Rattractor-Instant guidance of a rat into a virtual cage using the deep brain stimulation.

We developed "Rattractor" (rat attractor), a system to apply electrical stimuli to the deep brain of a rat as it stays in a specified region or a virtual cage to demonstrate an instant electrophysiological feedback guidance for animals. Two wire electrodes were implanted in the brains of nine rats. The electrodes targeted the medial forebrain bundle (MFB), which is a part of the reward system in the deep brain. Following the recovery period, the rats were placed in a plain field where they could move freely, but wired to a stimulation circuit. An image sensor installed over the field detected the subject's position, which triggered the stimulator such that the rat remained within the virtual cage. We conducted a behavioral experiment to evaluate the sojourn ratio of rats residing in the region. Thereafter, a histological analysis of the rat brain was performed to confirm the position of the stimulation sites in the brain. Seven rats survived the surgery and the recovery period without technical failures such as connector breaks. We observed that three of them tended to stay in the virtual cage during stimulation, and this effect was maintained for two weeks. Histological analysis revealed that the electrode tips were correctly placed in the MFB region of the rats. The other four subjects showed no apparent preference for the virtual cage. In these rats, we did not find electrode tips in the MFB, or could not determine their positions. Almost half of the rats tended to remain inside the virtual cage when position-related reward stimuli were triggered in the MFB region. Notably, our system did not require previous training or sequential interventions to affect the behavioral preferences of subjects. This process is similar to the situation in which sheep are chased by a shepherd dog in the desired direction.

Ketogenic diet feeding improves aerobic metabolism property in extensor digitorum longus muscle of sedentary male rats.

Recent studies of the ketogenic diet, an extremely high-fat diet with extremely low carbohydrates, suggest that it changes the energy metabolism properties of skeletal muscle. However, ketogenic diet effects on muscle metabolic characteristics are diverse and sometimes countervailing. Furthermore, ketogenic diet effects on skeletal muscle performance are unknown. After male Wistar rats (8 weeks of age) were assigned randomly to a control group (CON) and a ketogenic diet group (KD), they were fed for 4 weeks respectively with a control diet (10% fat, 10% protein, 80% carbohydrate) and a ketogenic diet (90% fat, 10% protein, 0% carbohydrate). After the 4-week feeding period, the extensor digitorum longus (EDL) muscle was evaluated ex vivo for twitch force, tetanic force, and fatigue. We also analyzed the myosin heavy chain composition, protein expression of metabolic enzymes and regulatory factors, and citrate synthase activity. No significant difference was found between CON and KD in twitch or tetanic forces or muscle fatigue. However, the KD citrate synthase activity and the protein expression of Sema3A, citrate synthase, succinate dehydrogenase, cytochrome c oxidase subunit 4, and 3-hydroxyacyl-CoA dehydrogenase were significantly higher than those of CON. Moreover, a myosin heavy chain shift occurred from type IIb to IIx in KD. These results demonstrated that the 4-week ketogenic diet improves skeletal muscle aerobic capacity without obstructing muscle contractile function in sedentary male rats and suggest involvement of Sema3A in the myosin heavy chain shift of EDL muscle.

Short-term fasting decreases excitatory synaptic inputs to ventromedial tuberoinfundibular dopaminergic neurons and attenuates their activity in male mice.

Tuberoinfundibular dopaminergic (TIDA) neurons in the arcuate nucleus (ARC) of the hypothalamus play a role in inhibiting prolactin (PRL) secretion from the anterior pituitary. PRL is involved in a variety of behaviors, including feeding. Consequently, we hypothesized that fasting might reduce the activity of TIDA neurons, which might alter PRL secretion. However, direct examinations of TIDA neuron activity are difficult. Recently, transgenic mice were generated that expressed green fluorescent protein (GFP) under the control of the rat tyrosine hydroxylase gene. We first determined that GFP in the dorsomedial ARC was a reliable marker of TIDA neurons. Then, we performed electrophysiology and immunocytochemistry in GFP-labeled TIDA neurons to examine whether different feeding conditions could change their activity. Eight-week-old male mice were fed or fasted for 24 h. After sacrifice, we prepared acutely isolated brain slices for conducting whole-cell voltage-clamp recordings. TIDA neurons were identified with fluorescence microscopy. The mean amplitude of miniature excitatory postsynaptic currents (mEPSCs) was significantly reduced in fasting mice compared to fed mice, but different feeding conditions did not affect the mean mEPSC intervals. This result suggested that fasting reduced the number of excitatory synaptic inputs to TIDA neurons. To determine whether a reduction in excitatory synaptic inputs would cause a reduction in TIDA neuron activity, we examined the effect of 24-h fasting on c-Fos expression in the ARC. We found that fasting significantly reduced the number of Fos-positive TIDA neurons. In addition, serum PRL levels were significantly increased. Taken together, the present findings suggested that short-term fasting attenuated TIDA neuron activity.

Functional structure of the intermediate and ventral hippocampo-prefrontal pathway in the prefrontal convergent system.

