Limits...
Electrophysiology of Hypothalamic Magnocellular Neurons In vitro: A Rhythmic Drive in Organotypic Cultures and Acute Slices.

Israel JM, Oliet SH, Ciofi P - Front Neurosci (2016)

Bottom Line: Here, we have tested whether a similar hypothesis can be derived from in vitro experiments in acute slices of the adult hypothalamus.To this aim we have screened our electrophysiological recordings of the magnocellular neurons, previously obtained from acute slices, with an analysis of autocorrelation of action potentials to detect a rhythmic drive as we recently did for organotypic cultures.This confirmed that the bursting behavior of magnocellular neurons is governed by central pattern generator networks whose rhythmic drive, and thus probably integrity, is however less satisfactorily preserved in the acute slices from adult brains.

View Article: PubMed Central - PubMed

Affiliation: U1215, Neurocentre Magendie, Institut National de la Santé et de la Recherche MédicaleBordeaux, France; Université de BordeauxBordeaux, France.

ABSTRACT
Hypothalamic neurohormones are released in a pulsatile manner. The mechanisms of this pulsatility remain poorly understood and several hypotheses are available, depending upon the neuroendocrine system considered. Among these systems, hypothalamo-neurohypophyseal magnocellular neurons have been early-considered models, as they typically display an electrical activity consisting of bursts of action potentials that is optimal for the release of boluses of the neurohormones oxytocin and vasopressin. The cellular mechanisms underlying this bursting behavior have been studied in vitro, using either acute slices of the adult hypothalamus, or organotypic cultures of neonatal hypothalamic tissue. We have recently proposed, from experiments in organotypic cultures, that specific central pattern generator networks, upstream of magnocellular neurons, determine their bursting activity. Here, we have tested whether a similar hypothesis can be derived from in vitro experiments in acute slices of the adult hypothalamus. To this aim we have screened our electrophysiological recordings of the magnocellular neurons, previously obtained from acute slices, with an analysis of autocorrelation of action potentials to detect a rhythmic drive as we recently did for organotypic cultures. This confirmed that the bursting behavior of magnocellular neurons is governed by central pattern generator networks whose rhythmic drive, and thus probably integrity, is however less satisfactorily preserved in the acute slices from adult brains.

No MeSH data available.


Related in: MedlinePlus

Electrical activities in VP neurons in hypothalamic acute slices. Mechanisms of burst generation in spontaneously active neurons (A) with and (B) without rhythmic drive (autocorrelograms in the insets). The raw recordings (upper traces) are expanded (lower traces) to reveal that the first AP in the burst is triggered by an EPSP (arrowheads) and is followed by a DAP (arrow) in (B) only (APs are truncated in B). The subsequent APs in the burst are essentially triggered by EPSPS in (A) and by both EPSPs and DAPs in (B). Note in the samples of inter-burst activity (stars) magnified in (C) the heightened synaptic activity in (A) reflected by the cumulative frequencies of EPSPs' intervals and amplitudes (mean amplitudes in dashed frame). The histogram shows that phasic-like neurons display EPSPs at lower frequency (Hz) and smaller amplitude (q) (green column = 100% for both frequency and amplitude of events recorded in truly rhythmic neurons; n = 4 each).
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4814512&req=5

Figure 4: Electrical activities in VP neurons in hypothalamic acute slices. Mechanisms of burst generation in spontaneously active neurons (A) with and (B) without rhythmic drive (autocorrelograms in the insets). The raw recordings (upper traces) are expanded (lower traces) to reveal that the first AP in the burst is triggered by an EPSP (arrowheads) and is followed by a DAP (arrow) in (B) only (APs are truncated in B). The subsequent APs in the burst are essentially triggered by EPSPS in (A) and by both EPSPs and DAPs in (B). Note in the samples of inter-burst activity (stars) magnified in (C) the heightened synaptic activity in (A) reflected by the cumulative frequencies of EPSPs' intervals and amplitudes (mean amplitudes in dashed frame). The histogram shows that phasic-like neurons display EPSPs at lower frequency (Hz) and smaller amplitude (q) (green column = 100% for both frequency and amplitude of events recorded in truly rhythmic neurons; n = 4 each).

