Contact-dependent regulation of N-type calcium channel subunits during synaptogenesis.

The developmental regulation of the N-type calcium channel during synaptogenesis was studied using cultured rat hippocampal neurons to elucidate the roles of extrinsic versus intrinsic cues in the expression and distribution of this channel. Prior to synapse formation, alpha1B and beta3 subunits of the N-type calcium channel were distributed diffusely throughout neurites, growth cones, and somata. As synaptogenesis proceeded, the subunit distributions became punctate and colocalized with the synaptic vesicle protein synaptotagmin. Isolated neurons were also examined to test for the requirement of extrinsic cues that control N-type calcium channel expression and distribution. These neurons expressed N-type calcium channel subunits, but their distributions remained diffuse. Functional omega-conotoxin GVIA-sensitive channels were expressed in isolated neurons, although the distribution of alpha1B subunits was diffuse. The distribution of the alpha1B subunit and synaptotagmin only became punctate when neuron-neuron contact was allowed. Thus, the expression of functional N-type calcium channels is the result of an intrinsic program while extrinsic regulatory cues mediated by neuron-neuron contact are required to control their distribution during synaptogenesis.

Glutamate-mediated synaptic transmission between neuron B4 and salivary cells of Helisoma trivolvis.

In this study, we have further characterized the morphology and physiology of the neuroglandular synapse between the identified buccal neuron, B4, and the salivary gland of Helisoma. We demonstrate that the coupling coefficient between salivary cells within an individual acinus is approximately 1.0. We also demonstrate that synapses within the salivary gland are located near a superficial muscle layer. We examine the effects of glutamate on the salivary gland and on the B4-salivary gland EPSP. L-glutamate produces a transient, rapid onset depolarization of salivary gland cells. The response is mimicked by high concentrations of L-homocysteic acid, but not by NMDA, L-aspartate, D-glutamate or kainate. The response is blocked by the presence of L- or D-glutamate in the bath, but not by CNQX, DNQX, DGG, D-AP5, or L-AP3. The depolarization is primarily dependent on the presence of calcium in the bathing solution. When either L- or D-glutamate is present in the bathing solution, the amplitude of the B4-salivary gland EPSP is reversibly reduced. The similar pharmacological properties of the response of the salivary gland to glutamate and the B4 epsp indicate that L-glutamate is a strong candidate for the fast excitatory neurotransmitter at the Helisoma neuroglandular synapse.

A lipoxygenase pathway of arachidonic acid metabolism mediates FMRFamide activation of a potassium current in an identified neuron of Helisoma.

The neuropeptide FMRFamide causes a presynaptic inhibition of neurotransmitter release from neuron B5 of Helisoma. In this study we demonstrate that one of FMRFamide's actions is to activate an outwardly rectifying potassium current. Arachidonic acid also activates an outward current in B5. The phospholipase A2 inhibitor, 4-bromophenacylbromide (BPB), and nordihydroguaiaretic acid (NDGA), an inhibitor of arachidonic acid metabolism, but not indomethacin, block FMRFamide's activation of the potassium current. Taken together these data demonstrate that one of FMRFamide's presynaptic actions is to activate a potassium current through a lipoxygenase pathway of arachidonic acid metabolism.

Theophylline-associated seizures with "therapeutic" or low toxic serum concentrations: risk factors for serious outcome in adults.

We report 12 adults with seizures associated with serum theophylline levels between 14 and 35 mg/l. The seizures were frequently prolonged, and outcome was generally poor with eight deaths. Although we did not identify comparable control groups, possible risk factors for serious outcome in theophylline-associated seizures were age, previous brain injury or disease, severe pulmonary disease, and possibly low serum albumin level. In patients with these risk factors, serum theophylline levels should be maintained below 10 to 15 mg/l.

Interactions between calcium channel blockers and the anticonvulsants carbamazepine and phenytoin.

We describe a retrospective analysis of the frequency of adverse interactions between calcium channel blockers and anticonvulsant drugs (phenytoin and carbamazepine) in a series of 43 patients. Ten patients receiving carbamazepine and three patients receiving phenytoin exhibited symptoms or signs of toxicity. Toxicity occurred with both diltiazem and verapamil, but not with nifedipine. These results emphasize the need for careful clinical and laboratory monitoring of patients receiving both classes of medication.

Analysis of a long-duration hyperpolarization produced by octopamine in an identified effector neuron of Helisoma.

Recent studies have demonstrated that patterned activity in the buccal ganglion of Helisoma trivolvis can be modulated by a variety of neuroactive substances. This study examines the effect of one of these substances, octopamine, on the identified buccal neuron B5. Perfusion of B5 with octopamine produces a 10-20 mV, long-duration hyperpolarization which is associated with an increase in membrane conductance. The magnitude of the hyperpolarization is dose-dependent with a dissociation constant of approximately 5 microM. The reversal potential for the octopamine-induced hyperpolarization (-84 mV) is nearly identical to the predicted potassium equilibrium potential (-85 mV). This result, together with the results of experiments in which extracellular potassium concentrations were altered, demonstrates that octopamine modulated a potassium current in B5.

Cerebellar venous infarction: case report with clinicopathologic correlation.

A diabetic man developed a severe hyperosmolar state resulting in coma. CT of the head showed bilateral cerebellar hemorrhages. Despite medical treatment, he deteriorated and died. At autopsy, the straight sinus was thrombosed. There were bilateral, hemorrhagic, cerebellar venous infarctions. This condition is rare because of abundant collateral venous drainage.

Nonconvulsive status epilepticus following cerebral angiography.

A 64-year-old man developed lethargy and aphasia immediately following cerebral arteriography with iothalamate meglumine. An electroencephalogram showed continuous epileptiform activity. The patient was treated with intravenous phenytoin with complete resolution of clinical symptoms and electroencephalographic epileptiform abnormalities. The diagnosis of nonconvulsive status epilepticus should be considered in cases of altered consciousness following cerebral arteriography.

A case of persistent cortical deafness: clinical, neurophysiologic, and neuropathologic observations.

A 61-year-old man became deaf after the second of two cerebral infarctions which successively involved the temporal and adjacent cortices. He remained completely deaf until death 27 months later. Click stimulation demonstrated normal short-latency potentials, middle-latency responses better developed to stimulation of the right than of the left ear, and absent long-latency potentials. Neuropathologic examination showed cystic infarctions involving both transverse temporal gyri and adjacent cortical areas with preservation of the brainstem auditory nuclei. Persistent deafness can result from bilateral lesions involving the auditory and adjoining cortices.