Excess nerve growth factor in the periphery does not obscure development of whisker-related patterns in the rodent brain

Abstract

We have addressed the issue of whether or not peripherally expressed nerve growth factor (NGF) influences the formation of whisker-specific patterns in the brain by regulating the survival of sensory neurons. Transgenic mice that overexpress an NGF cDNA in the skin were examined. In these animals, excess NGF expression is controlled by promoter and enhancer sequences of a keratin gene, thus restricting the higher levels of NGF expression to basal keratinocytes of the epidermis. Twice the number of trigeminal sensory neurons survive in transgenic mice as in normal animals, and a corresponding hyperinnervation of the whisker pad is noted, both around the vibrissa follicles and along the intervibrissal epidermis. However, the increased survival of sensory neurons and the enhanced peripheral projections do not interfere with the development of whisker-specific patterns in the trigeminal brainstem, in the ventrobasal thalamic complex or in the face-representation region of the primary somatosensory (SI) cortex. These results demonstrate that vibrissa-related central patterns are able to form in the virtual absence of trigeminal ganglion cell death and suggest that mechanisms other than a selective elimination of sensory neurons control the development of whisker-specific neural patterns in the brain.

Role of neurotrophins on postnatal neurogenesis in the thalamus: prenatal exposure to ethanol

“…Under- or over-expression of these proteins can directly affect the number of viable neurons. For example, in mice that over-express NGF, twice the normal numbers of trigeminal ganglion cells survive (Jhaveri et al, 1996). BDNF overexpression alters mouse behavior and the electrophysiological responses of cells (Croll et al, 1999; Cunha et al, 2009).…”

Assembly of the dorsal horn somatotopic map

“…For example, it has been shown that the number of surviving primary afferent ® bers is related to the amount of target tissue available for innervation (Frank and Wester® eld, 1982). More recently it has been shown that the overexpression of NGF in the skin rescues most if not all trigeminal ganglion cells (Jhaveri et al, 1996). Thus a higher concentration of individual neurotrophins or speci® c combinations of neurotrophins in skin covering the digits could allow for a higher innervation density.…”

Whisker-related circuitry in the trigeminal nucleus principalis: Ultrastructure

“…The purpose of this paper is to begin to provide this information. The present study was carried out in mice because transgenic mice are commonly used to reveal molecular substrates for barrel-like pattern formation and information processing (e.g., Li et al 1994;Cases et al 1996;Jhaveri et al 1996;Kutsuwada et al 1996;Abdel-Majid et al 1998;Maier et al 1999;Iwasoto et al 2000;Prakash et al 2000;Fukuchi-Shimogori and Grove 2001;Ding et al 2003).…”