Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2007 Apr 1;580(Pt 1):149-69.
doi: 10.1113/jphysiol.2006.124214. Epub 2007 Jan 18.

Robust correlations between action potential duration and the properties of synaptic connections in layer 4 interneurones in neocortical slices from juvenile rats and adult rat and cat

Afia B Ali  1 , A Peter Bannister, Alex M Thomson
Affiliations

Robust correlations between action potential duration and the properties of synaptic connections in layer 4 interneurones in neocortical slices from juvenile rats and adult rat and cat

Afia B Ali et al. J Physiol. .

Abstract

Many studies of cortical interneurones use immature rodent tissue, while many recordings in vivo are made in adult cats. To determine the extent to which interneuronal circuitry studied with one approach can transfer to another, we compared layer 4 interneurones and their local connections across two age groups and two species and with similar connections in layers 3 and 5, using two common recording techniques: dual whole cell recordings at 20 degrees C and dual sharp electrode recordings at 35 degrees C. In each group, a range of morphological and electrophysiological characteristics was observed. In all groups, however, positive correlations were found between the width of the action potential and rise times and widths at half-amplitude of EPSPs and IPSPs and the EPSP paired pulse ratio. Multipolar interneurones with narrow spikes generated the fastest IPSPs in pyramidal cells and received the briefest, most strongly depressing EPSPs, while bitufted interneurones with broader spikes and adapting and burst firing patterns activated the broadest IPSPs and received the slowest, most strongly facilitating/augmenting EPSPs. Correlations were similar in all groups, with no significant differences between adult rat and cat, or between layers, but events were four times slower in juveniles at 20 degrees C. Comparisons with previous studies indicate that this is due in part to age, but in large part to temperature. Studies in adults were extended with detailed analysis of synaptic dynamics, which appeared to decay more rapidly than at juvenile connections. EPSPs exhibited the complexity in time course of facilitation, augmentation and depression previously described in other adult neocortical connections. That is, the time course of recovery from facilitation or depression rarely followed a simple smooth exponential decay. Facilitation and depression were not always maximal at the shortest interspike intervals, and recovery was often interrupted by peaks and troughs in mean EPSP amplitude with a periodicity around 80 Hz.

