1. Changes in intracellular Ca2+ concentration ([Ca2+]1) induced by activation of GABAA receptors (synaptic stimulation or application of the GABAA agonist isoguvacine) were studied on pyramidal cells and interneurons from hippocampal slices of rats from two age groups (postnatal days (P) 2-5 and P12-13) using the fluorescent dye fluo-3 and a confocal laser scanning microscope. Cells were loaded with the dye either intracellularly, using patch pipettes containing fluo-3 in the internal solution, or extracellularly, using pressure pulses applied to an extracellular pipette containing the permeant dye fluo-3 AM. 2. Interneurons and pyramidal cells from P2-5 slices loaded with fluo-3 AM responded by an increase in [Ca2+]i to isoguvacine and to glutamate, in contrast to cells from P12-13 slices which responded to glutamate but not to isoguvacine. In the mammalian adult central nervous system, GABA postsynaptically localized GABAB receptors activate (y-aminobutyric acid) is the main inhibitory neuro-potassium conductances or decrease calcium currents transmitter, acting on two main classes of

We report here the technique for detection and measurement of the temperature changes in single cells using a recently devised microthermometer (a glass micropipette filled with the thermosensitive fluorescent dye Europium (III) thenoyltrifluoroacetonate trihydrate). We found that the heat production in a single HeLa cell occurred with some time delay after the ionomycin-induced Ca(2+) influx from the extracellular space. The time delay inversely depended on extracellular [Ca(2+)], and the increase in temperature was suppressed when Ca(2+)-ATPases were blocked by thapsigargin. These observations strongly suggest that the enzymatic activity of Ca(2+)-ATPases in endoplasmic reticulum leads to the heat production. This study has therefore paved the way for studying the thermogenesis at the single-cell level.

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1. Intracellular recordings were made from adult and neonatal rat hippocampal slices to study the postnatal development of GABAB-mediated inhibition in CA3 pyramidal neurons. 2. In the presence of glutamatergic receptor antagonists, direct electrical stimulation of the interneurons induced a biphasic GABAA- and GABAB-mediated inhibitory postsynaptic potential in adult [postnatal day (P) 30-P40] and young (P6-P8) CA3 pyramidal neurons. In contrast, in pups (P0-P3), electrical stimulation only induced a bicuculline-sensitive depolarizing GABAA synaptic potential. 3. The outward postsynaptic currents generated by bath-applications of baclofen (30 microM, 30 s) at P3 (78 +/- 60 pA, mean +/- SE) were 4 to 5 times smaller than those evoked between P6 (329 +/- 32 pA) and P30 (412 +/- 44 pA). At P0, baclofen failed to induce a postsynaptic current. 4. The outward currents generated by serotonin (50 microM, 30 s) and the A1 receptor agonist N-cyclopentyladenosine (40 microM, 30 s) ranged between 0 and 50 pA at P3 and between 200 and 400 pA at P6 and P30 (holding potential = -60 +/- 2 mV). 5. In the presence of potassium channel blockers, the amplitude of calcium current elicited by a depolarizing voltage step command (1 s) from a holding potential of -60 mV to a test potential of 0 mV was 2 +/- 0.15 nA at P6 (n = 9) and 0.73 +/- 0.14 nA at P3 (n = 8). Baclofen reversibly reduced the amplitude of calcium currents in young rats but not in pups. 6. Baclofen reversibly reduced the amplitude of the evoked GABAA-mediated and glutamatergic synaptic events at all developmental stages. These effects were dose dependent and antagonized by P-alpha 3-aminopropyl-P-diethoxymethyl-phosphinic acid (CGP) 35348 (500 microM). 7. We conclude that postsynaptic GABAB-mediated inhibition is absent or minimal during the first postnatal days in the CA3 region. In contrast, presynaptic GABAB inhibition is present at birth. We discuss the mechanisms and physiological consequences of these observations.

In the adult central nervous system, GABAergic synaptic inhibition is known to play a crucial role in preventing the spread of excitatory glutamatergic activity. This inhibition is achieved by a membrane hyperpolarization through the activation of postsynaptic gamma-aminobutyric acidA (GABAA) and GABAB receptors. In addition, GABA also depress transmitter release acting through presynaptic GABAB receptors. Despite the wealth of data regarding the role of GABA in regulating the degree of synchronous activity in the adult, little is known about GABA transmission during early stages of development. In the following we report that GABA mediates most of the excitatory drive at early stages of development in the hippocampal CA3 region. Activation of GABAA receptors induces a depolarization and excitation of immature CA3 pyramidal neurons and increases intracellular Ca2+ ([Ca2+]i)] during the first postnatal week of life. During the same developmental period, the postsynaptic GABAB-mediated inhibition is poorly developed. In contrast, the presynaptic GABAB-mediated inhibition is well developed at birth and plays a crucial role in modulating the postsynaptic activity by depressing transmitter release at early postnatal stages. We have also shown that GABA plays a trophic role in the neuritic outgrowth of cultured hippocampal neurons.

