These studies in fetal monkeys and ferrets show that the two fundamental types of thalamic GABA neuron populate the thalamus during widely separated developmental epochs. Those of the ventral thalamus (VT) and epithalamus (ET) appear very early in conjunction with the GABA cells of the substantia nigra, globus pallidus, and pretectum (PT). GABA neurons intrinsic to the dorsal thalamus (DT) appear later, long after proliferative activity has ceased in the wall of the third ventricle, after dorsal thalamic nuclei have differentiated and at the same time as principal neurons are acquiring a glutamatergic phenotype. The exact origins of the two waves of GABA cells are uncertain but some appear to arrive from extrinsic sources that include the ganglionic eminence (GE) of the basal forebrain.

The basic electrophysiological properties and responses to serotonin of thalamocortical (TC) neurons in the ferret, cat, and monkey pulvinar were compared. Morphologically, thalamocortical neurons in these three species were similar, except for the presence of beaded dendrites in many monkey neurons. In all three species, the neurons exhibited two distinct firing modes: single spike activity and low threshold Ca2+-spike mediated bursting. However, in monkeys, the low threshold Ca2+ spikes were followed by a prominent 50–100 ms afterhyperpolarization that could result in the generation of an additional rebound Ca2+ spike. The application of 5-HT to thalamocortical neurons in cat and monkey pulvinar resulted in a depolarization and an increase in membrane conductance through an enhancement of the hyperpolarization-activated cation current, Ih, apparently through the activation of 5-HT7 receptors. In contrast, the application of serotonin to ferret pulvinar neurons resulted in a prominent hyperpolarization, owing to an increase in membrane potassium conductance. In monkey and ferret, application of serotonin could result in barrages of IPSPs in thalamocortical neurons. These results indicate that there are significant species-dependent differences in both the electrophysiological and pharmacological properties of pulvinar thalamocortical neurons.

Voltage-activated calcium channels in thalamic neurons are considered important elements in the generation of thalamocortical burst firing during periods of electroencephalographic synchronization. A potent counterpart of calcium-mediated depolarization may reside in the activation of calcium-dependent potassium conductances. In the present study, thalamocortical relay cells that were acutely disso-ciated from the rat ventrobasal thalamic complex (VB) were studied using whole-cell patch-clamp techniques. The calcium-dependent potassium-current (IK(Ca)) was evident as a slowly activating component of outward current sensitive to the calcium ions (Ca2+)-channel blocker methoxyverapamil (10 μM) and to substitution of external calcium by manganese. The IK(Ca) was blocked by tetraethylam-monium chloride (1 mM) and iberiotoxin (100 nM), but not apamin (1 μM). In addition, isolated VB neurons were immunopositive to anti-α(913–926) antibody, a sequence-directed antibody to the a-subunit of “big” Ca2+-dependent K+-channel (BKCa) channels. Activators of the adenylyl cyclase cyclic adenosine monophosphate (cAMP) system, such as forskolin (20 μM), dibutyryl-cAMP (10 mM) and 3-isobutyl-1 -methylxanthine (500 μM), selectively and reversibly suppressed IK(Ca). These results suggest that a rise in intracellular cAMP level leads to a decrease in a calcium-dependent potassium conductance presumably mediated via BKCa type channels, thereby providing an additional mechanism by which neurotransmitter systems are able to control electrogenic activity in thalamocortical neurons and circuits during various states of electroencephalographic synchronization and de-synchronization.

Kainate receptors (KAR) remain the most poorly defined components of the glutamate receptor system in the CNS, mainly because of the difficulty of distinguishing currents gated by KAR from those mediated by α-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor activation, and because KAR are expressed at significantly lower levels than AMPA receptors in most parts of the CNS.

The corticothalamic projection exerts its effects on thalamic neurons via NMDA, non-NMDA and metabotropic glutamate receptors. AMPA receptor mediated effects tend to predominate in the mature thalamus, but the involvement of kainate receptors at corticothalamic synapses on relay neurons and reticular nucleus neurons had not been studied.

The present work compared KAR influences on neurons in the ventral posterior nucleus (VP) and reticular nucleus (RTN), using whole-cell recording in P14–P20 mouse thalamocortical slices. The results were correlated with quantitative immuno-electron microscopic localization of kainate receptor sub-units at corticothalamic synapses in these nuclei. Small kainate-induced inward currents could be recorded in thalamic neurons in response to bath application of kainate, but no KAR-mediated pre-synaptic effects could be detected and no synaptic responses could be evoked in these cells by corticothalamic stimulation. Morphologically, GluR5/6/7 sub-units were expressed at low levels in both VP and RTN and were confined to post-synaptic membranes at corticothalamic synapses in both VP and RTN. Many synapses, however, lacked GluR5/6/7 immunoreactivity.

