Brain-derived neurotrophic factor rapidly enhances synaptic transmission in hippocampal neurons via postsynaptic tyrosine kinase receptors

Although neurotrophins are primarily associated with long-term effects on neuronal survival and differentiation, recent studies have shown that acute changes in synaptic transmission can also be produced. In the hippocampus, an area critically involved in learning and memory, we have found that brain-derived neurotrophic factor (BDNF) rapidly enhanced synaptic efficacy through a previously unreported mechanism--increased postsynaptic responsiveness via a phosphorylation-dependent pathway. Within minutes of BDNF application to cultured hippocampal neurons, spontaneous firing rate was dramatically increased, as were the frequency and amplitude of excitatory postsynaptic currents. The increased frequency of postsynaptic currents resulted from the change in presynaptic firing. However, the increased amplitude was postsynaptic in origin because it was selectively blocked by intracellular injection of the tyrosine kinase receptor (Ntrk2/TrkB) inhibitor K-252a and potentiated by injection of the phosphatase inhibitor okadaic acid. These results suggest a role for BDNF in the modulation of synaptic transmission in the hippocampus.

Expression of cyclooxygenase-1 and cyclooxygenase-2 in human breast cancer

BACKGROUND

Numerous studies have demonstrated that the levels of prostaglandins are greater in various cancers, including breast cancer and colon cancer, than in normal tissues. In particular, the inducible form of cyclooxygenase (COX), the rate-limiting enzyme in prostaglandin biosynthesis, is overexpressed in colon tumors. Epidemiologic studies have demonstrated that the use of aspirin or other nonsteroidal anti-inflammatory drugs (NSAIDs) can reduce the risk of colon cancer and, to a lesser extent, the risk of breast cancer. NSAIDs are known to inhibit COX, suggesting that the beneficial effect of NSAIDs in colon cancer may be related to COX overexpression in this disease. This possibility led us to ask whether COX is also overexpressed in breast cancers.

METHODS

Surgical specimens from 44 patients with breast cancer who had undergone lumpectomy or mastectomy were analyzed by immunoblot analysis and immunohistochemical analysis to determine the expression profile of the constitutively expressed form of cyclooxygenase (COX-1) and the inducible form (COX-2); the specimens from 14 patients included normal breast tissue.

RESULTS

Expression of COX-1 protein was substantially higher in 30 of 44 tumor samples than in any of the 14 normal tissue specimens. Immunoblot analysis revealed extremely high levels of COX-2 protein in two tumor samples. Immunohistochemical staining of specimens that expressed COX-1 and/or COX-2 revealed that COX-1 was localized in stromal cells adjacent to the tumor but not in tumor cells. In contrast, COX-2 was localized primarily in tumor cells but also appeared in stromal cells.

CONCLUSION

Our results suggest that overexpression of COX may not be unique to colon cancer and may be a feature common to other epithelial tumors.

Brain-derived neurotrophic factor modulates hippocampal synaptic transmission by increasing N-methyl-D-aspartic acid receptor activity

Neurotrophins (NTs) have recently been found to regulate synaptic transmission in the hippocampus. Whole-cell and single-channel recordings from cultured hippocampal neurons revealed a mechanism responsible for enhanced synaptic strength. Specifically, brain-derived neurotrophic factor augmented glutamate-evoked, but not acetylcholine-evoked, currents 3-fold and increased N-methyl-D-aspartic acid (NMDA) receptor open probability. Activation of trkB NT receptors was critical, as glutamate currents were not affected by nerve growth factor or NT-3, and increased open probability was prevented by the tyrosine kinase inhibitor K-252a. In addition, the NMDA receptor antagonist MK-801 blocked brain-derived neurotrophic factor enhancement of synaptic transmission, further suggesting that NTs modulate synaptic efficacy via changes in NMDA receptor function.

