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.

Roles for arachidonic acid and GTP-binding proteins in synaptic transmission.

Using synapses which form between somata of Helisoma neurons in cell culture we have studied the presynaptic regulation of synaptic transmission. GTP-binding proteins play important roles in regulating synaptic transmission through their actions on calcium currents, potassium currents and secretory apparatus. Heterotrimeric G proteins continuously regulate the amount of transmitter released at the synapse. By interacting with the arachidonic acid second messenger system they modulate potassium channels, and could potentially control the secretory apparatus. Perturbations of the rab protein system did not affect action potential-evoked transmission, but did control the frequency of miniature inhibitory postsynaptic currents. This is consistent with the involvement of this type of GTP-binding protein in the control of secretory apparatus, but suggests that rab proteins are not used to regulate the amount of transmitter released at the synapse. Using the Helisoma cellular system which permits direct access to the presynaptic site of transmitter release we are going on to study further the role of arachidonic acid, Go, Gi and rab proteins on the regulation of the secretory apparatus.

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.

Acetylcholine-induced responses in the salivary gland cells of Helisoma trivolvis.

This study describes the actions of acetylcholine (ACh) on the salivary gland cells of Helisoma. Perfusion of the salivary gland cells with ACh produces a long-lasting depolarization accompanied by an increase in the input conductance of the gland cells. The depolarization is often followed by a long-lasting hyperpolarization. Carbamylcholine, tetramethylammonium, and choline also produce depolarizing responses. Nicotine and pilocarpine produce only a small depolarization in the gland cells. The following cholinergic antagonists are effective in blocking the gland-cell response to ACh: tetraethylammonium, atropine, hexamethonium, d-tubocurarine, and strychnine. A new preparation, the "isolated acinus," was utilized to obtain the reversal potential of the ACh response. The mean reversal potential in 10 preparations was -7 +/- 8 mV. The depolarizing phase of the response is dependent on the presence of both external calcium and external sodium ions. The long-lasting hyperpolarization is produced by the activity of an electrogenic sodium-potassium pump. The properties of the acetylcholine receptors on the salivary gland cells of Helisoma are compared with those described in other gastropod preparations.

Cryptococcal meningitis and cerebral toxoplasmosis in a patient with acquired immune deficiency syndrome.

A 34-year-old homosexual male developed cryptococcal meningitis as the initial manifestation of Acquired Immune Deficiency Syndrome (AIDS). With antifungal therapy he improved. Six weeks later he developed focal motor seizures and progressive hemiplegia. Computer assisted tomography revealed multiple, ring-enhancing, low density lesions. The patient expired and at necropsy he was found to have multiple toxoplasma brain abscesses as well as chronic cryptococcal meningitis. This case demonstrates that in a patient with AIDS with pre-existing central nervous system infection who develops new neurological symptoms the possibility of a second and potentially treatable infection must be considered and its diagnosis pursued vigorously.

Neuronal mechanisms for bilateral coordination of salivary gland activity in Helisoma.

The salivary neuroeffector system of Helisoma consists of the paired salivary glands and buccal ganglia. Previous work demonstrated that neuronal control was required for coordination of activity in the two salivary glands. This neuronal control is provided by a pair of identified buccal ganglion neurons, 4R and 4L. This study examines the organization of this neuronal control and addresses the questions of monosynaptic vs. polysynaptic pathways as well as the bilateral effects of each neuron 4. Action potentials in neuron 4 elicit one-for-one EPSPs in a subpopulation of the salivary cells. These EPSPs can, in some cases, be increased by TEA injection into a neuron 4 and are unaffected by the addition of six-times normal calcium. These data coupled with the constancy of synaptic transmission, as well as morphological evidence, further indicate the monosynaptic nature of the connection between neurons 4 and salivary secretory cells. Three different mechanisms exist to insure that activity in 4R and 4L result in coordinated activation of the salivary glands: (1) Lucifer Yellow injection and direct intracellular recording and stimulation demonstrate that both 4R and 4L can send axons to and innervate both salivary glands; (2) both 4R and 4L receive virtually identical synaptic input from higher-order buccal ganglion neurons; and (3) 4R and 4L are electrically coupled. Thus, the system is organized with a high degree of redundancy, and bilateral synchrony of glandular activity is assured by mechanisms at various levels of neuronal organization.