These results suggest that kainate receptor-mediated events are not major components of the responses of thalamic neurons to corticothalamic activation, either because of small numbers or their location in sites inaccessible to glutamate released from corticothalamic terminals.

The paraventricular thalamic nucleus (PVT) receives dense noradrenergic input, but little is known about α2 adrenoceptors (ARs) in this nucleus. We have investigated effects of the agonist α-methyl-norepinephrine (m-NE) on PVT neurons in vitro. Based on their physiological and morphological characteristics, three distinct classes of PVT neurons have been identified. The first class exhibits membrane hyperpolarization on stimulation with m-NE (0.05–25 µM). This hyperpolarizing effect is observed in the presence of tetrodotoxin (TTX; 0.5–1 µM), blocked by yohimbine (1 µM) and mimicked by clonidine (10 µM), which indicates that it is mediated by postsynaptic α2 ARs. Further experiments indicate that it is mediated through an increase in G protein-coupled K+ conductance. In a second class of neurons, m-NE (0.05–25 µM) induces a slow membrane depolarization that is mimicked by phenylephrine (5 µM) and blocked by prazosin (75 nM), which indicates the involvement of α1 ARs. The third class of neurons is insensitive to m-NE (5–25 µM), and has a lower input resistance and a larger dendritic tree compared to the two other classes. The three types of neurons differ in their resting properties, and their firing patterns are changed by m-NE. These findings indicate anatomical and functional specialization of PVT neurons.

Thalamic afferents and efferents primarily use the neurotransmitter glutamate, which acts through a variety of ionotropic (NMDA, AMPA, kainate) and metabotropic receptors. The NMDAR is composed of multiple subunits, NR1 and NR2A-D. The obligatory NRl subunit is expressed as one of eight isoforms, due to the alternative splicing of exons 5, 21, and 22. Each NRl splice variant is functionally distinct. For instance, alternative splicing of exons 21 and 22 renders two C-terminal variants, which differentially associate with NR2 subunits and intracellular molecules such the PSD-95 family of proteins. These PSD proteins play a pivotal role in NMDAR function by linking NMDARs to the cytoskeleton and downstream signal-transducing enzymes that can directly modulate NMDAR function and/or promote NMDAR-associated intracellular events.

Previous work reported that NRl is by far the most abundant NMDAR subunit expressed in the primate thalamus. In the current study, we extend these findings first by determining which NRl isoforms are predominantly expressed in the thalamus. Secondly, we characterize the expression of the NMDAR-associated PSD molecules, such as PSD-95, in the thalamus. Using in situ hybridization, we examined expression of the transcripts encoding NRl isoforms containing exons 5, 21, or 22, and transcripts encoding a set of the most well-characterized NMDAR-associated PSD proteins (NF-L, PSD93, PSD95, SAP102, and Yotiao). NRl exon 22-containing isoforms are the most abundant subunit transcripts, accounting for 40–50% of the NRl isoforms expressed in most thalamic nuclei. We also found that NF-L is by far the most abundant PSD protein expressed in the thalamus, followed by PSD-95, which is moderately and heterogeneously expressed. SAP102 and PSD-93 were expressed at moderate to low levels, with negligible amounts of Yotiao transcript expression. The PSD-95 family of molecules are critical for NMDAR function in the cell, and this study is the first to provide a detailed description of the expression of these molecules in primate thalamus. Our results demonstrate that NRl splice variants and associated PSD proteins are heterogeneously expressed across the thalamus, which is likely related to the intracellular events that occur in different thalamic nuclei.