Coupled two-way clustering analysis of gene microarray data

We present a coupled two-way clustering approach to gene microarray data analysis. The main idea is to identify subsets of the genes and samples, such that when one of these is used to cluster the other, stable and significant partitions emerge. The search for such subsets is a computationally complex task. We present an algorithm, based on iterative clustering, that performs such a search. This analysis is especially suitable for gene microarray data, where the contributions of a variety of biological mechanisms to the gene expression levels are entangled in a large body of experimental data. The method was applied to two gene microarray data sets, on colon cancer and leukemia. By identifying relevant subsets of the data and focusing on them we were able to discover partitions and correlations that were masked and hidden when the full dataset was used in the analysis. Some of these partitions have clear biological interpretation; others can serve to identify possible directions for future research.

Brain-derived neurotrophic factor rapidly enhances phosphorylation of the postsynaptic N-methyl-D-aspartate receptor subunit 1

Although neurotrophins have traditionally been regarded as neuronal survival factors, recent work has suggested a role for these factors in synaptic plasticity. In particular, brain-derived neurotrophic factor (BDNF) rapidly enhances synaptic transmission in hippocampal neurons through trkB receptor stimulation and postsynaptic phosphorylation mechanisms. Activation of trkB also modulates hippocampal long-term potentiation, in which postsynaptic N-methyl-D-aspartate glutamate receptors play a key role. However, the final common pathway through which BDNF increases postsynaptic responsiveness is unknown. We now report that BDNF, within 5 min of exposure, elicits a dose-dependent increase in phosphorylation of the N-methyl-D-aspartate receptor subunit 1. This acute effect occurred in hippocampal synaptoneurosomes, which contain pre- and postsynaptic elements, and in isolated hippocampal postsynaptic densities. Nerve growth factor, in contrast, caused no enhancement of phosphorylation. These results suggest a potential mechanism for trophin-induced potentiation of synaptic transmission.

BDNF acutely increases tyrosine phosphorylation of the NMDA receptor subunit 2B in cortical and hippocampal postsynaptic densities

While neurotrophins are critical for neuronal survival and differentiation, recent work suggests that they acutely regulate synaptic transmission as well. Brain-derived neurotrophic factor (BDNF) enhances excitatory postsynaptic currents in cultured dissociated hippocampal neurons within 2-3 min through postsynaptic, phosphorylation-dependent mechanisms. Moreover, BDNF modulates hippocampal long-term potentiation, in which postsynaptic NMDA (N-methyl-D-aspartate) receptors (NRs) play a key role. We now report that BDNF acutely increases tyrosine phosphorylation of the specific NMDA receptor subunit NR2B, which has recently been shown to play a role in long-term potentiation. Incubation of BDNF with cortical or hippocampal postsynaptic densities for 5 min increased tyrosine phosphorylation of the NR2B subunits in a dose-dependent manner. A maximal increase to 165% of control phosphorylation occurred at a BDNF concentration of 2 ng/ml. The BDNF action appeared to be specific, since nerve growth factor, another member of the neurotrophin gene family, had no effect on NR2B phosphorylation. Further, BDNF action was selective, since it did not alter tyrosine phosphorylation of NR2A subunits. Our results suggest that tyrosine phosphorylation of NR2B subunits of the NMDA receptor may contribute to neurotrophin modulation of postsynaptic responsiveness and long-term potentiation.

Chocolate craving and liking

Liking and craving for chocolate and related substances were surveyed in a sample of University of Pennsylvania undergraduates (n = 249) and their parents (n = 319). Chocolate was highly liked in all groups, with a stronger liking by females. Chocolate is the most craved food among females, and is craved by almost half of the female sample (in both age groups). Although this craving is related to a sweet craving, it cannot be accounted for as a craving for sweets. About half of the female cravers show a very well defined craving peak for chocolate in the perimenstrual period, beginning from a few days before the onset of menses and extending into the first few days of menses. There is not a significant relation in chocolate craving or liking between parents and their children. The current motivation for chocolate preference seems to be primarily, if not entirely, sensory. Liking for chocolate correlates significantly with liking for sweets and white chocolate. The liking for the sensory properties could originate in innate or acquired liking based on the sweetness, texture and aroma of chocolate, or it could be based in part on interactions between the postingestional effects of chocolate and a person's state (e.g., mood, hormone levels). Based on correlational data, we find little evidence for a relation between addiction to chocolate or the pharmacological (e.g., xanthine-based) effects of chocolate and the liking for chocolate.

