Sedimentary Ways

This paper is a thought experiment to attune to the geo-physical and geo-political materialities of sediment, a terra-aqueous substance produced when the earth's continental surfaces intra-act with the atmosphere and are chemically transformed by it. The paper is framed by questions of how to engage more closely with the dynamics of earth systems and of how social and political agency emerges alongside earth forces. Sediment is important to such questions because it is the mechanism by which the earth recycles itself and is thick with the climatological and geological histories that have conditioned the possibility of life on the planet. While acknowledging the import of Deleuze and Guattari's metaphysics to such questions, the paper takes a material approach to them. It is based on field work in Bangladesh, but also traverses a range of scientific, historical and theoretical literature. It is arranged in four sections that loosely correspond to the sedimentary cycle. It follows sediment from chemical processes on rock surfaces in the Himalayas, to its lively travels in monsoonal rivers across flood plains to its eventual deposition and subterranean diagenesis. In each section, the paper discusses the material processes at work, their socio-political enmeshments and the theoretical implications of these intra-actions. The paper concludes that sediment serves as a reminder not only of close entanglements of geo-physical and geo-political becomings, but also of the profound indifference of earth systems to human affairs, and asks what this might mean for the re-imagination of politics.

Functional GABA(A)-receptor-mediated inhibition in the neonatal dorsal horn

Neonatal nociceptive circuits and dorsal horn cells are characterized by an apparent lack of inhibitory control: receptive fields are large and thresholds low in the first weeks of life. It has been suggested that this may reflect immature GABA(A)-receptor (GABA(A)R) signaling whereby an early developmental shift in transmembrane anion gradient is followed by a longer period of low Cl- extrusion capacity. To investigate whether functional GABA(A)R-mediated inhibition does indeed undergo postnatal regulation at the level of dorsal horn circuits, we applied the selective GABA(A)R antagonist gabazine to the spinal cord in anesthetized rat pups [postnatal day (P) 3 or 21] while recording spike activity in single lumbar dorsal horn cells in vivo. At both ages, blockade of GABA(A)R activity resulted in enlarged hind paw receptive field areas and increased activity evoked by low- and high-intensity cutaneous stimulation, revealing comparable inhibition of dorsal horn cell firing by spinal GABA(A)Rs at P3 and P21. This inhibition did not require descending pathways to the spinal cord because perforated patch-clamp recordings of deep dorsal horn neurons in P3 spinal cord slices also showed an increase in evoked spike activity after application of gabazine. We conclude that spinal GABAergic inhibitory transmission onto single dorsal horn cells "in vivo" is functional at P3 and that low Cl- extrusion capacity does not restrict GABAergic function over the normal range of evoked sensory activity. The excitability of neonatal spinal sensory circuits could reflect immaturity in other intrinsic or descending inhibitory networks rather than weak spinal GABAergic inhibition.