PubMed Disclaimer

Figures

Figure 2
Figure 2. EPSPs and IPSPs elicited in juvenile layer 4 multipolar interneurones
In Aa, a multipolar interneurone reconstruction is illustrated (dendrites black, axon grey). The firing pattern of this interneurone is shown in Ab and its reciprocal connections with a simultaneously recorded spiny cell in Ac and Ad. In Ac, the paired pulse depression typical of fast excitatory inputs onto multipolar interneurones is illustrated, and in Ad the fast IPSP that this interneurone elicits in its pyramidal partner is shown. In B and C, recordings from two further multipolar interneurones that had fast APs but adapting firing patterns (Ba) are shown. The IPSP elicited by one of these cells with an extrapolated reversal potential of −69 mV and exhibiting paired pulse depression is shown in Bb. The fast, depressing EPSP elicited in another is shown in C. In each case, the presynaptic recording is a single sweep and the postsynaptic an average of 20–50 sweeps.
Figure 7
Figure 7. Facilitating excitatory connections from a layer 4 pyramidal cell to an adapting, parvalbumin-immunonegative bitufted Martinotti-like interneurone in cat visual cortex
In A, composite averages of responses to pairs of presynaptic APs at different interspike intervals demonstrate that second EPSPs do not exhibit a smooth recovery from paired pulse facilitation. Peaks and troughs are apparent in the decay. These are also apparent in the plot in F, to which a single exponential could be fitted (time constant 9.9 ms, correlation 0.83). The dominance of interspike interval over first EPSP amplitude in determining second EPSP amplitude can also be seen in the three-dimensional plot in C, in which second EPSP amplitude is plotted against first interspike interval and first EPSP amplitude as a three-dimensional plot rendered as a colour contour. Although when plotted against interspike interval (F) the decay of third EPSP amplitude against interval appears to parallel that of the second EPSP, a complex relationship between third EPSP amplitude and the two preceding interspike intervals can be seen in the composite averages in C and in the three-dimensional plot in D. The plots of fourth to sixth EPSP amplitudes against interspike intervals (G) demonstrate a pronounced ‘notch’ in the time course of recovery that results in the inconsistent facilitation seen in trains of EPSPs at some intervals (E). In A, traces are colour coded according to the average second EPSP amplitude, in C according to the average third EPSP amplitude and in E according to second-to-sixth EPSP amplitudes. The reconstruction of this interneurone and the pyramidal cells with which it was connected is shown in H. The interneurone dendrites are drawn in red and its axon in blue. The interneuronal dendrites extend through layers 4 and 3, and its axon ramifies adjacent to and above the soma in layers 4, 3/2 and 1. The presynaptic pyramid is drawn in black and its axon in grey, the postsynaptic pyramid in green (IPSPs not illustrated). In I, a portion of the reconstruction is shown at higher magnification to illustrate six points of close membrane apposition between the interneuronal axon and secondary, tertiary and quaternary dendrites of the postsynaptic pyramid (blue open circles), and between the pyramidal axon and one distal portion of a secondary interneuronal dendrite (black open circle). The immunofluorescent labelling of this slice, demonstrating that this cell was immunonegative for both parvalbumin (green) and calbindin (red), is shown in the inset in H.
Figure 5
Figure 5. Facilitating and augmenting excitatory connections from a layer 4 pyramidal cell to a burst firing, bitufted interneurone in rat somatosensory cortex
In A, composite averages of responses to pairs of presynaptic APs at different interspike intervals demonstrate that second EPSPs are facilitated/augmented at all interspike intervals tested, but not maximally at the shortest intervals. In addition, peaks and troughs are superimposed on a gradual increase then a decrease in EPSP amplitude. This is also apparent from the plots in B and for second to sixth EPSPs in H. In B, second EPSP amplitude is plotted against first interspike interval and first EPSP amplitude as a three-dimensional plot rendered as a colour contour. The effect of interspike interval can be seen to dominate. The composite averages shown in C and E and the three-dimensional plots in D and F demonstrate that third (C and D) and fourth (E and F) EPSP average amplitude is determined by complex relationships between preceding interspike intervals, neither the preceding interval nor the sum of all preceding intervals alone determining the amplitude of the next EPSP. Composite averages are colour coded according to the amplitude of the averaged second (A) third (C) and fourth EPSPs (E), respectively. G, this interneurone, which was only partly recovered (red dendrites, blue axon and green presynaptic pyramid dendrites) was also presynaptic to another layer 4 pyramid (drawn in black; IPSPs not illustrated).
Figure 1
Figure 1. Correlations between the AP width at half-amplitude and the time course of EPSPs and IPSPs associated with different classes of interneurones
In A and B, the 10–90% rise time of the EPSP (top) and the EPSP width at half-amplitude (half-width, middle) are plotted against the AP half-width and below, the EPSP half-width is plotted against EPSP rise time for juveniles (A) and adults (B). Similar plots for juvenile and adult IPSPs are shown in C and D. In A and C, measurements from multipolar juvenile interneurones are indicated by the filled circles and those from bitufted interneurones by the open circles. In B and D, adult rat measurements from all interneurones included in this study are shown as filled and adult cat measurements as open symbols. The regression lines were fitted to all juvenile rat data (A and C) and to adult rat data (B and D) for direct comparison. In E, the width at half-amplitude of the AP-AHP is plotted against the AP half-width for juvenile (open symbols) and adult interneurones (closed symbols). In F (adult rat) and G (cat), examples of interneuronal APs elicited with threshold depolarizations and of averaged EPSPs elicited in and IPSPs elicited by these interneurones are shown below superimposed for comparison. In each case, the narrower AP and associated PSP is shown by the thinner black lines and the broader AP and associated PSP by the thicker grey lines. Note that the time scales for APs and EPSP/IPSPs are different. The correlation coefficients for the plots are as follows: adult AP HW versus EPSP RT, 0.96; AP HW versus EPSP HW, 0.82; AP HW versus IPSP RT, 0.58; AP HW versus IPSP HW, 0.58; EPSP RT versus EPSP HW, 0.88; IPSP RT versus IPSP HW, 0.73; AP HW versus AHP amplitude, 0.88; juvenile AP HW versus EPSP RT, 0.68; AP HW versus EPSP HW, 0.90; AP HW versus IPSP RT, 0.83; AP HW versus IPSP HW, 0.59; EPSP RT versus EPSP HW, 0.63; IPSP RT versus IPSP HW, 0.76; and AP HW versus AHP amplitude, 0.60.
