Enhanced effect of dopaminergic stimulation on prepulse inhibition in mice deficient in the alpha subunit of G(z).

RATIONALE: G(z) is a member of the G(i) G protein family associated with dopamine D2-like receptors; however, its functions remain relatively unknown. The aim of the present study was to investigate prepulse inhibition (PPI) of acoustic startle, locomotor hyperactivity and dopamine D2 receptor binding in mice deficient in the alpha subunit of G(z). METHODS: We used automated startle boxes to assess startle and PPI after treatment with saline, amphetamine, apomorphine or MK-801. We used photocell cages to quantitate locomotor activity after amphetamine treatment. Dopamine D2 receptor density was determined by autoradiography. RESULTS: Startle responses and baseline PPI were not different between the Galpha(z) knockout mice and wild-type controls (average PPI 46+/-4 vs 49+/-3%, respectively). Amphetamine treatment caused a marked disruption of PPI in Galpha(z) knockouts (average PPI 22+/-2%), but less so in controls (average PPI 42+/-3%). Similar genotype-dependent responses were seen after apomorphine treatment (average PPI 23+/-3% vs 40+/-3%), but not after MK-801 treatment (average PPI 29+/-5 vs 33+/-2%). Amphetamine-induced locomotor hyperactivity was greater in Galpha(z) knockouts than in controls. There was no difference in the density of dopamine D2 receptors in nucleus accumbens. CONCLUSIONS: Mice deficient in the alpha subunit of G(z) show enhanced sensitivity to the disruption of PPI and locomotor hyperactivity caused by dopaminergic stimulation. These results suggest a possible role for G(z) in neuropsychiatric illnesses with presumed dopaminergic hyperactivity, such as schizophrenia.

Deletion of guanine nucleotide binding protein alpha z subunit in mice induces a gene dose dependent tolerance to morphine.

The mechanism underlying the development of tolerance to morphine is still incompletely understood. Morphine binds to opioid receptors, which in turn activates downstream second messenger cascades through heterotrimeric guanine nucleotide binding proteins (G proteins). In this paper, we show that G(z), a member of the inhibitory G protein family, plays an important role in mediating the analgesic and lethality effects of morphine after tolerance development. We blocked signaling through the G(z) second messenger cascade by genetic ablation of the alpha subunit of the G protein in mice. The Galpha(z) knockout mouse develops significantly increased tolerance to morphine, which depends on Galpha(z) gene dosage. Further experiments demonstrate that the enhanced morphine tolerance is not caused by pharmacokinetic and behavioural learning mechanisms. The results suggest that G(z) signaling pathways are involved in transducing the analgesic and lethality effects of morphine following chronic morphine treatment.

A one-step quantitative reverse transcription polymerase chain reaction procedure.

Our laboratory has developed a one-step quantitative reverse transcription polymerase chain reaction (RT-PCR) procedure in which the reverse transcriptase enzyme and Taq DNA polymerase are combined in the one tube and a single, non-interrupted, thermal cycling program is performed. In the past, RT-PCR has been carried out with two separate steps: (1) reverse transcription of RNA to generate a cDNA pool and (2) polymerase chain reaction amplification of the cDNA. The two-step method can affect the accuracy of the procedure as the total number of manipulations is greater, thereby allowing a greater chance for pipetting errors. Quantitation by our method is achieved in a single reaction by the use of a competitive internal standard that is identical in sequence to the target RNA except for a deletion of 107 base pairs and uses identical primers and cycling conditions. Using this method, we have been able to quantify the amount of message of a G protein (G(zalpha)), in small amounts of tissue, such as dorsal root ganglia, from embryonic as well as postnatal mice.

Tongue deviation in acute ischaemic stroke: a study of supranuclear twelfth cranial nerve palsy in 300 stroke patients.

It is generally believed that the supranuclear innervation of the hypoglossal nucleus is bilateral and symmetrical. The aim of this work is to study the frequency and clinical characteristics of supranuclear tongue palsy in unilateral stroke. 300 patients with acute unilateral ischaemic motor strokes (excluding those in the lower brainstem) and an equal number of normal controls were studied for the presence of tongue deviation in a standardised manner. 29% of stroke patients and 5% of controls had tongue deviation (p < 0. 00001). Deviation was always to the side of the limb weakness. In patients with a history of stroke, it occurred more frequently in those with previous stroke on the contralateral side. Tongue deviation was most common in patients with clinical features of the non-lacunar stroke subtype (56%) or in those with cortical or large subcortical infarctions on brain CT scan (55 and 45%, respectively). All tongue deviations were associated with supranuclear 7th nerve palsy. Dysphagia and dysarthria occurred in 43 and 90% of patients with tongue deviation. Weakness of the arm was significantly associated with presence of tongue deviation. Tongue deviation in unilateral stroke most likely results from asymmetrical supranuclear control of the 12th cranial nerve in many individuals. The finding that it occurs relatively commonly in large (non-lacunar) infarcts and its association with dysphagia may have clinical utility.