The hippocampo-prefrontal pathway is a unique projection that connects distant ends of the cerebral cortex. The direct hippocampo-prefrontal projection arises from the ventral to intermediate third of the hippocampus, but not from the dorsal third. It forms a funnel-shaped structure that collects information from the large hippocampal area and projects it to the prefrontal cortex. The anatomical regional differentiation of the projection has not been described. The hippocampal region is differentiated into structural and behavioural roles. For example, it has been shown that the ventral, but not the dorsal, hippocampus reciprocally connects with the amygdala and influences emotional behaviours. These data imply that hippocampal variation along the dorso-ventral axis is contained within the hippocampo-prefrontal pathway. Here, we present electrophysiological studies that demonstrate regional differences in short- but not long-term plasticity in the intermediate/posterior-dorsal and ventral routes of the hippocampo-prefrontal pathway. Furthermore, behavioural studies revealed that each route appears to play a different role in working memory. These results suggest that hippocampal regional information is processed through different routes, with the integration of individual regulatory functions in the prefrontal convergent system.

Telemetry system for recording neural activities in pigs-Comparison with cable system.

We recently developed a telemetry system for recording neural activity in the brains of unrestrained pigs. To test the fidelity of waveform reproduction, we compared local field potentials in the temporal hippocampus of six pigs by simultaneous recording with a cable system. We analyzed differences between the telemetry and cabled data filtered through a low-cut filter at 1, 4, or 30 Hz. Analysis of 10,000 data recorded while pigs were lying down showed a higher correlation with low-cut filtering at 4 or 30 Hz than at 1 Hz. Over 97% of differences in amplitude between the telemetry and cable data lay within the 95% confidence interval. Measurements were reproducible. A box plot of the differences clearly showed increased data symmetry and reduced skewness by low-cut filtering at 4 or 30 Hz. Almost the same results were obtained in two animals during feeding. Thus, the local field potentials in the temporal hippocampus were telemetered with almost the same accuracy as by cable measurement during both resting and feeding. However, artifacts in the first 100 ms (low-cut filtering at 1 or 4 Hz) or 5 ms (30 Hz) of measurements had to be removed for analysis.

Rat hippocampus-prefrontal multiple units and synaptic efficacy in vivo.

We recorded multiple unit activities of the CA1 region of the intermediate hippocampus and prelimbic area of the prefrontal cortex, and evoked responses in the prefrontal cortex by hippocampal stimulation in urethane-anesthetized rats. The multiple unit activities between these regions showed significant peaks of cross-correlograms, which indicated that firing initiated mainly from either the hippocampus (type HP) or the prefrontal cortex (type PH). In type HP, the slopes of evoked responses showed a significant inverse correlation with peak heights of cross-correlograms and number of bursts of multiple unit activities. These results suggest that multiple unit activity-based cross-correlograms (a measurement to test functional connectivity) are influenced by both evoked response (synaptic connectivity) and effects of local circuits.

Cross-correlogram between rat hippocampal and prefrontal neuronal activities.

We recorded spontaneous multiple unit activities (MUAs) of the hippocampus and prefrontal cortex in urethane-anesthetized rats and analyzed cross-correlograms between these MUAs to investigate the functional connectivity of neuronal activities. Results of these analyses reveal a significant correlation between MUAs in these regions, in which the firing initiated from either hippocampus (type H-P) or prefrontal cortex (type P-H) according to the significant peak of cross-correlograms. Furthermore, the MUA bursts were counted: a significant correlation was found between the peak height of cross-correlograms and MUA burst counts in type H-P, but not type P-H. These results suggest that the correlation between the hippocampus and prefrontal cortex MUAs that are related to the burst firing might reflect functional connectivity.

Rat prefrontal response and prestimulation local field potential power in vivo.

To determine whether spontaneous local field potential (LFP) activities in the rat medial prefrontal cortex influence the responses evoked by hippocampal stimulation, we investigated the relationship between the evoked responses and the LFP powers immediately before the stimulation using anesthetized rats. We demonstrated that the degrees of evoked response showed significant inverse correlations with the prefrontal LFP powers in a specific frequency band (including the gamma band) immediately before the stimulation. The results indicate that the specific frequency band activities in the prefrontal LFPs may be involved in prefrontal responsiveness. Spontaneous LFP activities may have a role in information processing in the hippocampus-prefrontal cortex pathway.

Involvement of the rat prefrontal cortex in a delayed reinforcement operant task.

To determine whether the rat medial prefrontal cortex (PFC) is involved in delayed reinforcement operant behavior, we studied the effects of transient inactivation of the medial PFC (or the hippocampus as a control) during a delayed reinforcement lever-press task. We demonstrated the involvement of the PFC in this task: PFC inactivation but not hippocampal inactivation significantly impaired performance. In a separate experiment, we also recorded the prefrontal multiple unit activities during the task to determine the roles of the PFC in detail. Neuronal activity decreased during the delay period, suggesting that this decrease plays a role in delayed reinforcement operant behavior.

Response patterns of vestibulospinal neurons to lumbar rotation in decerebrate rats.

In vestibulospinal neurons projecting to the lumbar enlargement, activities were modulated in response to alternate tilts of the caudal body around the vertebral axis. Three types of neurons were found: Type I (37.8%) showed faster firing during the ipsilateral side-down tilt; type II (51.1%) showed the reverse pattern; type III were unaffected. Types I and II may be important in the tonic lumbar reflex.