Physiological and morphological identification of hypothalamic magnocellular neuroendocrine cells in goldfish preoptic nucleus

Social control of neuronal soma size

Factors responsible for sexual maturation differ significantly among vertebrate species. In many, age is most important, whereas in others seasonal or social cues play a central role. Here we report that maturation in the African cichlid fish Haplochromis burtoni is socially controlled, and that this control includes regulation of soma growth in a population of preoptic neurons immunoreactive to gonadotropin-releasing hormone (irGnRH). Males reared in aquaria among fish of the same age mature sexually in about 3 months, whereas males reared in the presence of older, more aggressive conspecifics remain immature even at 5 months of age. Immature males display hypogonadism and have conspicuously undersized preoptic irGnRH neurons in comparison to those of mature siblings of the same age. This variable maturation rate increases the likelihood that individual males will survive to an age when they can successfully reproduce.

Neuronal and glial gap junctions in the goldfish preoptic area, a thin section and freeze-fracture study

In freeze-fracture, both large macular gap junctions and long thin gap junctions surrounded by a strand of tight junction were found on neurosecretory cells. Preoptic neurons show large areas of soma-to-soma apposition, but thin section showed no evidence for gap junctions between neuronal somata. Neurosecretory cell neurites formed parallel bundles in neuropil lateral to the nucleus, and gap junctions were found between the neurites. These junctions apparently correspond to macular junctions seen on neurosecretory elements in freeze-fracture. Some large macular gap junctions found in freeze-fracture presumably correspond to junctions seen between glial cells in thin section. However, glial membranes lacked characteristics distinguishing them from neuronal membranes. In one instance, a large apparent glial sheet process formed both macular and long thin gap junctions on different surfaces. The long thin gap junctions that were surrounded by a strand of tight junction were formed with a large neurosecretory cell soma. Extensive pinocytosis was observed at some membranes forming gap junctions.

Do antidromic latency jumps indicate axonal branching in nigrostriatal and hypothalamo-neurohypophysial neurons?

Neurons in many brain regions exhibit discontinuous decreases in antidromic latency with small increases in stimulating current. We used an electrophysiological test requiring a single stimulating electrode to determine whether these 'latency jumps' are due to shifts in the site of spike initiation to the same or different axon branches. Latency jumps in response to stimulation of the striatal terminal fields of substantia nigra, pars compacta neurons represent spike initiation on different branches while those seen in paraventricular neurons with pituitary stalk stimulation usually reflect a change in site on a single branch.

Patterns of spontaneous unit preoptic neurosecretory cell discharges in the rainbow trout, Salmo gairdneri

Extracellular antidromic potentials recorded from the neurosecretory cell body were characterized by the following criteria: constant latency, the ability to follow a high frequency rate of stimulation and the collision test. The latency of the antidromic potentials ranged from 12 to 24 ms (17.46 +/- 3.10 SD) which gave a mean conduction velocity of 0.19 m/s, typical of unmyelinated nerve fibers. Two components could be clearly distinguished in the antidromic potential. A small "A" spike which showed constant latency and a large "B" spike with a variable latency and amplitude. A delay of 6.5 ms between the two spikes could occur and sometimes the "B" spike was blocked leaving only the "A" spike. Four patterns of spontaneous activity seem to emerge: Type I (26% of units, M +/- SD = 0.77 +/- 0.32 sp/s) corresponds to a slow and irregular pattern of activity; Type II (28% of units, M = 1.58 +/- 0.47 sp/s) is hard to classify and may be related to an irregular bursting pattern of activity; Type III (28% of units, M = 2.59 +/- 1.19 sp/s) corresponds to a continuous pattern of activity; Type IV (18% of units) represents a rhythmic pattern of activity with an active phase of about 3 min (M = 2.42 +/- 0.90 min), a silent phase of about 4 min (M = 3.89 +/- 3.02 min) and a maximal frequency of unit discharge in the range 2-18 sp/s. No statistical differences exist for the mean dorsal aortic pressure (DAP) between the four types of neurosecretory cell activity.

