Single unit activity in the lateral septum and central nucleus of the amygdala in the elevated plus-maze: a model of exposure therapy?

The central nucleus of the amygdala (CeA) is a major output region of the amygdala involved in organizing the expression of fear. There is also evidence that the lateral septum (LS) provides inhibitory control of neurons in CeA and is involved in the relief of fear. This study examined single unit activity in the lateral septum (LS) and the central nucleus of the amygdala (CeA) in the open and closed arms of the elevated plus-maze, a highly validated animal model of fear and anxiety. The general presumption is that animals normally avoid the open arms because the open arms are relatively more anxiety provoking than the closed arms which represent relative safety. It was expected that neurons in CeA would increase their activity in the open arms relative to the closed arms indicative of increased anxiety and that LS neurons would decrease their activity on the open arms. Contrary to expectations it was found that the preponderance of units in CeA decreased their firing rates on the open arms compared to the closed arms. An increase in firing rates in LS was seen in the open arms compared to the closed arms. The data suggest that when animals are placed on the open arms a compensatory process takes place to suppress fear so that the animal can engage in adaptive behavior. We liken this process to that which takes place in exposure therapy for phobias in humans which involves the inhibition of fear resulting from Pavlovian extinction.

Mosquitoes of Thule Air Base, Greenland.

Thule Air Base in western Greenland had a previously uncharacterized mosquito pest problem. Swarms of bloodfeeding mosquitoes have been reported from June to late August, but the species were unknown. We conducted a base-wide mosquito vector survey from June to July 2012. One species of mosquito, Aedes impiger, was collected and > 3,000 were processed for polymerase chain reaction-based virus surveillance. Active mosquito breeding sites were located throughout the base and surrounding valley. Two pools of mosquitoes from Thule Air Base tested positive for an Orthobunyavirus; however, DNA sequencing of the viral amplicons was not complete enough to fully identify the agent.

Electrophysiological analysis of the interaction between the lateral septum and the central nucleus of the amygdala.

Evidence suggests that the lateral septum (LS) and the central nucleus of the amygdala (CeA) play opposing roles in the modulation of fear and anxiety. The current study examined the interaction of the two structures in the albino rat by electrically stimulating each and recording single-unit activity in the other. In each case, electrical stimulation consisted of 50 trains of 5 pulses 800µA in amplitude, 0.1ms in duration with a .01s interval between pulses. Electrical stimulation of LS had a predominant inhibitory effect upon cells in CeA. Contrariwise, stimulation of CeA had a predominant excitatory effect on cells in LS. The results of the study suggest a possible regulatory, negative feedback model of the interaction between LS and CeA.

Kindling of the lateral septum and the amygdala: effects on anxiety in rats.

Long-term kindling of limbic system structures may produce substantial changes in emotional behavior in rats. This study examined long-term changes in two kindled structures that have opposite effects on anxiety, the lateral septum and the central nucleus of the amygdala. The purpose of the experiment was to examine the specificity of the emotional effects of kindling by employing a double dissociation design. Animals were tested in two common animal models of anxiety, the water-lick conflict test and the elevated plus-maze. In the conflict test amygdala-kindled animals demonstrated a significant anxiolytic effect when compared with sham-kindled animals. This effect was potentiated by chlordiazepoxide. Septally-kindled animals exhibited a significant anticonflict effect when compared to sham-kindled animals in the first session. Septally-kindled animals spent significantly more time on the open arms of the elevated plus-maze than did sham-kindled animals. Observed changes persisted 6weeks after the termination of 150 kindling sessions. The effects of long-term kindling were highly consistent with those of disruption rather than facilitation.

Cognitive impairments and the prevention of homelessness: research and practice review.

Cognitive impairments can increase significantly a person's level of risk for becoming or remaining homeless. Five topics are explored that address these impairments in preventing homelessness: (1) the nature and estimated prevalence of cognitive impairments among people who are homeless, especially those with vulnerabilities like mental illness or substance abuse; (2) the multiple origins of these impairments; (3) how these impairments impact services for people at risk for homelessness; (4) good practice approaches to handling cognitive impairments in homeless shelters, supported housing programs, and other service systems for people at risk for homelessness; and, (5) important research and practice issues requiring further action.

Effects of chlordiazepoxide on single-unit activity in the septal region of the freely moving rat: aversive vs. non-aversive contexts.

Evidence suggests that stimuli that have the property of inhibiting fear in a Pavlovian fear conditioning paradigm increase cellular activity in the lateral septum, a result consistent with the idea that the lateral septum is actively involved in the inhibition of fear. The experiments reported here were designed to determine if an anxiolytic drug with fear-inhibiting properties would also increase neuronal activity in the lateral septum in a manner that might relate to its mechanism of action as an anxiolytic. An experiment was performed to compare the effects of the benzodiazepine anxiolytic chlordiazepoxide (CDP) upon single-unit activity in the septal region of the rat brain during Pavlovian aversive conditioning with the effects of CDP in a non-aversive context. During Pavlovian conditioning there was a decrease in unit activity in the more lateral regions of the septum, the dorsolateral and ventrolateral nuclei, when a stimulus signaling footshock (CS+) was presented. This conditioned suppression of unit activity was blocked by an intraperitoneal injection of CDP. Additionally, CDP increased baseline unit activity in these regions in the absence of conditioned stimuli. In the more medial regions of the septum, the intermediate lateral septum, we observed few consistent changes either to the conditioned stimuli or to the drug. In a non-aversive context CDP had either no effect at low to moderate doses, or a suppressant effect at a higher dose. The results support a fear-relief hypothesis of lateral septal functioning and suggest the lateral septum as a possible site for the anxiolytic action of benzodiazepines.

Corticotropin-releasing factor in the dorsal raphe nucleus regulates activity of lateral septal neurons.

Corticotropin-releasing factor (CRF) has substantial effects on brain serotonergic activity, especially in limbic structures related to stress and anxiety. For example, relatively low doses of CRF administered into the dorsal raphe nucleus (DRN) decrease DRN unit activity and serotonin release in the lateral septum (LS), a limbic target of the DRN. In contrast, higher doses of CRF tend to be excitatory on both endpoints. The present experiment sought to establish the functional connection between CRF effects in the DRN and the ultimate effect on activity in the LS as a terminal region. We recorded the effects of CRF (3, 10, 30 and 100 ng in 100 nl of artificial cerebrospinal fluid) administered into the DRN upon LS unit activity. In general, the lower doses of CRF (3 and 10 ng) had a facilitatory effect on LS unit activity, peaking at about 15-20 min post-injection. The higher doses had a more complex effect with an early suppression of unit responding maximizing at about 5 min followed by a facilitatory rebound, especially at the 100 ng dose, maximizing at about 20 min. Taken with previous studies demonstrating an inhibitory effect of 5-HT on neuronal activity in LS, the findings suggest that CRF regulation of the DRN is translated to changes in LS activity. This effect may underlie certain coping behaviors in response to stress.