1. The effects of brief applications of growth hormone-releasing hormone (GHRH) to male rat somatotrophs in culture were analysed with the perforated patch clamp technique to record changes in potential or with fura-2 imaging techniques to measure variations of cytosolic Ca2+ concentration ([Ca2+]1). 2. Silent somatotrophs (n = 61) had a mean resting potential of -37 + 1 mV and a mean basal [Ca2+]. of 30 + 4 nM. Brief GHRH applications (30 nM, 40 s) triggered rhythmic action potentials (23-6 + 0 9 mV, 613 + 82 ms, 0X21 + 0-02 Hz) and [Ca2+], increase (to 352 + 30 nM) followed by rhythmic [Ca2+]i transients (to 138 + 6 nM) that persisted up to 90 min after the last GHRH application. Both action potentials and [Ca2+], transients were totally and reversibly blocked by removing external Ca2P or Nae or by adding inorganic Ca2+ channel blockers or nifedipine (3 uM).3. Somatostatin (1-300 nM), carbamylcholine (0 1-1 /M) and muscarine (0 1-1 jM) each had a dose-dependent inhibitory effect, from a decrease of Ca2+ spike duration and frequency to a complete block of the GHRH-evoked action potentials. 4. The present results show that somatotrophs in culture have intrinsic membrane properties that allow them to sustain a pacemaker activity and subsequent long-lasting sequences of[Ca2+], oscillations triggered by short pulses of GHRH and inhibited by somatostatin and muscarinic agonists.Pulsatile growth hormone (GH) secretion by somatotrophs is a complex process that includes control by at least two hypothalamic factors with opposite actions, the GH-releasing hormone (GHRH) and somatostatin, the GH-releaseinhibiting hormone (see review by Bertherat, Bluet-Pajot & Epelbaum, 1995). In addition, a variety of substances, including neurotransmitters, neuropeptides, growth factors and cytokines, endogenous to the anterior pituitary gland, can act as local modulators of somatotroph activity in a paracrine or autocrine manner (Houben & Denef, 1990). In the male rat, GH release is characterized by a striking regular ultradian rhythm composed of GH peaks of 1 h duration every 3-4 h (Tannenbaum & Martin, 1976). In vitro, brief (4-10 min) GHRH applications evoke a longlasting GH secretion in perifused anterior pituitary cells (Sheppard, Moor & Kraicer, 1985;Kato & Suzuki, 1986; Weiss, Cronin & Thorner, 1987). For example, 10 min pulses of GHRH (3 nM) every 3 h each evoke a 1 h rise in GH secretion (Weiss et al. 1987). Studies with intracellular and patch clamp recording techniques of the effects of GHRH application in vitro have provided contradictory results; GHRH evokes either a small and transient depolarization (Chen, Israel & Vincent, 1989a;Naumov, Herrington & Hille, 1994) perfused at a rate of 2-5 ml min-'. The Na+-free solution was A prepared by substituting choline chloride or tris(hydroxymethyl) aminomethane (Tris) for NaCl in the standard solution. The low-Clsolution was prepared by substituting isethionic acid (sodium salt)for NaCl in the standard solution. The Ca2+-free solution was prepared by adding 1 mm EGTA to a Ca2+...

Somatotropes and GC cells, a GH-producing cell line, exhibit [Ca²⁺]_i oscillations that result from rhythmic Ca²⁺ action potentials. Determination of this operating mode required simultaneous recording of both parameters by fura-2 imaging and patch-clamp techniques. In order to test whether patch recording induces artificial alteration of the [Ca²⁺]_i oscillatory pattern, we recorded separately or simultaneously [Ca²⁺]_i and membrane potential. In the absence of any other stimulation, seal formation in patch-clamp recording evoked by itself a 2.5- to 4-fold persistent increase in basal [Ca²⁺]_i, speeded up their frequency (from 0.03–0.17 to 0.4 Hz) and changed their pattern to a tonic mode. Patch-induced [Ca²⁺]_i increase was reproduced by mechanical contact between the pipette and the membrane. It was reduced by nifedipine, a blocker of L-type Ca²⁺ channels, as well as by removal of external Na⁺. It was fully blocked by external Ca²⁺ removal or gadolinium. All patch-clamp-induced perturbations were reversed by membrane hyperpolarization. We propose that patch-clamp recording evokes Ca²⁺ entry through L-type Ca²⁺ channels either directly, or indirectly via membrane depolarization. This shows that patch recordings in endocrine cells showing mechanosensitivity have to be interpreted with caution, and explains why long-lasting patch recordings are so difficult to obtain.