Proceedings of The Physiological Society

King's College London (2011) Proc Physiol Soc 22, PC07

Poster Communications

Electrophysiological characterization of glutamic acid decarboxylase 65-GFP neurons in the lateral hypothalamic area

M. Karnani1, O. Paulsen2, D. Burdakov1

1. Department of Pharmacology, Cambridge University, Cambridge, United Kingdom. 2. Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, United Kingdom.

Gamma-aminobutyric acid (GABA) producing neurons of the lateral hypothalamus (LH) are functionally important in regulation of feeding (Leinninger et al., 2009). Some LH GABA neurons are also sleep-active (Hassani et al., 2010). The electrophysiological phenotypes of GABAergic neurons show considerable diversity all over the mammalian brain but their electrophysiology has not been studied in the LH before. Therefore in this study we characterised these neurons according to categories previously applied to cortical GABAergic neurons (Young and Sun, 2009). We used whole cell patch clamp recordings of glutamic acid decarboxylase 65 (GAD65) expressing neurons in acute slices prepared from transgenic mice expressing GFP under the GAD65 promoter (Erdélyi et al., 2002). Statistical testing was done using Student’s t-test and data are reported as mean ± sem. The majority of the cells (79/87) were spontaneously active with a mean firing rate of 11.6 ± 0.8 Hz (n = 79) at rest in slices prepared during the light period. Spontaneous firing was not significantly different in slices prepared during the dark period (firing at rest at 12.3 ± 1.6 Hz, n = 7/7, P = 0.77) whereas 7/7 GFP expressing cells in layer 1/2 of somatosensory cortex did not spike at rest and had resting membrane potential of -64.5 ± 0.9 mV (n = 7). By following the categorisation scheme of Young and Sun (2009), we were able to identify 11.5% of LH GAD65-GFP cells as low threshold spiking (LTS), 16.1% as late spiking (LS), 66.7% as regular spiking (RSNP) and 5.7% as fast spiking (FS) cells. 7/10 LTS cells expressed a type T calcium current whereas the other types of cells rarely showed this. LS cells expressed a significantly larger A-current than other GFP+ cells (1242 ± 146 pA in LS cells, n = 10; 316 ± 44 pA in others, n = 32, P < 0.0001). The FS cells had high maximum firing frequencies (> 250 Hz) and narrow action potentials (< 0.5 ms half-width) but, in contrast to published data on cortical FS neurons, showed considerable spike frequency adaptation (adaptation ratio was 0.44 ± 0.05, n = 5). In this poster we show that GABAergic cells in LH slices prepared during both night and day are spontaneously firing and can be divided into 4 subclasses, and we summarise relevant electrophysiological parameters for each class.

Where applicable, experiments conform with Society ethical requirements