Calcium currents in retrogradely labeled pyramidal cells from rat sensorimotor cortex

Our previous studies of calcium (Ca(2+)) currents in cortical pyramidal cells revealed that the percentage contribution of each Ca(2+) current type to the whole cell Ca(2+) current varies from cell to cell. The extent to which these currents are modulated by neurotransmitters is also variable. This study was directed at testing the hypothesis that a major source of this variability is recording from multiple populations of pyramidal cells. We used the whole cell patch-clamp technique to record from dissociated corticocortical, corticostriatal, and corticotectal projecting pyramidal cells. There were significant differences between the three pyramidal cell types in the mean percentage of L-, P-, and N-type Ca(2+) currents. For both N- and P-type currents, the range of percentages expressed was small for corticostriatal and corticotectal cells as compared with cells which project to the corpus callosum or to the general population. The variance was significantly different between cell types for N- and P-type currents. These results suggest that an important source of the variability in the proportions of Ca(2+) current types present in neocortical pyramidal neurons is recording from multiple populations of pyramidal cells.     

Simultaneous visualization of chromatolytic neurons and neurons retrogradely labeled with horseradish peroxidase

A method is described for visualization of neurons retrogradely labeled with horseradish peroxidase (HRP) in celloidin-embedded brain slabs. The preservation of cellular detail obtained with this technique facilitates (1) accurate delimination of nuclei or laminae in which HRP-positive neurons are found and (2) simultaneous identification of cells of origin of two central fiber systems, by combining the retrograde transport of HRP and the retrotrade degeneration technique. The latter approach has been used in adult cats and in kittens to identify cortical neurons which project to the dorsal column nuclei and to the spinal cord.     

Sodium currents in neurons from the rostroventrolateral medulla of the rat

Rapidly inactivating and persistent sodium currents have been characterized in acutely dissociated neurons from the area of rostroventrolateral medulla that included the pre-B?tzinger Complex. As demonstrated in many studies in vitro, this area can generate endogenous rhythmic bursting activity. Experiments were performed on neonate and young rats (P1-15). Neurons were investigated using the whole cell voltage-clamp technique. Standard activation and inactivation protocols were used to characterize the steady-state and kinetic properties of the rapidly inactivating sodium current. Slow depolarizing ramp protocols were used to characterize the noninactivating sodium current. The "window" component of the rapidly inactivating sodium current was calculated using mathematical modeling. The persistent sodium current was revealed by subtraction of the window current from the total noninactivating sodium current. Our results provide evidence of the presence of persistent sodium currents in neurons of the rat rostroventrolateral medulla and determine voltage-gated characteristics of activation and inactivation of rapidly inactivating and persistent sodium channels in these neurons.     

Specific actions of cyanide on membrane potential and voltage-gated ion currents in rostral ventrolateral medulla neurons in rat brainstem slices

The present study examined specific effects of sodium cyanide (CN) on the membrane potential (MP), spontaneous discharge (SD) and voltage-gated ion current of the identified bulbospinal rostral ventrolateral medulla (RVLM) neuron in the rat pup brainstem slice. 125 microM CN rapidly depolarized MP in the RVLM neuron by 11.6 mV as well as enhanced the SD rate by 300%. In contrast, the same dose of CN immediately hyperpolarized unlabeled, non-RVLM neurons by 4.8 mV. 50 microM CN did not significantly affect voltage-gated Ca(++) or A-type K(+) currents. The same concentration of CN, however, rapidly and reversibly suppressed voltage-gated Na(+) currents and sustained outward K(+) currents in the RVLM neuron by 22.5% and 23%, respectively. Tetraethylammonium could mimic the effect of CN on MP, SD and sustained K(+) current in the RVLM neuron. It is concluded that: (1) like that from the adult rat, the rat pup bulbospinal RVLM neuron can be selectively and rapidly excited by CN; (2) the hypoxia-sensitive, sustained outward K(+) channel may play an important role in the acute hypoxia-induced excitation of the RVLM neurons.     

Identification of cerebellar corticovestibular neurons retrogradely labeled with horseradish peroxidase.