An HRP study of afferent connections of the supracommissural ventral telencephalon and the medial preoptic area in himé salmon (landlocked red salmon, Oncorhynchus nerka)

The supracommissural ventral telencephalon and the medial preoptic area have been shown to play important roles in the sexual behavior of himé salmon (landlocked red salmon, Oncorhynchus nerka). In the present study, the sites of neurons projecting to these regions were examined by means of the retrograde horseradish peroxidase (HRP) tracing method. The morphology of neurons in these sites of origin was also studied by means of the Golgi method. The nucleus preopticus periventricularis and the rostral part of nucleus preopticus (NPP-rNPO) received bilateral projections from the middle parts of the area ventralis telencephali pars ventralis (Vv) and the area ventralis telencephali pars dorsalis (Vd), NPP and lateral part of the preoptic area (LPOA), ipsilateral projections from the caudal part of Vv, nucleus anterioris periventricularis (NAPv), nucleus ventromedialis thalami (NVM) at the level of the posterior commissure, nucleus lateralis tuberis pars medialis (NLTm), nucleus anterior tuberis (NAT), nucleus saccus vasculosus (NSV), nucleus recessus posterioris (NRP) and midbrain tegmentum (TG), and a projection from the nucleus posterior tuberis (NPT), which is situated on the midline of the brain. The area ventralis telencephali pars supracommissuralis and neighboring caudal ventral telencephalon (Vs-cV) received ipsilateral projections from almost all parts of the Vv, the middle and caudal parts of Vd, almost all parts of the NNP, the NPO at the level between the habenula and the posterior commissure, and the rostral part of the nucleus dorsomedialis thalami (NDM). The Vs-cV also received a projection from NPT. These findings seem to give anatomical bases for understanding the neural mechanisms involved in sexual behavior as well as neuroendocrine functions.

The organization of the diencephalon and the pretectum in the cichlid fish, Haplochromis burtoni

Although teleost fish comprise the largest vertebrate radiation, surprisingly little is known about the structure and development of their central nervous systems. Since teleosts are being used much more frequently as model systems in neurobiological research, particularly in understanding visual function, detailed information is needed about central nervous system structures and interconnections. By using the Bodian method with Nissl counterstaining we have analyzed the major nuclei in the diencephalon and pretectum of a cichlid fish, Haplochromis burtoni, which is dependent on vision for its survival. Although our results are broadly comparable with those from other teleost species, there are clear differences, particularly among the visual nuclei. By using animals of a range of sizes to confirm our descriptions we were able to identify possible developmental relationships among several nuclei.

Cytoarchitecture of the rat's supraoptic nucleus

There have been few Golgi studies dealing with the cytoarchitecture of the supraoptic nucleus (SON). This is due in part to resistance of supraoptic neurons to impregnation by Golgi methods. In this study, the structure of the SON was examined in normal S/D rats by using both Nissl and Golgi-silver methods. The purpose was to correlate shape, size and location of neurons within the SON as revealed by these two techniques. On the basis of size, neurons of the SON can be divided into 3 populations: greater than 200 micron2, (9%); 100-200 micron2, (64%); and less than 100 micron2, (27%). The larger neurons are located predominantly at mid-nuclear levels; the smaller at rostral and caudal levels of the nucleus. The perikarya of most SON neurons (64%) are only slightly elliptical in cross-section (L/W less than or equal to 2). The large neurons, however, tend to be more spherical whereas the smaller neurons are more elongated (L/W greater than or equal to 3). In Golgi preparations, a variety of randomly distributed bipolar and multipolar neurons were identified. One form of bipolar neuron had a large spherical or oval cell body that was intimately associated with blood vessels. Its thick, varicose dendrites usually lacked spines and were not extensively branched. A second form of bipolar neuron was distinguished by its smaller more fusiform cell body and lengthy dendrites which were often spinous and more extensively branched. Axons, when present emerged from the cell body or a proximal dendrite and were uniformly thin except for fusiform swellings along their length. Among multipolar neurons, the following variants were distinguished: spherical and polygonal neurons of various sizes with 3-5 dendrites and small triangular neurons with dendrites arising from each of the poles. The results of this study demonstrate the heterogeneity of the rat SON and of its neuronal components, some of which appear suited to function in a nonendocrine capacity, possibly as interneurons.

