Frequency-dependent expression of corticotropin releasing factor in the rat's cerebellum

Opposing actions of CRF-R1 and CB1 receptor on facial stimulation-induced MLI-PC plasticity in mouse cerebellar cortex

BACKGROUND

Corticotropin-releasing factor (CRF) is the major neuromodulator orchestrating the stress response, and is secreted by neurons in various regions of the brain. Cerebellar CRF is released by afferents from inferior olivary neurons and other brainstem nuclei in response to stressful challenges, and contributes to modulation of synaptic plasticity and motor learning behavior via its receptors. We recently found that CRF modulates facial stimulation-evoked molecular layer interneuron-Purkinje cell (MLI-PC) synaptic transmission via CRF type 1 receptor (CRF-R1) in vivo in mice, suggesting that CRF modulates sensory stimulation-evoked MLI-PC synaptic plasticity. However, the mechanism of how CRF modulates MLI-PC synaptic plasticity is unclear. We investigated the effect of CRF on facial stimulation-evoked MLI-PC long-term depression (LTD) in urethane-anesthetized mice by cell-attached recording technique and pharmacological methods.

RESULTS

Facial stimulation at 1 Hz induced LTD of MLI-PC synaptic transmission under control conditions, but not in the presence of CRF (100 nM). The CRF-abolished MLI-PC LTD was restored by application of a selective CRF-R1 antagonist, BMS-763,534 (200 nM), but it was not restored by application of a selective CRF-R2 antagonist, antisauvagine-30 (200 nM). Blocking cannabinoid type 1 (CB1) receptor abolished the facial stimulation-induced MLI-PC LTD, and revealed a CRF-triggered MLI-PC long-term potentiation (LTP) via CRF-R1. Notably, either inhibition of protein kinase C (PKC) with chelerythrine (5 µM) or depletion of intracellular Ca²⁺ with cyclopiazonic acid (100 µM), completely prevented CRF-triggered MLI-PC LTP in mouse cerebellar cortex in vivo.

CONCLUSIONS

The present results indicated that CRF blocked sensory stimulation-induced opioid-dependent MLI-PC LTD by triggering MLI-PC LTP through CRF-R1/PKC and intracellular Ca²⁺ signaling pathway in mouse cerebellar cortex. These results suggest that activation of CRF-R1 opposes opioid-mediated cerebellar MLI-PC plasticity in vivo in mice.

The role of the corticotropin-releasing hormone and its receptors in the regulation of stress response

Stress is an essential part of everyday life. The neuropeptide corticotropin-releasing hormone (CRH, also called CRF and corticoliberin) plays a key role in the integration of neuroendocrine, autonomic and behavioral responses to stress. The activation of the hypothalamic-pituitary-adrenal axis (HPA axis) by neurons of the paraventricular hypothalamic nucleus (PVN), the primary site of synthesis CRH, triggers stress reactions. In addition to the hypothalamus, CRH is widespread in extrahypothalamic brain structures, where it functions as a neuromodulator for coordination and interaction between the humoral and behavioral aspects of a stress response. The axons of neurons expressing CRH are directed to various structures of the brain, where the neuropeptide interacts with specific receptors (CRHR1, CRHR2) and can affect various mediator systems that work together to transmit signals to different brain regions to cause many reactions to stress. Moreover, the effect of stress on brain functions varies from behavioral adaptation to increased survival and increased risk of developing mental disorders. Disturbances of the CRH system regulation are directly related to such disorders: mental pathologies (depression, anxiety, addictions), deviations of neuroendocrinological functions, inflammation, as well as the onset and development of neurodegenerative diseases such as Alzheimer’s disease. In addition, the role of CRH as a regulator of the neurons structure in the areas of the developing and mature brain has been established. To date, studies have been conducted in which CRHR1 is a target for antidepressants, which are, in fact, antagonists of this receptor. In this regard, the study of the participation of the CRH system and its receptors in negative effects on hormone-dependent systems, as well as the possibility of preventing them, is a promising task of modern physiological genetics. In this review, attention will be paid to the role of CRH in the regulation of response to stress, as well as to the involvement of extrahypothalamic CRH in pathophysiology and the correction of mental disorders.