The projection from the cerebellar cortex of the anterior lobe to the vestibular nuclei has been studied in adult cats by using the retrograde axonal transport of horseradish peroxidase. The corticocerebellar projection to the vestibular nuclei, namely to the lateral vestibular nucleus of Deiters, originates from Purkinje cells located within a narrow longitudinal zone of the ipsilateral vermis. This cortical zone has an average medio-lateral dimension of 0.4–0.6 mm, and extends laterally to the midline. with its medial border being located on the average 0.5–0.8 mm lateral to the midsagittal plane within lobuli I–V (ventral part); this distance, however, increases to 1.5–1.6 mm at the level of the dorsalmost part of lobule V. The presence of a narrow medial zone and a larger lateral zone in the cerebellar anterior lobe, which did not contain labeled Purkinje neurons, suggests that these cortical areas project to cerebellar nuclei rather than to the vestibular nuclei.These findings confirm the principle of longitudinal organization of the corticofugal projection from the cerebellum, and indicate that this projection is arranged in a discrete and subtle way. The results obtained are discussed with particular regard to the problem of the selective afferent inputs impinging on the longitudinal corticocerebellar zone projecting to the lateral vestibular nucleus as well as to the possible influences exerted on this zone by the different inputs impinging on the neighboring cortical compartments.     

Response properties of whisker-associated trigeminothalamic neurons in rat nucleus principalis

Nucleus principalis (PrV) of the brain stem trigeminal complex mediates the processing and transfer of low-threshold mechanoreceptor input en route to the ventroposterior medial nucleus of the thalamus (VPM). In rats, this includes tactile information relayed from the large facial whiskers via primary afferent fibers originating in the trigeminal ganglion (NV). Here we describe the responses of antidromically identified VPM-projecting PrV neurons (n = 72) to controlled ramp-and-hold deflections of whiskers. For comparison, we also recorded the responses of 64 NV neurons under identical experimental and stimulus conditions. Both PrV and NV neurons responded transiently to stimulus onset (ON) and offset (OFF), and the majority of both populations also displayed sustained, or tonic, responses throughout the plateau phase of the stimulus (75% of NV cells and 93% of PrV cells). Average ON and OFF response magnitudes were similar between the two populations. In both NV and PrV, cells were highly sensitive to the direction of whisker deflection. Directional tuning was slightly but significantly greater in NV, suggesting that PrV neurons integrate inputs from NV cells differing in their preferred directions. Receptive fields of PrV neurons were typically dominated by a "principal" whisker (PW), whose evoked responses were on average threefold larger than those elicited by any given adjacent whisker (AW; n = 197). However, of the 65 PrV cells for which data from at least two AWs were obtained, most (89%) displayed statistically significant ON responses to deflections of one or more AWs. AW response latencies were 2.7 +/- 3.8 (SD) ms longer than those of their corresponding PWs, with an inner quartile latency difference of 1-4 ms (+/-25% of median). The range in latency differences suggests that some adjacent whisker responses arise within PrV itself, whereas others have a longer, multi-synaptic origin, possibly via the spinal trigeminal nucleus. Overall, our findings reveal that the stimulus features encoded by primary afferent neurons are reflected in the responses of VPM-projecting PrV neurons, and that significant convergence of information from multiple whiskers occurs at the first synaptic station in the whisker-to-barrel pathway.     

Ionic currents in the somatic membrane of rat dorsal root ganglion neurons —III. Potassium currents

Potassium transmembrane currents induced by membrane depolarization have been studied on isolated dorsal root ganglion neruons of 5–10 day-old rats using the voltage-clamp technique. The neurons were intracellularly dialysed with solutions containing a fixed amount of K⁺ ions, and the correspondence between the reversal potentials of the measured currents and the theoretical potassium equilibrium potential was determined. Sodium and calcium transmembrane currents were eliminated by replacement of Na⁺ ions in the extracellular solution and by introduction of fluoride into the cell.In all cells studied, the total potassium current could be separated into two components—fast and slow (I_K^f and I_K^sby changing the holding potential level. I_K^fwas inactivated comparatively fast obeying first-order kinetics. The dependence h_∝ (V) for this current was S-shaped with meanV₁₂ = ?75 mV. Therefore, this current could be almost completely switched off at holding potentials more positive than ?50 mV. On the contrary, the inactivation of I_K^s developed very slowly even at stronger depolarizing potential shifts. The mean activation time constants calculated on the basis of Hodgkin-Huxley model for potassium currents were 0.5 ms at zero testing potential for I_K^f and 40 ms at + 30 mV for I_K^s.The reversal potential for I_K^f determined from instantaneous current-voltage characteristics was close to the equilibrium potential for a potassium electrode. The reversal potential for I_K^s was shifted in the depolarizing direction by about 25 mV indicating lower selectivity of the corresponding channels.     

