Noradrenaline-induced enhancement of oscillatory local field potentials in the mouse accessory olfactory bulb does not depend on disinhibition of mitral cells.

The olfactory bulb differs from other brain regions by its use of bidirectional synaptic transmission at dendrodendritic reciprocal synapses. These reciprocal synapses provide tight coupling of inhibitory feedback from granule cell interneurons to mitral cell projection neurons in the accessory olfactory bulb (AOB), at the first stage of vomeronasal processing. It has been proposed that both the mGluR2 agonist DCG-IV and noradrenaline promote mate recognition memory formation by reducing GABAergic feedback on mitral cells. The resultant mitral cell disinhibition is thought to induce a long-lasting enhancement in the gain of inhibitory feedback from granule to mitral cells, which selectively gates the transmission of the learned chemosensory information. However, we found that local infusions of both noradrenaline and DCG-IV failed to disinhibit AOB neural activity in urethane-anaesthetised mice. DCG-IV infusion had similar effects to the GABA(A) agonist isoguvacine, suggesting that it increased GABAergic inhibition in the AOB rather than reducing it. Noradrenaline infusion into the AOB also failed to disinhibit mitral cells in awake mice despite inducing long-term increases in power of AOB local field potentials, similar to those observed following memory formation. These results suggest that mitral cell disinhibition is not essential for the neural changes in the AOB that underlie mate recognition memory formation in mice.

Titanium Imido Complexes with Tetradentate Schiff Base Ligands.

New mono- and binuclear titanium imido complexes supported by tetradentate, dianionic N(2)O(2)-donor Schiff base ligands were prepared in good yield from the readily available [Ti(NBu(t))Cl(2)(py)(3)] (1a). Thus treatment of 1a with Na(2)[substituted-salen] gave monomeric [Ti(NBu(t))(substituted-salen)] where substituted-salen = Et(2)salen (2) or Bu(t)(4)salen (4). In contrast, the binuclear complex [Ti(NBu(t)){&mgr;-(MeO)(2)salen}](2) (5) was obtained from 1a and Na(2)[(MeO)(2)salen]. The less sterically crowded compounds 2 and 5 undergo tert-butyl imide/arylamine exchange reactions to form [Ti(N-2,6-C(6)H(3)Me(2))(Et(2)salen)] (3) and [Ti(N-2,6-C(6)H(3)Me(2)){&mgr;-(MeO)(2)salen}](2) (6), respectively, whereas 4 does not exhibit this kind of reactivity. The compound 3 can also be obtained directly from Na(2)[Et(2)salen] and [Ti(N-2,6-C(6)H(3)Me(2))Cl(2)(py)(3)] (1b). Crystal data for 3: triclinic, P&onemacr;, a = 12.216(4) Å, b = 12.312(11) Å, c = 17.246(2) Å, alpha = 90.352(12) degrees, beta = 102.59(2) degrees, gamma = 104.96(2) degrees, V = 2440.3(8) Å(3), Z = 4, R = 0.051, R(w) = 0.066 for 7011 data with I > 2sigma(I). Crystal data for 5.CH(2)()Cl(2)(): orthorhombic, Pbca, a = 14.747(4) Å, b = 17.042(4) Å, c = 20.545(3) Å, V = 5163.5(13) Å(3), Z = 4, R(1) = 0.096, wR(2) = 0.086 for 3765 data with I > 2sigma(I). Crystal data for 6: monoclinic, C2/c, a = 17.902(5) Å, b = 12.411(4) Å, c = 21.068(5) Å, beta = 90.27(2) degrees, V = 4681(2) Å(3), Z = 4, R = 0.034, R(w)() = 0.039 for 3633 data with I > 2sigma(I).