Morphological characterization of the bursting and nonbursting neurones in the olfactory centre of the terrestrial slug limax marginatus

We investigated the morphological characteristics of physiologically characterized neurones in the procerebrum (PC) of the terrestrial slug Limax marginatus. The electrophysiological characteristics of the neurones were determined using the perforated patch recording technique. By comparing the shapes and sizes of somata, we found that the somata of bursting neurones were larger and had more oblong shapes than those of nonbursting neurones, indicating that the bursting and nonbursting neurones in the PC could be discriminated on the basis of the sizes and shapes of their soma. Injection of fluorescent dyes into the bursting and nonbursting neurones revealed morphological differences in the neurites. The bursting neurones had extensive projections within the cell body layer, and the major neurites of the bursting neurones were oriented along the dorsal-ventral axis. In contrast, the nonbursting neurones had neurites extending into the neuropile layers, where terminals of both sensory and presumed output neurones exist

Time-dependent reorganization of the brain components underlying memory retention in trace eyeblink conditioning.

Many studies have confirmed the time-limited involvement of the hippocampus in mnemonic processes and suggested that there is reorganization of the responsible brain circuitry during memory consolidation. To clarify such reorganization, we chose trace classical eyeblink conditioning, in which hippocampal ablation produces temporally graded retrograde amnesia. Here, we extended the temporal characterization of retrograde amnesia to other regions that are involved in acquisition during this task: the medial prefrontal cortex (mPFC) and the cerebellum. At a various time interval after establishing the trace conditioned response (CR), rats received an aspiration of one of the three regions. After recovery, the animals were tested for their CR retention. When ablated 1 d after the learning, both the hippocampal lesion and the cerebellar lesion group of rats exhibited a severe impairment in retention of the CR, whereas the mPFC lesion group showed only a slight decline. With an increase in interval between the lesion and the learning, the effect of the hippocampal lesion diminished and that of the mPFC lesion increased. When ablated 4 weeks after the learning, the hippocampal lesion group exhibited as robust CRs as its corresponding control group. In contrast, the mPFC lesion and the cerebellar lesion groups failed to retain the CRs. These results indicate that the hippocampus and the cerebellum, but only marginally the mPFC, constitute a brain circuitry that mediates recently acquired memory. As time elapses, the circuitry is reorganized to use mainly the mPFC and the cerebellum, but not the hippocampus, for remotely acquired memory

Attentional disengagement biases in social anxiety disorder

Social anxiety disorder (SAD) is a mental disorder characterized by significant fear and anxiety about social situations that may attract attention from others. Selective attention in social anxiety is characterized by a preferential attention to external threatening stimuli. The aim of this study is to test the influence of social anxiety on attentional disengagement bias. Attentional biases are phenomena where attention preferentially targets threatening stimuli. Attention is hypothesized to consist of three processes: engagement, shifting, and disengagement. Previous studies have suggested that people with SAD have impaired attentional engagement with the threatening stimuli. However, recent studies have used the dot-probe task to measure the attentional biases to show that people with SAD have impaired attentional disengagement. However, the dot-probe task is not suitable for separately assessing attentional disengagement or engagement biases. Therefore, we used a gap/overlap task, which can measure attentional disengagement bias, in 16 university students from high and low SAD groups. Faces were used as stimuli for the gap/overlap task (i.e., angry/happy/neutral). The results showed no significant difference between the high and low SAD groups in their attentional disengagement bias. We discussed the possible causes of this discrepancy between the previous studies and the current study in the relationship between social anxiety and attentional disengagement bias

Image analysis of olfactory responses in the procerebrum of the terrestrial slug Limax marginatus.

Neural oscillations have been found to occur in the olfactory centers of some vertebrates and invertebrates, including the procerebrum of the terrestrial slug Limax marginatus. Using optical recording with the potential-sensitive dye di-4-ANEPPS, we analyzed the spatiotemporal pattern of procerebral neural activities in response to odorants applied to an in vitro brain-superior tentacle preparation. The odor of rat chow, on which the slugs were normally fed, increased the frequency of the oscillation. Garlic odor, which induced aversive behavior in the slug, caused a transient increase in oscillation frequency during stimulation, followed by a second increase in oscillation frequency when the stimulus was terminated. Wave propagation from the distal to the proximal region of the procerebrum was accelerated in parallel with modulation of the frequency. The cycle-by-cycle average of the optical signals showed that a large area of the cerebral ganglia, including the procerebrum, was depolarized during the initial increase in frequency. During the second increase, however, the net depolarization was most prominent in the terminal mass of the procerebrum. These results suggest that the level of depolarization generated by interactions among the neurites projecting to the terminal mass, such as the neurites of the nonbursting neurons, may control neural oscillations in the procerebrum

Characterization of hippocampal theta rhythm in wild-type mice and glutamate receptor subunit delta2 mutant mice during eyeblink conditioning with a short trace interval.

