Noradrenaline hyperpolarizes identified rat mesopontine cholinergic neurons in vitro

Inhibition of brainstem cholinergic neurons by noradrenergic neurons of the locus ceruleus has long been suggested as a key mechanism of behavioral state control. In particular, the commonly held view is that noradrenaline (NA) plays a permissive role in rapid eye movement (REM) sleep generation by disinhibiting brainstem cholinergic neurons. While this notion has been supported by numerous investigations, the inhibition of cholinergic neurons by NA has never been directly demonstrated. The purpose of this study was to investigate the effects of NA upon identified cholinergic neurons in the rat mesopontine tegmentum. Using whole-cell patch-clamp recordings in slices, 175 cells were studied during bath application of 50 microM NA. Cholinergic neurons were positively identified by intracellular labeling with biocytin and subsequent staining with NADPH-diaphorase, a reliable marker for brainstem cholinergic neurons (Vincent et al., 1983). Successful intracellular labeling was obtained in 96 cells. Ninety-two percent (36 of 39) of cholinergic neurons hyperpolarized in response to NA, while noncholinergic cells (n = 57) exhibited mixed responses. Application of NA in a low-Ca2+, high-Mg2+ solution elicited the same hyperpolarizing effect as in normal solution, which indicated that the effect of NA on cholinergic neurons was direct. The noradrenergic hyperpolarization was mimicked by the alpha 2-adrenoceptor agonist UK-14,304, and was blocked by the alpha 2-adrenoceptor antagonist idazoxan, which suggested an alpha 2-mediated response. Finally, voltage-clamp experiments revealed that NA activates the inwardly rectifying potassium current, IKG.(ABSTRACT TRUNCATED AT 250 WORDS)     

Electrophysiological characterization of GABAergic neurons in the ventral tegmental area

GABAergic neurons in the ventral tegmental area (VTA) play a primary role in local inhibition of mesocorticolimbic dopamine (DA) neurons but are not physiologically or anatomically well characterized. We used in vivo extracellular and intracellular recordings in the rat VTA to identify a homogeneous population of neurons that were distinguished from DA neurons by their rapid-firing, nonbursting activity (19.1 +/- 1.4 Hz), short-duration action potentials (310 +/- 10 microseconds), EPSP-dependent spontaneous spikes, and lack of spike accommodation to depolarizing current pulses. These non-DA neurons were activated both antidromically and orthodromically by stimulation of the internal capsule (IC; conduction velocity, 2.4 +/- 0.2 m/sec; refractory period, 0.6 +/- 0.1 msec) and were inhibited by stimulation of the nucleus accumbens septi (NAcc). Their firing rate was moderately reduced, and their IC-driven activity was suppressed by microelectrophoretic application or systemic administration of NMDA receptor antagonists. VTA non-DA neurons were recorded intracellularly and showed relatively depolarized resting membrane potentials (-61.9 +/- 1.8 mV) and small action potentials (68.3 +/- 2.1 mV). They were injected with neurobiotin and shown by light microscopic immunocytochemistry to be multipolar cells and by electron microscopy to contain GABA but not the catecholamine-synthesizing enzyme tyrosine hydroxylase (TH). Neurobiotin-filled dendrites containing GABA received asymmetric excitatory-type synapses from unlabeled terminals and symmetric synapses from terminals that also contained GABA. These findings indicate that VTA non-DA neurons are GABAergic, project to the cortex, and are controlled, in part, by a physiologically relevant NMDA receptor-mediated input from cortical structures and by GABAergic inhibition.     

