Rho GTPases activated by GDP/GTP exchange factors (GEFs) play key roles in the developing and adult nervous system. Kalirin-7 (Kal7), the predominant adult splice form of the multifunctional Kalirin RhoGEF, includes a PDZ [postsynaptic density-95 (PSD-95)/Discs large (Dlg)/zona occludens-1 (ZO-1)] binding domain and localizes to the postsynaptic side of excitatory synapses. In vitro studies demonstrated that overexpression of Kal7 increased dendritic spine density, whereas reduced expression of endogenous Kal7 decreased spine density. To evaluate the role of Kal7 in vivo, mice lacking the terminal exon unique to Kal7 were created. Mice lacking both copies of the Kal7 exon (Kal7 KO ) grew and reproduced normally. Golgi impregnation and electron microscopy revealed decreased hippocampal spine density in Kal7 KO mice. Behaviorally, Kal7 KO mice showed decreased anxiety-like behavior in the elevated zero maze and impaired acquisition of a passive avoidance task, but normal behavior in open field, object recognition, and radial arm maze tasks. Kal7 KO mice were deficient in hippocampal long-term potentiation. Western blot analysis confirmed the absence of Kal7 and revealed compensatory increases in larger Kalirin isoforms. PSDs purified from the cortices of Kal7 KO mice showed a deficit in Cdk5, a kinase known to phosphorylate Kal7 and play an essential role in synaptic function. The early stages of excitatory synaptic development proceeded normally in cortical neurons prepared from Kal7 KO mice, with decreased excitatory synapses apparent only after 21 d in vitro. Expression of exogenous Kal7 in Kal7 KO neurons rescued this deficit. Kal7 plays an essential role in synaptic structure and function, affecting a subset of cognitive processes.

Copper (Cu) is an essential metal present at high levels in the CNS. Its role as a co-factor in mitochondrial ATP production and in other essential cuproenzymes is well defined. Menkes and Wilson’s diseases are severe neurodegenerative conditions that demonstrate the importance of Cu transport into the secretory pathway. Brain levels of Cu, which is almost entirely protein bound, exceed extracellular levels by more than a hundred-fold. Cu stored in the secretory pathway is released in a Ca2+-dependent manner and can transiently reach concentrations over 100 µM at synapses. The ability of low µM levels of Cu to bind to and modulate the function of γ-aminobutyric acid type A (GABAA) receptors, N-methyl-D-aspartate (NMDA) receptors and voltage-gated Ca2+ channels contributes to its effects on synaptic transmission. Cu also binds to amyloid precursor protein and prion protein; both proteins are found at synapses and brain Cu homeostasis is disrupted in mice lacking either protein. Especially intriguing is the ability of Cu to affect AMP-activated protein kinase (AMPK), a monitor of cellular energy status. Despite this, few investigators have examined the direct effects of Cu on synaptic transmission and plasticity. Although the variability of results demonstrates complex influences of Cu that are highly method-sensitive, these studies nevertheless strongly support important roles for endogenous Cu and new roles for Cu-binding proteins in synaptic function/plasticity and behavior. Further study of the many roles of Cu in nervous system function will reveal targets for intervention in other diseases in which Cu homeostasis is disrupted.

Invertebrate innexins and their mammalian homologues, the pannexins, are gap junction proteins. Although a large number of such proteins have been identified, few of the gap junctions that they form have been characterized to provide combined information of biophysical properties, coupling pattern, and molecular compositions. We adapted the dual whole cell voltage clamp technique to in situ analysis of electrical coupling in Caenorhabditis elegans body-wall muscle. We found that body-wall muscle cells were electrically coupled in a highly organized and specific pattern. The coupling was characterized by small (350 pS or less) junctional conductance (G j ), which showed a bell-shaped relationship with junctional potential (V j ) but was independent of membrane potential (V m ). Injection of currents comparable to the junctional current (I j ) into body-wall muscle cells caused significant depolarization, suggesting important functional relevance. The innexin UNC-9 appeared to be a key component of the gap junctions. Both Myc-and green fluorescent protein-tagged UNC-9 was localized to muscle intercellular junctions. G j was greatly inhibited in unc-9(fc16), a putative null mutant. Specific inhibition of UNC-9 function in muscle cells reduced locomotion velocity. Despite UNC-9 expression in both motor neurons and body-wall muscle cells, analyses of miniature and evoked postsynaptic currents in the unc-9 mutant showed normal neuromuscular transmission. These analyses provide a relatively detailed description of innexin-based gap junctions in a native tissue and suggest that innexin-based small conductance gap junctions can play an important role in processes such as locomotion.

The mammalian amygdala expresses various neuropeptides whose signaling has been implicated in emotionality. Many neuropeptides require amidation for full activation by peptidylglycine ␣-amidating monooxygenase (PAM), a transmembrane vesicular cuproenzyme and regulator of the secretory pathway. Mice heterozygous for the Pam gene (PAM ϩ/Ϫ ) exhibit physiological and behavioral abnormalities related to specific peptidergic pathways. In the present study, we evaluated emotionality and examined molecular and cellular responses that characterize neurophysiological differences in the PAM ϩ/Ϫ amygdala. PAM ϩ/Ϫ mice presented with anxiety-like behaviors in the zero maze that were alleviated by diazepam. PAM ϩ/Ϫ animals were deficient in short-and long-term contextual and cued fear conditioning and required higher shock intensities to establish fear-potentiated startle than their wild-type littermates. Immunohistochemical analysis of the amygdala revealed PAM expression in pyramidal neurons and local interneurons that synthesize GABA. We performed whole-cell recordings of pyramidal neurons in the PAM ϩ/Ϫ amygdala to elucidate neurophysiological correlates of the fear behavioral phenotypes. Consistent with these observations, thalamic afferent synapses in the PAM ϩ/Ϫ lateral nucleus were deficient in long-term potentiation. This deficit was apparent in the absence and presence of the GABA A receptor antagonist picrotoxin and was abolished when both GABA A and GABA B receptors were blocked. Both evoked and spontaneous excitatory signals were enhanced in the PAM ϩ/Ϫ lateral nucleus. Phasic GABAergic signaling was also augmented in the PAM ϩ/Ϫ amygdala, and this difference comprised activity-independent and -dependent components. These physiological findings represent perturbations in the PAM ϩ/Ϫ amygdala that may underlie the aberrant emotional responses in the intact animal.

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