Functional-anatomical studies on sperm release evoked by electrical stimulation of the olfactory tract in goldfish

Sperm release was evoked by electrical stimulation of the olfactory tracts in male goldfish. Thresholds as low as 5 microA were obtained using suction electrodes while slightly higher currents were necessary using metal electrodes (lowest thresholds of 15-20 microA). Several control procedures were carried out to insure that current-spread to nearby structures was not responsible for the evoked responses. Testing olfactory tract stimulation following transection of one or more divisions of the olfactory tract revealed that connections to the olfactory bulb and pathways involving the lateral olfactory tract were not necessary for the stimulation effect, whereas the medial olfactory tract appears to be both sufficient and necessary for mediation of evoked sperm release. The results are discussed with respect to possible involvement of each of the 3 known functional components constituting the medial olfactory tract: (1) secondary olfactory afferents; (2) olfactory efferents; and (3) fibers of the terminal nerve. The possibility that female sex pheromones normally influence central sperm release mechanisms via pathways in the medical olfactory tract is also considered.

Supraoptic neurons in the rat hypothalamo-neurohypophysial explant: double-labeling with Lucifer Yellow injection and immunocytochemical identification of vasopressin- and neurophysin-containing neuroendocrine cells

By combining intracellular electrophysiology with double-labeled intracellular dye-marking and immunocytochemical identification of the same magnocellular neuroendocrine cell, we studied supraoptic neurons in the rat hypothalamo-neurohypophysial explant in vitro. This report examines neurophysiological and light microscopical features of vasopressin- and neurophysin-immunoreactive, pituitary-projecting supraoptic neurons.

Influences of the limbic system on hypothalamo-neurohypophysial system

(1) Effects of stimulations of various limbic structures (the olfactory bulb, olfactory tubercle, prepyriform cortex, endopyriform nucleus and various parts of amygdaloid nuclei) on the neurosecretory neurons in the supraoptic (SON) and paraventricular nuclei (PVN) of the hypothalamus were studied. All regions stimulated received strong inputs from the olfactory bulb. (2) Out of 195 "identified' neurosecretory neurons tested one-half or more (49-74%, depending on the structures stimulated) were inhibited by stimuli consisting of 1-3 short pulses. The inhibition occurred immediately after the stimulus in approximately one-fifty of all inhibited neurons, in the remaining four-fifths inhibition occurred after more than 20 ms latency. Inhibition of neurosecretory neuron activity lasted for several hundred milliseconds, often followed by clear post-inhibitory excitation or rebound. (3) In 23 neurons, a distinct "evoked' response of brief duration occurred with a 30 ms latency following stimulation of the lateral and medical amygdala, olfactory tubercle and prepyriform cortex. In another 17 neurons, a general increase in background activity with a longer latency (50-100 ms) occurred following stimulation of nearly all amygdaloid nuclei, olfactory tubercle and the pyriform cortex: lateral amygdala stimulation caused an excitation of the largest proportion of neurosecretory cells (30%) while none was excited by stimulation of the olfactory bulb and endopyriform cortex, except those occurring as post-inhibitory excitation. (4) There was a convergence of afferent impulses on single neurosecretory cells. A large proportion (42%) of the neurons received inputs from 2 to 4 limbic regions. (5) Neurosecretory cells which were influenced by limbic stimuli were also inhibited by baroreceptor activation and excited by osmotic stimulation. "Unidentified' neurons within SON and PVN and "atypical neurosecretory cells' (those responding to pituitary stalk stimulation with varying latencies) were also affected by the forebrain stimulation; some of these were also affected by an osmotic stimulus. A part of this group may send their axons to the median eminence.

