NMDA and AMPA receptors on neocortical neurons are differentially distributed

Corpus callosum and visual cortex of mice with deletion of the NMDA-NR1 receptor: I. Accelerated development of callosal projection neurons

Many pharmacological experiments show that the ionotropic receptor NMDA has both neurotrophic and neuroexcitotoxic effects. The neurotrophic function is manifested in many ways including acceleration of neuronal development, enhancement of neuronal migration, neuroprotection, blockage of apoptosis, prevention of aging and prematurity, as well as effects on synaptic plasticity and synaptogenesis. On the other hand, the neuroexcitotoxic function is manifested in its role in neurological and psychiatric diseases such as epilepsy, Parkinson's disease and schizophrenia. The present study explores the consequences of complete and partial absence of NMDA-NR1 receptors throughout development. Using DiI tracing in vitro, the development of corpus callosum projection neurons in transgenic mice with deletion of the NMDA-NR1 receptor was observed in visual cortex. Compared to littermate controls, the histogenesis and neuronal development of corpus callosum cells of origin was found to be accelerated in NR1-/- mice. That is, the corpus callosum projection neurons in NR1 knockout mice developed earlier and faster than in littermate heterozygous and wild-type mice. However, the corpus callosum projection neurons in NR1 heterozygous mice developed earlier and faster than in littermate wild-type mice. This suggests that NMDA-NR1 receptors are involved in sequencing and/or temporal regulation of neuronal development, and that there is a gene-dose effect. Studies from other laboratories suggest that the observed phenomenon of prematurity or accelerated development is a direct effect of altered expression of genes found in mice with deletion of the NMDA-NR1 receptor.

Distribution and properties of functional postsynaptic kainate receptors on neocortical layer V pyramidal neurons

The distribution of glutamate receptor subtypes on the surface of neurons is highly relevant for synaptic transmission and signal processing. In the present study we investigated the location and properties of functional kainate receptors (KARs) on the somatodendritic membrane of rat neocortical layer V pyramidal neurons. Infrared-guided laser stimulation was used to apply glutamate photolytically to the soma and various sites along the apical dendrite. Electrical currents, resulting from the activation of pharmacologically isolated KARs, were measured by whole-cell patch-clamp recording. In addition, KARs on somatic and dendritic outside-out patches were activated while still within the brain tissue. We found that functional KARs are located on the entire somatodendritic membrane that was examined. Fast kinetics, a linear I-V relationship, and a relatively high single-channel conductance are characteristic features of these receptors. We provide evidence that the unitary properties of somatic and dendritic KARs are identical. Regarding the subcellular distribution of KARs, our results indicate that the density of these receptors increases toward the distal dendrite. They are located mainly at extrasynaptic sites but also mediate fast synaptic signaling triggered by afferent stimulation. The differential distribution speaks in favor of a selective targeting of KARs on central neurons and may reflect a mechanism for a location-dependent regulation of synaptic efficacy. Furthermore, it is feasible to assume that extrasynaptic KARs could be activated by a "spillover" of synaptically released glutamate, ambient glutamate in the CSF, or glutamate released from adjacent astrocytes.

Dendritic glutamate-induced bursting in the prefrontal cortex: further characterization and effects of phencyclidine