Resampling method for unsupervised estimation of cluster validity

We introduce a method for validation of results obtained by clustering analysis of data. The method is based on resampling the available data. A figure of merit that measures the stability of clustering solutions against resampling is introduced. Clusters that are stable against resampling give rise to local maxima of this figure of merit. This is presented first for a one-dimensional data set, for which an analytic approximation for the figure of merit is derived and compared with numerical measurements. Next, the applicability of the method is demonstrated for higher-dimensional data, including gene microarray expression data.

Consensus guidelines from The American Society of Peritoneal Surface Malignancies on standardizing the delivery of hyperthermic intraperitoneal chemotherapy (HIPEC) in colorectal cancer patients in the United States

BACKGROUND

The American Society of Peritoneal Surface Malignancies (ASPSM) is a consortium of cancer centers performing cytoreductive surgery with hyperthermic intraperitoneal chemotherapy (HIPEC). This is a position paper from the ASPSM on the standardization of the delivery of HIPEC.

METHODS

A survey was conducted of all cancer centers performing HIPEC in the United States. We attempted to obtain consensus by the modified method of Delphi on seven key HIPEC parameters: (1) method, (2) inflow temperature, (3) perfusate volume, (4) drug, (5) dosage, (6) timing of drug delivery, and (7) total perfusion time. Statistical analysis was performed using nonparametric tests.

RESULTS

Response rates for ASPSM members (n = 45) and non-ASPSM members (n = 24) were 89 and 33 %, respectively. Of the responders from ASPSM members, 95 % agreed with implementing the proposal. Majority of the surgical oncologists favored the closed method of delivery with a standardized dual dose of mitomycin for a 90-min chemoperfusion for patients undergoing cytoreductive surgery for peritoneal carcinomatosis of colorectal origin.

CONCLUSIONS

This recommendation on a standardized delivery of HIPEC in patients with colorectal cancer represents an important first step in enhancing research in this field. Studies directed at maximizing the efficacy of each of the seven key elements will need to follow.

Injectable medication for the treatment of multiple sclerosis: the influence of self-efficacy expectations and injection anxiety on adherence and ability to self-inject

The management of many chronic illnesses involves medications that must be injected on a frequent basis. With fewer support resources available, patients are increasingly being obliged to manage injectable medications themselves. Interferon beta-1a (IFNbeta-1a), recommended for the treatment of multiple sclerosis (MS), must be injected intramuscularly on a weekly basis. Patients are generally advised and taught to self-inject, if possible. This longitudinal study examined cognitive and affective contributions to the ability to self-inject and adherence to IFNbeta-1a over 6 months following initiation of medication. Participants were 101 patients with a relapsing form of MS. Injection self-efficacy expectations, injection anxiety, adherence expectations, method of injection administration, and 6-month adherence to IFNbeta-1a were fitted to a path analytic model. Pretreatment injection self-efficacy expectations were significantly related to 6-month adherence. This relation was mediated by the patient's ability to self-inject. Patients 'experienced level of injection anxiety was related to adherence but not to method of injection.

The Spiral Structure of the Outer Milky Way in Hydrogen

We produce a detailed map of the perturbed surface density of neutral hydrogen in the outer Milky Way disk, demonstrating that the Galaxy is a non-axisymmetric multiarmed spiral. Spiral structure in the southern half of the Galaxy can be traced out to at least 25 kiloparsecs, implying a minimum radius for the gas disk. Overdensities in the surface density are coincident with regions of reduced gas thickness. The ratio of the surface density to the local median surface density is relatively constant along an arm. Logarithmic spirals can be fit to the arms with pitch angles of 20 degrees to 25 degrees .