The ventral anterior (VA) nucleus of the thalamus is connected with prefrontal and premotor cortices and with the basal ganglia. Although classically associated with motor functions, recent evidence implicates the basal ganglia in cognition and emotion as well. Here, we used two complementary approaches to investigate whether the VA is a key link for pathways underlying cognitive and emotional processes through prefrontal cortices and the basal ganglia. After application of bidirectional tracers in functionally distinct lateral, medial, and orbitofrontal cortices, we found that projection neurons were embedded in much larger patches of axonal terminations found in the magnocellular part of VA (VAmc), and in the principal part of VA. Connections from medial prefrontal cortices occupied the dorsomedial and ventromedial VA, and orbitofrontal connections were found in ventrolateral VAmc. Moreover, about half of all projection neurons in orbitofrontal areas directed to the VA or VAmc were positive for calbindin but not parvalbumin, even though comparable populations of neurons were positive for each marker in the VA. We then applied tracers in VA and investigated simultaneously projections from all prefrontal areas, the internal segment of the globus pallidus (GPi), the substantia nigra reticulata (SNr), and the thalamic reticular nucleus. Projection neurons were most densely distributed in anterior cingulate areas 24 and 32, and dorsolateral areas 9 and 8, innervating the same VA sites that received projections from a large part of GPi and dorsal SNr. Nearly as many projection neurons originated from cortical layer V as from layer VI. There is evidence that cortical layer VI neurons innervate thalamic neurons that project focally to the middle cortical layers, whereas layer V neurons synapse with thalamic neurons projecting widely to cortical layer I. Projections from layer V to the VA may facilitate cortical recruitment for executive functions within a cognitive context through lateral prefrontal areas, and autonomic responses within an emotional context through anterior cingulate areas.

The somatotopic organization, mechanoreceptive field (RF) and response properties of nociceptive neurons in the ventral posteromedial thalamic nucleus (VPM) were studied in urethane/α-chloralose anesthetized rats. Microelectrode recordings were made of the activity of single neurons within VPM, and neurons were identified as either nociceptive [wide-dynamic-range (WDR), nociceptive-specific (NS)] or non-nociceptive [low-threshold mechanoreceptive (LTM)]. Of the 350 neurons tested, 317 responded to orofacial mechanical stimulation; all the RFs were contralateral. The incidence of NS neurons was significantly higher than that of WDR neurons (21.2% versus 4.2%) but LTM neurons were most common (62.9%). WDR and NS neurons were scattered among the LTM neurons in the VPM. NS neurons were significantly denser in rostral and caudal portions of VPM; most of the WDR neurons (87%) were located in the core of VPM. Neurons with an ophthalmic division RF were located most dorsally and those with a mandibular division RF most ventrally. The RF of most neurons (77%) was located in the maxillary region, with the RF of nociceptive neurons mainly in the intraoral region and that of most LTM neurons in the perioral region. The majority of LTM, WDR and NS neurons tested had a low spontaneous activity and there was a significant difference in spontaneous firing between WDR and NS neurons, and between WDR and LTM neurons. The mean mechanical activation threshold of NS neurons (195 ± 11.2 g) was significantly higher than that of WDR neurons (4.7 ± 1.3 g). Response magnitude and peak firing frequency to graded mechanical stimuli were significantly higher in the WDR neurons. These findings indicate significant differences in the spontaneous activity, RF and response properties between WDR and NS neurons in VPM. However, they also indicate that both types of nociceptive neurons can encode the spatial properties and intensity of a noxious orofacial stimulus and, thus, might contribute to the sensory-discriminative component of pain.

Visceral nociceptive responses to distention of the ureter, and responses to innocuous and noxious mechanical stimulation of the skin were recorded from neurons in the ventral posterior lateral nucleus of the thalamus in anesthetized rats. The ventral posterior lateral (VPL) neurons were classified by their responses to cutaneous stimuli as either low-threshold or wide-dynamic-range neurons. No high-threshold neurons were found in the population of VPL neurons sampled. Some VPL neurons that responded to distention of the ureter appeared to lack a cutaneous receptive field. The majority of VPL neurons that responded to noxious visceral stimulation of the ureter were classified as low-threshold neurons, based on their responses to cutaneous stimuli. Transection of the DC at an upper cervical level dramatically reduced the responses of VPL neurons to ureter distention and to innocuous mechanical stimulation of the skin, but the responses to noxious mechanical stimulation of the skin remained intact. Ureter distention and mechanical stimulation of the skin might activate dorsal horn neurons, including postsynaptic dorsal-column pathway (PSDC) neurons and spinothalamic tract (STT) cells. We conclude that both the DC pathway and the STT are likely to contribute to the visceral and somatic responses of some VPL neurons.