Hypothalamic neurons projecting to the rat caudal medulla oblongata, examined by immunoperoxidase staining of retrogradely transported horseradish peroxidase

Horseradish peroxidase (HRP), injected into the rat caudal medulla oblongata, was detected by immunoperoxidase staining in 120 microns frozen sections, allowing examination of both the distribution and morphology of transporting neurons. In the hypothalamus, several groups of HRP-labeled neurons could be distinguished on the basis of location of the neurons, neural cell size and morphology of the neural processes. Most HRP-labeled neurons were found in the posterior half of the hypothalamus, although scattered single neurons were present as far rostral as the anterior hypothalamus and preoptic area. Prominent groups of HRP-labeled neurons were found in the paraventricular, dorsomedial and arcuate nuclei, near the fornix at two separate levels, and in the lateral posterior hypothalamus. Based on comparison with peptide immunohistochemistry it seems likely that many magnocellular oxytocin, vasopressin and neurophysin neurons in the paraventricular nucleus, and a few ACTH/beta-endorphin neurons in the arcuate nucleus may project to the caudal medulla oblongata.     

Voltage-dependent currents prolong single-axon postsynaptic potentials in layer III pyramidal neurons in rat neocortical slices

1. Using isolated slices of rat cingulate and sensorimotor cortex, intracellular recordings were obtained from pyramidal neurons in layer III. Simultaneous extracellular recordings were obtained from neurons in ventral layer III and layer IV. Spike-triggered averaging was employed to investigate synaptic connections from neurons in layers III/IV to pyramidal cells in layer III. 2. Of 701 simultaneously recorded pairs of neurons, comprising 699 extracellularly and 128 intracellularly recorded neurons, synaptic connections were demonstrated in 30 pairs. Of these, 29 were excitatory postsynaptic potentials (EPSPs) and 1, an inhibitory postsynaptic potential (IPSP). Single-axon EPSPs with a wide variety of amplitudes were recorded: the range recorded at membrane potentials between -68 and -72 mV was 0.079-2.3 mV. Comparing recordings obtained from different cells, EPSP amplitude was found to be independent of both the membrane resistance of the postsynaptic neuron and the EPSP time course; i.e., the largest EPSPs were not necessarily those recorded from neurons with the highest input resistance, nor those with the briefest time course. 3. Shape indices: width at half amplitude and rise-time, indicative of both proximal and distal synaptic locations were obtained. Normalized rise-times were between 0.1 and 2 times the membrane time constant and half-widths between 0.8 and 20 times. 4. The majority of postsynaptic neurons displayed nonlinear voltage relations typical of pyramidal neurons, and the contribution to EPSP shape of voltage-dependent currents was investigated. EPSP amplitude and duration were found to be dependent on membrane potential. The majority of single-axon EPSPs (26 of 29), increased in amplitude and duration with membrane depolarization over the range -95 - -50 mV, despite the significant decrease in driving force for the EPSP that would be expected to accompany such large depolarizations. This increase coincided with an increase in the amplitude of voltage responses to small injected current pulses. 5. It is concluded that the amplitude and time course of single-axon EPSPs recorded in cortical pyramidal somata are affected not only by the amplitude of the postsynaptic current and the location(s) of the synapse(s) relative to the soma, but also by voltage-dependent currents. The possibility that the increase in amplitude and duration of these EPSPs with membrane depolarization is due to N-methyl-D-aspartate receptor involvement is discussed.     

Ionic currents of morphologically distinct peptidergic neurons in defined culture.