To understand the role of N-methyl-d-aspartate (NMDA) receptors in the prefrontal cortex (PFC) and to investigate how the psychotomimetic drug phencyclidine (PCP) may alter PFC function, we made whole-cell recordings from PFC neurons in rat brain slices. Our result showed that most deep layer pyramidal neurons in the PFC were regular spiking cells. They could fire repetitive bursts, however, when activated by glutamate focally applied to the apical dendrite. Application of NMDA to the same dendritic spot also induced bursting, whereas application of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) evoked single spikes only. Coapplication of AMPA with NMDA evoked more single spikes and decreased NMDA-induced bursting. Experiments with NMDA and AMPA antagonists further showed that dendritic glutamate (dGlu)-induced bursting required NMDA receptor activation and was enhanced when AMPA receptors were blocked. At subanesthetic concentrations, PCP decreased dGlu-induced bursting and altered the temporal characteristics of the bursts by decreasing spikes per burst and increasing interspike intervals within bursts. The latter two changes were not observed when AMPA receptors were blocked, suggesting that they are secondary to the increased AMPA receptor contribution to glutamate responses evoked in the presence of PCP. These results suggest that NMDA receptors are essential for PFC pyramidal cells to fire in bursts in response to dGlu input and that PCP suppresses dGlu-induced bursting. Since bursting is necessary for pyramidal cells to activate GABA interneurons, the suppression effect of PCP may further lead to a weakening of the connections from pyramidal cells and GABA interneurons, thereby contributing to PCP's psychotomimetic effects.

Circuitry of rat barrel cortex investigated by infrared-guided laser stimulation

Infrared-guided laser stimulation was used to examine the synaptic connectivity of neurons in rat barrel cortex. Layer V pyramidal neurons were visualized by infrared videomicroscopy and their membrane potential was recorded with patch pipettes. Presumptive presynaptic neurons were activated by uncaging glutamate with the light of a uv laser directed onto these neurons superfused with medium containing caged glutamate. Synaptic connections were identified by postsynaptic potentials following laser stimulation. The most frequent synaptic connections were found between layer V pyramidal neurons. The probability of this intralaminar input declined monotonically with the lateral distance between stimulated and recorded neuron. In contrast, input from layer II/III onto lamina V neurons showed a periodic organization. Synaptic connections originating from this lamina clearly reflected the barrel structure, with more input originating from the barrel column side, and less input from the barrel column centre. Thus, a barrel-specific organization seems to be especially pronounced for synaptic input from layer II/III to neurons of layer V.

Stimulating neurons with light

Recent technological advances have enabled the use of different optical methods to activate neurons, including 'caged' glutamate, photoactivation of genetically engineered cascades, and direct two-photon excitation. The ability to use light as a stimulation tool provides, in principle, a non-invasive method for the temporally and spatially precise activation of any neuron or any part of a neuron. When combined with two-photon excitation, excellent spatial control can be achieved even in complex and highly scattering preparations, such as living nervous tissue. Different methods that have been developed in the last several decades have been used to probe neuronal sensitivity, mimic synaptic input, and elucidate patterns of neural connectivity.

Neocortical long-term potentiation and long-term depression: site of expression investigated by infrared-guided laser stimulation

The synaptic site of expression of long-term potentiation (LTP) and long-term depression (LTD) is still a matter of debate. To address the question of presynaptic versus postsynaptic expression of neocortical LTP and LTD in a direct approach, we measured the glutamate sensitivity of apical dendrites of layer 5 pyramidal neurons during LTP and LTD. We used infrared-guided laser stimulation to release glutamate from its "caged" form with high spatial and temporal resolution. Responses to photolytically released glutamate and synaptically evoked EPSPs were recorded with patch-clamp pipettes from the neuronal somata. LTP and LTD could be induced by electrical stimulation at the same synapses in succession. The NMDA receptor-dependent LTD was accompanied by a decrease in the dendritic glutamate sensitivity, suggesting a postsynaptic expression of neocortical LTD. In contrast, LTP was never accompanied by a change in the dendritic glutamate sensitivity. A possible explanation for this finding is a presynaptic expression of neocortical LTP. Another set of experiments corroborated these results: Photolytic application of glutamate with a frequency of 5 Hz caused a long-lasting Ca2+ and NMDA receptor-dependent decrease in the dendritic glutamate sensitivity. In contrast, LTP of dendritic glutamate sensitivity was never induced by photostimulation, despite several experimental modifications to prevent washout of the induction mechanism and to induce a stronger postsynaptic Ca2+ influx. In conclusion, our findings provide strong evidence for a postsynaptic expression of neocortical LTD and favor a primarily presynaptic locus of neocortical LTP.

