Masahiko Nomura

Relationship between cholinergic dysfunction and discrimination learning disabilities in Wistar rats following chronic cerebral hypoperfusion

The effects of chronic hypoperfusion of cerebral blood flow (CBF) on central cholinergic indices and intellectual functions were investigated in rats. Male Wistar rats, aged 9 weeks, were anesthetized with pentobarbital, and the bilateral common carotid arteries were permanently ligated. Cortical CBF in the hypoperfused rats was markedly decreased at 6 weeks after the operation. In the hypoperfused group, cholinergic indices were changed to consist two phases after the operation, before (acute) and after (chronic) 6 weeks after the operation. At 6 weeks, choline acetyltransferase activity was restored to the sham-operated level compared with the changes in the frontal cortex and thalamus + midbrain at 3 weeks. On the other band, the maximum number of muscarinic acetylcholine receptors was reduced in the frontal cortex, hippocampus and striatum at 6 weeks and thereafter remained at this low level. In discrimination learning task, the percentage of correct responses in the hypoperfused rats was generally reduced in contrast with that of the sham-operated rats, although the number of total responses were not changed. As a consequence, cholinergic dysfunctions correlate with discrimination learning disabilities in the hypoperfused rats. These findings suggest that the hypoperfused rat may be useful for the cerebrovascular type dementia model to clarify pathophysiology.

Vascular endothelial growth factor increases fenestral permeability in hepatic sinusoidal endothelial cells

Abstract: Vascular endothelial growth factor (VEGF) is an important regulator of vasculogenesis and vascular permeability. Hepatic sinusoidal endothelial cells (SECs) possess sieve‐like pores that form an anastomosing labyrinth structure by the deeply invaginated plasma membrane. Caveolin is the principal structural protein in caveolae. In this study, we examined the role of VEGF on the fenestration and permeability of SECs and the relation with caveolin‐1. SECs isolated from rat livers by collagenase infusion method were cultured for 24 h with (10 or 100 ng/ml) or without VEGF. The cells were then examined by transmission and scanning electron microscopy (EM). The expression of caveolin was investigated by confocal immunofluorescence, immunogold EM, and Western blot. Endocytosis and intracellular traffic was studied using horseradish peroxidase (HRP) reaction as a marker of fluid phase transport in SECs.

Memory-related acetylcholine efflux from rat prefrontal cortex and hippocampus: a microdialysis study

To investigate the relationship between the prefrontal and hippocampal acetylcholine (ACh) systems and working memory, an in vivo microdialysis study was conducted. A group of rats was trained to perform a working memory task, delayed alternation, in an operant chamber for food reinforcement. The rats had to choose one of two response levers in an alternative manner in each trial, with a certain interval between trials. They had to remember which lever they chose in the previous trial without the assistance of external cues. Another group was trained to perform a reference memory task, cued alternation, in which the behavioral sequence was identical, but an external cue was provided. After stable behavior was established, a dialysis probe was implanted into the prefrontal cortex or the hippocampus of each rat. The extracellular concentration of ACh in the dialysates from the prefrontal cortex increased during performance of the delayed alternation task, while the hippocampal ACh showed a more distinct increase during performance of the cued alternation task. These results suggest that the prefrontal ACh is mainly related to working memory, whereas the hippocampal ACh is mainly related to reference memory.

Involvement of neurons sensitive to angiotensin II in the median preoptic nucleus in the drinking response induced by angiotensin II activation of the subfornical organ in rats

The involvement of neurons sensitive to angiotensin II (ANG II) in the median preoptic nucleus (MnPO) in mediating the drinking response caused by administration of ANG II either directly into the subfornical organ (SFO) or intravenously was examined in the conscious rat. In all rats (n = 16) having correct injector placement in both of these brain sites, injections of ANG II (10(-12) M) into the SFO elicited drinking. Previous injections of saralasin (10(-10) M), a specific ANG II antagonist, but not saline vehicle, into the MnPO significantly attenuated the drinking response to ANG II administration directly into the SFO. Intravenous infusions of ANG II (75 ng/kg) produced a drinking response in 12 of the 16 rats, and the response was significantly reduced by pretreatment with saralasin (10(-10) M), but not by saline, in the SFO. These results show the importance of MnPO neurons responsible for ANG II in mediating the dipsogenic response to ANG II acting at the SFO and suggest that the response may be implicated in angiotensinergic neural circuits from the SFO to the MnPO.

