It has been suggested that hyperexcitability in dorsal root ganglion (DRG) neurons due to altered sodium channel expression contributes to some chronic pain syndromes. To understand the role of the voltage-gated sodium channel alpha-SNS in inflammatory pain, we investigated the expression of alpha-SNS mRNA and tetrodotoxin-resistant (TTX-R) sodium current in small DRG neurons, which include nociceptive cells, following injection of carrageenan into the hind paw of the rat using in situ hybridization and patch-clamp recording. alpha-SNS mRNA expression in DRG neurons projecting to the inflamed limb was significantly increased 4 days following carrageenan injection, compared with DRG neurons from the contralateral side or naive (uninjected) rats (mean +/- s.d. optical density ratio: ipsilateral/contralateral, 1.77 +/- 0.17; ipsilateral/naive, 1.88 +/- 0.36). The amplitude of the TTX-R sodium current in small DRG neurons projecting to the inflamed limb was significantly larger than on the contralateral side 4 days post-injection (31.7 +/- 3.3 vs 20.0 +/- 2.1 nA). The TTX-R current density was also significantly increased. These results demonstrate the increased expression of alpha-SNS sodium channels in small DRG neurons following injection of carrageenan into their projection field, and suggest that alpha-SNS is involved in the development of hyperexcitability associated with inflammation.

Class V myosins are widely distributed among diverse organisms and move cargo along actin filaments. Some myosin Vs move multiple types of cargo, where the timing of movement and the destinations of selected cargoes are unique. Here, we report the discovery of an organelle-specific myosin V receptor. Vac17p, a novel protein, is a component of the vacuole-specific receptor for Myo2p, a Saccharomyces cerevisiae myosin V. Vac17p interacts with the Myo2p cargo-binding domain, but not with vacuole inheritance-defective myo2 mutants that have single amino acid changes within this region. Moreover, a region of the Myo2p tail required specifically for secretory vesicle transport is neither required for vacuole inheritance nor for Vac17p–Myo2p interactions. Vac17p is localized on the vacuole membrane, and vacuole-associated Myo2p increases in proportion with an increase in Vac17p. Furthermore, Vac17p is not required for movement of other cargo moved by Myo2p. These findings demonstrate that Vac17p is a component of a vacuole-specific receptor for Myo2p. Organelle-specific receptors such as Vac17p provide a mechanism whereby a single type of myosin V can move diverse cargoes to distinct destinations at different times.

Several families of voltage‐gated potassium channels (Kv), including a spectrum of subtypes, are involved in regulating and modifying the integration and transmission of electrical signals in the nervous system. However, the specific patterns of Kv expression in normal or injured dorsal root ganglion (DRG) neurons have not been studied. Previous studies have examined the expression of voltage‐gated sodium channels in DRG neurons, and also the selective up‐ and downregulation of several of these channels following axonal injury to the DRG neurons. In the present study, we used immunocytochemical methods to investigate the expression of Kv channels (Kv1.1, 1.2, 1.3, 1.4, 1.5, 1.6, and 2.1) in DRG cells cultured from control and axotomized adult rats. Kv1.2 and 2.1 immunoreactivity in DRG neurons showed large decreases following axotomy, whereas Kv1.1 and 1.3 showed smaller decreases. Kv1.4 and 1.6 immunostaining were not altered by axotomy, and Kv1.5 immunoreactivity was low in both control and axotomized DRG neurons. These results provide molecular correlates for the expression of multiple K+ currents in normal DRG neurons and indicate that, in relation to changes in sodium channel expression, there are decreases in specific potassium channels following axotomy in these cells. The alterations in K+ and Na+ channel expression following axonal injury may lead to changes in electrical excitability of the DRG neurons, and might contribute to chronic pain syndromes. © 1999 John Wiley & Sons, Inc. Muscle Nerve 22: 502–507, 1999.

