Position-dependent preferential outgrowth of cervical spinal neurites on membranes from rostral or caudal halves of the diaphragm. Rostral cervical segments (C1–C2) were compared with caudal cervical segments (C6–C8) by coculturing on alternating lanes of membranes from rostral diaphragm (RD) or caudal diaphragm (CD) muscles. A, Rostral cervical neurites (C1–C2) grow preferentially on rostral diaphragm membranes in 55% of cultures. B, Caudal cervical neurites (C6–C8) grow preferentially on caudal diaphragm membranes in 48%. C, Columns show the percentage of cultures showing preferential outgrowth on membranes from rostral sectors or caudal sectors of diaphragm muscle or no striking preference (random). Numbers indicate number of cultures in each category. A χ2 test for differences between rostral cervical (C1–C2) and caudal cervical (C6–C8) neurite outgrowth is highly significant (p < 0.001). Magnification: A, B, 140×.