Effects of discrimination learning on the rat amygdala dopamine release: a microdialysis study

Extracellular levels of dopamine (DA) and its metabolites were monitored with the in vivo microdialysis method in the amygdala of rats while and after they performed a discrimination learning task or a non-discrimination task. A group of rats was trained to discriminate between lamp-on and lamp-off states under an operant-type learning procedure. After a stable discriminative behavior was established, a dialysis probe was inserted into the basolateral amygdaloid nucleus of each rat. The concentrations of DA and its metabolite 3,4-dihydroxyphenylacetic acid significantly increased during the learning sessions as compared to their basal levels. In contrast, another group of rats trained on a similar, but non-discriminative task showed no such increases. These results suggest that the dopaminergic neural systems in the basolateral amygdaloid nucleus are activated during ongoing behavior maintained under the discrimination learning situation.

Effects of rat ventral and dorsal hippocampus temporal inactivation on delayed alternation task.

To determine the involvement of the hippocampal regions in a operant-type delayed alternation task of short delay or long delay, microinjections of muscimol into the hippocampus were used for temporal inactivation during the behavioral test in each rat. Dorsal hippocampal inactivation impaired the correct ratio of long delay. Ventral hippocampal inactivation showed no changes in the correct ratio, however, it increased the tendency of perseveration in long delay. These findings suggest hippocampus has regional differentiation in delayed alternation task.

Dopamine and acetylcholine elevation on lever-press acquisition in rat prefrontal cortex.

To determine whether the rat medial prefrontal cortex (PFC) is involved in acquiring operant learning, we observed changes in extracellular concentration of dopamine (DA) and acetylcholine (ACh) in the rat medial PFC during lever-press acquisition (acquisition group) or retrieval (retention group) using in vivo microdialysis. We found that DA or ACh elevation related to acquisition occurred. DA elevation was observed in the acquisition group only. These results indicate that the medical PFC is related to acquisition, and suggest that interaction between DA and ACh may be involved in learning acquisition.

Septo-hippocampal cholinergic system under the discrimination learning task in the rat : a microdialysis study with the dual-probe approach

To investigate regulation of the septo-hippocampal cholinergic system by dopaminergic inputs to the septum in rats which performed a discrimination learning task, an in vivo microdialysis method with the dual-probe approach was used. Rats were trained to discriminate between lamp-on and -off states under an operant-type learning procedure. After stable discriminative behavior was established, dialysis probes were implanted into the hippocampus and the lateral septum area of each rat. The concentration of dopamine (DA) in the septum rapidly increased within 20 min after the beginning of a learning session. However, another group of rats trained on a similar but non-discriminative task showed no such increase. The concentration of acetylcholine (ACh) in the hippocampus was significantly enhanced during the learning session and rapidly returned to the basal value after the session, but showed a delayed and diminished increase in the non-discrimination group. These results suggest that DAergic inputs to the septum may be involved in control of the septo-hippocampal cholinergic system which is of importance for discrimination learning behavior.

Effects of rat medial prefrontal cortex temporal inactivation on a delayed alternation task.

To determine the involvement of the medial prefrontal cortex (mPFC) in operant-type delayed alternation, microinjections of muscimol into the mPFC were used for temporal inactivation during behavioral tests in rats. The temporal mPFC inactivation showed effects related to both dorsal (decreased delay-dependent correct ratio, indicating working memory-related deficits) and ventral hippocampus inactivation (increased tendency to repeat errors) reported in our recent paper, without motor or sensory effects. These findings suggest that the mPFC integrates information from different hippocampal regions during a delayed alternation task.

Effects of Dorsal Column Spinal Cord Stimulation (DCS) on Reversibility of Neuronal Function—Experience of Treatment for Vegetative States

We have reported that DCS (dorsal column stimulation) improves the clinical symptoms of cases in persistent vegetative states. Since then, we have accumulated 23 cases who have been treated by DCS. We describe the clinical EEG, rCBF, and biochemical changes in cerebrospinal fluid (CSF) caused by DCS in patients in persistent vegetative states; (1) eight of these cases showed good clinical improvement; (2) most patients were young and the CTscan did not show large, diffuse, definite or bilateral low density areas in cortex, brainstem of thalmus; (3) neurostimulation increased rCBF (cerebral blood flow) in many parts of the brain in cases with vegetative states; blood flow increased in the cerebrum, cerebellum and brainstem; (4) neurostimuiation enhanced the metabolism of catecholamines in CSF, NE, DA, DOPAC, HVA, and 5H1AA increased, but 3MT and 5HT decreased in CSF. DCS increased rCBF, enhanced the metabolism of catecholamines in CSF, and improved the EEG in patients in persistent vegetative states.