Effects of intraperitoneal injection of lithium chloride on neurohypophyseal activity: implications for behavioral studies.

Intraperitoneal injections of lithium chloride (LiCl) were found to increase the activity of vasopressin-neurons and oxytocin-neurons as indexed by rises in plasma concentrations of vasopressin-associated neurophysin (VP-RNP) and oxytocin-associated neurophysin (OT-RNP). Plasma VP-RNP increased 12 and 4 times basal levels (greater than or equal to 20 fmol/ml) reaching values of 248 +/- 37 fmol/ml (3.0 mEq LiCl/kg body weight) and 89 +/- 10 fmol/ml (1.5 mEq LiCl/kg body weight) at 60 minutes. OT-RNP rose to 37-and 10-times basal levels (greater than or equal to 20 fmol/ml) with peak values of 749 +/- 100 fmol/ml and 188 +/- 48 fmol/ml ten minutes following injection of 3.0 or 1.5 mEq LiCl/kg body weight. Mean arterial pressure increased in response to lithium treatment by 31 +/- 6 mm Hg at 60 minutes in rats receiving 3.0 mEq LiCl/kg and by 22.5 +/- 5 mm Hg at 10 minutes in rats receiving 1.5 mEq LiCl/kg over pretreatment values (125 +/- 3 mm Hg). Heart rate decreased from a pretreatment value of 422 +/- 12 beats/min to 367 +/- 48 beats/min at 10 minutes and to 341 +/- 27 beats/min at 20 minutes for rats treated with the high and low dose of lithium, respectively. These findings suggest that the behavioral effects of LiCl could result from multiple mechanisms and involve its acute release of vasopressin and oxytocin. It is also possible that changes in cardiovascular function may act as cues when LiCl is used as an aversive stimulus.