Selective disruption of E-cadherin function in early Xenopus embryos by a dominant negative mutant

E-cadherin function was disrupted in vivo in developing Xenopus laevis embryos through the expression of a mutant E-cadherin protein lacking its cytoplasmic tail. This truncated form of E-cadherin was designed to act as a dominant negative mutant by competing with the extracellular interactions of wild-type endogenous E-cadherin. Expression of truncated E-cadherin in the early embryo causes lesions to develop in the ectoderm during gastrulation. In contrast, expression of a similarly truncated N-cadherin protein failed to cause the lesions. The ectodermal defect caused by the truncated E-cadherin is rescued by overexpression of wild-type E-cadherin, by co-injection of full-length E-cadherin RNA along with the RNA for the truncated form. Overexpression of full-length C-cadherin, however, is unable to compensate for the disruption of E-cadherin function and can actually cause similar ectodermal lesions when injected alone, suggesting that there is a specific requirement for E-cadherin. Therefore, E-cadherin seems to be specifically required for maintaining the integrity of the ectoderm during epiboly in the gastrulating Xenopus embryo. Differential cadherin expression reflects, therefore, the requirement for distinct adhesive properties during different morphogenetic cell behaviors.

Formation of hybrid cell-cell channels

The oocyte cell-cell channel assay was used to demonstrate that connexin-43 is a cell-cell channel-forming protein as previously shown for connexin-32. Expression of connexin-32 in one and connexin-43 in the other oocyte of a pair results in the formation of junctional conductances at rates similar to those observed when only one or the other connexin is expressed in both oocytes of a pair. This suggests that hybrid cell-cell channels form in the oocyte system. Hybrid channels also form when a connexin-43 mRNA-injected oocyte is paired with a noninjected oocyte expressing endogenous connexin. The latter hybrids have properties apparently contributed by both types of hemichannels. Pure connexin-43 channels are not voltage gated, whereas pure oocyte channels are voltage dependent; hybrids of these channels rectify.

Mutational analysis of gap junction formation

The paired oocyte cell-cell channel assay was used to investigate the mechanisms involved in the process of formation of gap junction channels. Single oocytes, injected with connexin-specific mRNAs, accumulate a pool of precursors from which cell-cell channels can form rapidly upon pairing. Several lines of evidence, including immunohistochemistry and surface labeling, indicate that part of this precursor pool is located in the cell membrane, probably in the form of closed hemichannels. The homophilic binding of hemichannels to each other can be mimicked by synthetic peptides representing the extracellular loop sequences of connexin32. The peptides specifically suppress channel formation. A crucial role is established for the six cysteines in the extracellular domains that are conserved in all vertebrate gap junction proteins. Change of any of these cysteines into serines results in absolute loss of function of the mutant connexin. The effects of thiol-specific reagents on channel formation suggest that docking and/or opening of channels involves disulfide exchange. Several of the variable amino acids in the extracellular loop sequences were found to determine specificity of connexin-connexin interactions.

Fialuridine and its metabolites inhibit DNA polymerase gamma at sites of multiple adjacent analog incorporation, decrease mtDNA abundance, and cause mitochondrial structural defects in cultured hepatoblasts

