Discharge Profiles of Juxtacellularly Labeled and Immunohistochemically Identified GABAergic Basal Forebrain Neurons Recorded in Association with the Electroencephalogram in Anesthetized Rats

Photomicrographs of recorded and juxtacellularly labeled Nb+/GAD+ or Nb+/GAD− neurons located in the basal forebrain cholinergic cell area. Nb was revealed with green fluorescent Cy2-conjugated streptavidin (left) and GAD immunostaining with red fluorescent Cy3-conjugated secondary antibodies (right). A, Nb+/GAD+ on (tonic) neuron in SI. B, Nb+/GAD+ off (tonic/cluster) neuron in MCPO.C, Nb+/GAD+ off (burst) neuron in MCPO.D, Nb+/GAD+ off (tonic) neuron in MCPO.E, Nb+/GAD− on (tonic) neuron in MCPO. The location of each cell is shown in the atlas inset to thebottom left of each cell, and together with other cells, as the largest symbol for its subgroup in this figure; the recording of each cell (A–E) is shown in order in subsequent figures (3–7, respectively). Scale bar, 20 μm.

Location of Nb+/GAD+ and Nb+/GAD− neurons in the basal forebrain [represented on atlas sections adapted from Gritti et al. (1993)]. Each subgroup of GAD+ cells (triangular symbols) and GAD− cells (circular symbols) is represented by a particular symbol (as indicated in the figure), and the exemplary cell from each subgroup (illustrated in Figs.1A–E, 3–7, respectively) is represented by the largest symbol. Scale bar, 1 mm. Acb, Accumbens nucleus;ac, anterior commissure; BST, bed of the stria terminalis; CPu, caudate putamen;DBB, diagonal band of Broca nucleus; f, fornix; FStr, fundus of striatum; GP, globus pallidus; LPOA, lateral preoptic area;LS, lateral septum; MCPO, magnocellular preoptic nucleus; MS, medial septum; oc, optic chiasm; OTu, olfactory tubercle;Pir, Piriform cortex; Ret, Reticularis nucleus; SIa, substantia innominata pars anterior;SIp, substantia innominata pars posterior;sm, stria medullaris.

Nb+/GAD+ on (tonic) cell (#98o18009/11 shown in Fig. 1A). I, EEG and unit recording during prestimulation and stimulation conditions. EEG (A) from retrosplenial cortex and unit discharge rate (B, PSH, plotting spikes per second) are shown for periods preceding and during somatic stimulation. The EEG (C) is expanded and shown with the unit traces (D) for each condition (below, left, and right). Note that the unit discharge is tonic during both the prestimulation and stimulation conditions and increases in rate in association with the stimulation-evoked EEG changes from irregular slow to rhythmic slow activity, indicative of cortical activation. II. EEG and unit analysis during prestimulation and stimulation conditions. EEG autocorrelation functions (ACF, in A, with correlation coefficient on vertical axes) and power spectra (with low- and high-frequency ranges, respectively, placed in left and right insets) are shown for prestimulation and stimulation records. These illustrate the shift from low-frequency irregular slow activity to a higher frequency rhythmic slow activity with stimulation and the concomitant increase in gamma amplitude seen in the high-frequency range of the power spectra. Unit autocorrelation histograms (ACH, inB, with normalized incidence on vertical axes) and ISIH (in insets on right) are shown for the same records. An expansion of the ACH is shown (below each) for shorter intervals along with the spectra of the ACH (as insetsin top right corners in which † indicates rhythmic activity according to established criterion). Note that the unit discharge is moderately high and relatively regular during the prestimulation condition with a frequency at ∼20 Hz and higher and very regular (such as to be considered rhythmic) with a frequency at ∼40 Hz during the stimulation-evoked increase in gamma activity and cortical activation.

Nb+/GAD+ off (tonic/cluster) cell (#03/25/LM2 shown in Fig. 1B). I, Note in the PSH (B), that the average rate of discharge decreases in association with cortical activation (A). At the same time, the pattern of discharge changed from tonic spiking during prestimulation to a cluster discharge pattern (D) in association with the appearance of rhythmic slow activity that occurred on the EEG (C) during stimulation. II, Note in the analysis, that after stimulation, the EEG shifted from irregular slow activity to a faster rhythmic slow activity, accompanied by an increase in gamma activity. During stimulation the unit discharge is rhythmic (in the ACH shown in B) at ∼2 Hz (as evident in the power spectrum of the ACH shown in inset ontop left). The expanded ACH for the stimulation condition (drop down) indicates that the high-frequency activity within the spike clusters is relatively regular at ∼40 Hz (but does not meet criterion for being rhythmic). STAs (shown in C) of the unit-to-EEG cross-correlation (with millivolts on vertical axes) indicate that the correlation for the unit (black line) is significantly different from that for the randomized-spike train (gray line, Wilcoxon test; *p< 0.05). The power spectrum for the unit-to-EEG STA is shown (ininset). Note that the cross-correlated unit-to-EEG activity occurs at a frequency of ∼2 Hz, which did not correspond to the prominent EEG rhythmic slow activity or spectral peak but to a secondary peak in the power spectrum (shown in A withinset on top left). See Figure 3 for further explanation of measures.

Nb+/GAD+ off (burst) neuron (#98n030016/19 shown in Fig. 1D). I, Note the virtual cessation of discharge (in the PSH in B) with somatic stimulation that evokes cortical activation in the EEG (A). In association with the irregular slow EEG activity during prestimulation (C), high-frequency bursting occurs (D, including inset with blow up below on left). II, Note in the analysis of the EEG a shift from irregular slow to faster rhythmic slow activity with stimulation. The unit analysis for prestimulation indicates the high-frequency spike mode (at ∼200 Hz in the ISIH inB) reflecting the bursting and the slower frequency activity reflecting the recurrence of the bursting at a similar frequency as the EEG activity (at ∼1.2 Hz, evident in the ISIH, ACH, and spectrum of the ACH for the unit in B and in the spectrum of the ACF for the EEG in A). The unit discharge was significantly cross-correlated with the EEG (as shown in the STA in C) at this same frequency (evident in power spectrum in inset). See Figures 3 and 4 for further explanation of measures.

Nb+/GAD+ off (tonic) cell (#98o16010 shown in Fig.1C). I, Note in the PSH (B), the marked decrease in discharge and in the recording (C), the relatively tonic slow discharge of the unit in association with the irregular slow activity of the EEG (C). II, Note in the analysis, the shift in EEG activity from the irregular slow activity to a higher frequency rhythmic slow activity. Also note, the slow (8.5 Hz mode in ISIH) and relatively irregular discharge of the unit (B) and the lack of relationship with the EEG (B, C). See Figures 3 and 4 for further explanation of measures.