Corticotrophin-Releasing Factor Modulates the Facial Stimulation-Evoked Molecular Layer Interneuron-Purkinje Cell Synaptic Transmission in vivo in Mice

Corticotropin-releasing factor (CRF) is an important neuromodulator in central nervous system that modulates neuronal activity via its receptors during stress responses. In cerebellar cortex, CRF modulates the simple spike (SS) firing activity of Purkinje cells (PCs) has been previously demonstrated, whereas the effect of CRF on the molecular layer interneuron (MLI)–PC synaptic transmission is still unknown. In this study, we examined the effect of CRF on the facial stimulation–evoked cerebellar cortical MLI-PC synaptic transmission in urethane-anesthetized mice by in vivo cell-attached recording, neurobiotin juxtacellular labeling, immunohistochemistry techniques, and pharmacological method. Cell-attached recordings from cerebellar PCs showed that air-puff stimulation of ipsilateral whisker pad evoked a sequence of tiny parallel fiber volley (N1) followed by MLI-PC synaptic transmission (P1). Microapplication of CRF in cerebellar cortical molecular layer induced increases in amplitude of P1 and pause of SS firing. The CRF decreases in amplitude of P1 waveform were in a dose-dependent manner with the EC₅₀ of 241 nM. The effects of CRF on amplitude of P1 and pause of SS firing were abolished by either a non-selective CRF receptor antagonist, α-helical CRF-(9-14), or a selective CRF-R1 antagonist, BMS-763534 (BMS, 200 nM), but were not prevented by a selective CRF-R2 antagonist, antisauvagine-30 (200 nM). Notably, application CRF not only induced a significant increase in spontaneous spike firing rate, but also produced a significant increase in the number of the facial stimulation–evoked action potential in MLIs. The effect of CRF on the activity of MLIs was blocked by the selective CRF-R1 antagonist, and the MLIs expressed the CRF-R1 imunoreactivity. These results indicate that CRF increases excitability of MLIs via CRF-R1, resulting in an enhancement of the facial stimulation–evoked MLI-PC synaptic transmission in vivo in mice.

Corticotropin releasing factor modulates excitatory synaptic transmission

The mammalian brain contains many regions which synthesize and release the hormone and transmitter corticotropin releasing factor. This peptide is a key player in the function of the hypothalamic-pituitary-adrenal axis and has major role in mediating the endocrine limb of the stress response. However, there are several regions outside of the paraventricular nucleus of the hypothalamus which synthesize this peptide in which it has a role more akin to a classical neurotransmitter. A significant body of literature exists in which its role as a transmitter and its cellular effects in many brain regions, as well as how it affects various forms of behavior, is described. However, the receptors which corticotropin releasing factor interacts with in the brain are G-protein coupled receptors, and therefore their activation promotes a multitude of cellular effects. Despite this, comparatively little research has been done to investigate how this peptide affects excitatory synaptic transmission in the brain. This is important because both excitatory and inhibitory regulation of physiology are important extrinsic factors in the operation of neurons which occur in conjunction with their intrinsic properties. By not taking into account how corticotropin releasing factor affects these processes, a complete picture of this peptide's role in brain function is not available. In this chapter, the limited body of research which has explicitly investigated how corticotropin releasing factor affects excitatory synaptic transmission in various brain regions will be explored.

Corticotrophin-Releasing Factor Modulates Cerebellar Purkinje Cells Simple Spike Activity in Vivo in Mice

