyramidal neurons of the rat neocortex have a spatially restricted low-threshold zone in the apical dendrite, the activation or interaction of which with the axonal action potential initiation zone is responsible for multiple forms of regenerative potentials critical for integrating and amplifying sensory and modulatory inputs.

Growth pulsations in symmetric dendritic crystallization in thin polymer blend films.

The crystallization of polymeric and metallic materials normally occurs under conditions far from equilibrium, leading to patterns that grow as propagating waves into the surrounding unstable fluid medium. The Mullins-Sekerka instability causes these wave fronts to break up into dendritic arms, and we anticipate that the normal modes of the dendrite tips have a significant influence on pattern growth. To check this possibility, we focus on the dendritic growth of polyethylene oxide in a thin-film geometry. This crystalline polymer is mixed with an amorphous polymer (polymethyl-methacrylate) to "tune" the morphology and clay was added to nucleate the crystallization. The tips of the main dendrite trunks pulsate during growth and the sidebranches, which grow orthogonally to the trunk, pulsate out of phase so that the tip dynamics is governed by a limit cycle. The pulsation period P increases sharply with decreasing film thickness L and then vanishes below a critical value L(c) approximately 80 nm. A change of dendrite morphology accompanies this transition.

A phase field model for spontaneous grain refinement in deeply undercooled metallic melts

The origin of spontaneous grain refinement in deeply undercooled metallic melts has been of enduring interest within the solidification literature. Here we present the results of phase field simulations of dendritic growth into pure undercooled melts, at growth velocities up to 35 m s −1. We find that, at low growth velocities, dendrite morphologies are broadly self-similar with increasing growth velocity. However, above ≈15 m s −1 the initiation of side-branching moves closer to the dendrite tip with increasing growth velocity. This appears to be related to the level of kinetic undercooling at the tip. Once side-branch initiation begins to occur within 1–2 radii of the tip, profound morphological changes occur, leading to severe thinning of the dendrite trunk and ultimately repeated multiple tip-splitting. This process can be invoked to explain many of the observed features of spontaneous grain refinement in deeply undercooled metallic melts.

The apical shaft of CA1 pyramidal cells is under GABAergic interneuronal control

Dendrites of pyramidal cells perform complex amplification and integration (reviewed in Refs 5, 9, 12 and 20). The presence of a large proximal apical dendrite has been shown to have functional implications for neuronal firing patterns 13 and under a variety of experimental conditions, the largest increases in intracellular Ca 2+ occur in the apical shaft. 4,8,15,16,19,21–23 An important step in understanding the functional role of the proximal apical dendrite is to describe the nature of synaptic input to this dendritic region. Using light and electron microscopic methods combined with in vivo labeling of rat hippocampal CA1 pyramidal cells, we examined the total number of GABAergic and non-GABAergic inputs converging onto the first 200 μm of the apical trunk. The number of spines associated with excitatory terminals increased from <0.2 spines/μm adjacent to the soma to 5.5 spines/μm at 200 μm from the soma, whereas the number of GABAergic, symmetric terminals decreased from 0.8/μm to 0.08/μm over the same anatomical region. GABAergic terminals were either parvalbumin-, cholecystokinin- or vasointestinal peptide-immunoreactive. These findings indicate that the apical dendritic trunk mainly receives synaptic input from GABAergic interneurons. GABAergic inhibition during network oscillation may serve to periodically isolate the dendritic compartments from the perisomatic action potential generating sites.