Passive electrical properties of ventral horn neurons in rat spinal cord slices

Recordings were made from large neurons located in the ventral horn of transverse spinal cord slices from young rats (7-15 days). Whole cell recordings were made simultaneously with two electrodes from the soma of these neurons, visualized using infra-red differential interference contrast optics. Positive identification of motoneurons could not always be achieved. The response of a neuron to a brief pulse of current delivered by one electrode, and recorded by the other electrode, were matched optimally to responses of a compartmental model of the same neuron with an identical current pulse as input. The compartmental model was based on a reconstruction of the neuron, using Biocytin staining. The compartmental model had three free parameters: specific membrane capacitance (Cm), membrane resistivity (Rm), and cytoplasmatic resistivity (Ri), all assumed to be uniform throughout the neuron. The experimental and model responses could be matched unequivocally for four neurons, giving Cm = 2.4 +/- 0.5 microF/cm2, Rm = 5.3 +/- 0. 9 kOmega/cm2, and Ri = 87 +/- 22 Omega/cm. No somatic shunt was required. For the remaining six neurons, a less perfect fit (but still within 95% confidence limits) was indicative of nonhomogeneous membrane properties. The electrotonic length of uncut dendrites was 0.85 +/- 0.14 lambda. The results resolve the issue of a somatic shunt conductance for motoneurons, relegating it to a microelectrode impalement artifact. They are consistent with previous reports on the electrical compactness of motoneurons to steady state currents and voltages. However, the much higher value of Cm (than the previously assumed 1 microF/cm2) implies much greater dendritic attenuation of fast synaptic potentials, and a much enhanced integrative response of motoneurons to synaptic potentials.     

Passive electrical properties of ventral horn neurons in rat spinal cord slices

Recordings were made from large neurons located in the ventral horn of transverse spinal cord slices from young rats (7-15 days). Whole cell recordings were made simultaneously with two electrodes from the soma of these neurons, visualized using infra-red differential interference contrast optics. Positive identification of motoneurons could not always be achieved. The response of a neuron to a brief pulse of current delivered by one electrode, and recorded by the other electrode, were matched optimally to responses of a compartmental model of the same neuron with an identical current pulse as input. The compartmental model was based on a reconstruction of the neuron, using Biocytin staining. The compartmental model had three free parameters: specific membrane capacitance (Cm), membrane resistivity (Rm), and cytoplasmatic resistivity (Ri), all assumed to be uniform throughout the neuron. The experimental and model responses could be matched unequivocally for four neurons, giving Cm = 2.4 +/- 0.5 microF/cm2, Rm = 5.3 +/- 0. 9 kOmega/cm2, and Ri = 87 +/- 22 Omega/cm. No somatic shunt was required. For the remaining six neurons, a less perfect fit (but still within 95% confidence limits) was indicative of nonhomogeneous membrane properties. The electrotonic length of uncut dendrites was 0.85 +/- 0.14 lambda. The results resolve the issue of a somatic shunt conductance for motoneurons, relegating it to a microelectrode impalement artifact. They are consistent with previous reports on the electrical compactness of motoneurons to steady state currents and voltages. However, the much higher value of Cm (than the previously assumed 1 microF/cm2) implies much greater dendritic attenuation of fast synaptic potentials, and a much enhanced integrative response of motoneurons to synaptic potentials.     

Nitric oxide synthase immunoreactivity in rat pontine medullary neurons

Nitric oxide synthase immunoreactivity was detected in neurons and fibers of the rat pontine medulla. In the medulla, nitric oxide synthase-positive neurons and processes were observed in the gracile nucleus, spinal trigeminal nucleus, nucleus of the solitary tract, dorsal motor nucleus of the vagus, nucleus ambiguus, medial longitudinal fasciculus, reticular nuclei and lateral to the pyramidal tract. In the pons, intensely labeled neurons were observed in the pedunculopontine tegmental nucleus, paralemniscal nucleus, ventral tegmental nucleus, laterodorsal tegmental nucleus, and lateral and medial parabrachial nuclei. Labeled neurons and fibers were seen in the interpeduncular nuclei, dorsal and median raphe nuclei, central gray and dorsal central gray, and superior and inferior colliculi. Double-labeling techniques showed that a small population (< 5%) of nitric oxide synthase-positive neurons in the medulla also contained immunoreactivity to the aminergic neuron marker tyrosine hydroxylase. The majority of nitric oxide synthase-immunoreactive neurons in the dorsal and median raphe nuclei were 5-hydroxytryptamine-positive, whereas very few 5-hydroxytryptamine-positive cells in the caudal raphe nuclei were nitric oxide synthase-positive. Virtually all nitric oxide synthase-positive neurons in the pedunculopontine and laterodorsal tegmental nuclei were also choline acetyltransferase-positive, whereas nitric oxide synthase immunoreactivity was either low or not detected in choline acetyltransferase-positive neurons in the medulla. The results indicate a rostrocaudal gradient in the intensity of nitric oxide synthase immunoreactivity, i.e. it is highest in neurons of the tegmentum nuclei and neurons in the medulla are less intensely labeled. The majority of cholinergic and serotonergic neurons in the pons are nitric oxide synthase-positive, whereas the immunoreactivity was either too low to be detected or absent in the large majority of serotonergic, aminergic and cholinergic neurons in the medulla.     

