Effect of apomorphine on striatal synaptotagmin 7 mRNA levels in reserpinized rats

Synaptotagmin 7 and SYNCRIP proteins are ubiquitously expressed in the rat brain and co-localize in Purkinje neurons

Synaptotagmin 7 (SYT7) is ubiquitously expressed calcium sensor, involved in neuronal membrane trafficking. Immunoprecipitation experiments demonstrated that SYT7 interacts with Synaptotagmin-binding, cytoplasmic RNA-interacting protein (SYNCRIP). SYNCRIP is a component of mRNA granules, which are transported to dendrites and are prerequisite for synaptic plasticity. Given the potential significance of SYT7 regulation in processes of neurodegeneration, which are characterized by high level of synaptic vulnerability, we aimed to analyse and compare the distribution of SYT7 and SYNCRIP proteins in the adult rat striatum, hippocampus, cerebral and cerebellar cortex. We investigated the degree of SYT7-SYNCRIP co-localization in order to examine possible functional interaction of these two proteins. We found that SYT7 is abundantly distributed in neuropil of all examined anatomical areas of the brain, most prominently in axons. On the contrary, SYNCRIP had cytoplasmic somatodendritic pattern of expression, which was most prominent in the hippocampus and cerebellum. In the striatum, hippocampus and cerebral cortex SYT7 and SYNCRIP immunofluorescent signals were mutually excluded, thus diminishing the probability for their physiological interaction. In somata of Purkinje neurons in the cerebellar cortex, both SYT7 and SYNCRIP were expressed and partially co-localized suggesting possible functional connection between SYT7 and SYNCRIP proteins in Purkinje neurons.

Differential patterns of synaptotagmin7 mRNA expression in rats with kainate- and pilocarpine-induced seizures

Previous studies in rat models of neurodegenerative disorders have shown disregulation of striatal synaptotagmin7 mRNA. Here we explored the expression of synaptotagmin7 mRNA in the brains of rats with seizures triggered by the glutamatergic agonist kainate (10 mg/kg) or by the muscarinic agonist pilocarpine (30 mg/kg) in LiCl (3 mEq/kg) pre-treated (24 h) rats, in a time-course experiment (30 min-1 day). After kainate-induced seizures, synaptotagmin7 mRNA levels were transiently and uniformly increased throughout the dorsal and ventral striatum (accumbens) at 8 and 12 h, but not at 24 h, followed at 24 h by somewhat variable upregulation within different parts of the cerebral cortex, amigdala and thalamic nuclei, the hippocampus and the lateral septum. By contrast, after LiCl/pilocarpine-induced seizures, there was a more prolonged increase of striatal Synaptotagmin7 mRNA levels (at 8, 12 and 24 h), but only in the ventromedial striatum, while in some other of the aforementioned brain regions there was a decline to below the basal levels. After systemic post-treatment with muscarinic antagonist scopolamine in a dose of 2 mg/kg the seizures were either extinguished or attenuated. In scopolamine post-treated animals with extinguished seizures the striatal synaptotagmin7 mRNA levels (at 12 h after the onset of seizures) were not different from the levels in control animals without seizures, while in rats with attenuated seizures, the upregulation closely resembled kainate seizures-like pattern of striatal upregulation. In the dose of 1 mg/kg, scopolamine did not significantly affect the progression of pilocarpine-induced seizures or pilocarpine seizures-like pattern of striatal upregulation of synaptotagmin7 mRNA. In control experiments, equivalent doses of scopolamine per se did not affect the expression of synaptotagmin7 mRNA. We conclude that here described differential time course and pattern of synaptotagmin7 mRNA expression imply regional differences of pathophysiological brain activation and plasticity in these two models of seizures.

Synaptotagmins in neurodegeneration

Synaptotagmins (Syts) are transmembrane proteins involved in the regulation of membrane trafficking. Here, we summarize literature data that provide growing evidence that several Syts are involved in the pathophysiological mechanisms of temporal lobe epilepsy and Parkinson's disease, as well as few reports related to brain ischemia and Alzheimer's disease (AD). We also report new data from our laboratories, showing changes of the expression of several Syts in Tg2576 mouse model of AD that may be related to neuroinflammation surrounding the beta-amyloid plaques. Furthermore, we demonstrate N-methyl-D-aspartate receptor-mediated upregulation of Syt 4 mRNA in a model of excitotoxic striatal lesion induced by unilateral striatal injection of quinolinic acid, associating the upregulation of Syt 4 with mechanisms of excitotoxicity. We propose that pharmacological manipulation of Syt expression in animal models of neurodegeneration should be further explored, as it may help to clarify the role of individual Syt isoforms in the regulation of membrane trafficking in neurodegeneration.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.