In the dorsal root ganglia (DRG) of mice latently infected with the herpes simplex virus type 1 mutant in1814, there are more neurons that contain latencyassociated transcripts (LATs) than in DRG of mice infected with a dose of equal infectivity of either a revertant or a wild-type virus. We investigated whether higher levels ofLAT + neurons resulted in more extensive reactivation either in vivo following neurectomy of the sciatic nerve or in vitro after explantation into culture.Neurectomy appeared to induce expression of immediate early 1 mRNA (IElmRNA) in neurons of mice latently infected with each of three viruses. However IElmRNA was detected in no more than 0"25 % of the neurons of DRG from animals 2 to 4 days after neurectomy, irrespective of the percentage of LAT ÷ neurons present. Of the 22 neurons shown to express IElmRNA, none expressed LATs also. However the lack of expression of viral antigen and the absence of a reduced potential for reactivation on explantation suggested that neurectomy had not induced full reactivation involving lytic replication leading to the death of the latently infected neurons. When DRG were explanted into culture, the distribution of the frequency of reactivation was similar to the distribution of DRG that contained LAT + neurons. The presence of a high proportion of LAT + neurons was not directly associated with earlier detection of reactivation but such experiments cannot be regarded as quantitative. We therefore concluded that neurectomy did not result in a reduced reactivation potential as described by others and that the frequency of expression of IElmRNA following neurectomy did not correlate with the number of LAT + neurons present.

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The herpes simplex virus type 1 (HSV-1) mutant in1814 lacks the ability to trans-activate immediate early gene transcription and enter lytic replication but it can establish and reactivate from latency. We therefore investigated the number of neurons that expressed latency-associated transcripts (LATs) in animals latently infected with in1814, the rescued revertant (1814R), or wild-type (wt) HSV-1. The percentage of LAT + neurons increased with increasing doses of each of the viruses. After inoculation of equal amounts of infectious virus many more LAT + neurons were observed in animals infected with in1814 than with 1814R or wt HSV-1.Whereas the LAT + neurons in animals infected with 1814R or wt HSV-1 were largely confined to lumbar dorsal root ganglia (DRG) L4/L5/L6 (those which innervate the lower leg), in animals infected with in1814 they were also present in DRG not directly involved with such innervation (thoracic 12 and 13, L1, L2 and L3).We concluded that the large number of LAT + neurons observed with in1814 was related to the high particle numbers in the inoculum and that spread of virus was related to limited replication as well as to the low neurovirulence of in1814. This spread was not unique to in1814 but when it occurred with more virulent viruses such as 1814R or wt HSV-1, it resulted in the death of the host.