Electrophysiological properties of cultured neonatal rat dorsal horn neurons containing GABA and met-enkephalin-like immunoreactivity

We have developed a culture of neurons dissociated from the most superficial laminae of the neonatal rat spinal cord dorsal horn (DH). By using the perforated patch-clamp technique, we distinguished four types of neurons based on their firing properties in response to intracellular injection of 900 ms lasting current pulses. Type 1 neurons were characterized by a tonic firing. Type 2 neurons displayed marked spike accommodation and fired brief (<500 ms) bursts of action potentials, whereas type 3 neurons fired a single spike. Type 4 neurons exhibited different types of firing patterns, but all of them possessed a time-dependent inwardly rectifying current activated by membrane hyperpolarization. Met-enkephalin-like immunoreactivity (met-ENK-LI) and glutamic acid decarboxylase-like immunoreactivity (GAD-LI) were colocalized in 42% of the neurons (n = 59), which were previously identified electrophysiologically. Type 1-4 neurons represented respectively 4, 64, 20, and 12% of the population of neurons colocalizing met-ENK-LI and GAD-LI. We conclude that the electrophysiological properties of DH neurons present in our cultures are similar to those described in acute slice or hemisected spinal cord preparations and that met-ENK-LI and GABA-LI are preferentially colocalized in type 2 neurons.     

Electrophysiological studies on rat dorsal root ganglion neurons after peripheral axotomy: changes in responses to neuropeptides

The effect of three peptides, galanin, sulfated cholecystokinin octapeptide, and neurotensin (NT), was studied on acutely extirpated rat dorsal root ganglia (DRGs) in vitro with intracellular recording techniques. Both normal and peripherally axotomized DRGs were analyzed, and recordings were made from C-type (small) and A-type (large) neurons. Galanin and sulfated cholecystokinin octapeptide, with one exception, had no effect on normal C- and A-type neurons but caused an inward current in both types of neurons after sciatic nerve cut. In normal rats, NT caused an outward current in C-type neurons and an inward current in A-type neurons. After sciatic nerve cut, NT only caused an inward current in both C- and A-type neurons. These results suggest that (i) normal DRG neurons express receptors on their soma for some but not all peptides studied, (ii) C- and A-type neurons can have different types of receptors, and (iii) peripheral nerve injury can change the receptor phenotype of both C- and A-type neurons and may have differential effects on these neuron types.     

Electrophysiological properties of neurons in intact rat dorsal root ganglia classified by conduction velocity and action potential duration