We have shown that glutamate receptor subunit delta2 (GluRdelta2) null mutant mice, which have serious morphological and functional deficiencies in the cerebellar cortex, are severely impaired in delay eyeblink conditioning but not in trace eyeblink conditioning, even with a 0-trace interval. Such 0-trace conditioning does not depend critically on the hippocampus in wild-type mice, but it does in GluRdelta2 mutant mice. Here we examined the hippocampal electroencephalogram (EEG) during 0-trace conditioning in GluRdelta2 mutant and wild-type mice. During the apparatus habituation sessions, the total hippocampal theta activity (4-12 Hz) of GluRdelta2 mutant mice was less than that of wild-type mice. Activity in the higher frequency band (8-12 Hz, type 1) in GluRdelta2 mutant mice was significantly less than it was in wild-type mice, but activity in the lower frequency band (4-8 Hz, type 2) was not. As learning proceeded during the acquisition sessions, the total theta activity decreased in many of the wild-type mice, while this phenomenon was less prominent in GluRdelta2 mutant mice. Further analysis showed that the type 1 activity in wild-type mice increased in the early sessions and then decreased, while that in GluRdelta2 mutant mice did not change. Type 2 activity tended to decrease in both types of mice as the conditioning proceeded. These results indicate that the distribution of hippocampal EEG frequency and its properties during conditioning are different between wild-type and GluRdelta2 mutant mice, suggesting that the cerebellar cortical dysfunction may cause an alteration in the electrophysiological characteristics of the hippocampus

NMDA receptor-dependent processes in the medial prefrontal cortex are important for acquisition and the early stage of consolidation during trace, but not delay eyeblink conditioning.

Permanent lesions in the medial prefrontal cortex (mPFC) affect acquisition of conditioned responses (CRs) during trace eyeblink conditioning and retention of remotely acquired CRs. To clarify further roles of the mPFC in this type of learning, we investigated the participation of the mPFC in mnemonic processes both during and after daily conditioning using local microinfusion of the GABA(A) receptor agonist muscimol or the NMDA receptor antagonist APV into the rat mPFC. Muscimol infusions into the mPFC before daily conditioning significantly retarded CR acquisition and reduced CR expression if applied after sufficient learning. APV infusion also impaired acquisition of CRs, but not expression of well-learned CRs. When infusions were made immediately after daily conditioning, acquisition of the CR was partially impaired in both the muscimol and APV infusion groups. In contrast, rats that received muscimol infusions 3 h after daily conditioning exhibited improvement in their CR performance comparable to that of the control group. Both the pre- and post-conditioning infusion of muscimol had no effect on acquisition in the delay paradigm. These results suggest that the mPFC participates in both acquisition of a CR and the early stage of consolidation of memory in trace, but not delay eyeblink conditioning by NMDA receptor-mediated operations

Comparative study on neural oscillation in the procerebrum of the terrestrial slugs Incilaria bilineata and

Coherent oscillatory activities in procerebral neurones have been described in Limax maximus; however, the electrical properties of the procerebrum of other terrestrial molluscs are less well understood. We have examined oscillatory activity in the procerebrum of Incilaria bilineata and Limax marginatus. The local field potential measured in the procerebrum of I. bilineata showed repetitive peaks which had the opposite polarity from those measured in L. marginatus. Optical measurement of membrane potential using a potential-sensitive dye, di-4-ANEPPS, showed that the oscillations in I. bilineata occurred mainly in the internal mass while those in L. marginatus were located in the cell mass. An analysis of the waveform revealed that the depolarizing phase of the oscillations consists of both a slow and a rapid component in both species. The rapid component was most pronounced in the internal mass of I. bilineata but was prominent in the cell mass of L. marginatus. The superior tentacle nerve, which projects to the terminal mass, also showed oscillations in synchrony with those of the procerebrum. These results suggest that oscillations in procerebral interneurones are commonly generated in a region adjacent to the terminal mass and that these oscillations may affect the membrane potential of the neurones constituting the superior tentacle nerve

Systems consolidation requires postlearning activation of NMDA receptors in the medial prefrontal cortex in trace eyeblink conditioning.

The importance of the hippocampus in declarative memory is limited to recently acquired memory, and remotely acquired memory is believed to be stored somewhere in the neocortex. However, it remains unknown how the memory network is reorganized from a hippocampus-dependent form into a neocortex-dependent one. We reported previously that the medial prefrontal cortex (mPFC) is important for this neocortex-dependent remote memory in rat trace eyeblink conditioning. Here, we investigate the involvement of NMDA receptors in the mPFC in this reorganization and determine the time window of their contribution using chronic infusion of an antagonist into the mPFC, specifically during the postlearning consolidation period. The rats with blockade of the mPFC NMDA receptors during the first 1 or 2 weeks after learning showed a marked impairment in memory retention measured 6 weeks after learning, but relearned normally with subsequent conditioning. In contrast, the same treatment had no effect if it was performed during the third to fourth weeks or during the first day just after learning. The specificity of NMDA receptor blockade was confirmed by the reduced long-term potentiation in the hippocampal-prefrontal pathway in these rats. These results suggest that successful establishment of remotely acquired memory requires activation of NMDA receptors in the mPFC during at least the initial week of the postlearning period. Such NMDA receptor-dependent processes may mediate the maturation of neocortical networks that underlies permanent memory storage and serve as a way to reorganize memory circuitry to the neocortex-dependent form