Corticotropin-releasing factor (CRF) is a major neuromodulator that modulates cerebellar neuronal activity via CRF receptors during stress responses. In the cerebellar cortex, CRF dose-dependently increases the simple spike (SS) firing rate of Purkinje cells (PCs), while the synaptic mechanisms of this are still unclear. We here investigated the effect of CRF on the spontaneous SS activity of cerebellar PCs in urethane-anesthetized mice by in vivo electrophysiological recording and pharmacological methods. Cell-attached recordings from PCs showed that micro-application of CRF in cerebellar cortical molecular layer induced a dose-dependent increase in SS firing rate in the absence of GABA_A receptor activity. The CRF-induced increase in SS firing rate was completely blocked by a nonselective CRF receptor antagonist, α-helical CRF-(9–14). Nevertheless, application of either a selective CRF-R1 antagonist, BMS-763534 (BMS, 200 nM) or a selective CRF-R2 antagonist, antisauvagine-30 (200 nM) significantly attenuated, but failed to abolished the CRF-induced increase in PCs SS firing rate. In vivo whole-cell patch-clamp recordings from PCs showed that molecular layer application of CRF significantly increased the frequency, but not amplitude, of miniature postsynaptic currents (mEPSCs). The CRF-induced increase in the frequency of mEPSCs was abolished by a CRF-R2 antagonist, as well as protein kinase A (PKA) inhibitors. These results suggested that CRF acted on presynaptic CRF-R2 of cerebellar PCs resulting in an increase of glutamate release through PKA signaling pathway, which contributed to modulation of the cerebellar PCs outputs in Vivo in mice.

Distribution of corticotropin-releasing factor neurons in the mouse brain: a study using corticotropin-releasing factor-modified yellow fluorescent protein knock-in mouse

We examined the morphological features of corticotropin-releasing factor (CRF) neurons in a mouse line in which modified yellow fluorescent protein (Venus) was expressed under the CRF promoter. We previously generated the CRF-Venus knock-in mouse, in which Venus is inserted into the CRF gene locus by homologous recombination. In the present study, the neomycin phosphotransferase gene (Neo), driven by the pgk-1 promoter, was deleted from the CRF-Venus mouse genome, and a CRF-Venus∆Neo mouse was generated. Venus expression is much more prominent in the CRF-Venus∆Neo mouse when compared to the CRF-Venus mouse. In addition, most Venus-expressing neurons co-express CRF mRNA. Venus-expressing neurons constitute a discrete population of neuroendocrine neurons in the paraventricular nucleus of the hypothalamus (PVH) that project to the median eminence. Venus-expressing neurons were also found in brain regions outside the neuroendocrine PVH, including the olfactory bulb, the piriform cortex (Pir), the extended amygdala, the hippocampus, the neocortices, Barrington's nucleus, the midbrain/pontine dorsal tegmentum, the periaqueductal gray, and the inferior olivary nucleus (IO). Venus-expressing perikarya co-expressing CRF mRNA could be observed clearly even in regions where CRF-immunoreactive perikarya could hardly be identified. We demonstrated that the CRF neurons contain glutamate in the Pir and IO, while they contain gamma-aminobutyric acid in the neocortex, the bed nucleus of the stria terminalis, the hippocampus, and the amygdala. A population of CRF neurons was demonstrated to be cholinergic in the midbrain tegmentum. The CRF-Venus∆Neo mouse may be useful for studying the structural and functional properties of CRF neurons in the mouse brain.

Corticotropin-releasing factor increases Purkinje neuron excitability by modulating sodium, potassium, and Ih currents

Corticotropin-releasing factor (CRF) is a neuromodulator closely associated with stress responses. It is synthesized and released in the central nervous system by various neurons, including neurons of the inferior olive. The targets of inferior olivary neurons, the cerebellar Purkinje neurons (PNs), are endowed with CRF receptors. CRF increases the excitability of PNs in vivo, but the biophysical mechanism is not clear. Here we examine the effect of CRF on the firing properties of PNs using acute rat cerebellar slices. CRF increased the PN firing rate, regardless of whether they were firing tonically or switching between firing and quiescent periods. Current- and voltage-clamp experiments showed that the increase in firing rate was associated with a voltage shift of the activation curve of the persistent sodium current and hyperpolarizing-activated current, as well as activation of voltage-dependent potassium current. The multiple effects on various ionic currents, which are in agreement with the possibility that activation of CRF receptors triggers several intracellular pathways, are manifested as an increase excitability of PN.