1. The X-organ sinus gland is a major peptidergic neurosecretory system in Crustacea, analogous to the vertebrate hypothalamoneurohypophyseal system. Neuronal somata isolated from the crab (Cardisoma carnifex) X-organ and maintained in primary culture in unconditioned, fully defined medium show immediate regenerative outgrowth. Outgrowth occurring as broad lamellipodia ("veiled") distinguishes neurons consistently showing crustacean hyperglycemic hormone immunoreactivity. Neurons that are immunoreactive against molt-inhibiting hormone and red pigment concentrating hormone antisera give rise to branched neurites ("branched"). 2. The whole-cell variation of the patch-clamp technique was used to study the electrophysiology of these two cell types 24-48 h after plating. Under current clamp, only veiled neurons fired overshooting action potentials either spontaneously or in response to depolarization. 3. Under voltage clamp, net current was predominantly outward. When solutions that suppressed outward current were used, only veiled neurons showed significant inward current. These included a tetrodotoxin (TTX)-sensitive Na current and a slow (time to peak 6-10 ms at 0 mV) Cd-sensitive Ca current (ICa) that was activated at potentials less than -30 mV, was maximal at 0 to +20 mV, and did not reverse at potentials up to +60 mV. 4. In TTX, the form of the Ca current I(V) curve was unchanged by changes of holding potential between -40 and -80 mV, and 75-100% of ICa was available from -40 mV. 5. ICa inactivated slowly and incompletely. Analysis with two-pulse regimes suggested that both inactivation and facilitation mechanisms were present. 6. Outward current was examined in the presence and absence of 0.5 mM Cd2+ (1 microM TTX was always present in the external medium). Cd2+ ions slightly reduced the peak outward current, usually by less than 10% (Vc = -10 to +20 mV; Vh = -80 mV). All additional observations were in the presence of TTX and Cd2+. 7. Both cell types expressed a 4-aminopyridine (4-AP)-sensitive transient current, analogous to IA, and a slower-rising (minimum time to peak 20 ms), sustained current that was partially sensitive to tetraethylammonium, analogous to IK. 8. The mean Vh at which IA was half inactivated was -46 mV, and the mean time constant for removal of inactivation was 46 ms.(ABSTRACT TRUNCATED AT 400 WORDS)     

A subpopulation of dorsal raphe nucleus neurons retrogradely labeled with cholera toxin-B injected into the inner ear

Previous studies have shown that: (1) raphe neurons respond to acoustic and vestibular stimuli, some with a latency of 10–15 ms; (2) alterations of the raphe nuclei alter the acoustic startle reflex; (3) the dorsal raphe nucleus (DRN) is the major source of serotonergic neurons; and (4) approximately 57% of the DRN neurons are nonserotonergic. In the present study, cholera toxin subunit-B (CTB) was injected into cat cochleas, and the brain tissue was examined after a survival period of 5–7 days. Aside from neurons which were known to project to the inner ear, i.e., olivocochlear and vestibular efferent neurons, a surprising new finding was made that somata of a subpopulation of DRN neurons were intensely labeled with CTB. These CTB-labeled neurons were densely distributed in a dorsomedian part of the DRN with some in a surrounding area outside the DRN. The present results suggest that a novel raphe-labyrinthine projection may exist. A future study of anterograde labeling with injections of a tracer in the DRN will be needed to establish the existence of a raphe-labyrinthine projection more thoroughly. A raphe-labyrinthine descending input, together with an ascending input from the inner ear to the DRN through intervening neurons, such as the juxta-acousticofloccular raphe neurons (JAFRNs) described by Ye and Kim, may mediate a brain stem reflex whereby a salient multisensory (including auditory and vestibular) stimulus may alter the sensitivity of the inner ear. As a mammal responds to a biologically important auditory-vestibular multisensory event, the raphe projections to the inner ear and other auditory and vestibular structures may enhance the mammal's ability to localize and recognize the sound and respond properly. The raphe-labyrinthine projection may also modulate the inner ear's sensitivity as a function of the sleep–wake arousal state of an organism on a slower time course.     

Neurons sensitive to pH in slices of the rat ventral medulla oblongata

The effects of extracellular pH changes on neurons in slices of the rat ventral medulla oblongata were investigated by extracellular recording. Changes in discharge rate were correlated with pH changes in the tissue next to the recorded cell, as measured by H⁺-selective microelectrodes. pH was altered by varying the bicarbonate concentration ([HCO₃ ^–]) in the superfusion solution. In 136 out of 316 neurons, the number of spontaneous or electrically evoked discharges per unit time increased with decreasing pH and decreased with increasing pH. Changes of only 0.01–0.04 pH unit were effective in these pH-sensitive neurons. The response was transient; the discharge rate returned to the control value within a few minutes. The pH sensitivity persisted in the presence of 0.5 M atropine, 20 M bicuculline and after replacing Ca²⁺ by Mg²⁺ in the superfusion solution to reduce synaptic transmission. The response to the same pH decrease was stronger when increasing PCO₂ than when reducing [HCO₃ ^–]₀. The pH-induced response significantly increased during hypoxia. The results show that in the ventral medulla oblongata neurons exist that transiently respond to small decreases and increases of pH. The pH sensitivity is an intrinsic property of these neurons; it is not due to a synaptic mechanism but is modulated by PCO₂ and PO₂.     

