The effect of mGlu8 deficiency in animal models of psychiatric diseases

The metabotropic glutamate receptor subtype 8 (mGlu(8)) is presynaptically located and regulates the release of the transmitter. Dysfunctions of this mechanism are involved in the pathophysiology of different psychiatric disorders. mGlu(8) deficient mice have been previously investigated in a range of studies, but the results are contradictory and there are still many open questions. Therefore, we tested mGlu(8)-deficient animals in different behavioral tasks that are commonly used in neuropsychiatric research. Our results show a robust contextual fear deficit in mGlu(8)-deficient mice. Furthermore, novel object recognition, chlordiazepoxide-facilitated extinction of operant conditioning and the acoustic startle response were attenuated by mGlu(8) deficiency. We found no changes in sensory processing, locomotor activity, prepulse inhibition, phencyclidine-induced changes in locomotion or prepulse inhibition, operant conditioning, conditioned fear to a discrete cue or in animal models of innate fear and post-traumatic stress disorder. We conclude that mGlu(8) might be a potential target for disorders with pathophysiological changes in brain areas where mGlu(8) modulates glutamate and gamma-amino butyric acid (GABA) transmission. Our data especially point to anxiety disorders involving exaggerated contextual fear, such as generalized anxiety disorders, and to conditions with disturbed declarative memory.

Early changes in lymphocyte traffic between distant lymph nodes following regional antigenic stimulation

Regional labeling of mice by injection of cytidine-3H ([3H]CR) into the footpad of the left hind leg was used to evaluate lymphocyte traffic from the left regional nodes to the right popliteal lymph node (PLN) within a 24-h period, with or without concomitant primary or secondary stimulation of the right PLN with fluid tetanus toxoid. Results indicate that 1) in the case of primary antigen injection the relative contribution of lymphocytes from the left regional nodes to the small lymphocyte population present in the stimulated right PLN 24 h after labeling was slightly, but not significantly, greater than in non-stimulated controls; 2) a booster injection of antigen into the right hind leg footpad resulted in a significantly smaller relative contribution of lymphocytes from the previously primed left regional nodes to the small lymphocyte population in the right PLN, 24 h after injection of [3H]CR and secondary stimulation, as compared with controls or animals given a primary stimulation to the receiver node; and 3) in contrast to controls and mice subjected to primary stimulation only, the right PLN 24 h after booster contained a significant number of large lymphoid cells which, or whose precursors, had migrated to this site from contralateral nodes within a day, possibly also in the form of small lymphocytes. These findings are discussed in relation to the problem of lymphocyte recruitment and divergent behavior of non-committed lymphocytes as compared with memory cells in the initial phase after primary or secondary antigenic stimulation.

Survival of tumor-bearing mice exposed to heavy water or heavy water plus methotrexate

Moderate body deuteration combined with a cytostatic drug [methotrexate (MTX)] significantly increases the survival time of young adult DBA/2 mice bearing transplantable P815. L5178Y, or L1210 tumors. Neoplastic cells were grown in vitro from tumor stock and injected i.p. into mice from two groups, one drinking tap water, and other drinking 30% heavy water in tap water. One-half of the animals in each of these two groups was given a single injection of MTX (4 mg/kg body weight) on 3 consecutive days per week. At death, extension of primary and metastatic tumors was examined and was found to be macro- and microscopically comparable in the corresponding groups. The mean survival time of untreated mice drinking tap water was about 2 weeks following injection of the fast-growing P815, L5178Y, or L1210 (V) tumors and approximately 5 weeks after injection of cells from a slower-growing L1210 subline. Body deuteration alone roughly doubled the survival time solely of mice bearing this L1210 subline. Treatment with MTX approximately doubled the mean survival time of hosts bearing one of the fast-growing tumors. Combined treatment with heavy water and MTX increased the mean survival time of the mice in all groups by 15 to 125% as compared to control values. The reasons for this effect are unknown. However, heavy water has been shown to exert antimitotic activity and to depress the incorporation of radioactive precursors into DNA of proliferating mammalian cells. The depression of antibody formation following antigenic stimulation and the reduction in numbers of nonneoplastic lymphoid cells of mice following moderate body deuteration may have contributed to the enhancement of MTX activity in addition to other effects of deuterium.

Kinetic studies on glial, Schwann and capsular cells labelled with [3H] thymidine in cerebrospinal tissue of young mice

Neuroglia, capsular and Schwann cell renewal and turnover in the cerebellum, the spinal cord and spinal ganglia have been evaluated in 2-months-old mice. The animals received intraperitoneal injections of [3H] thymidine at 8 hr intervals starting on the 28th day of postnatal life for a period of 30 days and were killed 1 hr after the last injection. Substantial numbers of labelled neuroglial cells but no labelled neurons were observed. Oligodendrocytes of the cerebellum and the spinal cord showed higher labelling indices (19.8% and 18.0%, respectively) than astrocytes (10.0%) and Bergmann's supporting cells (7.2%). The labelling indices of capsular cells in the spinal ganglia and Schwann cells in the spinal roots were 35.8% and 25.8%, respectively. The experiments failed to provide evidence for matrix cell layers in the cerebellum, the spinal cord and spinal ganglia. It may be concluded therefore that glial and Schwann cells in these parts of the nervous system proliferate in situ.

Pharmacological actions of the antihypertensive agent N-amidino-2-(2,6-dichlorophenyl)acetamide hydrochloride (BS 100-141)

Pharmacological properties characterizing N-amidino-2-(2,6-dichlorophenyl)acetamide hydrochloride (BS 100-141) as a centrally acting antihypertensive agent are described. Its action resembles that of clonidine in many respects but with important differences which are discussed. In DOCA-NaCl--hypertensive conscious rats, BS 100-141 lowers systemic blood pressure with oral doses of 0.3-5 mg/kg. Evidence for a central site of action is provided by the following findings. Infusion of BS 100-141 into the vertebral artery of anaesthetized dogs reduces blood pressure, the same dose being ineffective by i.v. route. Injection into the lateral cerebral ventricle of anaesthetized cats causes a marked reduction in blood pressure and heart rate, the same dose being ineffective when given i.v. The effects of intraventricular injection are inhibited by phentolamine administered by the same route. Intravenous administration of BS 100-141 induces dose-dependent reductions in the splanchnic (sympathetic) nerve activity in the cat. BS 100-141 reduces noradrenaline turnover in the brain stem of the rat as a result of central alpha-adrenoceptor stimulation. Doses which are effective in the hypertensive rat do not reduce dopamine turnover in the corpus striatum. The peripheral, direct alpha-sympathomimetic action of BS 100-141 was demonstrated by the transient increases in blood pressure observed in rats. These increases were unaffected by pretreatment with reserpine, but were antagonized by phentolamine. BS 100-141 was shown to induce contractions of isolated veins and arteries which were competitively inhibited by phentolamine. It stimulates presynaptic cardiac sympathetic alpha-adrenoceptors, thus inhibiting transmitter release to the heart. The sedative effects of BS 100-141 observed in dogs were slight compared to those of clonidine.