Interaction of dopamine D1 and NMDA receptors mediates acute clozapine potentiation of glutamate EPSPs in rat prefrontal cortex

The atypical antipsychotic drug clozapine effectively alleviates both negative and positive symptoms of schizophrenia via unclear cellular mechanisms. Clozapine may modulate both glutamatergic and dopaminergic transmission in the prefrontal cortex (PFC) to achieve part of its therapeutic actions. Using whole cell patch-clamp techniques, current-clamp recordings in layers V-VI pyramidal neurons from rat PFC slices showed that stimulation of local afferents (in 2 microM bicuculline) evoked mixed [AMPA/kainate and N-methyl-D-aspartate (NMDA) receptors] glutamate receptor-mediated excitatory postsynaptic potentials (EPSPs). Clozapine (1 microM) potentiated polysynaptically mediated evoked EPSPs (V(Hold) = -65 mV), or reversed EPSPs (rEPSP, V(Hold) = +20 mV) for >30 min. The potentiated EPSPs or rEPSPs were attenuated by elevating [Ca(2+)](O) (7 mM), by application of NMDA receptor antagonist 2-amino5-phosphonovaleric acid (50 microM), or by pretreatment with dopamine D1/D5 receptor antagonist SCH23390 (1 microM) but could be further enhanced by a dopamine reuptake inhibitor bupropion (1 microM). Clozapine had no significant effect on pharmacologically isolated evoked NMDA-rEPSP or AMPA-rEPSPs but increased spontaneous EPSPs without changing the steady-state resting membrane potential. Under voltage clamp, clozapine (1 microM) enhanced the frequency, and the number of low-amplitude (5-10 pA) AMPA receptor-mediated spontaneous EPSCs, while there was no such changes with the mini-EPSCs (in 1 microM TTX). Taken together these data suggest that acute clozapine can increase spike-dependent presynaptic release of glutamate and dopamine. The glutamate stimulates distal dendritic AMPA receptors to increase spontaneous EPSCs and enabled a voltage-dependent activation of neuronal NMDA receptors. The dopamine released stimulates postsynaptic D1 receptor to modulate a lasting potentiation of the NMDA receptor component of the glutamatergic synaptic responses in the PFC neuronal network. This sequence of early synaptic events induced by acute clozapine may comprise part of the activity that leads to later cognitive improvement in schizophrenia.

Four cell types with distinctive membrane properties and morphologies in lamina I of the spinal dorsal horn of the adult rat

Lamina I of the spinal dorsal horn plays an important role in the processing and relay of nociceptive information. Signal processing depends, in part, on neuronal membrane properties. Intrinsic membrane properties of lamina I neurons were therefore investigated using whole cell patch clamp recordings in a slice preparation of adult rat spinal cord. Based on responses to somatic current injection, four cell types were identified: tonic, which fire comparatively slowly but continuously throughout stimulation; phasic, which fire a high frequency burst of variable duration; delayed onset, which fire irregularly and with a marked delay to the first spike; and single spike, which typically fire only one action potential even when strongly depolarised. Classification by spiking pattern was further refined by identification of characteristic stimulus-response curves and quantification of several response parameters. Objectivity of the classification was confirmed by cluster analysis. Responses to stimulus trains and synaptic input as well as the kinetics of spontaneous synaptic events revealed differences in the signal processing characteristics of the cell types: tonic and delayed onset cells appeared to act predominantly as integrators whereas phasic and single spike cells acted as coincidence detectors. Intracellular labelling revealed a significant correlation between morphological and physiological cell types: tonic cells were typically fusiform, phasic cells were pyramidal, and delayed onset and single spike cells were multipolar. Thus, there are multiple physiological cells types in lamina I with specific morphological correlates and distinctive signal processing characteristics that confer significant differences in the transduction of input into spike trains.