Light- and electron-microscopic characterization of electrophysiologically-identified, horseradish peroxidase-injected magnocellular neuroendocrine cells in goldfish preoptic nucleus

We recorded intracellularly from neurons in the goldfish preoptic nucleus which were antidromically identified by electrical stimulation of the pituitary gland and marked by intracellular injection of horseradish peroxidase for subsequent localization. At the light-microscopic level, labeled neurons resembled profiles of Golgi-impregnated neurons and lay in the magnocellular portion of the preoptic nucleus. Densely labeled axons and dendrites projected to the lateral forebrain bundle, the medial forebrain bundle, fiber tracts in the preoptico-hypophysial tract, small blood vessels and capillaries, the ependymal lining of the third ventricle and toward the preoptic neurons. Occasionally, a lightly-labeled, large perikaryon lay adjacent to a large, heavily-labeled magnocellular neuron. Ultrastructural examination of these identified cells revealed dense reaction product in neuronal perikarya and processes. Heavily labeled perikarya had elaborate networks of endoplasmic reticulum, extensive Golgi apparatus, occasional somatic spines and infrequent axo-somatic contacts from unlabeled neurons. These labeled perikarya which were frequently in close somatic apposition with unlabeled profiles were sometimes adjacent to a large, lightly-labeled perikaryon. A thin glial sheath separated most labeled neurons and processes from brain capillary endothelium. Labeled dendrites had heavily labeled spines and axo-dendritic contacts from unlabeled neurons. Labeled axons abutted unlabeled-axons and -dendrites. Synaptic boutons innervating labeled structures always contained small clear synaptic vesicles and some boutons also contained large dense-core vesicles. These results demonstrate the complex connections of goldfish preoptic magnocellular neuroendocrine cells with other neurons, fiber systems, brain capillaries, ventricular ependyma and the pituitary and provide further support for non-endocrine as well as endocrine functions of magnocellular neurons.

A technique combining intracellular dye-marking, immunocytochemical identification and ultrastructural analysis of physiologically identified single neurons

A new method which produces an insoluble osmophilic polymer within Lucifer Yellow-injected neurons has allowed us to develop a technique for the ultrastructural examination of electrophysiologically characterized, immunocytochemically identified single neurons. In this initial report, we examine the light- and electron-microscopic features of neurophysin-containing, pituitary-projecting neurons in the goldfish nucleus.

Molecular mechanisms of general anaesthesia

This review aims to give a balanced view of the various mechanisms which have been proposed to explain the phenomenon of general anaesthesia on both a molecular and whole animal level. An attempt is made to interrelate these and produce one cohesive model.

Initial report on combined in vivo single cell recording and intracellular staining

This paper reports preliminary data obtained from the combination of extracellular single unit recording, microiontophoretic testing and intracellular staining of single neurons in the diencephalon of the anesthetized rat. Sixty neurons were recorded extracellularly and iontophoretically tested with glass multibarrelled micropipettes. Thirty-four of these neurons were identified by antidromic invasion from median eminence stimulation. Seventeen of these antidromically identified neurons were subsequently impaled with the micropipette and intracellularly stained with the fluorescent dye lucifer yellow-CH. The average diameter of the antidromically identified neuronal cell bodies was 7.4 microns. The iontophoretic response profiles of these stained neurons were similar to the profiles of non-stained antidromically identified neurons. Four of the remaining 26 neurons were synaptically activated from median eminence stimulation and were successfully marked with lucifer yellow. Average soma diameters of these neurons was 12.8 microns. Twenty-two neurons were not antidromically or orthodromically identified from median eminence stimulation. Three of these neurons were intracellularly stained with lucifer yellow and their soma diameters averaged 6.9 microns. Approximately 50% of all staining attempts, subsequent to extracellular recording and iontophoretic testing, were successful. The combination of these techniques is therefore a feasible approach to the in vivo study of the physiologic, pharmacologic and morphologic properties of single neurons.

