Increased local cerebral glucose utilization in the basal ganglia of the rolling mouse Nagoya

GABAA Receptor Expression in the Forebrain of Ataxic Rolling Nagoya Mice

The human CACNA1A gene encodes the pore-forming α₁ subunit of Ca_V2.1 (P/Q-type) calcium channels and is the locus for several neurological disorders, including episodic ataxia type 2 (EA2), spinocerebellar ataxia type 6 (SCA6) and Familial Hemiplegic Migraine type 1 (FHM1). Several spontaneous mouse Cacna1a mutant strains exist, among them Rolling Nagoya (tg^rol), carrying the R1262G point mutation in the mouse Cacna1a gene. tg^rol mice display a phenotype of severe gait ataxia and motor dysfunction of the hind limbs. At the functional level, the R1262G mutation results in a positive shift of the activation voltage of the Ca_V2.1 channel and reduced current density. γ-Aminobutyric acid type A (GABA_A) receptor subunit expression depends critically on neuronal calcium influx, and GABA_A receptor dysfunction has previously been described for the cerebellum of tg^rol and other ataxic Cacna1a mutant mice. Given the expression pattern of Ca_V2.1, it was hypothesized that calcium dysregulation in tg^rol might affect GABA_A receptor expression in the forebrain. Herein, functional GABA_A receptors in the forebrain of tg^rol mice were quantified and pharmacologically dissociated using [³H] radioligand binding. No gross changes to functional GABA_A receptors were identified. Future cell type-specific analyses are required to identify possible cortical contributions to the psychomotor phenotype of tg^rol mice.

The ataxic Cacna1a-mutant mouse rolling nagoya: an overview of neuromorphological and electrophysiological findings

Homozygous rolling Nagoya natural mutant mice display a severe ataxic gait and frequently roll over to their side or back. The causative mutation resides in the Cacna1a gene, encoding the pore-forming α₁ subunit of Ca_v2.1 type voltage-gated Ca²⁺ channels. These channels are crucially involved in neuronal Ca²⁺ signaling and in neurotransmitter release at many central synapses and, in the periphery, at the neuromuscular junction. We here review the behavioral, histological, biochemical, and neurophysiological studies on this mouse mutant and discuss its usefulness as a model of human neurological diseases associated with Ca_v2.1 dysfunction.

Local cerebral glucose utilization in the AS/AGU rat: a mutant with movement disorders

The AS/AGU mutant rat is characterized by a wide staggering gait and a movement disorder of the hindlimbs. Local cerebral glucose utilization in the brain was investigated using the [14C]2-deoxyglucose autoradiographic technique to map any functional alterations in the mutant AS/AGU (agu/agu) compared with Albino Swiss controls (+/+). Locomotor tests were also performed to confirm the phenotypic assignment of the animals. Statistically significant reductions in glucose utilization were apparent in 12 of the 44 regions examined in the AS/AGU animals. The regions showing the most significant differences (P < 0.01) from the control AS strain were the substantia nigra pars compacta (-23%) and medial geniculate body (-17%). Statistically significant decreases (P < 0.05 and P < 0.02) in glucose utilization ranging from -15 to -26% were also displayed in the superior colliculus superficial layer, auditory cortex, ventroposterior nucleus of the thalamus, molecular layer of the hippocampus, dentate gyrus, medial amygdaloid nucleus, median raphe nucleus, subthalamic nucleus, medial preoptic area of the hypothalamus and anterior hypothalamus. In no region studied was the mean value of glucose use in the AS/AGU rat greater than in the control animals. The results of this study complement previous behavioural and neurochemical characterization studies of this mutant, confirm that the disorder involves functional disturbances of the basal ganglia, and demonstrate the involvement of the limbic system and some sensory systems.

Increased preproenkephalin mRNA and preprotachykinin mRNA in the striatum of Rolling mouse Nagoya

Although Rolling mouse Nagoya (RMN) has been considered to demonstrate cerebellar dysfunction, our previous metabolic and electrophysiological studies also revealed a dysfunction of the basal ganglia, with the presumable primary site of dysfunction being the striatum. In the present study, we investigated the neurochemical functions of the striatum. In RMN, both preproenkephalin mRNA and preprotachykinin mRNA increased significantly in the striatum, with unaltered GAD mRNA, [(3)H]spiperone binding, [(3)H]QNB binding and preprosomatostatin mRNA, thus indicating the dysfunction of striatal projection neurons. These findings support the hypothesis that the site of primary dysfunction in the basal ganglia is in the striatum of RMN.