Intracellular recording and extracellular field potential (FP) recordings were obtained from spinal cord dorsal horn neurons (laminae I-IV) in a rat transverse slice preparation with attached dorsal roots. To study changes in synaptic inputs after neuroma formation, the sciatic nerve was sectioned and ligated 3 weeks before in vitro electrophysiological analysis. Horseradish peroxidase labeling of dorsal root axons indicated that Abeta fibers sprouted into laminae I-II from deeper laminae after sciatic nerve section. FP recordings from dorsal horns of normal spinal cord slices revealed long-latency synaptic responses in lamina II and short-latency responses in lamina III. The latencies of synaptic FPs recorded in lamina II of the dorsal horn after sciatic nerve section were reduced. The majority of monosynaptic EPSPs recorded with intracellular microelectrodes from lamina II neurons in control slices were elicited by high-threshold nerve stimulation, whereas the majority of monosynaptic EPSPs recorded in lamina III were elicited by low-threshold nerve stimulation. After sciatic nerve section, 31 of 57 (54%) EPSPs recorded in lamina II were elicited by low-threshold stimulation. The majority of low-threshold EPSPs in lamina II neurons after axotomy displayed properties similar to low-threshold EPSPs in lamina III of control slices. These results indicate that reoccupation of lamina II synapses by sprouting Abeta fibers normally terminating in lamina III occurs after sciatic nerve neuroma formation. Furthermore, these observations indicate that the lamina II neurons receive inappropriate sensory information from low-threshold mechanoreceptor after sciatic nerve neuroma formation.

Neurons respond to stimuli by integrating generator and synaptic potentials and generating action potentials. However, whether the underlying electrogenic machinery within neurons itself changes, in response to alterations in input, is not known. To determine whether there are changes in Na ؉ channel expression and function within neurons in response to altered input, we exposed magnocellular neurosecretory cells (MNCs) in the rat supraoptic nucleus to different osmotic milieus by salt-loading and studied Na ؉ channel mRNA and protein, and Na ؉ currents, in these cells. In situ hybridization demonstrated significantly increased mRNA levels for ␣-II, Na6, ␤1 and ␤2 Na ؉ channel subunits, and immunohistochemistr y͞immunoblotting showed increased Na ؉ channel protein after salt-loading. Using patch-clamp recordings to examine the deployment of functional Na ؉ channels in the membranes of MNCs, we observed an increase in the amplitude of the transient Na ؉ current after salt-loading and an even greater increase in amplitude and density of the persistent Na ؉ current evoked at subthreshold potentials by slow ramp depolarizations. These results demonstrate that MNCs respond to salt-loading by selectively synthesizing additional, functional Na ؉ channel subtypes whose deployment in the membrane changes its electrogenic properties. Thus, neurons may respond to changes in their input not only by producing different patterns of electrical activity, but also by remodeling the electrogenic machinery that underlies this activity.The nervous system responds to environmental stimuli with altered patterns of electrical activity that trigger physiological responses and behaviors that tend to protect the organism and͞or help it adapt to its environment. The molecular and cellular mechanisms underlying these altered patterns of neuronal activity are not fully understood. They depend, in part, on the integration of generator potentials and excitatory and inhibitory postsynaptic potentials that impinge on neurons within the circuit under study. Whether the electrogenic machinery responsible for this signal integration within these neurons itself changes, however, in response to environmental changes is not well understood.A model for studying the neuronal response to environmental changes is provided by the magnocellular neurosecretory cells (MNCs) in the supraoptic nucleus (SON), which send axons to the neurohypophysis and fire in bursts so as to release vasopressin in response to increases in plasma osmolality. Vasopressin release is a function of action potential frequency in these cells (1, 2) and firing frequency, in turn, is modulated by osmotic stimuli (3-5). Action potential activity in these cells is Na ϩ dependent and tetrodotoxin (TTX) sensitive, indicating that it is mediated by Na ϩ channels (6-9). While it is known that eight types of Na ϩ channels, encoded by distinct genes, are expressed in neurons (10-17), the identity of the Na ϩ channels in supraoptic MNCs is not known. Moreover, the basic mechanisms that ...