Hypophysiotropic neurons in the goldfish hypothalamus demonstrated by retrograde transport of horseradish peroxidase

The horseradish-peroxidase (HRP) technique was used to visualize the cell bodies of axons projecting to the goldfish pituitary. Following intravenous injections of HRP, HRP reaction products were observed in axons of the rostral pars distalis, proximal pars distalis, neurointermediate lobe, pituitary stalk and in axons coursing from the pituitary into the hypothalamus. HRP-labelled cells in the brain were localized in two regions only - the nucleus preopticus (NPO) pars magnocellularis and pars parvocellularis, and the nucleus lateralis tuberis (NLT) of the hypothalamus. These observations suggest that the NPO and NLT are the source of the neurosecretory innervation of the goldfish pituitary.

Osmoreceptors or sodium receptors: an investigation into ADH release in the rhesus monkey

1. ADH secretion was studied in trained, preoperated conscious monkeys undergoing water diuresis after administration of isosmolar hypertonic solutions of different substances into any one of the following sites: (i) anterior third ventricle, (ii) the hypothalamus, just anterior to the third ventricle and (iii) common carotid artery. 2. Free water clearance was continuously monitored and the ADH released was measured by bio-assay on the same animals after administering graded doses of standard arginine vasopressin in a comparable manner. 3. Intraventricular infusions of hypertonic solutions of NaCl or Na acetate released significant amounts of ADH while sucrose or mannitol of comparable osmolality were ineffective. Graded increases in the concentration of NaCl infused into the c.s.f. resulted in secretion of ADH proportional to log Na concentration. 4. Infusion of the same hypertonic solutions into the anterior hypothalamus released ADH, though Na salts were more effective than the sugars. 5. Hypertonic solutions of NaCl, Na acetate, sucrose or mannitol were effective in releasing ADH when injected via the carotid artery, but hypertonic solutions of NaCl were significantly more effective than the other solutions. 6. These findings may be explained by the hypothesis that the 'osmoreceptors' of Verney are Na sensitive receptors composed of dendrites innervating the specialized ependyma of the anterior part of the third ventricle.

Functional and morphological studies of peptide-containing neuroendocrine cells in goldfish hypothalamus

We report the development of a double-label method which combines intracellular recording, dye-marking, and immunocytochemistry for the study of functional and morphological aspects of peptide-containing neurons in the magnocellular preoptic nucleus of the goldfish hypothalamus. Using multiple techniques, we distinguish three types of peptide-containing neurons: enkephalin (27%), isotocin (49%), and vasotocin (24%). Drawings of serial sections containing the dye-injected cells were the basis for subsequent reconstruction. These peptide-containing cells measure 14-56 micrometer in somata diameter, are unipolar, bipolar, or multipolar in somata shape and lie 6-244 micrometer from the ependymal lining of the preoptic recess of the third ventricle. Their electrophysiological properties match those of other mammalian and fish magnocellular neuroendocrine cells. This report confirms the one neuron, one hormone (peptide) hypothesis, supports synaptic over electrotonic coupling between peptidergic and adjacent hypothalamic neurons, and suggests that chemical and functional classification of single electrophysiologically and neuroanatomically studied central neurons is feasible technologically.

