SummaryChronobiology International

1993, Vol. 10, No. 6, Pages 442-448

Effects of Intracisternally Injected Serotonin on Cerebral Blood Flow inCats During Winter and Summer, and After Dark Exposure

Phillip E. Vinall1†

, John J. Michele1, David A. Gordon

1, Christopher Deitch

1and Frederick A. Simeone

2

1Department of Nenrosurgery, Pennsylvania Hospital, Philadelphia, Pennsylvania

2Division of Neurosurgery, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania, USA

†Correspondence: Phillip E. Vinall, Neuroscience Research Institute, Pennsylvania Hospital, 800 Spruce Street,

Philadelphia, PA, 19107, USA

This investigation reports on two experiments: (a) The examination of the effects of intracisternallyinjected serotonin on cerebral blood flow and systemic pressure in cats during winter (1/10–3/7) andsummer (7/6–9/3) at a latitude of 39' 40, and (b) the effects of similarly injected serotonin on the sameparameters in 11 cats after exposure to 3 days of continuous darkness during the summer months.Serotonin (5 mg) injected intracisternally produced significant decreases in cerebral blood flow andsystemic pressure that lasted from 60 to 180 min after injection. Blood flow decreases, expressed aspercentage change from baseline, seen during winter (n = 24) periods were significantly greater [analysisof variance (ANOVA), p < 0.02] from decreases seen during summer (n = 25) periods. Followingserotonin injection, systemic pressure decreases between the winter and summer cats were notsignificantly different. Eleven summer cats were subjected to 3 days of continuous darkness before beinginjected with serotonin. Blood flow decreases in the dark-exposed cats were significantly (p < 0.05)greater than those seen in normal light-exposed cats, whereas systemic pressure changes were notdifferent. These studies suggest that the seasonal photoperiod may affect the sensitivity of cerebralvessels to intracisternally injected serotonin in cats.