Infrared-guided laser stimulation of neurons in brain slices

Infrared-guided laser stimulation is a new technique that allows precise and rapid stimulation of visualized neurons in brain slices. Infrared imaging of neurons with a new contrast system is combined with the photolytic release of caged neurotransmitters by an ultraviolet (UV) laser. Addition of caged neurotransmitters to the superfusion medium of neurons in brain slices allows local excitation in the micrometer range with a focused spot of UV light. In this way, the distribution of glutamate or gamma-aminobutyric acid (GABA) receptors on neuronal dendrites can be mapped. Furthermore, this technique can be used to map the connectivity of neuronal networks through the controlled stimulation of neighboring neurons. Because the laser stimulation can be performed much faster than can paired recording, it is also possible to search for synaptic connections between distant neurons that have a low probability of connectivity.

Region-specific developmental specialization of GABA-glycine cosynapses in laminas I-II of the rat spinal dorsal horn

The spinal dorsal horn is the first level of the CNS in which nociceptive input from sensory afferents is integrated and transmitted. Although inhibitory control in this region has a crucial impact on pain transmission, the respective contribution of GABA and glycine to this inhibition remains elusive. We have previously documented co-release of GABA and glycine at the same inhibitory synapse in spinal laminas I-II of adult rats [older than postnatal day 30 (P30)]. However, despite this co-release, individual miniature inhibitory postsynaptic currents (mIPSCs) were mediated by either glycine receptors (GlyR) or GABA(A) receptors (GABA(A)R), yet never by the two together. In contrast, recent studies of ventral horn immature inhibitory synapses (</=P21) reported individual mIPSCs that were mediated by both GABA(A)Rs and GlyRs. This raises the question of whether mixed mIPSCs are present in immature lamina I-II neurons yet are lost through a maturation-dependent synaptic specialization. To test this, we recorded mIPSCs using patch-clamp techniques in lamina I-II neurons in spinal slices taken at different stages of development. We found that, in neurons younger than P23, both GlyR-only and GABA(A)R-only mIPSCs could be recorded, in addition to mixed GABA(A)R-GlyR mIPSCs. With maturation however, both lamina I-II neurons gradually discontinued exhibiting mixed mIPSCs, although with differing patterns of specialization. Yet, at all developmental stages, benzodiazepine administration could unmask mixed mIPSCs. Together, these findings indicate that, although GABA and glycine are continually co-released throughout development, junctional codetection ceases by adulthood. This indicates an age-dependent postsynaptic tuning of inhibitory synapses that occurs in a region-specific manner.

Voltage-gated sodium channels shape subthreshold EPSPs in layer 5 pyramidal neurons from rat prefrontal cortex

The role of voltage-dependent channels in shaping subthreshold excitatory postsynaptic potentials (EPSPs) in neocortical layer 5 pyramidal neurons from rat medial prefrontal cortex (PFC) was investigated using patch-clamp recordings from visually identified neurons in brain slices. Small-amplitude EPSPs evoked by stimulation of superficial layers were not affected by the N-methyl-D-aspartate receptor antagonist D-2-amino-5-phosphonopentanoic acid but were abolished by the AMPA receptor antagonist 6-cyano-7-nitroquinoxalene-2,3-dione, suggesting that they were primarily mediated by AMPA receptors. AMPA receptor-mediated EPSPs (AMPA-EPSPs) evoked in the apical dendrites were markedly enhanced, or increased in peak and duration, at depolarized holding potentials. Enhancement of AMPA-EPSPs was reduced by loading the cells with lidocaine N-ethylbromide (QX-314) and by local application of the Na(+) channel blocker tetrodotoxin (TTX) to the soma but not to the middle/proximal apical dendrite. In contrast, blockade of Ca(2+) channels by co-application of Cd(2+) and Ni(2+) to the soma or apical dendrite did not affect the AMPA-EPSPs. Like single EPSPs, EPSP trains were shaped by Na(+) but not Ca(2+) channels. EPSPs simulated by injecting synaptic-like current into proximal/middle apical dendrite (simEPSPs) were enhanced at depolarized holding potentials similarly to AMPA-EPSPs. Extensive blockade of Ca(2+) channels by bath application of the Cd(2+) and Ni(2+) mixture had no effects on simEPSPs, whereas bath-applied TTX removed the depolarization-dependent EPSP amplification. Inhibition of K(+) currents by 4-aminopyridine (4-AP) and TEA increased the TTX-sensitive EPSP amplification. Moreover, strong inhibition of K(+) currents by high concentrations of 4-AP and TEA revealed a contribution of Ca(2+) channels to EPSPs that, however, seemed to be dependent on Na(+) channel activation. Our results indicate that in layer 5 pyramidal neurons from PFC, Na(+), and K(+) voltage-gated channels shape EPSPs within the voltage range that is subthreshold for somatic action potentials.

