The effects of environmental isolation on behavior and regional rat brain tyrosine hydroxylase and tryptophan hydroxylase activities

Cortical depth changes in enriched and isolated mice

“…In terms of environmentally induced changes, most researchers have found that the isolated rats weigh more than the enriched (Altman & Das, 1964;Segal, Knapp, Kuczenski, & Mandell, 1973) and that the brain weight of the enriched animals exceeds that of the isolated (Coyle & Singer, 1975;La Torre, 1968;Rosenzweig, Bennett, & Diamond, 1972). The results of the present study in mice are in substantial agreement with the literature.…”

Brain Tryptophan in Isolated Aggressive Mice

“…This in turn, is influenced by a number of variables {Hamon and Glowinski, 1975): the availability of oxygen (the second substrate of the en zyme), the concentration of the enzyme co factor, whether or not the enzyme exists in the free or bound state, and the enzyme concentra tion, all or one of which could be precipitating factors in the altered 5-HT metabolism evi denced by isolated aggressive mice. In point of fact, reduced tryptophan hydroxylase activity, has already either been proposed (Diez et al, 1976), or demonstrated (Segal et al, 1973), to exist in isolated animals. Nonetheless, the re duced level of brain tryptophan, coincident with both the absence of any significant circa dian rhythm of this 5-HT precursor and the augmented daily food intake, suggests quite strongly that a severely altered metabolism of brain tryptophan prevails in such isolated ani mals, and such an altered tryptophan metab olism is unlikely to proceed without imparting consequences on the metabolism of 5-HT.…”

Aggressiveness by Isolation and Brain Serotonin Turnover Changes in Different Strains of Mice

“…These consist in the observations that: (a) isolated-aggressive mice require longer than normal mice to reach a 50% increase in brain 5-HT after monoamineoxidase blockade ( Valzelli, 1966;Welch and Welch, 1971); (b) forebrain 5-HT is reduced in isolated-aggressive mice (Lagerspetz et al, 1967); (c) brain 5-H1AA is decreased in isolated-aggressive mice (Garattini et al, , 1969Welch and Welch, 1968); (d) brain 5-HT turnover is reduced in isolated-aggressive mice (Garattini et al, , 1969Giacalone et al, 1968;Essman, 1968Essman, , 1969Essman, , 1971Valzelli, 1971 );(e) isolated-aggres sive mice have decreased tryptophan-hydroxy lase activity in septal area (Segal et al, 1973); (f) brain tryptophan is reduced in isolatedaggressive mice (Miller et al, 1978;Pacliter et al, 1978); (g) inhibition of brain 5-HT synthe sis by p-chloro-N-methylamphetamine (PCMA) increases isolation-induced aggression in mice (Hodge and Butcher, 1974); (h) brain 5-HT depletion induced by p-chlorophenylalanine (PCPA) is accompanied by increased irritability and sometimes overt aggressiveness in normal rats (Koe and Weissman, 1966) and by facilita tion or induction of muricidal behavior in isolated or brain lesioned rats (Di Cliiara et al, 1971;Popova et al, 1975;Sheard, 1969); (i) olfactory bulb ablation decreases amygdaloid 5-HT to about 85% of baseline value and induces muricidal behavior in laboratory rats (Karli et al, 1969(Karli et al, , 1972Sakata et al, 1975); (j) lesion of midbrain raphe area, a neural region from which most of tire serotonergic projections arise, lowers forebrain serotonin, and to varying extents either increases or in duces muricidal aggression in rats (Banerjee, 1974;Breeze et al, 1974;Grant et al, 1973;Popova et al, 1975;Vergnes et al, 1974) and facilitates the onset of aggressiveness due to isolation in mice (Valzelli, 1977); (k) isolationinduced muricidal behavior in rats is accompa nied by a decrease of brain 5-HT turnover …”

“…The results from different laboratories concerning altered brain monoamine levels or turnover in isolated aggressive animals are at best equivocal. However, brain serotonergic mechanisms have been shown to be involved in the majority of studies (Bocknik and Kulkarni, 1974;Butcher and Dietrich, 1973;Di Chiara el al., 1971;Garattini et al, 1969;Giacalone et al, 1968;Essman, 1969Essman, , 1971Hodge and Butcher, 1974;Miller et al, 1911, Segal et al, 1973Valzelli, 1966Valzelli, , 1971Valzelli, , 1973Valzelli, , 1974Valzelli and Garattini, 1972;Welch and Welch, 1968).…”