The thymidine analog fialuridine deoxy-2-fluoro-beta-D-arabinofuranosyl)-5-iodouracil (FIAU) was toxic in trials for chronic hepatitis B infection. One mechanism postulated that defective mtDNA replication was mediated through inhibition of DNA polymerase-gamma (DNA pol-gamma), by FIAU triphosphate (FIALTP) or by triphosphates of FIAU metabolites. Inhibition kinetics and primer-extension analyses determined biochemical mechanisms of FIAU, 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl) -5-methyluracil (FAU), 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)uracil triphosphate (TP) inhibition of DNA pol-gamma. dTMP incorporation by DNA pol-gamma was inhibited competitively by FIAUTP, FMAUTP, and FAUTP (K1=0.015, 0.03, and 1.0 microM, respectively). By using oliginucleotide template-primers. DNA pol-gamma incorporated each analog into DNA opposite a single adenosine efficiently without effects on DNA chain elongation. Incorporation of multiple adjacent analogs at positions of consecutive adenosines dramatically impaired chain elongation by DNA pol-gamma. Effects of FIAU, FMAU, and FAU on HepG2 cell mmtDNA abundance and ultrastructure were determined. After 14 days, mtDNA decreased by 30% with 20 microM FIAU or 20 microM FMAU and decreased less than 10% with 100 microM FAU. FIAU and FMAU disrupted mitochondria and caused accumulation of intracytoplasmic lipid droplets. Biochemical and cell biological findings suggest that FIAU and its metabolites inhibit mtDNA replication, most likely at positions of adenosine tracts, leading to decreased mtDNA and mitochondrial ultrastructural defects.

Malignant nerve-sheath neoplasms in neurofibromatosis: distinction from benign tumors by using imaging techniques

Malignant peripheral nerve-sheath neoplasms frequently complicate neurofibromatosis causing pain, enlarging masses, or neurologic deficits. However, similar findings sometimes also occur with benign nerve neoplasms. Our study was done retrospectively to determine if imaging techniques can differentiate malignant from benign nerve tumors in neurofibromatosis. Eight patients with symptomatic neoplasms (three benign, five malignant) were studied by CT in eight, MR in six, and 67Ga-citrate scintigraphy in seven. Uptake of 67Ga occurred in all five malignant lesions but not in two benign neoplasms studied. On CT or MR, all eight lesions, including three benign neoplasms, showed inhomogeneities. Of five lesions with irregular, infiltrative margins on CT or MR, four were malignant and one was benign. Of three lesions with smooth margins, one was malignant and two were benign. One malignant neoplasm caused irregular bone destruction. Accordingly, CT and MR could not generally distinguish malignant from benign lesions with certainty. However, both CT and MR provided structural delineation to help surgical planning for both types of lesion. 67Ga scintigraphy appears promising as a screening technique to identify lesions with malignant degeneration in patients with neurofibromatosis. Any area of abnormal radiogallium uptake suggests malignancy warranting further evaluation by CT or MR. Biopsy of any questionable lesion is essential.

Comparison of computed tomography and other imaging modalities in the evaluation of musculoskeletal tumors

An algorithmic approach for the evaluation of musculoskeletal tumors is proposed on the basis of a prospective comparison of different imaging techniques in 50 unselected patients. Conventional radiography was superior to other techniques in predicting the nature of primary bone tumors. Computed tomography proved the most effective method for assessing the extent of musculoskeletal tumors and therefore had a significant influence on management in 66% of patients studied. CT was more informative than angiography and also provided more anatomical detail than ultrasound. Radionuclide scanning was mainly of value in detecting unsuspected skeletal metastases in patients with apparently solitary skeletal lesions.

Functional trkB neurotrophin receptors are intrinsic components of the adult brain postsynaptic density

Neurotrophins have long been thought to act as target-derived factors that regulate the survival and differentiation of afferent neurons. Recently, brain-derived neurotrophic factor (BDNF) was shown to elicit rapid increases in synaptic activity of cultured hippocampal neurons by enhancing responsiveness to excitatory input. These findings suggest a postsynaptic localization of neurotrophin receptors. In this study, we examined the expression of trkB, a high-affinity receptor for BDNF, in the postsynaptic density (PSD), a proteinaceous specialization of the postsynaptic membrane. Western blot analyses with antibodies to trkB revealed localization to the PSD in adult rat cerebral cortex and hippocampus. Only the full-length, active form of trkB was detected in PSD samples. BDNF treatment of the adult cortical PSD resulted in a 5-fold increase in trkB autophosphorylation, supporting the contention that the PSD contains functional trkB. Truncated trkB, which does not contain the tyrosine kinase signaling domain, though present in membrane fractions, was undetectable in the PSD. The presence of trkB in the PSD is consistent with a role for neurotrophins in the regulation of synaptic activity via direct postsynaptic mechanisms.