Evidence for TNFα action on excitatory and inhibitory neurotransmission in the central amygdala: a brain site influenced by stress

Anxiety-like responses to stress are accompanied by elevation of brain cytokine-mRNAs. Because cytokines microinjected into central-amygdala (CeA) substitute for stress in a behavioral paradigm, the possibility was raised that cytokines increased by stress influence behavior by affecting CeA-neural activity. Previously, cytokines increased firing-rate of CeA-neurons comparable to that induced by corticotropin-releasing factor (CRF). In this investigation, tumor-necrosis-factor-α (TNFα) increased amplitude, but not frequency of mEPSCs from CeA-neurons. Additionally, TNFα decreased the threshold for triggering action potentials from CeA-neurons without altering membrane-properties during current-clamp recording. Glutamate-receptor-antagonist blockade of mEPSCs and the TNFα-induced reduction in firing threshold implicated glutamate in these changes. A phosphatidyl-inositol-3-kinase-antagonist prevented the TNFα-induced increased in amplitude of mEPSCs, documenting a TNFα intracellular influence. Additionally, TNFα increased frequency, but not amplitude of mIPSCs. CRF-receptor-antagonists were found to prevent the TNFα-induced increase in mIPSC-frequency, without altering the TNFα-induced amplitude increase in mEPSCs or the reduced threshold for action-potentials by TNFα. To clarify how TNFα was increasing CRF-release in the presence of tetrodotoxin, the possibility tested was whether preventing glial-activation would prevent this elevated mIPSC-frequency blocked by CRF-receptor antagonists. Minocycline, which blocks glial activation, prevented the TNFα-induced increase in mIPSC-frequency - a finding consistent with glia contributing to the CRF-involvement in this TNFα action. To fully understand the means by which a CRF1-receptor-antagonist and minocycline prevent TNFα from increasing mIPSC-frequency will require further clarification. Nonetheless, these data provide convincing evidence that release of TNFα by stress could alter neural activity of CeA-neurons by influencing GABA-and glutamate function.

Paternal deprivation affects the development of corticotrophin-releasing factor-expressing neurones in prefrontal cortex, amygdala and hippocampus of the biparental Octodon degus

Although the critical role of maternal care on the development of brain and behaviour of the offspring has been extensively studied, knowledge about the importance of paternal care is comparatively scarce. In biparental species, paternal care significantly contributes to a stimulating socio-emotional family environment, which most likely also includes protection from stressful events. In the biparental caviomorph rodent Octodon degus, we analysed the impact of paternal care on the development of neurones in prefrontal-limbic brain regions, which express corticotrophin-releasing factor (CRF). CRF is a polypeptidergic hormone that is expressed and released by a neuronal subpopulation in the brain, and which not only is essential for regulating stress and emotionality, but also is critically involved in cognitive functions. At weaning age [postnatal day (P)21], paternal deprivation resulted in an elevated density of CRF-containing neurones in the orbitofrontal cortex and in the basolateral amygdala of male degus, whereas a reduced density of CRF-expressing neurones was measured in the dentate gyrus and stratum pyramidale of the hippocampal CA1 region at this age. With the exception of the CA1 region, the deprivation-induced changes were no longer evident in adulthood (P90), which suggests a transient change that, in later life, might be normalised by other socio-emotional experience. The central amygdala, characterised by dense clusters of CRF-immunopositive neuropil, and the precentral medial, anterior cingulate, infralimbic and prelimbic cortices, were not affected by paternal deprivation. Taken together, this is the first evidence that paternal care interferes with the developmental expression pattern of CRF-expressing interneurones in an age- and region-specific manner.