Hypertolerance to morphine in G(z alpha)-deficient mice.

Our laboratory has generated a mouse deficient in the alpha (alpha) subunit of the G protein, G(z), (G(z alpha)) gene and we have examined the involvement of G(z alpha) in spinal and supraspinal analgesia and tolerance mechanisms. Spinal analgesia was tested by the response times to heat or cold tail flick times in a water bath at 50 degrees C or -5 degrees C and supraspinal analgesia was tested by the times for paw licking and jumping from a plate at 52 degrees C or 0.5 degrees C. Tolerance to morphine was induced in wild type and G(z alpha)-deficient mice over a 5 day period and the behavioral tests were performed daily. The tail flick reaction times to both hot and cold stimuli did not differ between the wild type and G(z alpha)-deficient mice. Analysis of the reaction times from the hot and cold plate tests showed the G(z alpha)-deficient mice developed tolerance to morphine to a greater degree and at a faster rate than wild type mice. Opioid binding assays were performed on synaptic membranes prepared from naive and morphine tolerant wild type and G(z alpha)-deficient brains. No changes in the affinity of morphine for its receptor or in the density of mu and delta opioid receptors were found between the two groups of mice in the naive or morphine tolerant state. This indicates that the absence of G(z alpha) does not affect opioid receptor affinity or receptor up or down regulation. Our results suggest that the presence of G(z alpha) delays the development of morphine tolerance and represents a possible therapeutic target for improving the clinical use of morphine.

Developmental expression of messenger RNA levels of the alpha subunit of the GTP-binding protein, Gz, in the mouse nervous system.

There has been recent evidence that Gz may play a role in the transmission of the neurotrophic signal from nerve terminals to the cell bodies [Johanson, S.O., Crouch, M.F., Hendry, I.A., Signal transduction from membrane to nucleus: the special case for neurons, Neurochem. Res. 21 (1996) 779-785]. We examined the developmental expression of the alpha subunit of Gz (Gzalpha) in the peripheral and central nervous systems of the mouse. Our laboratory has developed a quantitative reverse transcription-polymerase chain reaction (RT-PCR) for Gzalpha which makes use of a fragment of the PCR product shortened by 107 base pairs creating a standard which mimics the original RNA. Serial dilutions of the mouse RNA with a constant concentration of mimic RNA were made and the point where equal amounts of product are formed allows accurate measurement of Gzalpha mRNA in the tissue. We have demonstrated that in the developing mouse superior cervical ganglion (SCG), dorsal root ganglion (DRG) and trigeminal ganglion the expression of Gzalpha mRNA is highest perinatally. From 3 weeks of age, in all tissues with the exception of the SCG, Gzalpha mRNA levels fall to lower levels in the adult animal. The developmental pattern of expression of Gzalpha in both the cerebellum and the brain differs from the peripheral nervous system. In the cerebellum, Gzalpha mRNA expression is highest around birth and in the brain it is highest around third postnatal week and then the levels decline as adulthood is approached. These results suggest that the highest level of Gzalpha mRNA is expressed at the time when target tissue innervation is occurring. This further strengthens the hypothesis that Gzalpha is important in the transfer of information from target tissues to the innervating nerve cells.

Visual and phonological pathways to the lexicon: evidence from Chinese readers.

In this study, we investigated the role of visual and phonological information in lexical access of Chinese characters. Homophonic English words have been the main source of stimuli for word recognition research. However, since these stimuli also often look alike, visual and phonological information may be confounded in reported experiments. In contrast, many homophonic Chinese characters are visually distinct. In addition, visually similar characters often have very different pronunciations. These characteristics allow a more controlled investigation of the roles of visual and phonological information in activation of meaning. In the present study, two types of Chinese characters were used in a semantic categorization paradigm: integrated characters, which contain strokes that are not separable; and compound characters, which contain at least two clearly identifiable components. The results show that the recognition of a Chinese integrated character depends primarily on visual information, whereas the recognition of a Chinese compound character relies on visual, phonological, and semantic information. It is concluded that visual information plays a greater role in Chinese character recognition than has previously been documented.