1. L4 and L5 dorsal root ganglia of rats aged 4-5 wk were isolated in vitro with their dorsal roots and sciatic nerves intact. With the use of intracellular microelectrodes, conduction velocity (CV) was determined along both peripheral and central axons and active and passive membrane properties were investigated with the use of a single-electrode switching clamp. 2. Neurons were classified into one of the three subgroups, A alpha/beta, A delta, and C, on the basis of a combination of axonal CV and action potential duration. Soma diameters overlapped between these groups. 3. Action potentials elicited by nerve stimulation in all cells and by a somatic current step in A alpha/beta-cells were always blocked by tetrodotoxin (TTX) 0.1-1 microM), whereas somatic action potentials in a proportion of A delta-cells and all C cells were TTX-resistant. 4. Passive electrical properties differed significantly between A alpha/beta-, A delta-, and C cells. The contribution of the additional membrane of the axons to the recorded electrical properties was analyzed with the use of a compartmental model of the neurons (see APPENDIX). 5. Most neurons discharged only a single action potential at the onset of a depolarizing current step, but 33% of A alpha/beta-cells fired repetitively throughout the step. This was associated with a lower threshold for action potential initiation by depolarizing current and a shorter afterhyperpolarization than in other A alpha/beta-cells. 6. Afterhyperpolarizations varied in size and duration between neurons and most were either not or only slightly affected by replacing Ca2+ in the bathing solution with Co2+ or Ba2+ or by adding tetraethylammonium (1 and 10 mM). Outward tail currents following an active response could be fitted with one fast exponential (time constant = 13 +/- 1 ms, mean +/- SE) and, in 65% of cells, one to three slower time course currents (to which exponentials with time constants of approximately 50, 300, or 1,500 ms could be fitted). A very slow late-onset current (detected in 33% of C cells) resembled a Ca(2+)-dependent K+ conductance described in several other neurons. 7. Voltage transients showed "sag" during maintained hyperpolarizing current steps in 90% of A alpha/beta-cells and 70% of A delta-cells but only 13% of C cells. Time-dependent inward currents were recorded when membrane potential was hyperpolarized. These currents had mean activation time constants of approximately 40 ms at -120 mV and were Cs+ sensitive and Ba2+ insensitive. 8. The proportion of neurons with a transient outward current, IA, increased as CV decreased (36% of A alpha/beta-cells, 56% of A delta-cells, 63% of C cells). Outward currents in cells of all subgroups had either one or two of three inactivation time constants (means approximately 22, 120, and 800 ms). 9. This study shows that many of the electrical characteristics of isolated dorsal root ganglion neurons can be demonstrated in intact ganglia in which the neurons can be better identified functionally. The currents underlying the afterhyperpolarization in these cells are diverse across all subgroups and require further investigation. The electrical effects of retaining the axonal projections of the cells and the use of microelectrodes filled with 0.5 M KC1 are discussed in relation to the differences from data recorded in dissociated neurons.     

Electrophysiological studies of rat substantia nigra neurons in an in vitro slice preparation after middle cerebral artery occlusion

We studied sequential changes in electrophysiological profiles of the ipsilateral substantia nigra neurons in an in vitro slice preparation obtained from the middle cerebral artery-occluded rats. Histological examination revealed marked atrophy and neurodegeneration in the ipsilateral substantia nigra pars reticulata at 14 days after middle cerebral artery occlusion. Compared with the control group, there was no significant change in electrical membrane properties and synaptic responses of substantia nigra pars reticulata neurons examined at one to two weeks after middle cerebral artery occlusion. On the other hand, there was a significant increase in the input resistance and spontaneous firing rate of substantia nigra pars compacta neurons at 13-16 days after middle cerebral artery occlusion. Furthermore, inhibitory postsynaptic potentials evoked by stimulation of the subthalamus in substantia nigra pars compacta neurons was suppressed at five to eight days after middle cerebral artery occlusion. At the same time excitatory postsynaptic potentials evoked by the subthalamic stimulation was increased. Bath application of bicuculline methiodide (50 microM), a GABA(A) receptor antagonist, significantly increased the firing rate of substantia nigra pars compacta neurons from intact rats. These results strongly suggest that changes in electrophysiological responses observed in substantia nigra pars compacta neurons is caused by degeneration of GABAergic afferents from the substantia nigra pars reticulata following middle cerebral artery occlusion. While previous studies indirectly suggested that hyperexcitation due to deafferentation from the neostriatum may be a major underlying mechanism in delayed degeneration of substantia nigra pars reticulata neurons after middle cerebral artery occlusion, the present electrophysiological experiments provide evidence of hyperexcitation in substantia nigra pars compacta neurons but not in pars reticulata neurons at the chronic phase of striatal infarction.     

Visceral pain: responses of the reticular formation neurons to gallbladder distension

Visceral projection (gallbladder distension) to the gigantocellular nucleus of the reticular formation of the cat was tested in neurons classified as pain (P), nonpain-pain (NP-P) and nonpain (NP) units, according to their responses to noxious and/or innocuous natural stimuli from the somatic areas. 96% of P neurons (23 out of 24) responded to gallbladder distension. Quantitative criteria showed comparable effectiveness of the somatic and visceral inputs. NP-P neurons reacted to the gallbladder stimulation in 71% of cases (22 out of 31); NP neurons were activated less effectively. Stimulation of either the central tegmental field or "nonspecific" thalamic nuclei evoked direct responses in 38% of P and 26% of NP-P units, which, in most of the P neurons were followed by excitatory and inhibitory phases. The duration of the latter was approximately one second and it greatly affected the responses of the units to somatic as well as to visceral inputs. A large proportion of P neurons responding to a visceral input documents the important role of the reticular formation in the mechanisms of visceral pain. Findings concerning comparable modifying influences upon reactions of P units both in the case of visceral and painful somatic afferentation indicated that similar control mechanisms could be involved.     