Climbing fiber signaling and cerebellar gain control

The physiology of climbing fiber signals in cerebellar Purkinje cells has been studied since the early days of electrophysiology. Both the climbing fiber-evoked complex spike and the role of climbing fiber activity in the induction of long-term depression (LTD) at parallel fiber-Purkinje cell synapses have become hallmark features of cerebellar physiology. However, the key role of climbing fiber signaling in cerebellar motor learning has been challenged by recent reports of forms of synaptic and non-synaptic plasticity in the cerebellar cortex that do not involve climbing fiber activity, but might well play a role in cerebellar learning. Moreover, cerebellar LTD does not seem to strictly require climbing fiber activity. These observations make it necessary to re-evaluate the role of climbing fiber signaling in cerebellar function. Here, we argue that climbing fiber signaling is about adjusting relative probabilities for the induction of LTD and long-term potentiation (LTP) at parallel fiber synapses. Complex spike-associated, dendritic calcium transients control postsynaptic LTD and LTP induction. High calcium transients, provided by complex spike activity, do not only favor postsynaptic LTD induction, but simultaneously trigger retrograde cannabinoid signaling, which blocks the induction of presynaptic LTP. Plasticity of the climbing fiber input itself provides additional means to fine-tune complex spike associated calcium signaling and thus to adjust the gain of heterosynaptic climbing fiber control. In addition to dendritic calcium transients, climbing fiber activity leads to the release of the neuropeptide corticotropin-releasing factor (CRF), which facilitates LTD induction at both parallel fiber and climbing fiber synapses.

Increased connexin 43 expression as a potential mediator of the neuroprotective activity of the corticotropin-releasing hormone

CRH is a major central stress mediator, but also a potent neuroprotective effector. The mechanisms by which CRH mediates its neuroprotective actions are largely unknown. Here, we describe that the gap junction molecule connexin43 (Cx43) mediates neuroprotective effects of CRH toward experimentally induced oxidative stress. An enhanced gap junction communication has been reported to contribute to neuroprotection after neurotoxic insults. We show that CRH treatment up-regulates Cx43 expression and gap junctional communication in a CRH receptor-dependent manner in IMR32 neuroblastoma cells, primary astrocytes, and organotypic hippocampal slice cultures. MAPKs and protein kinase A-cAMP response element binding protein -coupled pathways are involved in the signaling cascade from CRH to enhanced Cx43 function. Inhibition of CRH-promoted gap junction communication by the gap junction inhibitor carbenoxolone could prevent neuroprotective actions of CRH in cell and tissue culture models suggesting that gap junction molecules are involved in the neuroprotective effects of CRH. The extent of oxidative stress-induced protein carbonylation and cell death inversely correlated with Cx43 protein levels as shown by Cx43 small interfering RNA knockdown experiments. Coculture studies of primary neurons and astrocytes revealed that astrocytic Cx43 likely contributes to the neuroprotective effects of CRH. To our knowledge this is the first description of Cx43 as a potential mediator of the neuroprotective actions of CRH.

Stimulation of the inferior olivary complex alters the distribution of the type 1 corticotropin releasing factor receptor in the adult rat cerebellar cortex

In a previous study, it was shown that populations of climbing fibers, derived from the inferior olivary complex (IOC) contain the peptide corticotropin releasing factor (CRF) and that the expression of this peptide in climbing fibers could be modulated by the level of activity in olivary afferents. The intent of this study was to determine if there was comparable plasticity in the distribution of the type 1 CRF receptor (CRF-R1) in the cerebellum of the rat. Our results indicate that CRF-R1 was localized primarily to Purkinje cell somata and their primary dendrites and granule cells. In addition, scattered immunolabeling was present over the somata of Golgi cells, basket cells and stellate cells, as well as Bergmann glial cells and their processes. IOC stimulation for 30 min at 1 Hz increased CRF-R1 expression in molecular layer interneurons and processes of Bergmann glial cells. Little to no effect on CRF receptor distribution was observed in Purkinje cells, granule cells, or Golgi cells. IOC stimulation at 5 Hz however, increased CRF-R1 expression in the processes of Bergmann glial cells while decreasing its expression in basket, stellate and, to some extent, in Purkinje cells. The present results suggest that there is activity-dependent plasticity in CRF-R1 expression that must be considered in defining the mechanism by which the CRF family of peptides modulates activity in cerebellar circuits. The present results also suggest that the primary targets of CRF released from climbing fibers are Bergmann glial cells and interneurons in the molecular layer. Further, interneurons responded with a decrease in receptor expression following more intense levels of stimulation suggesting the possibility of internalization of the receptor. In contrast, Bergmann glial cells showed an increased expression in receptor expression. These data suggest that CRF released from climbing fibers may modulate the physiological properties of basket and stellate cells as well as having a heretofore unidentified and potentially unique effect on Bergmann glia.