Mentions: In the following, by convention, the activity of VP neurons will be referred to as truly phasic when the AAA revealed a CPG drive, and phasic-like when the AAA did not. We re-examined through AAA our previous (Israel and Poulain, 2000) recordings of VP neuron activity in acute hypothalamic slices from nursing female rats taken on L5 and L21. These magnocellular neurons were identified post-hoc as VP neurons each recorded from a different SON section (L5, n = 21; L21, n = 57). Irrespective of lactation day, about half (37/78 cells; 47%) of the VP neurons had a low resting membrane potential close to −58 mV and remained silent, displaying only a few spontaneous APs (Figure 3A). These cells were healthy as they generated a brief burst of APs in response to a short electrical stimulation, a robust firing following bath application of glutamate, and a continuous activity when depolarized above spike threshold (Figure 3A). When these various patterns of activity were subjected to the AAA, no rhythmic drive was detected (n = 4 cells for glutamate pulse; n = 10 cells for depolarization-induced firing). The remaining population (41/78 cells) of VP neurons had a more depolarized resting membrane potential (≈−50 mV) and spontaneously displayed phasic-like activity (Figure 3B). There was a great cell-to-cell heterogeneity in the firing patterns that were made of irregular long bursts (10–200 s in length) interspersed with silent periods of varying duration (10–300 s in length) (Figure 3B), and two sub-populations clearly emerged with respect to their mean burst-duration (20–50 s and 75–150 s). When subjected to the AAA, only the short-burst (20–50 s) population qualified for a CPG drive (cp = 41.3 ± 16.1 s; a = 0.36 ± 11) (short-burst n = 8; long-burst, n = 17) (Figures 3C, 4) and this population also exhibited a more robust excitatory synaptic activity (Figure 4C). It is noteworthy that in these neurons APs were essentially triggered by EPSPs (Figure 4A, lower trace).


Electrophysiology of Hypothalamic Magnocellular Neurons In vitro: A Rhythmic Drive in Organotypic Cultures and Acute Slices.

Israel JM, Oliet SH, Ciofi P - Front Neurosci (2016)

Electrical activities in VP neurons in hypothalamic acute slices. Mechanisms of burst generation in spontaneously active neurons (A) with and (B) without rhythmic drive (autocorrelograms in the insets). The raw recordings (upper traces) are expanded (lower traces) to reveal that the first AP in the burst is triggered by an EPSP (arrowheads) and is followed by a DAP (arrow) in (B) only (APs are truncated in B). The subsequent APs in the burst are essentially triggered by EPSPS in (A) and by both EPSPs and DAPs in (B). Note in the samples of inter-burst activity (stars) magnified in (C) the heightened synaptic activity in (A) reflected by the cumulative frequencies of EPSPs' intervals and amplitudes (mean amplitudes in dashed frame). The histogram shows that phasic-like neurons display EPSPs at lower frequency (Hz) and smaller amplitude (q) (green column = 100% for both frequency and amplitude of events recorded in truly rhythmic neurons; n = 4 each).
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4814512&req=5