The involvement of the thalamus in infectious diseases of the nervous system has been hitherto rather neglected by investigators in clinical and basic neuroscience, despite numerous reports indicating that the thalamus, and territories within this region, can be attacked by different types of microbes. This topic is here reviewed. First, an overview is provided on general principles of spread of microbes to the brain (through peripheral nerves, or through the blood or cerebrospinal fluid) and their interactions with neurons and immune cells to cause acute, transient or persistent infections. Examples are given on how non-cytolytic infections can cause long-lasting disturbances in synaptic activities and neuronal networks as a result of a “hit-and-run” mechanism, or as an effect of factors released in the microenvironment to control the neuronal infection. Emerging data on how molecules functioning at the “immunological synapse” (the site of contact between immune cells and target infected cells) may affect nervous system synapses are pointed out. An account is then given of clinical and experimental infections of the thalamus caused by viruses (rabies and herpes viruses, influenza A virus, flaviviruses, HIV virus), the parasite Toxoplasma gondii, and prions. The implications and consequences of the attack of these microbes to the thalamus are discussed. Of special interest is the potential persistence of latent infections in thalamic neurons, which could cause disturbances of neuronal functions in the absence of overt structural lesions. Altogether these data recall attention on the pathogenesis and consequences of acute and persistent infections in the mammalian thalamus.

The goal of the present study was to determine the ascending sources to the pre-supplementary motor area (pre-SMA) in macaque monkeys using multiple labeling techniques. We labeled the pallidothalamic projections using biotinylated dextran amine (BDA) and the cerebellothalamic projections using wheatgerm agglutinin conjugated to horseradish peroxidase. The pre-SMA thalamocortical projections neurons were also labeled using cholera toxin subunit b following identification of the pre-SMA by location, and by movements evoked by intracortical microstimulation. The extent of pre-SMA was later confirmed by identifying characteristics from Nissl cytoarchitecture and SMI-32 immunoreactivity. Thalamic nuclear boundaries were based on Nissl cytoarchitecture, acetylcholinesterase chemoarchitecture and Cat-301 immunoreactivity. Cerebellothalamic afferents were distributed predominantly to ventral lateral posterior nucleus (VLp), including medial and dorsal VLp, while the pallidothalamic afferents projected more rostrally to ventral lateral anterior nucleus (VLa) and ventral anterior nucleus (VA). The pre-SMA thalamocortical projection neurons were primarily found in VA and medial VLp. However, scattered cells were also found in VLa, dorsal VLp, central lateral nucleus (CL) and mediodorsal nucleus (MD). Scattered pre-SMA projecting cells overlapped foci of cerebellar label in medial VLp. Additionally, limited overlap of pre-SMA cells and pallidothalamic labeling was found in caudal VA. These findings suggest that the pre-SMA is uniquely positioned to integrate ascending basal ganglia and cerebellar information after a relay from VA and medial VLp. These anatomical findings are consistent with the recent hypothesis that the pre-SMA acts as the coordinator of visual and motor loops in motor learning [J. Cogn. Neurosci. 13 (2001) 626].

GABA-ergic thalamic reticular neurons function generically or singularly in a state-dependent manner: during quiet sleep they synchronously and rhythmically inhibit thalamocortical neurons (TCNs) via bursts, thereby eliciting the low-threshold Ca2+ potentials in TCNs that are crucial to oscillatory network behavior in the thalamo-reticulo-cortical system; during wakefulness they shape the flux of ascending sensory information by inhibiting TCNs with asynchronous and arrhythmic single-spikes. To investigate how the reticulo-thalamic synapses, which occur throughout TCN dendrites, are able to effect such disparate functions, we have: (1) used a 1416 compartment model of a 3D reconstructed TCN; (2) triggered dendritic miniature (TTX-independent) and unitary (single-afferent) conductance-based synaptic events, and (3) recorded axial currents and voltage transients in all 1416 compartments simultaneously. For synapses at all dendritic locations, more than 79% of the charge transfer reached the soma, where it dispersed into other dendritic trees to return to the extracellular space. In accord, dendritic synapses in 80% of the arbor induced voltage responses that were severely attenuated at the soma (>75% loss). Spatio-temporal aspects of distributed postsynaptic responses were examined as well. Except for synapses in the 13 most proximal compartments, the amplitude and phase of the voltage responses degraded rapidly within a focal region that did not extend beyond the host tree, and was limited most often to a subtree. The bulk response (outside the focal region) was highly synchronous and uniform. Interestingly, there were not 1403 different focal regions, but only 20, each clearly distinct from the rest and sharply delineated. Structural attributes of the arbor determined their boundaries. Boundaries were invariant when the analysis was repeated on rescaled versions (length, diameter) of the reconstructed arbor. Unitary events also induced focal/bulk structures for both burst and single-spike triggers – paradigms that correspond to single-afferent drives during quiet sleep and arousal, respectively. Such qualities differ dramatically from previously proposed motifs of dendritic clustering, each of which carried nonlinear sensitivities to parameter values. We propose that dendritic clustering underlies the role of reticulo-thalamic synapses in the early processing of ascending sensory information and that bulk responses contribute robustness to the induction and maintenance oscillations in the thalamo-reticulo-cortical network.