Glutamate receptors form hot spots on apical dendrites of neocortical pyramidal neurons

Apical dendrites of layer V cortical pyramidal neurons are a major target for glutamatergic synaptic inputs from cortical and subcortical brain regions. Because innervation from these regions is somewhat laminar along the dendrites, knowing the distribution of glutamate receptors on the apical dendrites is of prime importance for understanding the function of neural circuits in the neocortex. To examine this issue, we used infrared-guided laser stimulation combined with whole cell recordings to quantify the spatial distribution of glutamate receptors along the apical dendrites of layer V pyramidal neurons. Focally applied (<10 microm) flash photolysis of caged glutamate on the soma and along the apical dendrite revealed a highly nonuniform distribution of glutamate responsivity. Up to four membrane areas (extent 22 microm) of enhanced glutamate responsivity (hot spots) were detected on the dendrites with the amplitude and integral of glutamate-evoked responses at hot spots being three times larger than responses evoked at neighboring sites. We found no association of these physiological hot spots with dendritic branch points. It appeared that the larger responses evoked at hot spots resulted from an increase in activation of both alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptors and not a recruitment of voltage-activated sodium or calcium conductances. Stimulation of hot spots did, however, facilitate the triggering of both Na+ spikes and Ca(2+) spikes, suggesting that hot spots may serve as dendritic initiation zones for regenerative spikes.

GABA(A) and GABA(B) receptors on neocortical neurons are differentially distributed

The distribution of functional neurotransmitter receptors on the surface of neurons is highly relevant for synaptic transmission and signal processing. To map functional GABA(A) and GABA(B) receptors on the somadendritic membrane of rat neocortical layer V pyramidal neurons we used patch-clamp recording in combination with infrared-guided laser stimulation to release gamma-aminobutyric acid (GABA) photolytically. The data strongly suggest that relatively more GABA(A) receptors are located at the apical dendrite and relatively more GABA(B) receptors near the soma. Such a specific distribution of GABA(A) and GABA(B) receptors may serve to compensate for differences in electrotonic voltage attenuation between GABA(A) and GABA(B) receptor-mediated inhibitory postsynaptic potentials (IPSPs).

Calcium dynamics associated with action potentials in single nerve terminals of pyramidal cells in layer 2/3 of the young rat neocortex