The neuropeptide corticotropin-releasing factor regulates excitatory transmission and plasticity at the climbing fibre-Purkinje cell synapse

The climbing fibre (CF) input controls cerebellar Purkinje cell (PC) activity as well as synaptic plasticity at parallel fibre (PF)-PC synapses. Under high activity conditions, CFs release not only glutamate, but also the neuropeptide corticotropin-releasing factor (CRF). Brief periods of such high CF activity can lead to the induction of long-term depression (LTD) at CF-PC synapses. Thus, we have examined for the first time the role of CRF in regulating excitatory postsynaptic currents (EPSCs) and long-term plasticity at this synapse. Exogenous application of CRF alone transiently mimicked three aspects of CF-LTD, causing reductions in the CF-evoked excitatory postsynaptic current, complex spike second component and complex spike afterhyperpolarization. The complex spike first component is unaffected by CF-LTD induction and was similarly unaffected by CRF. Application of a CRF receptor antagonist reduced the expression amplitude and induction probability of CF-LTD monitored at the EPSC level. Collectively, these results suggest that under particular sensorimotor conditions, co-release of CRF from climbing fibres could down-regulate excitatory transmission and facilitate LTD induction at CF-PC synapses. Inhibition of either protein kinase C (PKC) or protein kinase A (PKA) attenuated the effects of CRF upon CF-EPSCs. We have previously shown that CF-LTD induction is PKC-dependent, and here demonstrate PKA-dependence as well. These results suggest that both the acute effects of CRF on CF-EPSCs as well as the facilitating effect of CRF on CF-LTD induction can be explained by a CRF-mediated recruitment of PKC and PKA.

Evidence for the presence of the type 2 corticotropin releasing factor receptor in the rodent cerebellum

Corticotropin releasing factor (CRF), localized in afferent inputs to the cerebellum, binds to two receptors defined as the Type 1 (CRF-R1) and the Type 2 (CRF-R2alpha). CRF-R1 has been localized to the cerebellum, as has a truncated isoform of CRF-R2alpha. Evidence for the presence of the full length isoform of CRF-R2alpha in the cerebellum is conflicting. We used RT-PCR, immunohistochemical, and physiologic techniques to resolve this conflict. RT-PCR data show low levels of CRF-R2alpha in the vermis and hemisphere of the cerebellum. These observations were confirmed by the Gene Expression Nervous System Atlas (GENSAT) database. A CRF-R2alpha antibody was used to determine the cellular distribution of the receptor in the cerebellum. The vast majority of the receptors are localized to Bergmann glial cells located throughout the cerebellum, as well as astrocytes in the granule cell layer. Neuronal labeling is present in sub-populations of Purkinje cells, Golgi cells, basket cells, and cerebellar nuclear neurons. Physiologic data show that urocortin II, which binds selectively to CRF-R2alpha, increases the firing rate of both Purkinje cells and nuclear neurons; this response can be blocked by the CRF-R2alpha-specific antagonist, antisauvagine-30. The present results confirm that CRF-R2alpha is present in the cerebellum and functions in circuits that modulate the firing rate of Purkinje cells and cerebellar nuclear neurons. A comparative analysis showed that the patterns of distribution of CRF-R1, CRF-R2alpha and CRF-R2alpha-tr are distinct. These data indicate that the CRF family of peptides modulates cerebellar output by binding to multiple CRF receptors.

Exposure to neonatal separation stress alters exploratory behavior and corticotropin releasing factor expression in neurons in the amygdala and hippocampus