Response properties of saccade-related burst neurons in the central mesencephalic reticular formation

We studied the activity of saccade-related burst neurons in the central mesencephalic reticular formation (cMRF) in awake behaving monkeys. In experiment 1, we examined the activity of single neurons while monkeys performed an average of 225 delayed saccade trials that evoked gaze shifts having horizontal and vertical amplitudes between 2 and 20 degrees . All neurons studied generated high-frequency bursts of activity during some of these saccades. For each neuron, the duration and frequency of these bursts of activity reached maximal values when the monkey made movements within a restricted range of horizontal and vertical amplitudes. The onset of the movement followed the onset of the burst by the longest intervals for movements within a restricted range of horizontal and vertical amplitudes. The range of movements for which this interval was longest varied from neuron to neuron. Across the population, these ranges included nearly all contraversive saccades with horizontal and vertical amplitudes between 2 and 20 degrees. In experiment 2, we used the following task to examine the low-frequency prelude of activity that cMRF neurons generate before bursting: the monkey was required to fixate a light-emitting diode (LED) while two eccentric visual stimuli were presented. After a delay, the color of the fixation LED was changed, identifying one of the two eccentric stimuli as the saccadic target. After a final unpredictable delay, the fixation LED was extinguished and the monkey was reinforced for redirecting gaze to the identified saccadic target. Some cMRF neurons fired at a low frequency during the interval after the fixation LED changed color but before it was extinguished. For many neurons, the firing rate during this interval was related to the metrics of the movement the monkey made at the end of the trial and, to a lesser degree, to the location of the eccentric stimulus to which a movement was not directed.     

Neurotrophin effects on survival and expression of cholinergic properties in cultured rat septal neurons under normal and stress conditions

These studies tested the hypothesis that survival-promoting effects of neurotrophins on basal forebrain cholinergic neurons are enhanced under stress. Septal neurons from embryonic day 14-15 rats exposed for 10-14 d to neurotrophin [nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 (NT-3), or neurotrophin-4 (NT-4), each at 100 ng/ml] showed a two- to threefold increase in choline acetyltransferase (ChAT) activity, with little evidence of synergistic interactions. Neurotrophins produced no significant increase in the survival of total or acetylcholinesterase (AChE)-positive neurons at moderate plating density (1200-1600 cells/mm2). However, with very low plating densities (2-28 cells/mm2) BDNF, NT-3, and NT-4 (but not NGF) increased total neuronal survival, and BDNF increased survival of AChE-positive neurons. NGF and BDNF enhanced ChAT activity and survival of cholinergic neurons after a 24 hr hypoglycemic stress, even when added 1 hr after stress onset. All four tested neurotrophins increased total neuronal survival after hypoglycemic stress. These results suggest that neurotrophins are important for preservation of central cholinergic function under stress conditions, with different neurotrophins protecting against different stresses. The stress-associated survival-promoting effects of neurotrophins were not limited to the cholinergic subpopulation.     

Mitochondrial density of ventral horn neurons in the rat spinal cord

Mitochondrial density in neurons of the dorsolateral region of the ventral horn at the L5 spinal cord segment in rats was examined using electron microscopy. The gamma motoneurons had a higher density of mitochondria (25.1 +/- 4.2%, n = 19) in the cytoplasm compared to the alpha motoneurons which had a mitochondrial density of 19.4 +/- 4.5% (n = 38). An inverse relationship between cell body size and mitochondrial density was found for alpha (n = 38) and alpha plus gamma (n = 57), but not for gamma (n = 19), motoneuron populations. The higher densities of mitochondria in the smaller neurons correspond well with their metabolic properties since the smaller neurons have the highest oxidative enzyme activities.     