Calcium dynamics associated with a single action potential (AP) were studied in single boutons of the axonal arbor of layer 2/3 pyramidal cells in the neocortex of young (P14-16) rats. We used fluorescence imaging with two-photon excitation and Ca2+-selective fluorescence indicators to measure volume-averaged Ca2+ signals. These rapidly reached a peak (in about 1 ms) and then decayed more slowly (tens to hundreds of milliseconds). Single APs and trains of APs reliably evoked Ca2+ transients in en passant boutons located on axon collaterals in cortical layers 2/3, 4 and 5, indicating that APs propagate actively and reliably throughout the axonal arbor. Branch point failures are unlikely to contribute to differences in synaptic efficacy and reliability in the connections made by layer 2/3 pyramidal cells. AP-evoked Ca2+ transients in boutons were mediated by voltage-dependent Ca2+ channels (VDCCs), predominantly by the P/Q- and N-subtypes. Ca2+ transients were, on average, of significantly larger amplitude in boutons than in the flanking segments of the axon collateral. Large amplitude Ca2+ transients in boutons were spatially restricted to within <= 3 m of axonal length. Single AP-evoked Ca2+ transients varied up to 10-fold across different boutons even if they were located on the same axon collateral. In contrast, variation of Ca2+ transients evoked by successive APs in a given single bouton was small (coefficient of variation, c.v. <= 0.21). Amplitudes of AP-evoked Ca2+ signals did not correlate with the distance of boutons from the soma. In contrast, AP-evoked Ca2+ signals in spines of basal dendrites decreased slightly (correlation coefficient, r2 = -0.27) with distance from the soma. Measurements with the low-affinity Ca2+ indicator Magnesium Green suggest that the volume-averaged residual free [Ca2+]i in a bouton increases on average by 500 nM following a single AP. Higher concentrations of indicator caused, on average, a decrease in the amplitude and an increase in the decay time constant of Ca2+ transients. Assuming a single-compartment model the concentration dependence of decay time constants suggests a low endogenous Ca2+ binding ratio close to 140, indicating that of the total Ca2+ influx ( approximately 2 fC) less than 1% remained free. The indicator concentration dependence of decay time constants further suggests that the residual free Delta[Ca2+]i associated with an AP decays with a time constant of about 60 ms (35 C) reflecting a high Ca2+ extrusion rate of about 2600 s(-1). The results show that AP-evoked volume-averaged Ca2+ transients in single boutons are evoked reliably and, on average, have larger amplitudes than Ca2+ transients in other subcellular compartments of layer 2/3 pyramidal cells. A major functional signature is the large variation in the amplitude of Ca2+ transients between different boutons. This could indicate that local interactions between boutons and different target cells modify the spatiotemporal Ca2+ dynamics in boutons and cause target cell-specific differences in their transmitter release properties.

Distribution of functional glutamate and GABA receptors on hippocampal pyramidal cells and interneurons

The distribution of functional neurotransmitter receptors is an important determinant of neuronal information processing. To map the location of functional glutamate and GABA receptors on individual hippocampal neurons, we photolyzed "caged" glutamate and GABA while measuring the electrical currents resulting from activation of these receptors. Responses to uncaged neurotransmitters were spatially nonuniform and varied according to the type of receptor and type of neuron. Every region of CA1 pyramidal cells responded to glutamate and GABA, but glutamate and GABA receptors increased in density along the length of their distal dendrites. Similar gradients of glutamate receptors were found in stratum radiatum interneurons, while GABA responses were detectable only in the perisomatic region of these interneurons. These regional variations in receptor distribution indicate the selective targeting of receptors on central neurons and may reflect a mechanism for local regulation of synaptic efficacy.

Visualization of lamina I of the dorsal horn in live adult rat spinal cord slices

The superficial dorsal horn of the spinal cord, particularly lamina I, plays a key role in the integration and relay of pain related sensory input. To study the physiology of lamina I neurons in slices, a clear delineation of this layer can be greatly advantageous. Yet, it has remained difficult to distinguish this layer in live tissue in conventional transverse spinal slices because of its very narrow thickness at the edge of the dorsal horn. We describe here the criteria we used to delineate lamina I in live tissue using gradient contrast videomicroscopy in 400 microm-thick parasagittal spinal cord slices from adult rats (30-60-day-old). Because of the longitudinal orientation of the neurons in this layer, the resulting distinctive reticulated appearance of lamina I made it possible to readily distinguish it from lamina II. The usefulness of this distinguishing parameter is demonstrated by our ability to contrast synaptic properties of neurons in lamina I from those in lamina II. Complete morphological identification of lamina I neurons however also requires visualization of the cell in the horizontal plane. To maintain compatibility with the parasagittal slice, we used 3D reconstructions from confocal images of the recorded neurons. Rotation of the neuron in space allowed for its morphological characterization in all three planes (horizontal, parasagittal, and transverse). This approach therefore presents optimal conditions for systematic electrophysiological recording from visually identified lamina I neurons.