Intracellular recordings from the paraventricular nucleus in slices of rat hypothalamus

1. The electrical activity of thirty-five neurones in the lateral area of the paraventricular nucleus (p.v.n.) was recorded intracellularly in vitro from slices of rat hypothalamus. 2. Spontaneously occurring action potentials were observed in twenty-four of the neurones. The temporal pattern of action potentials was generally slow and irregular; occasionally some cells fired bursts of action potentials. 3. Depolarizations with a fast rising phase and slow decay occurred spontaneously in most cells. These depolarizations exhibited a wide range of amplitudes in each cell (up to 33 mV), showed temporal summation, and could serve as pre-potentials for spontaneously occurring action potentials. Presumably, these depolarizations were excitatory post-synaptic potentials (e.p.s.p.s.). 4. Depolarizing current injection could evoke action potentials. Extracellular stimuli dorsolateral to the fornix column occasionally elicited action potentials which had a short and invariant latency and which could respond to stimulation rates of 100 Hz. In some cases, extracellular stimuli in the same area evoked depolarizations which had long and variable latency and were similar to those occurring spontaneously. These two types of responses probably represent antidromic and orthodromic activation respectively. 5. Intracellular injections of horseradish peroxidase suggest that these recordings were obtained primarily, but not exclusively, from magnocellular neuroendocrine cells. This is consistent with previous anatomical studies on the location of magnocellular elements in p.v.n.

Intracellular dye-marked enkephalin neurons in the magnocellular preoptic nucleus of the goldfish hypothalamus

A method that combines intracellular recording, dye marking, and immunocytochemistry makes the study of functional and morphological aspects of enkephalin neurons in the magnocellular preoptic nucleus of the goldfish hypothalamus feasible. By use of multiple techniques, enkephalin neurons can be distinguished from other brain cells and can be reconstructed from drawings of serial sections containing the dye-injected opioid cells. These enkephalin cells and their processes measure 14-42 micron in somata diameter and are unipolar, bipolar, or multipolar. Their electrophysiological properties match those of other mammalian and fish magnocellular endocrine cells. This report confirms the one neuron-one hormone (peptide) hypothesis, supports synaptic over electronic coupling between enkephalin and adjacent hypothalamic neurons, and suggests that chemical and functional classification of single electrophysiologically and neuroanatomically studied central neurons can be achieved.

Isotocinergic neurons in the goldfish hypothalamus: physiological and morphological studies on chemically identified cells

Isotocinergic (IT) neurons show physiological and morphological characteristcs that are similar to those of the other preoptic neuroendocrine cells in the goldfish. Preoptic IT cells show resting membrane potentials of 20-55 mV, action potentials of up to 100 mV, and physiological evidence of axonal branching. Dye-marked IT cells measure 14-56 micrometers, their dendrites projecting to the ependyma and into the hypothalamic neuropil, their multiple beaded axons projecting to the pituitary. Indirect immunofluorescence identifies these dye-marked cells as IT. By combining electrophysiological, dye-marking and immunocytochemical techniques we can now, for the first time, study single, antidromically-identified peptidergic neurons of a specific type in vertebrate and invertebrate species.

Immunocytochemical identification of enkephalinergic neurons in the hypothalamic magnocellular preoptic nucleus of the goldfish, Carassius auratus

Our immunocytochemical investigation of the magnocellular neuroendocrine system in the goldfish hypothalamus reveals enkephalin (ENK)-containing neurons interspersed among the vasotocin (VT)- and isotocin (IT)-containing neurons of the preoptic nucleus. The perikarya of the ENK, VT, and IT neurons do not show distinct morphological differences at the level of light microscopy and are not located preferentially within the nucleus. Separate ENK, VT and IT fibers course laterally and ventrally through the hypothalamus as they descend toward the pituitary gland. All three fiber types form terminals around blood vessels in the neurohypophysis.