Adrenergic responses in silent and putative inhibitory pacemaker-like neurons of the rat rostral ventrolateral medulla in vitro

Noradrenaline and adrenergic agonists were tested on pacemaker-like and silent neurons of the rat rostral ventrolateral medulla using intracellular recording in coronal brainstem slices as well as in punches containing only the rostral ventrolateral medullary region. Noradrenaline (1-100 microM) depolarized or increased the frequency of discharge of all cells tested in a dose-dependent manner. The noradrenaline-induced depolarization was associated with an apparent increase in cell input resistance at low concentrations and a decrease or no significant change at higher concentrations. Moreover, it was voltage dependent and its amplitude decreased with membrane potential hyperpolarization. Noradrenaline caused a dose-related increase in the frequency and amplitude of spontaneous inhibitory postsynaptic potentials. The alpha 1-adrenoceptor antagonist prazosin (0.5 microM) abolished the noradrenaline depolarizing response as well as-the noradrenaline-evoked increase in synaptic activity and unmasked an underlying noradrenaline dose-dependent hyperpolarizing response associated with a decrease in cell input resistance and sensitive to the alpha 2-adrenoceptor/antagonist yohimbine (0.5 microM). The alpha 1-adrenoceptor agonist phenylephrine (10 microM) mimicked the noradrenaline depolarizing response associated with an increase in membrane resistance as well as the noradrenaline-induced increase in synaptic activity. The alpha 2-adrenoceptor agonists UK-14,304 (1-3 microM) and clonidine (10-30 microM) produced only a small hyperpolarizing response, whereas the beta-adrenoceptor agonist isoproterenol (10-30 microM) had no effect. Baseline spontaneous postsynaptic potentials were abolished by strychnine (1 microM), bicuculline (30 microM) or both. However, only the strychnine-sensitive postsynaptic potentials had their frequency increased by noradrenaline or phenylephrine and they usually occurred with a regular pattern. Tetrodotoxin (1 microM) eliminated 80-95% of baseline spontaneous postsynaptic potentials and prevented the increase in synaptic activity evoked by noradrenaline and phenylephrine. Similar results were obtained in rostral ventrolateral medulla neurons impaled in both coronal slices and punches of the rostral ventrolateral medulla. It is concluded that noradrenaline could play an important inhibitory role in the rostral ventrolateral medulla via at least two mechanisms: an alpha 2-adrenoceptor-mediated hyperpolarization and an enhancement of inhibitory synaptic transmission through activation of alpha 1-adrenoceptors located on the somatic membrane of glycinergic interneurons. Some of these interneurons exhibit a regular discharge similar to the pacemaker-like neurons and might, at least in part, constitute a central inhibitory link in the baroreceptor-vasomotor reflex pathway.     

Developmental changes in the electrophysiological properties of neonatal rat oculomotor neurons studied in vitro

The electrophysiological properties of oculomotor neurons were studied in neonatal rats aged 1-15 days. Action potentials were recorded from brainstem slices (frontal section) using the intracellular recording method at 35 degrees C. No significant age-dependent differences were detected in the resting potential (around -55 mV) and in the amplitude of the action potential (approximately 60 mV). However, the input resistance of oculomotor neurons declined with age from a mean of 60.8 M omega for rats 1-3 days old to 17.0 M omega for rats 14-15 days old. In addition, the duration of the action potential measured at the half-amplitude gradually decreased from 0.74 ms to 0.34 ms with increasing age. Increases were detected in the maximum rate of rise (from 117 V/s to 181 V/s) and the maximum rate of fall (from -67 V/s to -103 V/s) of the action potential. When long-lasting (500 ms) depolarizing current pulses were applied to oculomotor neurons, some neurons exhibited continuous repetitive discharge (i.e. tonic firing) while others showed transient discharge (phasic firing). The proportion of tonic-type neurons increased with age: the value was 9% for rats 1-5 days old, 37% for rats 6-10 days old and 54% for rats 11-15 days old. Concomitantly, the number of neurons showing a time-dependent inward rectification increased and the average maximum frequency of the discharge rose from 150 to 420 Hz, approximately, with age. Furthermore, it was found that the electrophysiological properties of oculomotor neurons of rats 14-15 days old were similar to those in adult rats. It is concluded that oculomotor neurons in neonatal rats show rapid alterations in their electrophysiological properties and that the ratio of tonic-type to phasic-type neurons changes during the early stages of development.     

