The difficulties with vitamin B12.

A 22-year-old woman presented with progressive sensory ataxia and optic neuropathy. Previous investigation by her general practitioner had found a low serum vitamin B12, which had been corrected with oral supplementation. Neurological investigations showed raised plasma homocysteine and methylmalonic acid towards the upper limit of normal with a low serum vitamin B12 MRI showed an extensive cord lesion in keeping with subacute combined degeneration of the spinal cord. We treated her with high dose parenteral vitamin B12 and she has made a partial recovery. We discuss the management of patients who present with neurological manifestations of vitamin B12 deficiency; highlighting the fact that parenteral replacement is needed in such cases, even if the serum vitamin B12 level appears to be normal. We also discuss ancillary investigations that should be performed in patients with suspected vitamin B12 deficiency.

Building blocks of pain: the regulation of key molecules in spinal sensory neurones during development and following peripheral axotomy.

The pathways, synapses and molecules involved in pain processing in the newborn are not only required to trigger repair and recuperation but are also involved in the process of forming a mature nervous system. Sensory neurons in the dorsal root ganglion and dorsal horn express a phenomenal array of molecules which contribute to their structural and functional characteristics and many of these are developmentally regulated both pre- and postnatally. In order to understand nociceptive signalling and pain in the neonate we need a clear picture of that regulation. This review concentrates on the changing expression of selected key molecules, receptors and channels in the embryo, neonate and adult, which both characterise the sensory neuron and contribute to its response to painful stimuli in normal and pathological conditions.

A role for NT-3 in the hyperinnervation of neonatally wounded skin.

Neurotrophin-3 (NT-3) is a target-derived neurotrophic factor that regulates sensory neuronal survival and growth. Here we report that NT-3 plays a critical permissive role in cutaneous sensory nerve sprouting that contributes to pain and sensitivity following skin wounding in young animals. Sensory terminal sprouting in neonatally wounded dermis and epidermis is accompanied by increased NT-3 transcription, NT-3 protein levels, and NT-3 protein release 3-7 days post skin injury in newborn rats and mice. Functional blockade of NT-3 activity with specific antibodies greatly reduces sensory neurite outgrowth induced by wounded skin, but not by naïve skin, in dorsal root ganglion/skin co-cultures. The requirement for NT-3 for sensory terminal sprouting in vivo is confirmed by the absence of wound-induced hyperinnervation in heterozygous transgenic mice (NT-3(+/-)lacZ). We conclude that upregulation of NT-3 in neonatally wounded skin is a critical factor mediating the sensory nerve sprouting that underlies hypersensitivity and pain following skin injury.

Ephrin-A4 inhibits sensory neurite outgrowth and is regulated by neonatal skin wounding.

The mechanisms for directing and organising sensory axons within developing skin remain largely unknown. The present study provides the first evidence that signalling occurs between A-ephrins and Eph-A receptors during the development of rat cutaneous sensory innervation both during normal development and following skin injury. Specifically, our data indicate that ephrin-A4 mRNA and protein are expressed in the epidermis during late embryogenesis and the early postnatal period (E16-P3), and expression is significantly down-regulated postnatally. In addition, Eph-A receptors are expressed on dorsal root ganglia (DRG) cells at birth. The pattern of ephrin-A4 expression is mirrored by epidermal innervation, so that sensory terminals are restricted to epidermal regions devoid of ephrin-A4 but increase as ephrin-A4 expression subsides postnatally. Neonatal skin wounding causes sensory hyperinnervation and a differential screen of wounded vs. nonwounded skin revealed down-regulation of epidermal ephrin-A4 following neonatal skin wounding. Expression studies showed that this down-regulation is below the wound and coincides exactly with the onset of hyperinnervation. In vitro experiments show a function for ephrin-A4-Fc in inhibiting rat DRG neuronal growth and guidance when presented as either substratum-bound stripes of ephrin-A4-Fc or as soluble clustered proteins. In conclusion, these observations suggest that the Eph family ligand ephrin-A4 has an inhibitory influence on neonatal cutaneous nerve terminals from DRG sensory neurons in the hindlimb, and may serve to prevent inappropriate innervation of cutaneous regions. In addition, the absence of ephrin-A4 following neonatal skin wounding may play a critical permissive role in the sprouting response.