Relationship between in vitro chromosomal radiosensitivity of peripheral blood lymphocytes and the expression of normal tissue damage following radiotherapy for breast cancer

BACKGROUND AND PURPOSE

There is a need for rapid and reliable tests for the prediction of normal tissue responses to radiotherapy, as this could lead to individualization of patient radiotherapy schedules and thus improvements in the therapeutic ratio. Because the use of cultured fibroblasts is too slow to be practicable in a clinical setting, we evaluated the predictive role of assays of lymphocyte chromosomal radiosensitivity in patients having radiotherapy for breast cancer.

MATERIALS AND METHODS

Radiosensitivity was assessed using a micronucleus (MN) assay at high dose rate (HDR) and low dose rate (LDR) on lymphocytes irradiated in the G(0) phase of the cell cycle (Scott D, Barber JB, Levine EL, Burril W, Roberts SA. Radiation-induced micronucleus induction in lymphocytes identifies a frequency of radiosensitive cases among breast cancer patients: a test for predispostion? Br. J. Cancer 1998;77;614-620) and an assay of G(2) phase chromatid radiosensitivity ('G(2) assay') (Scott D, Spreadborough A, Levine E, Roberts SA. Genetic predisposition in breast cancer. Lancet 1994; 344: 1444). In a study of acute reactions, blood samples were taken from breast cancer patients before the start of radiotherapy, and the skin reaction documented. 116 patients were tested with the HDR MN assay, 73 with the LDR MN assay and 123 with the G(2) assay. In a study of late reactions, samples were taken from a series of breast cancer patients 8-14 years after radiotherapy and the patients assessed for the severity of late effects according to the'LENT SOMA' scales. 47 were tested with the HDR assay, 26 with the LDR assay and 19 with the G(2) assay. For each clinical endpoint, patients were classified as being normal reactors or 'highly radiosensitive patients' (HR patients (Burnet NG. Johansen J, Turesson I, Nyman J. Describing patients' normal tissue reactions: Concerning the possiblity of individualising radiotherapy dose presciptions based on potential predictive assays of normal tissue radiosensitivity. Int. J. Cancer 1998;79:606-613)).

RESULTS

The HR patients could be identified in some of the assays. For example, for acute skin reactions, 9/123 patients were judged as HR; they had significantly higher G(2) scores than normal reactors (P=0.004). For the late reactions, the mean HDR MN scores were higher for the 4/47 patients who had severe telangiectasia (P=0.042) and the 8/47 patients had severe fibrosis (P=0.055). However, there were no trends towards increased chromosomal radiosensitivity with the micronucleus scores at HDR or LDR, or with G(2) chromosomal radiosensitivity.

CONCLUSIONS

While these results support the concept of using lymphocytes to detect elevated sensitivity to radiotherapy (as an alternative to fibroblasts), these assays are unlikely to be of assistance for the prediction of normal tissue effects in the clinic in their present form.