Anti-ataxic effects of TRH and its analogue, TA-0910, in Rolling mouse Nagoya by metabolic normalization of the ventral tegmental area

1. The mechanism of the anti-ataxic action of thyrotropin-releasing hormone (TRH) and its analogue. TA-0910, in the Rolling mouse Nagoya (RMN), an ataxic mutant mouse, has been investigated. 2. TRH (30 mg kg-1, i.p.) and TA-0910 (3 mg kg-1, i.p.) reduced the fall index (number of falls/spontaneous motor activity), an index of ataxia, 10-30 and 10-60 min after administration, respectively. 3. Relative local cerebral glucose utilization (LCGU) in the cerebellum and ventral tegmental area (VTA) of the rolling mouse was significantly smaller than that in normal animals. TRH (30 mg kg-1, i.p.) and TA-0910 (3 mg kg-1, i.p.) increased the relative LCGU value of the VTA but not of the cerebellum in rolling mice to the level of normal animals. 4. These results suggest that the ataxia of the rolling mouse may be due to dysfunction of the cerebellum and VTA, and that amelioration by TRH and TA-0910 could result from metabolic normalization of the VTA.

Physiological correlates of abnormal behaviors in magnesium-deficient rats

In order to elucidate the mechanism of behavioral alterations in magnesium-deficient rats, changes in the electroencephalogram (EEG) and electrocardiogram (ECG) were studied during auditory stimulation and correlated with the behavioral alterations. Weanling rats were fed either a Mg-deficient diet or a control synthetic diet for 2-3 weeks before the experiment. EEGs were recorded from the hippocampus and the sensorimotor and auditory cortices, and ECGs with a telemetry system. White noise with an intensity of 100 dB was given continuously to induce behavioral changes. The Mg-deficient rats developed consistent and graded behavioral changes in response to the stimulation, showing running-jumping behavior (stage 1), followed by tonic limb convulsion (stage 2) and finally by falling down on the floor (stage 3). The EEGs also showed consistent changes with spike activity, initiating in the hippocampus (stage 2) and then spreading to the neocortices bilaterally (stage 3). These findings indicate that the behavioral changes induced by auditory stimulation in the Mg-deficient rats are due to seizures arising in deeper brain structures, particularly in the limbic system, and projecting secondarily to the neocortices. The ECG changes, mainly consisting of marked bradyarrhythmia, occurred as early as the appearance of the EEG spikes, indicating that they were also related to the seizure. We conclude therefore that Mg deficiency in rats causes increased excitability of the central nervous system, resulting in seizures possibly originated in the limbic system, later developing secondary generalization, and also causing cardiac dysfunctions.

Rolling mouse Nagoya as a mutant animal model of basal ganglia dysfunction: determination of absolute rates of local cerebral glucose utilization

In order to elucidate the neuronal mechanism of the motor disturbances of the Rolling mouse Nagoya (rolling), a neurological mutant mouse (genotype rol/rol) showing frequent lurching and falling over on walking, we determined absolute rates of local cerebral glucose utilization (LCGU) with the [14C]deoxyglucose method. The rates were compared with those of heterozygote (+/rol) with normal behavior, and of normal mice (+/+) of the same strain (C3Hf/Nga). Rolling showed marked and significant increases in LCGU in the structures of the basal ganglia such as the globus pallidus, entopeduncular nucleus, substantia nigra pars compacta and pars reticulata, and subthalamic nucleus, confirming our previous finding with semiquantitative LCGU determination. Additional significant but much less marked increases in LCGU of rolling were found in some structures of the brainstem and limbic system, such as the pedunculopontine nucleus, red nucleus, ventral tegmental area, lateral habenula, and CA1 and CA3 of the hippocampus. Although rolling has been regarded as an animal model of cerebellar ataxia, rolling showed no alterations of LCGU in the cerebellum. The heterozygote showed intermediate increases in LCGU between rolling and normal mice in the basal ganglia structures such as the globus pallidus, substantia nigra pars reticulata and subthalamic nucleus. Our findings indicate that rolling has a definite, genetically determined dysfunction of the basal ganglia. The primary site of the basal ganglia dysfunction might probably be in the striatum, involving both the neostriatum and limbic striatum, and resulting in secondary dysfunction in their target structures.