Electrophysiological effects of pressure-ejected bombesin-like peptides on hamster suprachiasmatic nucleus neurons in vitro

The suprachiasmatic nuclei (SCN) of the rodent hypothalamus function as a light entrainable circadian pacemaker. The SCN contain moderate to high concentrations of a number of neuropeptides including peptides showing structural homology with the amphibian derived tetradecapeptide, bombesin (BN), called bombesin-like peptides (BNLPs). BNLPs include the 27 amino acid peptide, gastrin releasing peptide (GRP1-27), a smaller decapeptide (GRP18-27) and another decapeptide with less structural homology, neuromedin B (NmB). Immunoreactivity for BN and receptors for BNLPs have been demonstrated in the region of the rat SCN receiving photic input. We studied the effects of local pressure ejections of BNLPs dissolved in saline/1% bovine serum albumin (BSA) vehicle on the extracellularly recorded firing rates of Syrian hamster SCM neurons in a hypothalamic slice preparation. In one study, an ejecting electrode containing BN (10(-8) to 10(-4) M) was positioned 20 to 60 microm from a recording electrode. Of 74 cells tested with BN, 50 (67.6%) showed significant increases in firing rate, while 3 of 29 cells (15.8%) tested with vehicle ejections were activated. In a second study, a single electrode was used for both recordings and pressure ejections. Of 48 cells tested, BN (10(-6) to 10(-4) M) activated 30 (62.5%) and suppressed firing in 4 (8.3%). Of 208 cells tested with GRP1-27 (10(-9) to 10(-4) M), 105 (50.5%) were activated and 2 (1.0%) were suppressed. The percentage of cells responding increased with the concentration of GRP1027 used in the electrode. No circadian variation in responsiveness to GRP1-27 was detected. GRP18-27 (5 x 10(-5) to 10(-4) M) activated 10 out of 18 cells tested (55.6%), while NmB (10(-4) M) activated 2 out of 30 cells tested (6.7%) and vehicle ejections activated 1 out of 36 cells tested (2.8%). GRP1-27, GRP18-27 and BN, the BNLPs showing the greatest degree of structural homology, activate approximately 50% of SCN cells, apparently via the BN/GRP-preferring receptor subtype, and may play a role in photic entrainment.     

Fos expression in rat pontine tegmental neurons following activation of the medial preoptic area

Because murine myeloma plasma cells and normal human lymph node plasma cells express BCL-X, we evaluated BCL-X expression in malignant human plasma cells. BCL-X expression was detected in several human myeloma cell lines, as well as in CD38-sorted bone marrow cells obtained from some patients. Only the antiapoptotic long form of BCL-X (BCL-X-L), was detected. Because BCL-X-L expression can protect tumor cells from apoptotic death induced by chemotherapeutic agents, we tested the clinical relevance of expression in 55 archival bone marrow biopsies. The biopsies were stained by immunohistochemistry, and BCL-X expression was correlated with the subsequent response to treatment. BCL-X expression in malignant plasma cells strongly correlated with decreased response rates in patient groups treated with either melphalan and prednisone or vincristine, Adriamycin, and dexamethasone. Response rates were 83-87% in non-BCL-X-expressing cases and 20-31% in BCL-X-expressing cases. In addition, BCL-X expression was more frequent in specimens taken from patients at relapse (77%), when compared to those at initial diagnosis (29%). Further support for the association of drug resistance with BCL-X-L expression came from studies of the 8226 dox-40 cell line. This line, which expresses p-glycoprotein and serves as a model of multidrug resistance in multiple myeloma cells, demonstrated an up-regulated expression of BCL-X-L, which was relatively specific, in that BCL-2 or BAX expression was not altered. In addition, dox-40 cells demonstrated a generalized resistance to apoptosis that was induced by several different agents. These results indicate that malignant plasma cells can express BCL-X-L and that such expression may be a marker of chemoresistant disease.     