Morphological features of physiologically identified hypothalamic neurons as revealed by intracellular marking

In the in vitro slice preparation intracellular recordings and injections of procion yellow (PY) were made in neurons of the hypothalamus. Of these neurons, one medial preoptic-anterior hypothalamus (MPO-AH) and four arcuate-ventromedial hypothalamus (ARC-VM) neurons were driven by electrical stimulation of the median eminence area (ME). Two other MPO-AH and five other ARC-VM neurons were driven by stimulation of the stria terminalis (ST). On the basis of the PY injections two morphologically distinct cell types were delineated: a larger multipolar cell type with a polygonal perikaryon was found with equal frequency in the MPO-AH and the ARC-VM. A smaller fusiform cell type was encountered mainly in the ARC-VM. On the secondary dendrites of both cell types spine-like appendages were seldom seen, but dendritic swellings were common. Some of the dendrites projected to capillaries in both areas and presumably contacted them. The axons were usually tortuous and could only be traced a short distance.

Comparison of firing patterns and sensory responsiveness between supraoptic and other hypothalamic neurons in the unanesthetized sheep

Adult Southdown ewes were surgically prepared with pituitary stimulating electrodes, carotid and jugular cannulae, and a cranial platform-cylinder arrangement for chronic single unit recording. Isolated neurons (n = 112) in the region of the supraoptic nucleus (SON) were identified by pituitary stalk stimulastion as AD + (antidromically invaded) SON neuroendocrine cells (n = 75) or AD--(not antidromically invaded) SON neurons (n = 37). Spontaneous firing pattern distribution and sensory evoked behavior of these SON region neurons were compared with activity recorded from 112 randomly located non-identified neurons of extra-SON areas of the hypothalamus. Spontaneous discharge activity was categorized into six distinct firing pattern types: continuously active slow (CAS), continuously active fast (CAF), continuously active bursting (CAB), continuously active regular (CAR), low frequency bursting (LFB), and high frequency bursting (HFB). These 6 firing pattern types were characterized by computer analysis and their mean order independent statistical parameters compared. Bursting discharge patterns (LFB, HFB, and CAB) were compared with respect to mean burst duration, burst mean firing rate, and interburst interavls. Ninety-three per cent of all neurons maintained a stable discharge pattern in the absence of apparent stimuli. Occasionally CAS and CAF neurons spontaneously generated spike clusters sufficient to give the transient appearance of a bursting discharge pattern and LFB neurons lapsed spontaneously into CAS acitivity. All 6 firing pattern types recorded from non-identified extra-SON neurons were also recorded in the SON region. However, spontaneously discharging AD+ SON neurons exhibited only continuously active slow (CAS), continuously active fast (CAF), and low frequency bursting (LFB) activity. The total absence of high frequency bursting (HFB), continuously active regular (CAR), and continuously active bursting (CAB) patterns of discharge from AD+ SON neurons suggests that AD- SON neurons exhibiting these firing patterns may function as interneurons, pacemaker neurons, or receptor neurons. A significant number of LFB discharging neurons were recorded in widespread extra-SON regions of the hypothalamus, indicating this discharge pattern may not be unique to magnocellular neuroendocrine cells. AD+ SON LFB neurons sampled in this study demonstrated a significantly longer mean interburst interval (20.86 sec) compared to extra-SON LFB neurons (12.43 sec). No AD+ SON neuron tested was significantly sensitive to non-specific sensory arousal or sleep-waking state changes. In extra-SON areas of the hypothalamus, 11 of 75 neurons tested to sensory arousal and 6 of 19 neurons tested to sleep-waking changes responded with significant changes in mean firing rate (MFR); no significant difference between firing pattern types was demonstrated in arousal or sleep-waking sensitivity...

Reversal of the action of amino acid antagonists by barbiturates and other hypnotic drugs