Figure 4: Electrical activities in VP neurons in hypothalamic acute slices. Mechanisms of burst generation in spontaneously active neurons (A) with and (B) without rhythmic drive (autocorrelograms in the insets). The raw recordings (upper traces) are expanded (lower traces) to reveal that the first AP in the burst is triggered by an EPSP (arrowheads) and is followed by a DAP (arrow) in (B) only (APs are truncated in B). The subsequent APs in the burst are essentially triggered by EPSPS in (A) and by both EPSPs and DAPs in (B). Note in the samples of inter-burst activity (stars) magnified in (C) the heightened synaptic activity in (A) reflected by the cumulative frequencies of EPSPs' intervals and amplitudes (mean amplitudes in dashed frame). The histogram shows that phasic-like neurons display EPSPs at lower frequency (Hz) and smaller amplitude (q) (green column = 100% for both frequency and amplitude of events recorded in truly rhythmic neurons; n = 4 each).
Mentions: In the following, by convention, the activity of VP neurons will be referred to as truly phasic when the AAA revealed a CPG drive, and phasic-like when the AAA did not. We re-examined through AAA our previous (Israel and Poulain, 2000) recordings of VP neuron activity in acute hypothalamic slices from nursing female rats taken on L5 and L21. These magnocellular neurons were identified post-hoc as VP neurons each recorded from a different SON section (L5, n = 21; L21, n = 57). Irrespective of lactation day, about half (37/78 cells; 47%) of the VP neurons had a low resting membrane potential close to −58 mV and remained silent, displaying only a few spontaneous APs (Figure 3A). These cells were healthy as they generated a brief burst of APs in response to a short electrical stimulation, a robust firing following bath application of glutamate, and a continuous activity when depolarized above spike threshold (Figure 3A). When these various patterns of activity were subjected to the AAA, no rhythmic drive was detected (n = 4 cells for glutamate pulse; n = 10 cells for depolarization-induced firing). The remaining population (41/78 cells) of VP neurons had a more depolarized resting membrane potential (≈−50 mV) and spontaneously displayed phasic-like activity (Figure 3B). There was a great cell-to-cell heterogeneity in the firing patterns that were made of irregular long bursts (10–200 s in length) interspersed with silent periods of varying duration (10–300 s in length) (Figure 3B), and two sub-populations clearly emerged with respect to their mean burst-duration (20–50 s and 75–150 s). When subjected to the AAA, only the short-burst (20–50 s) population qualified for a CPG drive (cp = 41.3 ± 16.1 s; a = 0.36 ± 11) (short-burst n = 8; long-burst, n = 17) (Figures 3C, 4) and this population also exhibited a more robust excitatory synaptic activity (Figure 4C). It is noteworthy that in these neurons APs were essentially triggered by EPSPs (Figure 4A, lower trace).

Bottom Line: Here, we have tested whether a similar hypothesis can be derived from in vitro experiments in acute slices of the adult hypothalamus.To this aim we have screened our electrophysiological recordings of the magnocellular neurons, previously obtained from acute slices, with an analysis of autocorrelation of action potentials to detect a rhythmic drive as we recently did for organotypic cultures.This confirmed that the bursting behavior of magnocellular neurons is governed by central pattern generator networks whose rhythmic drive, and thus probably integrity, is however less satisfactorily preserved in the acute slices from adult brains.

View Article: PubMed Central - PubMed

Affiliation: U1215, Neurocentre Magendie, Institut National de la Santé et de la Recherche MédicaleBordeaux, France; Université de BordeauxBordeaux, France.

ABSTRACT
Hypothalamic neurohormones are released in a pulsatile manner. The mechanisms of this pulsatility remain poorly understood and several hypotheses are available, depending upon the neuroendocrine system considered. Among these systems, hypothalamo-neurohypophyseal magnocellular neurons have been early-considered models, as they typically display an electrical activity consisting of bursts of action potentials that is optimal for the release of boluses of the neurohormones oxytocin and vasopressin. The cellular mechanisms underlying this bursting behavior have been studied in vitro, using either acute slices of the adult hypothalamus, or organotypic cultures of neonatal hypothalamic tissue. We have recently proposed, from experiments in organotypic cultures, that specific central pattern generator networks, upstream of magnocellular neurons, determine their bursting activity. Here, we have tested whether a similar hypothesis can be derived from in vitro experiments in acute slices of the adult hypothalamus. To this aim we have screened our electrophysiological recordings of the magnocellular neurons, previously obtained from acute slices, with an analysis of autocorrelation of action potentials to detect a rhythmic drive as we recently did for organotypic cultures. This confirmed that the bursting behavior of magnocellular neurons is governed by central pattern generator networks whose rhythmic drive, and thus probably integrity, is however less satisfactorily preserved in the acute slices from adult brains.

No MeSH data available.


Related in: MedlinePlus