Visual receptive-field properties of single neurons in cat's ventral lateral geniculate nucleus

1. Visual receptive-field characteristics were determined for 154 cells in the ventral lateral geniculate nucleus (VLG) of cats anesthetized with nitrous oxide. All cells were verified histologically to be within the VLG. Responses of 182 cells from laminae A and A1 of the dorsal lateral geniculate nucleus (DLG) were tested for comparison. 2. The VLG cells could be grouped into one of seven classes according to their responses to light stimulation. Twenty-seven percent of the cells had uniform receptive fields. They responded maximally to stationary stimuli flashed on or off anywhere within the receptive field and showed no evidence for antagonistic surround mechanisms. About 19.5% of the VLG cells had concentric receptive fields. They were similar to the uniform type, with the addition of a concentric inhibitory surround. Eight percent of the VLG cells had ambient receptive fields. These cells were characterized by an unusually regular maintained discharge which varied in rate in relation to the level of receptive-field illumination or of full-field ambient illumination. About 4% of the VLG cells were movement sensitive. They gave little or no response to stationary stimuli flashed on or off in the receptive field, and responded best to a contour moving across the receptive field in any direction. An additional 2.5% of the VLG cells were direction sensitive. Their response was dependent on the direction of stimulus movement through the receptive field. Sixteen percent of the VLG cells had indefinite receptive fields. They responded to whole-eye illumination or to localized visual-field stimulation; however, specific receptive-field properties could not be adequately defined. Approximately 23% of the VLG cells studied gave no convincing response to visual stimulation. 3. Responses of DLG cells agreed with those reported in previous studies. Almost all (97%) had concentric receptive fields, and a few (3%) had uniform receptive fields with no apparent antagonistic surround. None of the DLG cells had receptive fields like those in the other classes found for VLG cells. 4. The VLG cells tended to have large receptive fields; mean diameter was 10.6 degrees of visual arc. This was substantially larger than the diameter of receptive fields for DLG cells. In addition, VLG cells generally required larger stimuli than DLG cells to respond. There was no consistent relationship between receptive-field size and visual-field eccentricity for VLG cells, in contrast to the DLG. Most (57%) VLG cells were driven only by the contralateral eye, 30% were binocularly driven, and 13% were driven only by the ipsilateral eye. 5. A systematic visuotopic organization was present in the VLG. The lower visual field was represented anteriorly in the nucleus and the upper visual field posteriorly. The vertical meridian was represented along the dorsomedial border of the VLG where it abuts the DLG, and the temporal periphery was represented ventrolaterally. 6. Responses to electrical stimulation of the optic chiasm were studied for 55 VLG cells...     

Development of cholinergic and inhibitory non-adrenergic non-cholinergic responses in the rat gastric funds

1. Cholinergic contractions and inhibitory non-adrenergic non-cholinergic (NANC) relaxations were studied in longitudinal muscle strips of the gastric funds of 2, 4 and 8 week old rats. 2. Contractions induced by electrical stimulation of the cholinergic neurones and by administration of acetylcholine decreased during development. The potentiating effect of physostigmine was similar in the 3 age groups. 3. Short train stimulation in NANC conditions induced fast relaxations, which were more pronounced in 4 and 8 week than in 2 week old rats. These relaxations were almost completely inhibited by NG-nitro-L-arginine methyl ester (L-NAME) in the 3 age groups. The nitric oxide-induced relaxations did not change during development. 4. Sustained electrical stimulation in NANC conditions induced an initial relaxation, which was almost totally blocked by L-NAME, followed by an almost complete recovery of tone at lower frequencies of stimulation. At higher frequencies of stimulation, the recovery of tone was incomplete or absent. This sustained relaxation was only partially reduced by L-NAME and almost abolished by L-NAME plus alpha-chymotrypsin. The initial relaxations increased during development, while the sustained relaxations remained similar during this period. Vasoactive intestinal polypeptide-induced relaxations were also similar in the 3 age groups. 5. These results show that the sensitivity of the gastric fundus to acetylcholine decreases from 2 weeks to 8 weeks postnatally, while the importance of the nitrergic innervation increases during this period.