Striatal dysfunction in Rolling mouse Nagoya: an electrophysiological study

To elucidate the neuronal mechanism of the motor disturbances of the Rolling mouse Nagoya (rolling, genotype rol/rol), an experimental neurologic mutant mouse, we studied the physiological characteristics of neurons of the globus pallidus (GP) in rolling, comparing them with those of the behaviorally normal heterozygotes (+/rol) and normal controls (+/+). Forty-nine units in rolling, 41 in heterozygotes and 48 in controls were recorded under urethane anesthesia. The group mean of the interspike interval (ISI) of the spontaneous unit discharges was significantly shorter in rolling (42.2 +/- 2.6 msec, mean +/- SEM) than that of controls and of heterozygotes (55.4 +/- 2.4 msec, P < 0.001 and 50.4 +/- 2.6 msec, P < 0.05, respectively), indicating a significantly higher rate of spontaneous unit activity in the GP of rolling. In the controls and heterozygotes, about 60% of the GP neurons responded to striatal (ST) electrical stimulation with a predominantly inhibitory response, whereas a significantly smaller number of the GP neurons (22%, P < 0.001) exhibited inhibitory responses in rolling. The positive field potentials recorded in the GP evoked by ST stimulation were significantly smaller in amplitude in rolling (1.04 +/- 0.10 mV, mean +/- SEM) than that of the controls and heterozygotes (1.78 +/- 0.15 mV, P < 0.001 and 1.97 +/- 0.17 mV, P < 0.001, respectively). These results are in agreement with our previously reported findings of increased glucose metabolism and reduced concentration of GABA in the GP and substantia nigra pars reticula (SNr) in rolling.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotransmitter receptors of the rolling mouse Nagoya: a quantitative autoradiographic study

The distribution of neurotransmitter and neuromodulator receptors was studied in the brain of the rolling mouse Nagoya (RMN) and in controls, using in vitro receptor autoradiography. Quantitative autoradiography was used to map adenosine A1 (labeled with [3H]cyclohexyladenosine), GABAA [( 3H]muscimol), opiate [( 3H]naloxone), L-glutamate [( 3H]L-glutamate), benzodiazepine [( 3H]flunitrazepam), and muscarinic cholinergic [( 3H]quinuclidinyl benzilate) receptors. In the cerebellar cortex, GABAA and adenosine A1 binding sites were significantly reduced in the RMN, whereas other transmitter binding sites were not significantly altered. Adenosine A1 binding sites were also reduced in the cerebral cortex and caudate-putamen. Benzodiazepine binding was significantly decreased in the cerebral cortex and increased in the CA1 subfield of the hippocampus. These results suggest that neurochemical alterations in the caudate-putamen as well as in the cerebellar cortex play important roles in the ataxia and motor dysfunction of the RMN.

Pure cortical ischemia versus striatal ischemia. Circulatory, metabolic, and neuropathologic consequences

Selective ischemic damage was produced either involving only the cortex or together with the striatum by occlusion of the middle cerebral artery proximal or distal to the lenticulostriate artery in the rat. The consequences in local cerebral blood flow, local cerebral glucose utilization, and neuropathology were investigated in the acute stage of ischemia. Caudate damage produced by proximal occlusion resulted in such secondary alterations as enhanced blood flow and metabolism in areas remote from the main lesion, such as in the globus pallidus and substantia nigra ipsilateral to occlusion. After distal occlusion, however, there were two patterns distinctly different from each other in the appearance of the autoradiograms. One was ipsilateral and the other was contralateral enhancement of blood flow and metabolism involving the striato-pallido-nigral axis without any striatal damage. We therefore suggest that these secondary alterations in circulation and metabolism contribute to a varied neurological dysfunction after focal cerebral ischemia. Furthermore, our currently introduced model of selective ischemic lesioning is important in studying the roles of cortical and striatal influences in ischemic pathophysiology.

Local cerebral glucose utilization altered in rats with unilateral electrolytic striatal lesions and modification by apomorphine

Alterations in local cerebral glucose utilization (LCGU) in rats with unilateral striatal lesions and the modification by apomorphine were investigated. Electrolytic lesions were made in the rostral part of the right striatum, and 1, 7, and 30 days later, LCGU was observed in terms of relative and absolute LCGU values, using the [14C]deoxyglucose method. A definite change in the pattern of LCGU was seen only at 7 days. These were increases in LCGU in the globus pallidus, entopeduncular nucleus and substantia nigra pars reticulata, and decreases in the ventroanterior-ventrolateral (VAL) and ventromedial (VM) thalamic nuclei and lateral habenula, all on the lesioned side. The circling behavior following the lesion, however, was maximal after 2 days and disappeared after 7 days. Intravenous administration of apomorphine (1.5 mg/kg) produced different modifications in the LCGU pattern between the intact and lesioned sides, at 7 days after producing the lesions. On the intact side, there were increases in LCGU in the striatum, globus pallidus, entopeduncular nucleus, substantia nigra pars reticulata and subthalamic nucleus, and a decrease in the lateral habenula. No such changes were observed on the lesioned side. These results indicate firstly that electrolytic striatal lesions induce LCGU increases or decreases in the structures which receive the striatal input, secondly that the mechanism of this change differs from that of the circling behavior seen in case of striatal lesions, and finally that the majority of the LCGU changes in the basal ganglia and thalamus following intravenous administration of apomorphine are brought about by an altered input of neuronal activity from the striatum to these structures.