The thalamic reticular nucleus (TRN) is an integral part of the thalamic circuitry that mediates the transfer of information to the cortex in the major sensory pathways. Here, we consider its role in visual processing. The TRN provides an inhibitory, GABA-mediated input to relay cells in the thalamus. A key feature of TRN cells is that, because of the extent of their dendritic arborization, they have the capacity to collate visual information from the ascending relay cells and feedback axons from the cortex over a wide retinotopic area, but they feed it back to the thalamus in a narrowly focused retinotopic projection. The corticofugal input to TRN cells is mediated by a higher proportion of AMPA receptors than that to thalamic relay cells and produces sharp EPSCs. We suggest that this might bias the TRN cells to precisely timed, feature-driven feedback from the visual cortex. TRN cells are particularly well driven by either phasic or moving stimuli, so the influence on relay cells provides a strong, transient, inhibitory modulation of relay-cell activity. This might aid image segmentation and highlight responses to moving contours. Although the role of the TRN has been especially linked to selective attention, we suggest that, for vision, its function is linked more closely to the operation of the thalamocortico-thalamic loop as a whole, and that retinotopically selective attentional effects draw on the interaction with the cortical mechanism that influences TRN and relay-cell circuitry equally.

Although a tremendous honour, it is with great sadness that this review is dedicated to Mircea's memory. Mircea has been, not only an inspiration throughout my career, but a generous and supportive friend whose kindly, incisive criticism has been a constant reminder that what we study in vitro must eventually be understood in the context of the whole system. Quoting from the Preface to his elegant monograph ‘The evolution of work on extremely simplified preparations has reached the point where some investigators are not shy to jump from single-cell properties to global brain functions, such as arousal and sleep, paroxysmal events of the epileptic type, and even conscious thinking.’ (Steriade, 2001). Bearing in mind that the properties both of single neurons and the connections between them might vary in different brain states and in different phases of cortical rhythms, in this review I summarize studies of the local circuitry of the thalamo-recipient layers 4 and 6 focussing on results obtained with dual intracellular recordings and biocytin-labelling in adult neocortical slices.

The Eph family of receptor tyrosine kinases and their partner ligands, the ephrins, mediate cell–cell interactions in the developing nervous system. Signaling events between Eph receptors and ephrin ligands on interacting cells affect the growth, maturation, migration and connectivity of individual neurons and neural networks. Here we review the known roles of Eph–ephrin signaling in the development of the thalamus and its connections, and pose new questions for experimental study.

The intrinsic electrophysiological properties of medial geniculate body (MGB) neurons and their responses to noise bursts/pure tones were examined in the pentobarbital anesthetized guinea pig through intracellular recording. Discharge rate was calculated in the absence of acoustic stimuli over varied membrane potentials which were changed by intracellular injection of current or through automatic drifting. The non-acoustically-driven firing rate was 45.8 ± 23.3 Hz (mean ± S.D., n = 8) at membrane potentials of −45 mV, 30.6 ± 19.4 Hz (n = 14) at −50 mV, 18.0 ± 12.9 Hz (n = 14) at −55 mV, and significantly decreased to 5.7 ± 7.4 Hz at −60 mV, and to 0.7 ± 1.5 Hz (n = 10) at −65 mV (ANOVA, P < 0.001). The maximum non-acoustically-driven rate observed in the present study was 160 Hz. The auditory responsiveness of the MGB neurons was examined at membrane potentials over a range of −45 to −75 mV: the higher the membrane potential, the greater the responsiveness and vice versa. A putative non-low-threshold calcium spike (non-LTS) burst was observed in the present study. It showed significantly longer inter-spike intervals (11.6 ± 6.0 ms, P < 0.001, t-test) than those associated with the putative LTS bursts (6.7 ± 2.4 ms, P < 0.001, t-test). The dependence of the temporal structure of the spikes/spike bursts on the stimulus may provide insight into the temporal coding of sound information in the auditory system.