1 The effects of pentobarbitone (PB) and other sedative/hypnotic drugs have been examined in relation to gamma-aminobutyric acid (GABA) in vitro on the superfused isolated superior cervical ganglion of the rat and in vivo on single units in the brain stem of the anaesthetized rat.2 PB, and other barbiturates, depolarized the ganglion in a dose-dependent manner (threshold concentration 100-300 muM, cf. GABA depolarization threshold 1 muM). The depolarization was reduced in the presence of the selective GABA antagonist (+)-bicuculline methochloride (Bic). Other non-barbiturate sedatives e.g. chlordiazepoxide, amitriptyline, promethazine at concentrations up to 2mM produced no depolarization.3 PB, tested at concentrations up to 80 muM, produced variable effects on the dose-response curve to GABA. On most occasions a slight potentiation occurred in responses to low concentrations of GABA (below 10 muM) coupled with a depression in the responses to concentrations of GABA greater than 10 muM.4 Superfusion with PB in the presence of Bic reversed the depression in the response to GABA produced by Bic. This reversal phenomenon occurred at concentrations of PB too low to depolarize the ganglion and was dependent not only on the concentration of PB but also on that of Bic.5 The reversal potency within an homologous series of barbiturates increased with the size of the alkyl substituent (R2) at C5 on the barbiturate ring. The most potent occurred when the substituent contained 5 carbon atoms (pentobarbitone and amylobarbitone); above this, activity decreased.6 PB reversed the effects of the other GABA antagonists, tetramethylenedisulphotetramine and isopropyl bicyclophosphate and also the non-selective antagonism produced by strychnine. A concomitant reduction by strychnine of responses to the cholinomimetic, carbachol, was not reversed by PB.7 Non-barbiturate sedative/hypnotics also reversed the GABA antagonism produced by Bic. The benzodiazepines were effective at lower concentrations than PB (chlordiazepoxide threshold concentration 0.5 muM, cf. PB 5 muM), however, they only produced a partial reversal even at concentrations much higher than the maximally effective concentration of PB.8 The Bic reversal effect of chloridazepoxide (and other benzodiazepines) lasted many hours after removal from the superfusion solution. By contrast the effect of PB lasted only 15-30 min after its removal.9 Chlordiazepoxide (30 muM) applied in the absence of Bic did not affect the response to GABA but did reduce the depression produced by the subsequent application of Bic even though the chlordiazepoxide had been removed 40 min earlier.10 In the rat brain stem in vivo PB, applied iontophoretically in amounts which neither decreased the spontaneous neuronal firing rate nor affected the response to GABA or glycine, reversed the GABA antagonism induced by iontophoretic application of Bic (in all 23 neurones tested). PB also reversed the antagonism produced by strychnine of responses to glycine although this was less readily observed (5 out of 14 neurones tested).11 Iontophoretic application of other barbiturates and chlordiazepoxide also reversed the effect of Bic. Chlordiazepoxide only produced a partial reversal, as in the isolated ganglion, and no reversal could be demonstrated with flurazepam.12 Intravenous administration of thiopentone (1.3 mg/kg) pentobarbitone (0.4-5.5 mg/kg) hexobarbitone (0.4-0.8 mg/kg) and clonazepam (0.1-0.2 mg/kg) also reversed the effect of iontophoretically applied Bic. The reversal by clonazepam was of much longer duration than that produced by the barbiturates.13 It is suggested that the reversal exhibited by PB and the other hypnotics may be explained by assuming that the amino acids and their antagonists bind to the membrane at separate sites. If the reversal agent has particular affinity only for the antagonist binding site then it may displace the antagonist without affecting the receptor.

Actions and interactions of dipropylacetate and penicillin on evoked potentials of excised prepiriform cortex of guinea pig

Slices from guinea pig brain containing the lateral olfactory tract (LOT) and the prepiriform cortex were studied in vitro. Field potentials, evoked by stimulation of the LOT, were recorded extracellularly. This field potential comprises a compound action potential, a surface negative wave (identified as EPSP), and superimposed positive peaks ("population spikes" or PSs) reflecting postsynaptic activity. In a previous article the penicillin-induced increase of EPSP and of both amplitude and number of PSs was described. Now we are reporting the slight depression of EPSP and PSs and the prevention of the appearance of penicillin-induced PSs by an antiepileptic drug sodium dipropylacetate (Depakine). The effect was dose-dependent. Models explaining the effects of penicillin and dipropylacetate are discussed.