Pharmacological characterization of glycine-gated chloride currents recorded in rat hippocampal slices

An inhibitory role for strychnine-sensitive glycine-gated chloride channels (GlyRs) in mature hippocampus has been overlooked, largely due to the misconception that GlyR expression ceases early during development and to few functional studies demonstrating their presence. As a result, little is known regarding the physiological and pharmacological properties of native GlyRs expressed by hippocampal neurons. In this study, we used pharmacological tools and whole cell patch-clamp recordings of CA1 pyramidal cells and interneurons in acutely prepared hippocampal slices from 3- to 4-wk old rats to characterize these understudied receptors. We show that glycine application to recorded pyramidal cells and interneurons elicited strychnine-sensitive chloride-mediated currents (I(gly)) that did not completely desensitize in the continued presence of agonist but reached a steady state at 45-60% of the peak amplitude. Additionally, the inhibitory amino acid, taurine, which has been shown to activate GlyRs in other systems, activated GlyRs expressed by both pyramidal cells and interneurons, although with much less potency than glycine, having an EC(50) 10-fold higher. To examine the potential subunit composition of hippocampal GlyRs, we tested the effect of the GABA(A) receptor antagonist, picrotoxin, on I(gly) recorded from both cell types. At low micromolar concentrations of picrotoxin (< or =100 microM), which selectively block alpha homomeric GlyRs, I(gly) was partially attenuated in both cell types, indicating that alpha homomeric receptors are expressed by pyramidal cells and interneurons. At picrotoxin concentrations < or =1 mM, approximately 10-20% of the whole cell current remained, suggesting that alphabeta heteromeric GlyRs are also expressed because this subtype of GlyR is relatively resistant to picrotoxin antagonism. Finally, we examined whether hippocampal GlyRs are modulated by zinc. Consistent with previous reports in other preparations, zinc elicited a bidirectional modulation of GlyRs, with physiological zinc concentrations (1-100 microM) increasing whole cell currents and concentrations >100 microM depressing them. Furthermore, the same concentration of zinc that potentiates I(gly) suppressed currents mediated by the N-methyl-D-aspartate subtype of the glutamate receptor. Thus we provide a pharmacological characterization of native GlyRs expressed by both major neuron types in hippocampus and show that these receptors can be activated by taurine, an amino acid that is highly concentrated in hippocampus. Furthermore, our data suggest that at least two GlyR subtypes are present in hippocampus and that GlyR-mediated currents can be potentiated by zinc at concentrations that suppress glutamate-mediated excitability.     

Morphology,response properties,and collateral projections of trigeminothalamic neurons in brainstem subnucleus interpolaris of rat

Summary Intracellular recording, electrical stimulation and horseradish peroxidase (HRP) injection techniques were used to delineate the structural and functional characteristics of trigeminothalamic projection neurons in subnucleus interpolaris of the trigeminal brainstem nuclear complex in rat. Eleven such neurons were successfully characterized and recovered. All were medium to large multipolar neurons in the ventral part of interpolaris and all except one also projected to the superior colliculus. Six of these cells also sent axon collaterals to subnucleus principalis and the medullary parvicellular reticular formation and had local collaterals within interpolaris. None of these trigeminothalamic cells were antidromically activated from the cerebellum. All but one of the recovered cells were responsive to deflection of any one of a number (4–19) of vibrissae. The remaining cell was discharged by displacement of mystical guard hairs. Analysis of electrophysiological and anatomical data revealed significant correlations between receptive field size and dendritic area, thalamic conduction latency and axon diameter, and number of targets innervated and axon diameter.     