The effects of different dendritic geometries and distal dendritic Na+ current distributions on the propagation of action potentials (APs) and sensory EPSPs were investigated using a multi-compartment model of thalamocortical (TC) neurones where the somatic and proximal dendritic distribution of voltage-gated channels matched the ones measured experimentally, i.e. a uniform distribution of K+ currents and a non-uniform distribution of Na+ and T-type Ca2+ currents.

Our simulations indicated that the distal dendritic Na+ channel density has not to be larger than 50% of the somatic density in order to reproduce the electrical activities recorded experimentally from the soma and proximal dendrites of TC neurones. Moreover, we could highlight the existence of a distinct threshold density of distal dendritic Na+ channels necessary to support the regeneration of APs in this part of the dendritic tree: this threshold density was smaller for non-branching than for heavily branching dendrites.

The amplitude of the somatic EPSP mainly depended on the number of simultaneously activated synapses on any dendritic branch, despite large differences in the size of the dendritic EPSPs. The amplitude of the EPSP on a proximal dendrite was also dependent on the number and relative location of simultaneously activated synapses on all other proximal dendritic branches. The dendritic geometry did not affect these features of the simulated sensory EPSPs. In addition, the duration of somatic and proximal dendritic EPSPs was markedly increased (100%) in the presence of somatic and proximal dendritic T-type Ca2+ current.

The backpropagation of EPSPs to distal dendrites was affected by the dendritic Na+ channel distributions, but even in the absence of distal dendritic Na+ channels the EPSP reached the dendritic ends with less than 40% decrease in amplitude. Overall, the amplitude of the backpropagating EPSP was not greatly affected by the dendritic geometry, though a smaller amplitude reduction in unbranched than in heavily branching dendrites was observed.

Spindle oscillation is generated in intrathalamic circuits and thalamic reticular (RE) neurons act as pacemakers. To assess the consequences of this oscillation on membrane properties of RE neurons, we performed in vivo intracellular recordings in anesthetized cats during periods of intense synaptic activity, represented by spindle waves, compared to silent periods (interspindle lulls) that corresponded to a hyperpolarization of about −75 mV. During spindles, the massive activation of T-currents generated powerful low-threshold spikes (LTSs) that changed the membrane potential of RE cells by 10–20 mV and increased their membrane fluctuations by one order of magnitude (from 1–3 mV to 10 mV). Besides, the generation of LTSs decreased the apparent input resistance by ∼80% for ∼20–30 mseconds, in a cyclic way. The changes in basic membrane properties proved to be functionally significant for RE neurons, because both synaptic and intrinsic responsiveness were enhanced during active network states. Thus, synaptic responses tested by stimulating afferent (corticothalamic and thalamo-RE) pathways displayed increased spiking. The same result was found for intrinsic responses using positive and negative current pulses, and sinusoidal wave currents. Bursting discharges, responsible for the generation of the above changes, proved to be a very robust and reliable firing pattern in RE neurons. Our data demonstrate that ongoing network activity of RE neurons during spindle oscillations influence the expression of intrinsic properties of these pacemaking neurons, similarly to the previously shown effect exerted by spontaneously occurring synaptic activity on the intrinsic properties of thalamocortical and neocortical neurons.

Activation of cyclic AMP response element-binding protein (CREB) in the spinal dorsal horn may be a crucial contributor to the activity-dependent synaptic plasticity that is thought to underlie the development of persistent pain following peripheral nerve injury. In this study, we examined the early period of CREB activation following chronic constriction injury (loose ligation) of the sciatic nerve in rats. The estimated levels of Ser133-phosphorylated (activated) CREB significantly increased at 2 hours (424 ± 85%) and remained elevated at 4 hours (349 ± 97%) and 8 hours (258 ± 69%) after sciatic ligation compared with control animals. By contrast, activated CREB levels in sham-operated animals were not significantly greater than in control animals except at 1 hour (176 ± 6%) and 8 hours (288 ± 16%). The maximal ligation-associated activation of CREB at 2 hours occurred bilaterally and was dependent, at least partly, on NMDA-receptor activation because pretreatment with 20 µg MK-801 significantly attenuated the ligation-associated activation of CREB. The levels of non-phosphorylated CREB in ligated and sham-operated animals did not differ significantly from controls at the time-points examined.

These data establish a significant, persistent increase in CREB phosphorylation within hours of loose ligation of the sciatic nerve and indicate an early but consequential injury-related shift in the manner in which spinal dorsal horn neurons processed sensory information. The data lend further support to the notion that ligation-associated CREB-dependent synaptic plasticity in the spinal dorsal horn might underlie the development of persistent pain following peripheral nerve injury.