Soft-tissue tumors of the foot: value of MR imaging for specific diagnosis

We reviewed MR imaging findings in 14 patients with primary soft-tissue tumors of the foot and compared them with surgical and pathologic findings to determine the value of MR imaging in anatomic localization, delineation, and characterization of such lesions. Nine tumors (64%) were benign, and five (36%) were malignant. The anatomic location (compartment, space, relation to specific tendon) and extent of all tumors were accurately shown by MR imaging. Twelve tumors (86%) were correctly characterized as benign or malignant. Eight (89%) of nine benign lesions showed distinctive MR imaging features that correctly suggested a specific diagnosis. These included hemangioma (high T2-weighted intensity and internal septa), ganglion cyst (homogeneous, high T2-weighted weighted intensity and peritendinous location), plantar fibromatosis (nodularity of plantar aponeurosis with low intensity on all sequences), and pigmented villonodular synovitis (low T2-weighted intensity and lower intensity rim). Aggressive fibromatosis (one case) could not be characterized. Four (80%) of five malignant neoplasms had MR imaging findings suggesting soft-tissue sarcoma. Two synovial sarcomas were inhomogeneous and showed extensive peritendinous growth. Two clear cell sarcomas arose at the origin of the plantar aponeurosis and infiltrated adjacent muscle. A small clear cell sarcoma could not be characterized as benign or malignant. MR imaging of the foot is accurate in showing the extent of soft-tissue tumors, which is helpful for surgical planning. Determination of their specific anatomic location may help characterize some tumors. Although our series is small, it appears that MR imaging often suggests a specific diagnosis in certain benign soft-tissue tumors of the foot and may often correctly distinguish benign from malignant tumors.

Brain-derived neurotrophic factor increases activity of NR2B-containing N-methyl-D-aspartate receptors in excised patches from hippocampal neurons

Growth factors, including members of the neurotrophin gene family, play a central role in the regulation of neuronal survival and differentiation during development. In addition to these relatively long-term actions of neurotrophins, recent studies have shown that these factors also rapidly modulate synaptic transmission. Brain-derived neurotrophic factor (BDNF), in particular, regulates both pre- and postsynaptic aspects of hippocampal synaptic transmission. The postsynaptic effects include an increase in glutamate responsiveness, mediated by the N-methyl-D-aspartate (NMDA) glutamate receptor subtype. It is not clear, however, where BDNF-trkB signal transduction is initiated, because trkB receptors are located in both pre- and postsynaptic membranes. In the present study, we used excised membrane patches from cultured hippocampal neurons to determine whether BDNF directly modulates postsynaptic NMDA receptor activity. The results indicate that acute exposure to BDNF increases NMDA single channel open probability via postsynaptic trkB receptors and that this effect is dependent on the presence of the NR2B subunit of the NMDA receptor.

Activity of cat locus coeruleus noradrenergic neurons during the defense reaction

The single-unit activity of locus coeruleus noradrenergic (LC-NE) neurons was recorded in freely moving cats during naturally induced defense reactions. Defense reactions, consisting of arched back, piloerection, flattened ears and mydriasis, were elicited by exposing the cat either to a dog, or to a cat displaying aggressive behavior induced by electrical stimulation of the hypothalamus. LC-NE neurons were identified using previously established criteria, including suppression of firing during rapid eye movement (REM) sleep and in response to clonidine administration. Exposure to a dog evoked defense reactions and increased the tonic firing rate of LC-NE neurons (n = 8) from a baseline of approximately 0.9 spikes/s to approximately 2.5 spikes/s. Exposure to an aggressive cat evoked defense reactions that were qualitatively very similar to those produced by dog exposure, and elevated the tonic firing rate of LC-NE neurons (n = 8) from a baseline of approximately 1.0 spikes/s to approximately 2.5 spikes/s. In addition to these tonic elevations of activity, LC-NE neurons discharged in phasic bursts (as high as 10 spikes in a 500 ms period) in close association with specific threatening acts made by the dog or hypothalamically stimulated cat. The mere presence of a dog was sufficient to evoke tonic activation of LC-NE neurons, even in the absence of threatening advances by the dog, whereas exposure to a hypothalamically stimulated cat produced LC-NE neuronal activation only when the stimulated cat showed aggressive behavior. These results extend our previous work, which examined the response of LC-NE neurons to environmental and physiological stressors, into a more ethologically relevant domain, and suggest that LC-NE neuronal activation may play a role in the response to threatening or challenging situations.