ASIC-like, proton-activated currents in rat hippocampal neurons

The expression of mRNA for acid sensing ion channels (ASIC) subunits ASIC1a, ASIC2a and ASIC2b has been reported in hippocampal neurons, but the presence of functional hippocampal ASIC channels was never assessed. We report here the first characterization of ASIC-like currents in rat hippocampal neurons in primary culture. An extracellular pH drop induces a transient Na⁺ current followed by a sustained non-selective cation current. This current is highly sensitive to pH with an activation threshold around pH 6.9 and a pH_0.5 of 6.2. About half of the total peak current is inhibited by the spider toxin PcTX1, which is specific for homomeric ASIC1a channels. The remaining PcTX1-resistant ASIC-like current is increased by 300 μ m Zn²⁺ and, whereas not fully activated at pH 5, it shows a pH_0.5 of 6.0 between pH 7.4 and 5. We have previously shown that Zn²⁺ is a co-activator of ASIC2a-containing channels. Thus, the hippocampal transient ASIC-like current appears to be generated by a mixture of homomeric ASIC1a channels and ASIC2a-containing channels, probably heteromeric ASIC1a+2a channels. The sustained non-selective current suggests the involvement of ASIC2b-containing heteromeric channels. Activation of the hippocampal ASIC-like current by a pH drop to 6.9 or 6.6 induces a transient depolarization which itself triggers an initial action potential (AP) followed by a sustained depolarization and trains of APs. Zn²⁺ increases the acid sensitivity of ASIC channels, and consequently neuronal excitability. It is probably an important co-activator of ASIC channels in the central nervous system.     

Ionic currents in the somatic membrane of rat dorsal root ganglion neurons-I. Sodium currents

Measurements of sodium transmembrane ionic currents evoked by depolarizing shifts in membrane potential have been performed on isolated dorsal root ganglion neurons of 5–10-day-old rats. Potassium currents were eliminated by dialysing the neurons with potassium-free solutions. In 10–15% of investigated neurons a tetrodotoxin-resistant component has been revealed in the sodium inward current which differs in its potential-dependent and kinetic characteristics from the main tetrodotoxinsensitive one. The activation kinetics of the tetrodotoxin-sensitive sodium current could be described by the Hodgkin-Huxley model using the cubic power of the m-variable, whereas the activation kinetics of the tetrodotoxin-resistant one can be described using only the square power of m. The time constants of activation and inactivation of the tetrodotoxin-resistant current were about ten times longer than those of the tetrodotoxin-sensitive current. The tetrodotoxin-resistant current was highly sensitive to all extracellular agents which are known as effective blockers of calcium channels (Co²⁺, Mn²⁺, Cd²⁺, D-600 and its derivatives). At the same time, the selectivity of the corresponding channels did not differ significantly from the selectivity of the tetrodotoxin-sensitive sodium channels. The sequence of relative permeabilities for univalent cations wasP_Na: P_Li: P_hydrazinium:P_NH4:P_{hydroxylammonium}:P_K = 1.0:0.79:0.43:0.33:0.25:0.18 for the tetrodotoxin-sensitive channels and 1.0:0.98:0.47:0.42:0.26:0.26 for the tetrodotoxin-resistant ones.Thus, the tetrodotoxin-resistant sodium channels combine some features of sodium (the selective filter) and calcium (gating mechanism and binding properties) channels.     

Ionic currents in the somatic membrane of rat dorsal root ganglion neurons-II. Calcium currents

The experiments have shown that the introduction of cyclic adenosine monophosphate, adenosine 5'-triphosphate and Mg²⁺ ions into dialysed isolated dorsal root ganglion neurons of 5–8 day-old rats not only prevents the rapid decline of calcium inward currents during the course of dialysis but restores to a considerable extent the calcium conductance. Introduction of adenosine 5'-triphosphate and Mg²⁺ has a much weaker stabilizing effect. This finding made it possible to separate and to investigate in detail the calcium current (I_Ca) in the somatic membrane of all investigated neurons. The maximal amplitude of I_Ca was proportional to the concentration of Ca²⁺ ions in the extracellular solution between 2 and 14mM; with higher concentration a saturation effect was observed. Replacement of Ca²⁺ by Ba²⁺ caused about a two-fold increase in the maximal amplitude of inward currents. Addition of Co²⁺, Mn²⁺, verapamil and related substances blocked the calcium current. The activation kinetics of I_Ca could be approximated by a modified Hodgkin-Huxley equation using a square power of the m-variable. The activation time constantτ_m changed in the range from 16 to 1.8 ms with testing potential change from ?40 to +20 mV. The inactivation of I_Ca was extremely slow; the half value of steady-state inactivation was observed at holding potential about ?60 mV. The potential-dependent and kinetic characteristics of the calcium currents obtained on several neurons from adult rats were similar to those for neurons of new-born ones.It is concluded that the somatic membrane of the rat neurons has a system of electrically-operated selective calcium channels, the normal functioning of which is dependent on intracellular cyclic nucleotide metabolism.