Precisely localized LTD in the neocortex revealed by infrared-guided laser stimulation

In a direct approach to elucidate the origin of long-term depression (LTD), glutamate was applied onto dendrites of neurons in rat neocortical slices. An infrared-guided laser stimulation was used to release glutamate from caged glutamate in the focal spot of an ultraviolet laser. A burst of light flashes caused an LTD-like depression of glutamate receptor responses, which was highly confined to the region of "tetanic" stimulation (<10 micrometers). A similar depression of glutamate receptor responses was observed during LTD of synaptic transmission. A spatially highly specific postsynaptic mechanism can account for the LTD induced by glutamate release.

Ca2+ fluorescence imaging with pico- and femtosecond two-photon excitation: signal and photodamage

The signal and limitations of calcium florescence imaging using nonresonant multiphoton absorption of near-infrared femto- and picosecond laser pulses were examined. The fluorescence changes of various Ca(2+)-indicators induced by transient increases of the intradendritic calcium concentration were evaluated by evoking physiological activity in neocortical neurons in rat brain slices. Photodamage was noticeable as irreversible changes in the parameters describing the calcium fluorescence transients. At higher two-photon excitation rates, a great variety of irregular functional and structural alterations occurred. Thus, signal and observation time were limited by phototoxic effects. At lower excitation rates, photodamage accumulated linearly with exposure time. Femtosecond and picosecond laser pulses were directly compared with respect to this cumulative photodamage. The variation of the pulse length at a constant two-photon excitation rate indicated that a two-photon excitation mechanism is mainly responsible for the cumulative photodamage within the investigated window of 75 fs to 3.2 ps. As a direct consequence, at low excitation rates, the same image quality is achieved irrespective of whether two-photon Ca(2+)-imaging is carried out with femto- or picosecond laser pulses.

Chemokine Receptor Expression and Signaling in Macaque and Human Fetal Neurons and Astrocytes: Implications for the Neuropathogenesis of AIDS

Chemokines are believed to play a role in the neuropathogenesis of AIDS through their recruitment of neurotoxin-secreting, virally infected leukocytes into the CNS. Levels of chemokines are elevated in brains of patients and macaques with HIV/SIV-induced encephalitis. The chemokine receptors CCR3, CCR5, and CXCR4 are found on subpopulations of neurons in the cortex of human and macaque brain. We have developed an in vitro system using both macaque and human fetal neurons and astrocytes to further investigate the roles of these receptors in neuronal response to inflammation. Here we report the presence of functional HIV/SIV coreceptors CCR3, CCR5, and CXCR4 on fetal human and macaque neurons and CCR5 and CXCR4 on astrocytes immediately ex vivo and after several weeks in culture. Confocal imaging of immunostained neurons demonstrated different patterns of distribution for these receptors, which may have functional implications. Chemokine receptors were shown to respond to their appropriate chemokine ligands with increases in intracellular calcium that, in the case of neurons, required predepolarization with KCl. These responses were blocked by neutralizing chemokine receptor in mAbs. Pretreatment of neural cells with pertussis toxin abolished responses to stromal-derived factor-1α, macrophage inflammatory protein-1β, and RANTES, indicating coupling of CCR5 and CXCR4 to a Giα protein, as in leukocytes. Cultured macaque neurons demonstrated calcium flux response to treatment with recombinant SIVmac239 envelope protein, suggesting a mechanism by which viral envelope could affect neuronal function in SIV infection. The presence of functional chemokine receptors on neurons and astrocytes suggests that chemokines could serve to link inflammatory and neuronal responses.