Evidence is accumulating that early emotional experience interferes with the development of the limbic system, which is involved in perception and regulation of emotional behaviors as well as in learning and memory formation. Limbic brain regions, as well as hypothalamic regions and other, nonlimbic areas contain specific neuron subpopulations, which express and release corticotropin releasing factor (CRF). Since these neurons serve to connect limbic function to endocrine, stress-related responses, we proposed that stressful experience during early postnatal brain development should interfere with the development of CRF-containing neurons, particularly in brain regions essential for emotional regulation. Applying neonatal separation stress (daily 1 h separation from the parents and litter mates) as stressor, the number of immunocytochemically identified CRF-expressing neurons/fibers was quantified in the amygdala, hippocampus, paraventricular nucleus of the hypothalamus, piriform cortex, and the somatosensory cortex of 3-week-old stressed and nonstressed Octodon degus, a semi-precocial rodent. Compared to controls neonatally stressed animals showed significantly lower levels of CRF-positive fibers (-60%) in the central amygdala, significantly less CRF-positive neurons in the dentate gyrus (-28%) and the CA1 region (-29%) and significantly lower CRF cell densities in the somatosensory cortex (-26%). On the other hand, we found significantly higher numbers of CRF-immunoreactive neurons in the basolateral amygdaloid complex (+192%) of stressed animals compared to nonstressed controls. No differences in CRF-immunoreactive cell densities were detected in the other regions. Additional behavioral analysis revealed significantly elevated exploratory behavior (+34%) in stressed animals compared to controls, which might indicate reduced anxiety in the stressed animals.

Long-term potentiation (LTP) in the central amygdala (CeA) is enhanced after prolonged withdrawal from chronic cocaine and requires CRF1 receptors

The amygdala is part of the brain reward circuitry that plays a role in cocaine-seeking and abstinence in animals and cocaine craving and relapse in humans. Cocaine-seeking is elicited by cocaine-associated cues, and the basolateral amygdala (BLA) and CeA are essential in forming and communicating drug-related associations that are thought to be critical in long-lasting relapse risk associated with drug addiction. Here we simulated a cue stimulus with high-frequency stimulation (HFS) of the BLA-CeA pathway to examine mechanisms that may contribute to drug-related associations. We found enhanced long-term potentiation (LTP) after 14-day but not 1-day withdrawal from 7-day cocaine treatment mediated through N-methyl-d-aspartate (NMDA) receptors (NRs), L-type voltage-gated calcium channels (L-VGCCs), and corticotropin-releasing factor (CRF)(1) receptors; this was accompanied by increased phosphorylated NR1 and CRF(1) protein not associated with changes in NMDA/AMPA ratios in amygdalae from cocaine-treated animals. We suggest that these signaling mechanisms may provide therapeutic targets for the treatment of cocaine cravings.

Presynaptic localization of a truncated isoform of the type 2 corticotropin releasing factor receptor in the cerebellum

It is now well established that corticotropin releasing factor is present in two major excitatory afferent systems to the cerebellum, namely climbing fibers and mossy fibers. Two major classes of corticotropin releasing factor receptors, each with unique binding characteristics, have been identified as type 1 and type 2. In this study we used an antibody made to the n-terminus of the type 2 corticotropin releasing factor receptor. Characterization of this antibody showed that it strongly labeled a protein with a molecular weight of 16-32 kDa and only faintly labels a 62-83 kDa protein. The lower molecular weight protein corresponds to the weight of a recently described truncated isoform of this receptor that is designated corticotropin releasing factor-type 2alpha-truncated isoform. We carried out transfection paradigms using corticotropin releasing factor-type 2alpha-truncated isoform constructs and confirmed that the antibody recognized the truncated isoform of the type 2 corticotropin releasing factor receptor. Further, light and electron microscopic studies were carried out in mice and rats to define the distribution of the truncated receptor. Immunoreactivity is evident in the basal region of many, but not all Purkinje cell bodies and their initial axonal segments, as well as the initial axonal segments of isolated Golgi cells, and cerebellar nuclear neurons. In addition, punctate elements in the molecular layer were immunolabeled. The localization of the receptor to the initial segment of Purkinje cells was confirmed with electron microscopy. Further, the punctate labeling in the molecular layer was localized to parallel fibers and their terminals. In conclusion, evidence has been presented to show that distinct isoforms of the corticotropin releasing factor receptor are present in the cerebellum. The complex interactions between corticotropin releasing factor and other members of the corticotropin releasing factor family of peptides with both pre- and postsynaptic receptors support a growing concept that corticotropin releasing factor plays an important role in modulating activity in cerebellar circuits and ultimately in controlling motor behavior.

