Modulation of bistratified cell IPSPs and basket cell IPSPs by pentobarbitone sodium, diazepam and Zn²⁺: dual recordings in slices of adult rat hippocampus

Abstract

Simultaneous intracellular recordings from presynaptic Stratum pyramidale interneurons and postsynaptic pyramidal cells in adult rat hippocampal slices were performed to investigate the strength of the modulation of single-axon inhibitory postsynaptic potentials (IPSPs) by the GABAA receptor modulators pentobarbitone, diazepam and zinc. The processing of biocytin-filled interneurons for light microscopy revealed that these single-axon IPSPs were generated by basket cells (n = 33), bistratified cells (n = 18) and axo-axonic cells (n = 2). The IPSPs generated by these three groups of interneurons had amplitudes and widths at half amplitude with similar ranges, but when bistratified cell IPSPs were compared with basket cell IPSPs with similar half widths their rise times were slower. Pentobarbitone sodium (250 microM) powerfully enhanced 13 tested IPSPs generated by all three cell types. Amplitudes were enhanced by 82 +/- 56%, 10-90% rise times by 150 +/- 101% and the widths at half amplitude by 71 +/- 29%. Diazepam (1-2 microM) also increased all IPSPs tested, although the changes were more moderate in basket cell IPSPs (amplitudes increased by 19 +/- 11%, n = 8) than in bistratified cell IPSPs (amplitudes increased by 66 +/- 48%, n = 5). Basket cell IPSP 10-90% rise times and widths at half amplitude were not significantly increased. Bistratified cell IPSP 10-90% rise times were increased by 44 +/- 24% and the widths at half amplitude by 32 +/- 35%. The one tested IPSP generated by an axo-axonic cell was also diazepam-sensitive. Zinc, 250 microM, decreased four out of 10 IPSPs generated by basket cells and four out of five IPSPs generated by bistratified cells. The one tested axo-axonic cell IPSP was zinc-insensitive. These data suggest that IPSPs generated in CA1 pyramidal cells by basket and bistratified cells display different pharmacologies and may be mediated by different receptors or receptor combinations.

Characterization of Neurons in the CA2 Subfield of the Adult Rat Hippocampus

“…All CA1 basket cells in this study displayed similar dendritic and axonal patterns and resembled those reported previously (Sik et al, 1995;Freund and Buzsaki, 1996;Ali et al, , 1999Pawelzik et al, 1999). They had relatively narrow vertically oriented dendritic arbors that extended through SO, in some cases entering the alveus, and through SR and into SLM (Fig.…”

“…All dendrites were aspiny and were often beaded. CA1 basket cell axons whose major branches were often myelinated, ramified extensively in SP, and, in some cases, in the most proximal regions of SR and SO (previously described as "wide arbor basket cells") (Buhl et al, 1996;Freund and Buzsaki, 1996;Pawelzik et al, 1999Pawelzik et al, , 2002. The majority of these CA1 basket cells were found to be PV immunopositive and CB immunonegative (16:23).…”

“…Like CA1 basket cells (Sik et al, 1995;Buhl et al, 1996;Freund and Buzsaki, 1996;Ali et al, , 1999Pawelzik et al, 1999Pawelzik et al, , 2002, CA2 basket cells recorded in SP or proximal SO had dendrites that extended through SO, sometimes entering the alveus, and through SR and into SLM. Their axons arborized extensively in SP, in some cases ramifying also in proximal SO and SR. Two distinct types of CA2 basket cells were identified.…”

“…Cc, Superimposition of the drawing of the bistratified cell on an image of the ␣-actinin 2 staining. Freund and Buzsaki, 1996;Pawelzik et al, 1999Pawelzik et al, , 2002, extended through SO and SR without entering SLM, suggesting that these cells receive Schaffer collaterals but not inputs from entorhinal cortex. The dendrites of two of these cells, however, extended much further horizontally than those of CA1 bistratified cells, into all three CA subfields.…”

Neuronal Diversity in GABAergic Long-Range Projections from the Hippocampus

“…This activity might lead to a suppression of the majority of cells (Dragoi et al, 1999) and disrupt the generation of theta oscillations. Their local axons in the CA1 area innervate pyramidal cell dendrites, as shown here (but see Gulyas et al, 2003), and cooperatively release GABA with the bistratified cells, which fire at high frequency (Klausberger et al, 2004) during the ascending phase of the extracellular ripple cycle and innervate the same pyramidal cell domains acting on GABA A receptors (Pawelzik et al, 1999). Together, they temporally structure the excitation of the CA3 input in CA1 pyramidal dendrites at ripple frequency.…”