Figure 4
Figure 4. EPSPs elicited in a large multipolar parvalbumin-immunopositive interneurone by a simultaneously recorded pyramidal cell in adult rat somatosensory cortex
In A, the fast, depressing EPSPs elicited in this interneurone by a simultaneously recorded pyramid are illustrated. Responses to three different firing patterns are shown. The presynaptic pyramidal recording is a single sweep and the postsynaptic records are composite averages including 20–50 sweeps per component. In B, the continuous firing that could be elicited in this stuttering/stopping interneurone when a gradually increasing ramped current pulse was applied is shown. The reconstruction of this layer 4 interneurone shows the partly myelinated axon (blue) and dendrites (red) extending into layers 3 and 6, with significant axonal arborization in layers 3, 4 and 6. The presynaptic pyramid is drawn in black (axon grey). The immunofluorescent identification of parvalbumin (green) in this biocytin-labelled cell (blue fluorescence; black, HRP) and the absence of choleycystokinin (CCK, red) are shown in D.
Figure 6
Figure 6. Depressing excitatory connections from a layer 4 pyramidal cell to a narrow spike, stuttering, parvalbumin-immunopositive multipolar interneurone in cat visual cortex
The stuttering firing pattern of this interneurone in response to a suprathreshold depolarizing pulse is shown in A. In B, composite averages of responses to pairs of presynaptic APs at different interspike intervals demonstrate that second EPSPs do not exhibit a smooth recovery from paired pulse depression. Peaks and troughs are apparent in the decay and result in modest facilitation between 35 and 42 ms. This can also be seen in the three-dimensional plot in C, in which second EPSP amplitude is plotted against first interspike interval and first EPSP amplitude as a three-dimensional plot rendered as a colour contour, and in F, where second and third EPSP amplitudes are plotted against interspike interval. The complex relationship between third EPSP amplitude and the two preceding interspike intervals can be seen in the composite averages in D and the three-dimensional plot in E. In D, a single presynaptic sweep is also illustrated. In B, traces are colour coded according to the average second EPSP amplitude and in D according to the average third EPSP amplitude. The reconstruction of this interneurone and the pyramidal cell with which it was reciprocally connected is shown in G. The interneurone dendrites are drawn in red and its axon in blue. The interneuronal dendrites extended into layers 3 and 5 and its axon ramified largely adjacent to and below the soma and extended throughout layers 4, 5 and 6, projecting weakly into layer 3. The pyramid which was reciprocally connected to the interneurnone is drawn in black and its axon in grey (IPSPs not illustrated). In H, a portion of the reconstruction is shown at higher magnification to illustrate points of close membrane apposition between the interneurone axon and a secondary basal pyramidal dendrite (blue open circle) and between the pyramidal axon and two secondary interneuronal dendrites (black open circles). The immunofluorescent labelling of parvalbumin (green) in this interneurone is shown in I.
Figure 3
Figure 3. EPSPs and IPSPs elicited in juvenile layer 4 bitufted interneurones
In Aa, a bitufted interneurone reconstruction is illustrated (dendrites black, axon grey). The non-adapting firing pattern of this interneurone is shown in Ab and the slow IPSP it elicits in a spiny cell in Ac. In B, recordings from another bitufted interneurone that had broad APs and an adapting firing pattern (Ba) are shown. The IPSP elicited by one of these cells in a simultaneously recorded pyramidal cell exhibited modest paired pulse facilitation, but no augmentation (Bb). The slow, facilitating EPSP elicited by the reciprocally connected pyramid is shown in Bc. In each case, the presynaptic recording is a single sweep and the postsynaptic an average of 20–50 sweeps.
Figure 8
Figure 8. Correlation between EPSP paired pulse ratios and interneuronal AP width at half-amplitude
Adult (A) and juvenile measurements (B) are plotted. For juvenile EPSPs only interspike intervals of 50 ms were studied. For adult EPSPs a range of intervals is plotted (5, 10, 20 and 50 ms; see key for symbols). Linear regressions fitted to the data demonstrated strong correlations between paired pulse ratio and AP width at half-amplitude (correlation at 5 ms 0.68; at 10 ms 0.89; at 20 ms 0.93; and at 50 ms 0.95) with the slope becoming less steep (from 783% average amplitude per millisecond AP HW at 5 ms to 593% ms−1 at 50 ms) and the intercept less negative with increasing interspike intervals (from −147% at 5 ms to −93% at 50 ms). Only one regression line fitted to the complete adult data set is illustrated for clarity (adult correlation 0.91; juvenile 0.90). A single outlying point (* in A) represents the only bipolar interneurone in which EPSP paired pulse effects were studied (Supplemental Fig. 5) shown for an interval of 20 ms.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Ali AB, Nelson C. Distinct Ca2+ channels mediate transmitter release at excitatory synapses displaying different dynamic properties in rat neocortex. Cereb Cortex. 2006;16:386–393. - PubMed
    1. Angulo MC, Lambolez B, Audinat E, Hestrin S, Rossier J. Subunit composition, kinetic, and permeation properties of AMPA receptors in single neocortical nonpyramidal cells. J Neurosci. 1997;17:6685–6696. - PMC - PubMed
    1. Bannister AP, Thomson AM. Dynamic properties of excitatory synaptic connections involving layer 4 pyramidal cells in adult rat and cat neocortex. Cereb Cortex. 2006 Epub ahead of print DOI 10.1093/cercor/bh/126. - DOI - PubMed
    1. Beierlein M, Gibson JR, Connors BW. Two dynamically distinct inhibitory networks in layer 4 of the neocortex. J Neurophysiol. 2003;90:2987–3000. - PubMed
    1. Buhl EH, Tamas G, Szilagyi T, Stricker C, Paulsen O, Somogyi P. Effect, number and location of synapses made by single pyramidal cells onto aspiny interneurons of cat visual cortex. J Physiol. 1997;500:689–713. - PMC - PubMed

Publication types

MeSH terms

LinkOut - more resources

-