Regulation of Synaptic Transmission by CRF Receptors

Corticotropin-releasing factor (CRF or CRH) and its family of related peptides have long been recognized as hypothalamic-pituitary-adrenal (HPA) axis peptides that function to regulate the release of other hormones, e.g., ACTH. In addition, CRF acts outside the HPA axis not as a hormone, but as a regulator of synaptic transmission, pre- and post-synaptically, within specific CNS neuronal circuits. Synaptic transmission within the nervous system is today understood to be a more complex process compared to the concepts associated with the term 'synapse' introduced by Sherrington in 1897. Based on more than a century of progress with modern cellular and molecular experimental techniques, prior definitions and functions of synaptic molecules and their receptors need to be reconsidered (see Glossary and Fig. 1), especially in light of the important roles for CRF, its family of peptides and other potential endogenous regulators of neurotransmission, e.g., vasopressin, NPY, etc. (see Glossary). In addition, the property of 'constitutive activity' which is associated with G-protein coupled receptors (GPCRs) provides a persistent tonic mechanism to fine-tune synaptic transmission during both acute and chronic information transfer. We have applied the term 'regulator', adapted from the hormone literature, to CRF, as an example of a specific endogenous substance that functions to facilitate or depress the actions of neuromodulators on fast and slow synaptic responses. As such, synaptic neuroregulators provide a basic substrate to prime or initiate silently plastic processes underlying neurotransmitter-mediated information transfer at CNS synapses. Here we review the role of CRF to regulate CNS synaptic transmission and also suggest how under a variety of allostatic changes, e.g., associated with normal plasticity, or adaptations resulting from mental disorders, the synaptic regulatory role for CRF may be 'switched' in its polarity and/or magnitude in order to provide a coping mechanism to deal with daily and life-long stressors. Thus, a prominent role we assign to non-HPA axis CRF, its family of peptides, and their receptors, is to maintain both acute and chronic synaptic stability.

[125I]-Galanin binding in brain of wildtype, and galanin- and GalR1-knockout mice: Strain and species differences in GalR1 density and distribution

Widespread production of knockout and transgenic mice has led to an increased use of mice as animal models for studies of normal- and patho-physiology. Hence, the precise mapping of central transmitter/peptide systems in the mouse has become essential for the interpretation of functional studies and for the correct correlation with findings obtained in the rat, primates and/or human. In this regard, the current study reports the autoradiographic localization of [(125)I]-galanin (GAL) binding sites in brain of the common C57BL/6J and 129OlaHsd mouse strains, as well as in GAL and galanin receptor-1 (GalR1) knockout (KO) mice. In C57BL/6J and 129OlaHsd mice, [(125)I]-GAL binding sites were detected throughout the brain, including moderate-high relative densities in the basal ganglia (caudate putamen, nucleus [n.] accumbens, olfactory tubercle, substantia nigra), limbic regions (septum, bed n. stria terminalis, ventral hippocampus, amygdala), cingulate, retrosplenial, entorhinal cortex, centro-lateral/medial thalamic n., preoptic/lateral hypothalamus, midbrain (superior colliculus, periaqueductal gray), pons/medulla oblongata (parabrachial, pontine reticular and solitary tract n.) and cerebellar cortex. [(125)I]-GAL binding levels were low or absent in main olfactory bulb, neocortex, ventrolateral/geniculate thalamic n., dorsal hippocampus, inferior colliculus and cranial motor n. In simultaneous determinations, relative [(125)I]-GAL binding site densities in brain were generally lower in C57BL/6J than in 129OlaHsd mice, while the density and distribution of central binding in the GAL-KO mouse was essentially identical to that in its background-129OlaHsd strain. In contrast, no specific [(125)I]-GAL binding was detected in any region of GalR1-KO mouse brain, revealing that under the experimental conditions used, the peptide ligand binding is predominantly (exclusively) to the GalR1 subtype. This evaluation of GAL receptor site distribution in mouse brain has revealed similarities and some differences with the equivalent system in rat and provides a valuable reference for future comparative studies of central GAL transmission.